Saturday, August 1, 2015

Two Nasty Bolts: The Front Fork

I haven't been updating since two months. Now after all that time, for those of you who might think that I'll pull a red satin cloth before the audience to reveal the shiny bright as new R25/3 - always keep your rose-tinted glasses on!

I managed to overhaul the final drive the last time, renewed all the gaskets, seals and bolts on it. It's been waiting for the moment that I finally fill it up with fresh oil and mount it where it belongs to.

I classified the Beemer into four major "systems", if you recall. After I'm done with the final drive, I decided to move on with the front forks, as they are the only step left before the paint job, and also I thought it'd be rather straightforward. After all, it hardly takes me an hour to take out, replace the oil and redo the front forks of my 2008 bike, which basically work with the same principle. How difficult can this be?

Guess what - I was dead wrong again...

How about some theory first?

The front forks have a very simple mechanism. Two pipes one inside the other, made oil tight with a seal, a spring inside to absorb the shock and oil to damp the oscillation by compressing the air gap. 
The bottom part (shiny one in the photo) holds the front wheel, where the upper part is attached to the handle. Of course, we have two of these. 
And this is the spring inside and the steel rod that keeps it aligned and also holds the bottom part attached. At the very bottom, you can see the bolt that attaches the bottom part. And at the top, the big bolt to attach to the handlebar piece.
Right here. The bottom clamps hold the forks, while the rod in the center goes through the chassis and gets fixed at the top, connected to the top clamps. Thus, the two forks get fixed at two points and form the whole front assembly. Of course, with the two bearings, at the top and bottom of the rod, for rotation. We'll get to that soon.

French poet and writer Antoine de Saint Exupery, best known with his novel The Little Prince, once said

“Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away.”. When you compare the two fork assemblies produced 50 years in between, you notice that the newer one is build much simpler, also using fewer number of parts, even though they are still based on exactly the same principle.

"Yeah, right, enough with nonsense, so what have you been doing the past two months?" - all right, I'm getting to the point.... 

These huge bolts on top the the springs are the ones that fix the forks ot the top clamp. So I have been fighting with these very bolts for two months, trying to loose them.

They are exactly 45mm wide. For that size, I had just a huge old fashioned wrench. It did not take so long to give up with it and go get a 46mm head for my wrench. Oddly, there is no such standard size as 45mm anymore. Whatever, it's just a millimeter, it shouldn't be that precise.

Just a regular bolt, and it shouldn't be that tight there anyway, right? As I push down the wrench, the opposite end of the 10kg frame rises. If I were into acrobatics, I could have stood on the tiny wrench handle. The only thing that doesn't move a tiny bit, is the bolts themselves. I don't know how many evenings I spent wrestling with it.

Yeah, I've seen that before, with the strange shaped bolt that was holding the final drive. I'll take the same way. With all my determination, WD-40 and hot air gun, I confront the two problems once again. After several evenings of failure, half a can of WD-40 and the odd smell of the hot air gun in the entire house, one of the bolts finally give up. Such a relief.

Great, so one down, one more to go. I keep on with the same approach for days, but every single attempt fails, without the slightest hint of progress. Until last weekend. 

I have a friend of mine, managing a car service shop. After countless failed attempts, I decided to visit him. So I took the frame and hit the road. I took the gearbox with me in a plastic bucket, as I had two broken bolts there. The guys took me to a small metal shop nearby. 

The guy was a real old school expert. Instead of my pathetic hot air gun, he carefully heated the bolt with his blowtorch until it glows red. Then he quickly cooled it down with water, then heated and cooled again. You can see what remains from the black paint.

Then while I was holding the frame tight, he gave the bolt a very strong but precise hit with his hammer and chisel right at the corner of the hex bolt. I guess it was the first time after maybe 30 years that the bolt moved at all. After the second hit, it came loose enough to go on by the hand. Then he removed the gear lever bolt with a suitable pin, and the little speedo wire screw by welding a steel rod on top and unscrewing it. A great demonstration how experience and proper tools make it look easy.

Can you guess, from the photo above, which of the two bolts was the nasty one?

I came back home and unscrewed the whole front end. As I removed, the steering head bearing balls all came loose. You can see the remaining balls stuck onto the grease in the photo. You can see the bottom end of the bearing right at the bottom of the steering head axle.
The top cap looks the same with its bearing and balls. (Say hi to the good ol' WD-40.) Despite the mess, the bearings are not in a bad condition. But they will be replaced.

The mechanism remains exactly the same, but we have a more reliable and better design, called "tapered roller bearing" instead of these.  Probably they weren't developed yet back then.

Now it's time to get brand new steering head bearings, fork seals and get rid of those ugly welded footpegs on the frame. Then we'll be ready for the paint job.

I must admit that when I was doing the research and trying to learn the detals of the Beemer, I was't aware of what sort of a challenge I was going to take on. I simply underestimated the effect of such a significant amount of time even for human life, let alone for an industrial product. Facing all such difficulties and low pace of work, I often feel overwhelmed, but I am not by any means disappointed or discouraged at all. As I slowly progress, it gives me more courage for the next big obstacle. The long periods of silence are probably very boring to follow, but this routine will go on until the happy end.

Next stop: the frame...

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