1938 DKW SB350 Restoration Update April 2025

After we discovered that the clutch was not really operable, the clutch basket was pulled from the bike and I ordered a new set of cork plugs. These arrived surprisingly quickly from Germany on 11 April. See the proceeding post for the details here: https://dkwautounionproject.blogspot.com/2025/04/1938-dkw-sb350-restoration-update-march.html

I had cleaned up and polished the metal plates in the proceeding weeks. The condition was pretty good as far as I was concerned.

I had some time over Easter so I set to it. The cork plugs are twice the height required in the clutch, so each plug was cut in half using a craft knife. Some plugs were a little more accurate than others but all will need to be sanded down to a flat surface when they're mounted in the plates.

The cork needs to be boiled to make it soft and pliable enough to fit in the holes. Half an hour on a rolling boil was enough. It must be noted that once out of the hot water they cool down very quickly, so it's best to fit them in small batches while the rest 'cook.'

To my surprise, the cork was very easy to install. There was some inevitable losses due to seams and weaknesses in some of the cork plugs, but the bags contain more than sufficient for two sets of clutches.

The bottom plate was actually the easiest to fit.

It took about half an hour to fit all the small plugs. The big plugs follow the exact same process.

Almost done.

Job completed. It was a very easy and quite satisfying task. Now, the cork needs to dry as they were thoroughly cooked out.

Once it was dry I gave each of the cork plates a good sand to make them smooth and flat. The cork sanded very easily.

The clutch 'reassembled'. The clutch plates will need a finer sanding to get them to the right thickness and fit. I will leave that to the experts to do as I don't want to sand anything down too far that would undo the good work above. Hopefully this will be the last fix before the bike can be ridden.

And I received the call a few hours after I dropped off the clutch that the bike is now running, rideable and ready for collection!

I've got a few little things to sort out and then learn how to ride it.

1935 DKW Front and Schwebeklasse Range

1938 DKW SB350 Restoration Update March 2025

It's been a while since I've reported on progress with the DKW SB motorcycle so a recap is in order. I dropped my bike to some mechanic friends to sort out the carburetor and ignition issues back in November 2024. Those issues were quickly resolved, but like the proverbial loose thread on a jumper, other issues quickly unraveled. https://dkwautounionproject.blogspot.com/2024/11/1938-dkw-sb350-restoration-update.html

New tyres were obtained but when the guys removed the old tyres they found that the rims were completely rusted through from the inside. It was probably the rust that was holding them together. New rims were built from NOS stock rims and new spokes.

As the rims were new, they needed to be painted to look 'age appropriate.' They look great.

The guys managed to remove the old speedometer from its housing and install the new speedometer. Apparently there were some very tiny screws in the speedometer back holding it on. The original speedometer housing looks much better than the modern reproduction, which was not a match at all.

Next step was to start her up and take her for a test ride. The clutch proved to be barely functional. Well, after 80 years this is hardly a surprise. We pulled off the covers and took a look at the clutch.

Prewar DKW motorcycles used plates with cork plugs, approximately the same size as a cork bottle stop. Over time these decay and fall apart. As soon as we opened it up some cork plugs fell out.

This ring of cork plugs looks like it was original. All the plugs were consistently sized but blackened and inflexible. You can see some plugs are missing from the disc.

This ring of cork has been repaired / replaced at some point. Some cork plugs are original but replacements have been cut from square pieces of cork, probably from a cork bottle.

It's much more apparent in this disc. A little pressure on the plugs and they all came out easily enough. The metal plates were in good condition.

A new set of corks is on order. Below is a video showing how the cork is fitted.

This will be my next job!

After soaking the plates in petrol....

The cork arrived on 11 April 2025. It only took two weeks from Germany. Generally post from Germany takes 4-6 weeks, but it was a light package.

November 2024 update: https://dkwautounionproject.blogspot.com/2024/11/1938-dkw-sb350-restoration-update.html

The next step - April 2025: https://dkwautounionproject.blogspot.com/2025/04/1938-dkw-sb350-restoration-update-april.html