51 BMW 1973 R75/5 Refinish Steering Damper Knob

I decided to refinish the steering damper rod which showed every bit of its 40 years of service. I’ve not tried to restore plastic parts before and I wanted to see how closely I could bring it back to its original condition.

Steering Head Grunge & Damper

Steering Damper Dings and Steering Head Grunge

Sanding Out the Scratches

I started with 220 grit wet sanding paper to remove the nicks and gouges. I use water with a drop or two of dish detergent to float the sanding fines off the surface and to help keep the paper from clogging.   Then I moved down to 600 grit. Here is the result after 600 grit.

Steering Damper 600 Grit

Steering Damper after 600 Grit

I proceeded to finer papers, 1500, 2000 and finally 2500 grit and I arrived at this result.

Steering Damper 2500 Grit

Steering Damper After 2500 Grit

It shows a slight shine and there are some scratches visible, but all the large nicks and dings are now gone and surface feels smooth to the touch.

Polishing the Plastic

I purchased Griot’s set of polishes and I have a 3 inch random orbital sander and a palm sander. I and used the palm sander with the 3 inch foam polishing pads.  Here’s Griot’s #1 polish with the foam pad mounted on the palm sander,

Griots Polish #1

Griot’s Polish #1

and the damper after working in the polish and removing most of the residue with a clean shop towel.

Steering Head Polish #1

Steering Head After Polish #1

And now, on to Polish #2

Griots Polish #2

Griot’s Polish #2

and the result.

Steering Damper Polish #2

Steering Damper After Polish #2

Then, Polish #3

Griots Polish #3

Griot’s Polish #3

and the result. The finish is approaching a “like new” shine.

Steering Damper Polish #3

Steering Damper After Polish #3

And this is Polish #4 for light swirl marks,

Griots Poilish #4

Griot’s Polish #4

and the final product. Almost a mirror finish which closely matches the shine on the stem of the damper rod.  I’m pretty pleased with this first attempt at refinishing plastic parts.

Steering Head Polish $4

Steering Head After Polish #4

I lost some of the detail in the center. I should have masked that off before I started, but I mistakenly thought I could control the sanding to avoid that area. Lesson learned.

Adding a Modern BMW Emblem to Damper Knob

So, I’m going to update the center of the damper knob and add a BMW medallion from a 2004 R1150-RS which I think will be very distinctive touch.

Source: MAX BMW Parts Fiche, Part # 51 14 2 308 800

I need to drill a shallow hole with a flat bottom in the center of the damper knob. I got a 3/4 inch Forstner drill bit at Home Depot.

3/4" Forstner Bit

3/4″ Forstner Bit

Forstner Bit

Forstner Bit

This style bit is designed for drilling a flat bottom hole. The emblem is very close to 7/8 inch, but I couldn’t find a 7/8 inch bit, only a 3/4 and 1 inch. I opted for the 3/4 and figured I could taper the top of the hole by hand to insert the emblem.

I drew two pencil lines at 90 degrees across the center of the knob. It took a couple tries to get the center located. Then I clamped the damper in my vice with rubber jaws. I used my battery powered variable speed drill and drilled at a slow speed to prevent melting the plastic material.

Drilling Hole

Drilling Hole at Slow Speed

The emblem is about 3 mm thick so I was careful to make the hole just a bit deeper. Since I have to taper the top edge with a knife, I don’t want the hole too deep.

Flat Bottom Hole

Flat Bottom Hole about 4 mm deept

I used a utility knife with a new blade and slowly carved an angled edge to the hole test fitting the emblem until it set at the right depth. The back of the emblem has a glued material used to stick it to the plastic bracket on the 1150-RS. I trimmed away the protective paper so I could insert the emblem.

Beveling the Hole Using Sharp Knife

Beveling the Hole Using Sharp Knife

As you can see the knife slipped a couple times. 🙁 SO, back to sanding and polishing the knob to remove those. I used 220 grit wet sanding to get the scratch out, then moved to 320, 400, 500, 1500 and finished up with 2000 grit.

Wet Sanding

Wet Sanding to Remove Knife Nics

To polish, I used the Griot 3 inch polisher and started with #1 polish (coarse) and finished up with #4 (extra fine).

Griot's 3 inch Sander and Polishing Compound

Griot’s 3 inch Sander and #1 Polishing Compound

I installed the emblem using black silicone seal. I peeled the protective paper off the back and put enough silicone seal in the hole to have the back of the emblem touching it with just a bit squeezing out the side. I cleaned the excess silicone off with a clean blue shop towel. Last, I used a little Armor All on the knob.

After about 2 hours of work, here is the final product installed on the bike with the polished upper fork brace. I think the emblem adds a nice touch to the R75/5.

Polished Steering Damper Knob with BMW Emblem

Polished Steering Damper Knob with BMW Emblem

One thought on “51 BMW 1973 R75/5 Refinish Steering Damper Knob

  1. Pingback: 1973 BMW R75/5 Rebuild: Refinishing Headers, Headlight and Steering Damper | Motorcycles & Other Musings

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