Category Archives: 1973 BMW R75/5 Rebuild Blogs

1973 BMW R75/5 Rebuild: Replace Alternator Brushes and Front Crankshaft Seal

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I had replaced the leaking camshaft seal earlier and you can read about how I did that here:

The alternator has 97,500 miles on it, so I decided to replace the brushes.  I hadn’t seen evidence of oil leaks from the front crankshaft seal, but it turns out its very easy to replace it when I was replacing the alternator brushes.  I also cleaned the rust and flaking paint off the starter motor and then painted it to stop any further rusting.

You can read about what I did on both of these tasks here:

I bought the brushes at Euro Motoelectrics which is here in Denver, CO.  I also picked up a hardened bolt to extract the alternator rotor from the tapered nose of the crankshaft.

Rotor Puller Bolt and New Brushes

Rotor Puller Bolt and New Brushes

These jobs went pretty quickly and were straight forward.  I found I needed a  200/260 watt soldering iron to remove the old solder and solder the new brushes as they are soldered to a large plate that dissipates heat pretty well.  My 140 watt gun wasn’t up to the task.

Old Brushes Removed from Holder

Old Brushes Removed from Holder

New Brushes Installed

New Brushes Installed

Shaft Seal Puller Installed

Shaft Seal Puller Installed With Adjustable Pivot Pin Resting on Engine Housing

At this point, the engine work I planned is done.  Here is the painted starter motor installed and the engine after polishing up the cases.

Painted Starter Motor Installed

Painted Starter Motor Installed

Polished Engine

Polished Engine

Polished Engine

Polished Engine

1973 R75/5 Rebuild: New Oil Pan Gasket and Camshaft Seal

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Both of these showed signs of leaking oil and I replaced them.  You can read about how I did this here:

When replacing the oil pan gasket, I also cleaned the oil pickup screen and checked to be sure the bolts holding the pickup are tightened to the proper torque, 72 INCH/Pounds, not FOOT/Pounds.  I used an INCH/Pound torque wrench on them and also on the oil pan bolts which were set to 70 INCH/Pounds in several stages.  These bolts are easy to strip out unless you use an INCH/Pound torque wrench.

I put in new points and a condenser when I replaced the cam shaft seal and replaced the timing plate machine screws with two Allan head cap screws, M4x0.7×10. Now its easy to adjust the timing plate points cam with the centrifugal advance weights installed with a small Allan head wrench. And, I won’t be wallowing out the slot on machine screws as happened in the past.

I used my larger adjustable seal puller to remove the camshaft seal, but it makes me nervous since the camshaft seal is small and I don’t want to score the camshaft. After I got the camshaft seal pulled, I looked for a puller for small seals. I found a very promising one, Lisle 58430 shaft seal puller. It’s available at some auto parts stores, but I ordered mine from Amazon.

Lisle_58430SealPuller

Lisle 58430 Shaft Seal Puller

I think this will work very well on future seal pulling jobs.

 

 

 

 

Here are a few pictures of the work.

Replacing Oil Pan Gasket

Engine on Side to Remove Oil Pan

Engine on Side to Remove Dirty Oil Pan

Permatex Gasket Remover Soaking In

Permatex Gasket Remover Soaking In

Checking Torque (72 INCH/pounds) on Oil Pickup Bolts

Checking Torque (72 INCH/pounds) on Oil Pickup Bolts

Clean Pan Mating Surface

Clean & Polished Pan Mating Surface

Clean Oil Pan with New Pan Gasket

Clean Oil Pan with New Pan Gasket

Replacing Camshaft Seal

Leaking Cam Shaft Seal

Leaking Cam Shaft Seal

Points Plate

Points Removed and Timing Plate Ready to Remove

Old Seal

Old Seal

Driving Cam Shaft Seal

Driving Cam Shaft Seal with 5/8 Inch Spark Plug Socket

New Points and Allen Head M4x10 Cap Screws

New Points and Allen Head M4x10 Cap Screws

1973 R75/5 Rebuild: Installing a New Clutch

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I decided to replace the original clutch after inspecting it and measuring the parts. Many were close to, or past, the minimum thickness. You can read about the procedure I used to install the new clutch in this web page:

I ordered the new clutch parts from Tom Cutter at Rubber Chicken Racing Garage who sent me the following:

21 21 1 250 035 Diaphram Spring (Heavy Duty)
21 21 1 251 801 Pressure Plate
21 21 1 236 332 Clutch Plate
21 21 1 231 666 Compression Ring
21 21 1 231 463 Filister Head Cap Screw (6)

Here are a couple of the pictures included in write-up.

Old (top) & New Clutch Parts

Old (top) & New Clutch Parts, Inside to outside, Left-to-Right

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Supplies and Special Tools to Mount the Clutch

Toothpick Application of Thin Layer of Honda 60 Molypaste to Edge of Fingers of Diaphragm Spring

Toothpick Application of Thin Layer of Honda 60 Molypaste to Edge of Fingers of Diaphragm Spring

Clutch Diaphragm Spring Against Face of Flywheel

Clutch Diaphragm Spring Against Face of Flywheel

New Clutch Bolts and Long Bolts

New Clutch Bolts Inserted and Long Bolts Ready to be Removed.

Transmission Aligned with Engine

Transmission Aligned and Tight to the Engine Clutch Housing

1973 R75/5 Rebuild: Remove/Install Flywheel, Replace Rear Main Seal, Oil Pump Cover and O-ring

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I posted a new page on removing the flywheel, replacing the rear main seal, oil pump cover and cover o-ring and installing the flywheel. This also covers a repair to a leak I found in one of the crankshaft flywheel bolt holes.

The work I did was guided by a lot of advice and web content shared by others who have gone before me.  I’d like to acknowledge folks who regularly participate on the BMW Airhead forum on Micapeak.  In particular, Tom Cutter who runs  Rubber Chicken Racing Garage and Bob (Snowbum) Fleischer who has a great technical library on all things BMW motorcycles, answered questions I posted on the Micapeak forum and in personal Email and phone conversations.  I also used web materials posted on  Duane Ausherman’s site.

Here a few pictures from the write up.

Make-do Engine Stand

Make-do Engine Stand

10mm Long Bolt in Alternator to Block Crackshaft

10mm Long Bolt in Alternator to Block Crackshaft

Flywheel Bolts out And Oil Leaking

Flywheel Bolts Out And Oil Leaking From Crankshaft Hole

Removing Oil Pump Cover with Impact Driver

Removing Oil Pump Cover with Impact Driver

Tightening Bolt to Pull Rear Main Seal

Tightening Bolt to Pull Rear Main Seal

Heated to 220 F

Heating Flywheel Bolt Circle to 220 F Prior To Installation

1973 R75/5 Rebuild: Clutch Removal and Inspection

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After I had removed the engine, I removed the clutch to inspect it.  Based on the inspection and information I found on  Duane Ausherman’s site, I decided to replace the entire clutch.

Here is the web page I wrote up on removing and inspecting the clutch.

I’ll document the installation of a new clutch when I complete the work in another web page.

I’d like to acknowledge folks who regularly participate on the BMW Airhead forum on Micapeak.  In particular, Tom Cutter who runs  Rubber Chicken Racing Garage and Bob (Snowbum) Fleischer who has a great technical library on all things BMW motorcycles, answered questions I posted on the Micapeak forum and in personal Email and phone conversations.  Their knowledge makes the life of a “hobbyist”, such as I, less stressful and much more fun.

Here are a couple of pictures from the web page writeup.

Bar Preventing Rotation When Removing Clutch Bolts

Bar Preventing Rotation When Removing Clutch Bolts

Backing Off Clutch Pressure 1/2 Turn Per Bolt at a Time

Backing Off Clutch Pressure 1/2 Turn Per Bolt at a Time

Clutch Parts Order: Bottom Clutch Pressure Ring, Top Clutch Diaphragm Spring

Clutch Parts Order: Bottom Clutch Pressure Ring, Top Clutch Diaphragm Spring

Diaphragm Spring Finger-Wear on Edges

Diaphragm Spring Finger-Wear on Edges

Clutch Pressure Plate Facing Engine Showing Grooves from Diaphragm Spring

Clutch Pressure Plate Facing Engine Showing Grooves from Diaphragm Spring