51 BMW 1973 R75/5 Paint the Tank, Fenders, Fairing and Tail Light

I have done a fair amount of work so far to get ready for painting the tank, fenders and fairing. You can see what I’ve done in these write-ups.

And, I’m going to repaint the R75/6, aka. Grey Ghost, that was my first attempt at painting, as I made a mistake on the primer and the paint job failed. So, I’ve stripped two bikes worth of tanks, fenders, fairings, and for the Grey Ghost, side panels.

My Plan for Painting The Parts

I am using Glasurit paint I purchased from Holt BMW which is the supplier of the paint BMW uses. Kent Holt assembles a paint kit with the right type and amount of material you need to paint whatever parts you have in whatever color you want.

This is a two part paint system with a base coat, aka, color coat, and a hard clear coat on top. Underneath that, directly on the metal and plastic, is a two component–called “2K” in the trade–epoxy primer that seals the metal tank and plastic from moisture and resists the solvents in the base and clear coats. I failed to use 2K primer on the Grey Ghost and the paint floated on top of the primer causing the paint job to fail. Lesson learned.

Primer is the foundation for the the paint job and any blemishes in the primer show right through the color coat. As I am an amateur at paint work, I make mistakes, so I plan to sand the first primer coat to get any rough spots out before applying the second coat. I will lightly sand out the high spots using wet 220 grit paper and try to avoidsanding through it to the metal or plastic underneath.

Next, I repair any dents or gouges with polyester filler (aka, Bond) and sand that smooth with wet 220 grit. I dry the bondo with a heat gun to get the water out of it. Others dry sand the Bondo. I apply glazing putty to fill the small low spots and any blemishes in the filler and sand that out with wet 320 grit. I plan to apply the filler and putty to the first primer coat since it seals the metal tank from moisture. Since the filler and putty don’t stop moisture from getting through, I want to sandwich them between layers of primer so I don’t get any rust.

Then, I apply the second primer coat. I sand the second primer coat down in stages using wet 220 girt to remove any rough spots, then wet 320 or 400 to level the surface and I finish up with wet 600 grit to get as smooth a surface as I can.

When the primer is as good as I can get it, I spray two coasts of the base color. If there are any blemishes or “dust bunnys”, I sand those out with 2000 grit and apply more base coat over the sanded spots. I apply clear coat using three coats. When I spray clear coat it typically drys with an orange peel surface so I will use very fine paper (1500, 2000 and 2500 wet) to sand out the peel for a smooth surface. I use a soft sanding block so the clear coat is flat being very careful on raised edges and corners to try and avoid sanding through the clear coat. Then I polish the clear coat with Griot’s polish starting with a coarse buffing compound (#1) and finishing up with a fine polishing compound (#4). If it all works out, it should be kinda pretty to look at.

Why You Need A Respirator When You Paint

On the right is the particulate filter pads from my respirator after painting the base and clear coats. On the left is a new particulate filter.

Repirator Particulate Filters: Left New, Right Used

Repirator Particulate Filters: Left New, Right Used

The materials in these paints need to be treated with respect. Always use a new activated charcol filter when you paint and change the particulate filer when it is coated with material.

<===DANGER===>
* YOU DO NOT WANT TO BREATH PRIMER, PAINT OR CLEAR COAT VAPORS.
* YOU DO NOT WANT IT ON YOUR SKIN OR IN YOUR EYES.
* HARDENERS FOR PRIMER & CLEAR COAT CONTAIN ISOCYANURATE
* ISOCYANURATE CAN DAMAGE YOUR LUNGS, BRAIN, ETC. PERMANENTLY
<===DANGER===>

Applying the First Primer Coat

I have the paint booth and drying area set up and turn on the heat in the workshp to get everything up to 70 F.

Thermometer - 70 F

Thermometer at 70 F

Setting Up the Compressor

I turn on the compressor and adjust the output pressure from the tank to 55 PSI and the inlet pressure to the gun to 29 PSI.

Delivery Pressure Setting on Compressor

Delivery Pressure Setting on Compressor

LESSON LEARNED: Lower Gun Inlet Pressure From The Maximum

I found that a lower pressure, about 20 PSI was much better than the paint gun specification that stated 29 PSI. This provides a good description of the best way to setup a LPHV paint gun.

Unfortunately, I found this after struggling with the primer, but it helped me understand why a lower inlet pressure can produce better paint atomoization.

Pressure Regulator at Paint Gun Snapon Fitting

Pressure Regulator at Inlet to Paint Gun- TOO HIGH !!!

LESSON LEARNED: Replace Fittings With High Flow Fittings

The video above mentioned high flow fittings to allow more air volume to the gun. I painted using the standard fittings and had problems getting good atomization. I invested in high flow fittings from Eastwood. I had these when I had to repair a section of the fairing clear coat when I sanded throught it.

I bought some High-Flow fittings from Eastwood that are made by a premium spray gun company, Devilbiss. I feel I am still not getting enough air volume and the video about how to get the best performance from HVLP spray guns talks about how high flow fittings can really help.

Here is the difference in the inside diameter of the stock fittings and the Devilbiss High Flow fittings. It’s quite a difference.

Stock Quick Connect Fitting On the Compressor

Stock Quick Connect Fitting On the Compressor

Devilbiss High-Flow Quick Connect Fitting

Devilbiss High-Flow Quick Connect Fitting-MUCH BIGGER!!

Male Quick Connect: Left What I Had, Right, Devilbiss High-Flow

Male Quick Connect: Left What I Had, Right, Devilbiss High-Flow

I made this change after I finished the painting, but before I had to do the major repair to two sections of clear coat on the fairing.

Cleaning the Parts

Now, I clean the parts with paint prep to remove the dust and grit from sanding and any oils or other contaminants from my fingers. I wear a clean pair of nitrile gloves so I don’t get finger print oil on the parts. I already washed the parts twice, but you can see the paint prep still removes contaminats from the parts.

Paint Prep and Towels

Paint Prep For Cleaning Just Before Painting

Debris Removed by Pre-Paint Cleaner

Contaminats Removed by Pre-Paint Cleaner

Mixing the Primer

The primer has three components, primer, hardener and reducer.

Primer Materials and HVLP Paint Guns in Stand

Primer Materials and HVLP Paint Guns in Stand

The specification sheet shows I need to mix them in the ratio 4:1:1.

Primer Specifications and Instructions

Primer Specifications and Instructions

I bought some calbrated measuring cups so I can easily pour the right amount of primer, then the hardener and finally the reducer to make up as much mixture as I want. The cup has markings for various common mixtures with different final amonts so I can mix little (the “1” levels) or a lot (the “6” levels).

Container with Easy To Use Mixing Ratios

Container with Easy To Use Mixing Ratios

After I pour the ingredients into the mixing cup, I stir it for about a minute with a wooden stir stick to be sure all three components are completely mixed. Then I filter the mixture as I pour it into the container of the paint gun.

Paint Filter with Stand

Paint Filter with Stand

HVLP Gravity Feed Gun with Primer in Container

HVLP Gravity Feed Gun with Primer in Container

Now that the gun is filled and in the stand, I clean the tops of the cans to remove any material that ends up in the groove before replacing the lids. This ensures the lids seal tight, dried paint doesn’t get into the can and air won’t leak around the edge of the lid.

Keep Groove For Lid Clean To Prevent Drying Out

Keep Groove For Lid Clean To Prevent Drying Out

Paint Spraying Techniques

These You Tube video from Eastwood where I bought the guns provides a good review of painting techniques with HVLP spray guns.

Part 1

Part 2

I use newspaper folded over a scrap 1/4 inch piece of plywood to see how well the gun sprays the primer. Later, I found using masking paper was a better idea particulary with light colored primer and clear coat.

Test Panel

Test Panel

The instruction sheet with the gun tells me which knobs I can use to adjust the gun. I have three adjustment, spray pattern, paint flow and air flow.

Insructions for Adjusting the Paint Gun

Insructions for Adjusting the Paint Gun

I just bought this gun and I am not an experienced painter. I find it hard to get the gun to deliver the primer with in an even coat. It doesn’t want to flow very well. After several tests on the newspaper,I still have a splotchy pattern. I disconnect the gun from the air hose and take it back to the mixing bench. I empty the paint out of the gun back into the mixing container and add one more part reducer, mix it well, and then pour it back into the container on the gun. It flows a bit better but I still can’t spray the primer with a smooth even coat. So, I do the best I can in adjusting the gun, and dive in spraying the primer. It’s frustrating but I finally get all the parts primed with the first coat. Sometimes paint has its way with you and you just have to live with it and tell yourself that sand paper fixes all paint problems 🙂 When painting the parts I hang them with solid core wire and bunge cords hooked over some scrap romex cable in the paint booth.

========
NOTE: Later I found that reducing the inlet pressure to the gun to about 20 PSI greatly improved atomization.  Live and learn 🙂
========

Paint Booth Romex with Hangers

Paint Booth Romex with Hangers

I use more wire & bunge cords to carry the painted parts to the drying area and hang them up. I  arrange the drying area so the hanging parts won’t be in the way as I refill the gun and hang new parts. But with two bikes of parts to paint, the workshop gets pretty full when I finish.

Parts in Drying Area with First Coat of Primer

Parts in Drying Area with First Coat of Primer

Parts in Drying Area with First Coat of Primer

Parts in Drying Area with First Coat of Primer

Cleaning the Paint Gun

It’s very important to clean the gun after you finish painting. The “pot life” gives you some idea of how long the mixture can sit before it will harden. If that happens while the material is in the gun, you have a problem, a lot of work , or potentially, you junk the gun. Each gun has it’s own cleaning instructions. Mine says to remove the paint cup, clean it out with lacquer thinner, add clean thinner to the cup, spray it through the gun until clear, then disassemble the gun removing the nozzle, flow needle needle adjusting knob and spring and cleaning the parts and gun in lacquer thinner.  Here is the disassembled gun with the supplied cleaning brush and wrench for removing the mixing nozzle.

Disassembled HVLP Gun After Cleaning

Disassembled HVLP Gun After Cleaning

I soak the parts in an old 2 quart sauce pan with enough lacquer thinner to flood all the internal passages in the gun. I pour the dirty thinner into a clean quart paint can so I can reuse it. After a day or so, the solids drop to the bottom of the can and I can gently pour used thinner into the 2 quart pan to clean the gun again.

Results

I forgot there would be wet primer on the floor of the booth and it would get on my boots. When I was done, I had footprints on the bare concrete. I also managed to step in a pile of extra test panel newspaper sheets on the floor. Talk about the embarasment of having toliet paper on your shoe. 🙂 No worries. I tape some plastic on the floor to keep from adding to the mess. I can get the paint foot prints off the concrete when I’m done.

Oops ... Need to Put Plastic on the Conrete

Oops! I Need to Put Plastic on the Concrete Because …

Primer and Newspaper on the Soles of My Shoes

I Get Primer on the Soles of My Shoes

The parts are pretty rough as I wasn’t able to get the primer to spray very smoothly. The first part I primed, the rear fender, was the worst as I got the gun adjusted to work a bit better as I went along. I am not real happy with this, but I know I can remove all the drips and bumps with sand paper, so it’s not a catastrophe.

Primer Went on Too Thick-Runs and Bumpy

Primer Went on Too Thick-Runs and Bumpy

Preparing for the Second Primer Coat

I start by sanding out all the runs, bumps and high spots using wet 220/320 grit paper. My goal is to level the first coat so the low spots, dings and dents can be filled and sanded. I use the 320 where there are raised edges like the center rib of the front fender to avoid sanding through the primer. This is what the front fender looked like after I sanded out the run and bumps. You can see I managed to sand through in a couple of places.

Run Sanded Out

Run Sanded Out

Here are some of the dings and dents I need to fill. If you have good light and look at the parts along the side, the shiny areas are the low spots.

Low Spot at Crack Repair Needs Filling

Low Spot at Crack Repair Needs Filling

Dings in R75/5 Tank Need Filling

Dings in R75/5 Tank Need Filling

Gouges in Rear Fender Need Filling

Gouges in Rear Fender Need Filling

R75/6 Tank Ding From My First Road Race

R75/6 Tank Dent From My First Road Race

Filling Dents With Polyester Filler

I fill any dents first and if there are any blemishes after sanding the filler down, I fill them with glazing putty which I also use to fill in small low spots. The R75/6 has a deeper dent in the gas tank and needs polyester filler. This is the filler I am using.

Body Filler for Dents

Body Filler for Dents

It has two parts, the grey filler and the red hardener. The instructions give you guidance on how much of each to use.

Filler and Hardener (Red)

Filler and Hardener (Red)

I mix them on a plastic board I have, but you can use cardboard. I smear the two parts together with a plastic paddle, spreading them top to bottom and left to right and then scaping the mixture back into a pile and continue until I can’t see any more streaks of red in the mixture.

Mixing Filler and Hardner to Uniform Color

Mixing Filler and Hardner to Uniform Color

I use the plastic paddle to apply the filler. I found pulling it down over the dent seemed to work best for this dent. I want to shape it fairly close to the contour of the tank and I want to have it proud of the tank surface if I can.

Applying Filler Over Dent-This Direction Worked Best

Applying Filler Over Dent-This Direction Worked Best

If the dent is deep, I add filler in layers letting the lower one dry before adding the next. I let my final filler layer dry overnight.

Filler Settiing Up

Filler Settiing Up

I sand the filler with wet 220 grit to smooth it and then finish it with wet 320 grit. There are some small dimples and blemishes visible and I use the glazing putty fill those in and sand that smooth with wet 320 grit.  When I have the surface smooth, I use my heat gun to heat up the filler and glaze to evaporate any absorbed moisture.

Feathered Filler on Tank, Still Some Shallow Voids

Feathered Filler on Tank, Still Some Shallow Voids

Filling Low Spots with Glazing Putty

The R75/5 gas tank has dents near the front and some low spots on the rear of the tank. The rear fender has a couple shallow gouges and some low spots where I repaired some of the mounting holes in the fenders. This glazing putty hardens in a couple minutes. I use the plastic paddle to apply it and smooth it over the low spots.

Glazing Putty

Glazing Putty

I apply some to the R75/5 rear fender.

Low Spots Filled with Putty

Low Spots Filled with Putty

And to the rear and front of the gas tank.

Tank Dings Filled with Putty

Tank Dings Filled with Putty

Tank Dings Filled with Putty

Tank Dings Filled with Putty

I let it harden for several hours and then lightly wet sand it with wet 320 grit. Then I use my heat gun to remove any aborbed mositure. You can see the before and after in the pictures below. I try to feather the edge of the putty so it blends into the primer.

Glaze After Drying

Glaze After Drying

Sanded Glaze with Edges Feathered Into Primer

Sanded Glaze with Edges Feathered Into Primer

I use my fingers to feel where I feathered the putty into the primer. When I can’t feel an edge, it’s blended in.

Use A Finger Tip to Feel Ridges and Rough Spots

Use A Finger Tip to Feel Ridges and Rough Spots

Sometimes the edge of the putty is raised more than the center. I fold the paper to get a sharp edge and gently sand down the high ridge of the putty. This helps prevent sanding down the lower areas of the putty so much they don’t fill the low spot any more. Once I have the edge smoothed down, I use a small block of wood to gently level the glaze uniformly.

Use Folded Sand Paper Edge to Feather High Edge of the Glaze

Use Folded Sand Paper Edge to Feather High Edge of the Glaze

Applying the Second Primer Coat

I ended up getting two different colors of primer. This is a nice idea as it is much easier to see where you need to spray the second coat if the colors are different.  I washed all the parts and let them dry overnight and then used more pre-paint prep to clean them and remove the last traces of dust and finger print oil. I hung the parts in the booth when I sprayed the first coat of primer but I decided to also have some supports so I can put the tank and fenders horizontal to make it easier to paint the sides. I used some jack stands and clean shop clothes to pad the supports.

Jack Stands for Fender & Tank Supports

Jack Stands for Fender & Tank Supports

Tank on Supports

Tank on Supports

Fender on Supports

Fender on Supports

As I did before, I measure the primer materials, mix them well, filter them into the paint cup on the gun and then shoot the primer on newspaper test strips to adjust the gun. But, this primer floww even less than the first coat of primer. I was not able to get the gun to lay the primer down very evenly.

========
NOTE: Later I found that reducing the inlet pressure to the gun to about 20 PSI greatly improved atomization.  Live and learn 🙂
========

So, quite frustrated, I apply the second coat as best I can to the parts. As you can see, it went on very rough with sags drips and ripples. Everything looks pretty ugly at this point. I was pretty discouraged and needed to just step away from the project for a couple of days to get my enthusiasm back 🙁

Very Chunky 2nd Primer Coat on Tank :-(

Very Chunky 2nd Primer Coat on Tank 🙁

Front Fender Has Sags

Front Fender Has Sags

I cleaned up the shop and let the primer dry for 48 hours before I started sanding out the parts. As I said earlier, the nice thing about paint is sand paper fixes all mistakes. Here is the front fender with runs and lots of rough spots.

Rear Fender is Bumpy with Drips

Rear Fender is Bumpy with Drips

Here is the fender after using wet 220 grit to remove sags and rough spots. You can see some pits and some bumps along the raised center rib of the fender.

Uneven Primer Along Raised Center Rib

Uneven Primer Along Raised Center Rib

I switched to 320 and then 400 grit. Using the 400 grit paper folded to get a sharp edge, I carefully sand out the bumps along the seam of the center rib. In time, everything gets smoother.

Getting Much Better

Getting Much Better

I try not to sand through both coats of primer, but I manage to to do it anyway. I planned on having to shoot more primer to fix some sand through spots such as these, but I want to keep them to a minimum. The long straight white lines in the picture below are reflections, not sanded through streaks. The sanded through spots are on the edge of the lower fender raised trim and an oval section in the middle of the fender.

Spots I Sanded Through Both Layers of Primer Need Spot Priming

Spots I Sanded Through Both Layers of Primer Need Spot Priming

And, the rear fender around the tail light bracket hole is a bit high so I manage to over do it there as well.

Rear Fender Sand Through Needs Spot Priming

Rear Fender Sand Through Needs Spot Priming

I use my halogen shop light to illuminate the surface at an angle so I can see low spots after I smooth out the primer with wet 220 grit.

Strong LIght Helps Find Low Spots & Blemishes

Strong LIght Helps Find Low Spots & Blemishes

The light reflects off any low spots as you can see in the picture below. I need to sand these out using 320 or 400 grit until they are gone and the primer is smooth and even. It is okay if I sand through the top primer coat which I have to do in several places to get a smooth surface.

Low Spots Are Shiny-Need More Work with 400 Grit

Low Spots Are Shiny-Need More Work with 400 Grit

When I can’t see any shiny spots, I final sand the part lightly with wet 600 grit paper in a circular motion so there are no deep linear scratches. Patience is a virtue and going slow with finer grit paper where there are raised areas helps keep from sanding through the primer again. It takes awhile to smooth out the raised trim section along the edge of the fenders and the seams along the edge of the gas tank.  A light easy touch with a folded edge of the paper andI get the bumps out.

Patching Primer Sand Through

After sanding out the lumpy second primer coat, there were a couple places where I sanded through and I need to patch the primer. If the second coat had gone on smooth, likely I would have just sanded it down with 600 grit and been done. But I had to use 220, then 400 and finish with 600 and its hard to keep from sanding through the primer. For small spots and along trim edges, I use a small artists paint brush to paint the primer on.

Small Brush for Patching Small Sand Through Spots

Small Brush for Patching Small Sand Through Spots

I did this on the edge of the gas tank seams where it’s hard to spray the primer smoothly.

Applying Primer to Tank Seam Edges

Applying Primer to Tank Seam Edges

And for small spots, the paint brush is the best way repair a sand through. But there were several areas where I needed to spray the primer to cover body filler areas that were visible.

Getting the Gun To Spray Primer Smoothly

The primer data sheet calls for a 1.5 mm tip but I had 1.4 and 1.8 tips. When I first sprayed the primer I tried the 1.4 mm tip and the primer sprayed very spotty so I used the 1.8 mm tip for the first and second coats. I decided to experiment more with the gun.  I figured I need more air flow through the nozzle to atomize the primer better. The gun instructions state that air supply to the gun can be 29 PSI and the gun will maintain 10 PSI at the cap.

I started the compressor and tried boosting the supply pressure to 32 PSI to see if I could hear and feel more air on my hand.  In fact, the air flow seemed to drop!!! That was completely unexpected.  So I cut the supply pressure back to 25 PSI and the air flow through the nozzle increased and it increased even more at 20 PSI. Ah, now we are getting somewhere. Reducing, not increasing, supply pressure to the gun provides more air flow and better atomization. Completely counter-intuative.

I did some searching on the web and found a short video that talks about HVLP guns and the affects of pressure reduction on atomization. I put a link to it here.

If I heard this correctly, lowering the supply pressure to the supply side of the gun can improve atomization as the cap is better able to mix the slow moving liquid paint with the fast moving air. Since the supply pressure was the maximum 29 PSI, there was too little time for the air and paint to mix in the cap for good atomization. If that’s true, I think it was the cause for the trouble I had spraying the primer.

This time, I use the 1.4 mm nozzle and needle. I mix up a small amount of light colored primer at a 4-1-2 ratio. I set the air supply to 21 PSI and spray some primer on the test panel. Oh Joy. Smooth even application with no lumps, drips or sags !!!!

Lower Inlet Pressure to Gun Works Better

Lower Inlet Pressure to Gun Works Better

I shot the larger spots on tank and rear fender areas on the R75/5 and the tank and R90/S fairing for the R75/6. While I let it flash for 10 minutes before spraying a second coat, I touched up the small spots with the small paint brush.  After the second coat, some of the sprayed areas only showed some minor orange peal. Much, much better.

Minor Orange Peel in Primer is Easy to Sand Out with 600 Grit

Minor Orange Peel in Primer is Easy to Sand Out with 600 Grit

Rear Fender Primer Patch Is Nice and Smooth

Rear Fender Primer Patch Is Nice and Smooth

The repairs are easy to sand with 600 grit and I’m ready to shoot the base coat. Next weekend is the three day Memorial Day holiday, and I hope to finish painting both bikes then.

Peeling The Tape Off the Fairing After Priming

The fairing is the only piece that has tape masking off the edge of the primer. I decided to peel the tape off and apply new tape before applying the base and clear coats. I want to prevent damaging the paint when I peel the tape and if there is a large build up on it (2 coats of primer, 2-3 coats base, 3 coats clear), it’s easy to damage the paint when I peel the tape.

I use a new single edge razor blade to score the edge of the primer next to the tape edge and then gently peel the tape bending vertical and away from the primer edge and go slowly.

Pulling Masking Tape Off The Fairing with Primer Coats

Pulling Masking Tape Off The Fairing with Primer Coats

It comes off with a clean edge. I apply a new layer of tape before spraying the base and clear coat layers.

Spraying The Base Coat (Color Coat)

The data sheet for the base, or color, coat calls for a 1.2 mm needle and tip. The mixing ratio of color to reducer is 2:1. I shake up the color can for a couple of minutes and then open it and stir the contents with a paint stick to ensure a good mixture of metal flakes with paint.

I mark the 2:1:1 column on the plastic paint cup with a Sharpie. I’ve been using the 4:1:1 column with the primer, and I don’t want to get the mixture wrong out of “habit”.

Monza Blue Paint and Syringe for Adding Reducer

Monza Blue Paint and Syringe for Adding Reducer

When I poured the reducer into the primer mixture, it always dripped down the outside of the can. I decided to use a large syringe to suck it out of the can and add it to the mixing cup. This worked fine as long as I slowly pushed the plunger down to keep from splashing.

Instead of newspaper, I used masking paper to calibrate the spray gun. I pulled the trigger in a quick on/off motion with the gun about 4 to 6 inches from the paper. The pattern should be a uniform oval shape with more paint in the center than the edges.

Testing Gun Pattern for a Nice Oval Shape

Testing Gun Pattern for a Nice Oval Shape

I tweaked the paint flow setting a bit and then, the moment of truth. It’s time to put color on the parts.

I plan to shoot 2 coats and then a final light coat to get the metal flake looking uniform. The HVLP guns really work best when they are 4-6 inches from the part. The older style syphon gun I used befoere need to be 8-10 inches from the part. Since I shoot multiple coats, the first coat doesn’t have to completely hide the primer. I aim for an even coating and avoid the urge to over spray the part. You can see the darker primer showing through on the gas tank after the first coat and some areas near an edge with not very much paint.

First Base Coat with Dark Primer Showing Through

First Base Coat with Dark Primer Showing Through

The paint will flash, or appear dull, in about 5 to 7 minutes. I wait for all the paint to flash and then shoot my second coat. I wait for that to flash, and then apply the light 3rd coat. When that has flashed, I carefully inspect the part in strong light looking for any spots I missed or where I can see primer showing through. Then I hang it in the drying area of the shop to dry.

As shown on the fairing, I got a build up of metal flake in a spot where I sprayed the paint a bit thicker. No worries. The 3rd coat will even this out.

Almost a Sag on Fairing with Metal Flake Build Up

Almost a Sag on Fairing with Metal Flake Build Up

Here is what that same area looks when it was drying. You can’t see the build up any more.

Fairing Base Coat Complete

Fairing Base Coat Complete

Drying time is two hours. By the time I finish spraying the parts and then cleaning the gun for use with the clear coat, its about 3 hours from when I started.

Rear Fender Base Coat Complete

Rear Fender Base Coat Complete

Gas Tank Base Coat Complete

Gas Tank Base Coat Complete

Spraying the Clear Coat

The clear coat calls for a 1.3 to 1.5 mm needle and tip. After cleaning the gun, I put in the 1.4 mm tip and needle and test spray on the masking paper. It’s too thick. I empty the paint cup into the mixing cup, replace the 1.4 mm with 1.2 mm needle and tip, put the 1.4 mm parts in lacquer thinner to soak and then test spray again. This sprays more evenly and doesn’t look like it is going on too thick.

The goal with clear coat is to get a smooth glass like surface. But, I’m not that good and I know I will have orange peel and rough spots in the clear coat. I try for the smoothest surface I can get. The clear coat takes about 10 mins to flash between coats and I spray three coats. If I get a run or sag, again, I can sand that out, so no need to panic.

Here are the clear coated parts. You can see orange peel and some roughness they will disappear when I sand out the clear coat. That’s the next task.

Clear Coated Fenders

Clear Coated Fenders

Clear Coated Fairing

Clear Coated Fairing

Clear Coated Tank

Clear Coated Tank

Fixing Problems When Painting

Removing a Schmutz or Dust Bunny

I’m also spraying my 1975 R75/6 in Smoke Silver. I had a problem on the fairing after I applied the silver base coat. I got a schmutz or two caused by some fibers getting into the paint. I waited for the coat to flash and then used some 1500 grit dry, not wet, paper to carefully sand out the fibers. I don’t want to apply any water to the paint, so I keep the paper dry and expose a clean surface when it loads up with paint so I don’t create deeper scratches in the soft paint.

R75/6 1500 Grit Dry Sand Out of Schmutz

R75/6 Showing a Sanded Out Schmutz with 1500 Grit Dry Paper

Next, I sprayed a small amount of pre-paint cleaner on a clean towel and gently remove the sanding debris until the towel is clean. I blow some air from the paint gun on the spot to dry it completely. Then I spray over the spots, let them flash and then continue with the 2nd coat of silver. Here is what it looked like after the light third blending coat. You can’t tell the difference.

R75/6 2nd Base Coat and the Schmutz is All Gone

R75/6 2nd Base Coat and the Schmutz is All Gone

Base Coat Build up On Edges and Seams

The other problem I get is paint build up on raised ridges, trim edges and the tank seams. The HVLP gun will only shoot air if you pull the trigger just a bit. I shoot air on these areas after I paint to help set the paint it prevent drips and runs. If I get a run in the base coat, I let it flash, spray some air on it to set it and then I use 1500 grit dry, not wet, paper to level it. Then I reshoot that area, let it flash and then shoot another light coat to help blend the spot and to have 2 coats on top of the sanded surface.

Clear Coat Runs and Sags

If I get runs or sags in the clear coat, I use the air from the gun to flatten them out as much as I can and then let that coat flash. I continue adding my next coat. When everything is dry and ready for sanding out the orange peel and rough spots, I sand out any clear coat sags to blend into the finish. There is no need to use a clean rag to remove a clear coat sag while painting; that can create more problems than it solves.

Sanding Out and Buffing the Clear Coat

I let the painted parts sit for several days so the paint has time to dry completely. On my first paint project, I used 600 grit wet to speed up removal of the rough spots and orange pee and then sanded with 1500, 2000 and finally 2500 wet paper. However, I had some scratches that I couldn’t get out. So, this time, I won’t use anything more coarse than 1500 grit wet on the runs and sags in the clear coat.

I want to protect the edges of the parts while I work, so I put the parts on top of my jack stands on the work bench. I can sand and not worry about damaging the paint on the edge of the parts.

Keep Fender Edges off the Work Bench with Jack Stands

Keep Fender Edges off the Work Bench

Here is a close up of the rear fender showing a reflection in the clear coat. You see even though the surface is very shiny, the roughness in the clear coat makes the edges of the reflection wavy and the image is hazy.

Blurry Reflection From Clear Coat

Blurry Reflection From Clear Coat

I start with 1500 wet paper. I want to remove all the shine in the clear coat. You can see here the peaks and valleys in the surface. This is why the reflection is blurry and hazy.

1500 Grit Wet Sanding Shows Hills & Valleys

1500 Grit Wet Sanding Shows Hills & Valleys

If you listen to your paper as you sand and feel the resistence of the paper on the surface, you will know when the surface is getting smooth. The paper will glide over the surface with no drag and you just hear a faint woosh rather than a grinding sound. You don’t want to take off any more clear coat than is needed to completely level the surface and have a uniform dull reflection.

When I can’t see any more shiny spots in the surface, it’s time to use the 2000 wet paper. When I get done, the hazy clear coat is beginning to reflect the light again as you can see next to my finger.

Slight Reflection After 2000 Grit Wet Sanding

Slight Reflection After 2000 Grit Wet Sanding

Next, I lightly sand with 2500 wet paper. The surface is shining a little bit more.

Now I am ready to buff out the clear coat and make it shine. I use Griot’s Garage polishing compounds. There are four different grits; #1 is the most coarse and #4 is a very fine polishing compound.

Griot's Polishing Compounds-Start with #1, Finish with #4

Griot’s Polishing Compounds-Start with #1, Finish with #4

To be clear, these are not waxes, but polishing compounds. I don’t put wax on the parts for several months after they are painted so the paint has time to harden completely.

I use a 3 inch random orbital sander and use a clean pad for each polish number.

Apply Griot's Polish with 3 Inch Random Orbital Polisher

Apply Griot’s Polish with 3 Inch Random Orbital Polisher

I don’t want to use a pad that has coarse grit, add some fine grit polish, and continue polishing. I polish a small section at a time. For the gas tank, I polish the top, then each side and then the bottom side. I add enough polish to the pad to cover it and then continue to polish the section until the polish starts looking thin. I wipe off the layer of polish with a clean micro fiber cloth. Like the pads, I use a separate cloth with each polish grit. I have different color clothes so I don’t get them confused. After I finish polishing a part, I wash out all the pads and micro fiber cloths with water and dry them so they don’t accumulate bits of clear coat that can scratch the surface.

Here is set of pictures showing the result after polishing the center section of the rear fender with different polishing grits. The left side of the fender isn’t polished but is sanded with 2500 wet paper for comparision.

Griot's #1 Polish on Center of Rear Fender

Griot’s #1 Polish on Center of Rear Fender

Griot's #2 Polish on Center of Fender

Griot’s #2 Polish on Center of Fender

Griots's #4 Polish on Center Section

Griots’s #4 Polish on Center Section

The clear coat is smooth enough to reflect the newspaper like a mirror. When I look closely at the surface, there are no scratches visible and that’s the goal. If I see some scratches, I go back with a more coarse polish and see if I can remove it and so on. If that won’t work, I go back to 2500 wet paper and sand over that area and then work back up through the polish grits until the scratches are no longer visible.

Here is the gas tank and front fender after sanding and polishing with the four Griot’s polishes. They are a great improvement from the mess I had after spraying the second coat of primer.

Gas Tank Polished

Gas Tank Polished

Front Fender Polished

Front Fender Polished

Patching Minor Clear Coat Sand Through

I wasn’t watching close enough and managed to sand through the clear coat and paint on the raised edge of the rear fender :-(.

Sand Through Clear Coat on Raised Edge of the Rear Fender

Sand Through Clear Coat on Raised Edge of the Rear Fender

NOTE: To avoid this, I learned that you should apply masking tape over the raised edges. That way, the sanding block won’t scuff the edge when sanding the rest of the part.  To avoid the chance of peeling your new paint when you remove the tape, “whet” it by dragging the sticky side across your pants a couple times. This removes some of the adhesive and reduces the stickiness.

Unlike the old days with lacquer, where you could blend in a patch since the solvents would melt the old paint and integrate the new paint with the old (it’s thermoplastic paint) you can’t really apply new clear coat on top of old and get it blend. It cures via a chemical reaction (it’s thermosetting) so the new clear coat does not blend in, but sits on top adhering only through a mechnical bond via the scratches in the old clear coat that the new flows into.

However, for a small spot like this, I am going to patch the base and clear coat. It will last for awhile and then need to be repaired again. But the fender edges get stone chips anyway, so I’ll likely have to patch them over time, or just let them go until I redo the paint again.

I found that polishing out the rest of the fender before doing a minor clear coat patch protects the repair better. After polishing the rear fender I use some of the Monza Blue with reducer I saved for just this situation. I have several small hobby paint brushes and pick one that is about the width of the exposed primer. I apply the paint very lightly, dry with my heat gun for a few seconds, add another layer and dry it again. After a couple hours, I mix 1/2 teaspoon of clear coat with 1/4 teaspoon of hardner (2:1 ratio) and lightly brush it over the paint repair. I dry it and add a second coat. Then with 2000 wet paper, I very lighly sand the clear coat to remove the roughness and then a light sand with 2500 wet paper. I use the #3 and #4  Griot’s polish (finest polish) and lightly polish the repair to blend it in. All better.  The white streaks are from the polishing compound and are not new sand through areas 🙂

Repaired Clear Coat Sand Through After Polishing

Repaired Clear Coat Sand Through After Polishing

Paint the Rear Tail Light Assembly

I decided to use rattle can paint to repaint the rear tail light assembly. I sanded it down with 600 wet paper.

Sanded Tail Light Assembly

Sanded Tail Light Assembly

I spray two coats of primer for plastic and then 4 light coats of semi-gloss black. When  I use rattle can paint, there are inevitably schmutz in the paint. I sand the tail light with 1500, 2000 and then 2500 wet paper as I did with the Glasurite paint and then polish it using all four Griot’s polishes. It came out very nice.

Rattle Can Painted Tail Light Housing After Sanding and Polishing

Rattle Can Painted Tail Light Housing After Sanding and Polishing

Next up is painting the white pin stripes on the fenders and the tank. I am debating if I want to put white pin stripes on the Windjammer fairing or not and I still have to sand and polish the fairing so I have some time to think about what I want to do.

6 thoughts on “51 BMW 1973 R75/5 Paint the Tank, Fenders, Fairing and Tail Light

  1. Pingback: 1973 R75/5 Rebuild: Painting Tank, Fenders, Windjammer & Tail Light | Motorcycles & Other Musings

  2. Pingback: 1973 R75/5 Rebuild: Assembling Windjammer II Fairing | Motorcycles & Other Musings

  3. excellent write up as always, Brook – question: for the tail light paint, why semi-gloss as opposed to gloss … ?

    thank you and best regards,

    –Luis

    • Luis,

      The short answer is, it’s what I had on hand. Since I planned to sand out and polish the paint, it ended up with a nice level of gloss.

      Best.
      Brook.

Leave a Reply

Your email address will not be published. Required fields are marked *