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1974 R90/6 refurb

The rear wheel is off and the bearings removed. One of the bearing races came out w/o heat, which is bad. They are supposed to be held in by the normal contraction of the heated hub around a frozen race, and then require heat to remove.

I read a lot about it on line, and I will use red locktite to glue in the race. But, this makes it close to impossible to remove the race in the future. Therefore, I'll buy new bearings since these are a bit used, pitted, and rusted. That way, once it is together, I should be done with it for the rest of its life, at least its life with me.

The drive gear on the wheel hub (that mates to the final drive gear) is worn. I think I will let it slide for now. They are still available for about $85 which is nice. If the trans and clutch work out well, and it runs well, I'll likely drop a new one on at that time. The teeth are getting pretty bad, I'll post a picture later.

Has anyone replaced this gear on the hub? I see it is riveted on. I can buy the rivets, too, but don't really have any means to use them. I was thinking proper diameter grade 8 bolts would work just as well. I figure if I mated the parts on the bike to hold the position, I could bolt the hub in place and use red locktite to make it permanent.


Here is the inner spacer on the lathe. I read that if you reduce the diameter a slight amount, it will go in and out without having to remove the bearing races. Since I don't want to remove them ever again, I did the reduction. Yeah, it's a wood lathe, but on low speed, for light metal, it works fine. It fit into the drive chuck perfectly, and the conical tail chuck holds it well and centered. I need to reduce the diameter of the two thin disc like ridges. The one on the left was too close to the head drive chuck so I put on an O-ring to push it away from the chuck so I could turn it down a fraction with the gouge. Worked perfectly. New bearings are on order and will have them by the weekend.

Wife wants to go to a Cirque du Soleil show, but all I want to do is be in the shop.
030spacer-lathe.jpg
 
Fairing

If memory serves me correctly, the Luftmeister fairing uses the original BMW
headlight and chrome ring, the Windjammer uses a stock automotive headlight.
Also noted in the pictures, the fork brace has been replaced with an upgraded
model.
I would rebuild the forks, I would be willing to bet you'll find stuff inside them
you really don't want to see.
 
Yes, the forks, when I drained them, had nasty fluid and some particulates. What's involved in a fork rebuild? Seals, gaskets, O rings? If the hard parts are good, what kind of cost am I looking at?
 
There is a rubber bumper for bottoming in the sliders, which has likely disintegrated into goo, plus little chunks trying to plug your damping rod holes. You will want to drop the sliders and clean all that up, both from damping rods and inside sliders.

IIRC correctly the soft service parts are the aforementioned bumpers; the fork seals; gaiters if yours are toast; large crush ring under that large bottom nut; tiny crush ring which goes on the end of the damping rod; possibly some little felt strips.

If the forks are currently working smooth, take note of all the washers/shims associated with attaching that fork brace to your sliders. It is a real PITA to shim these so your forks are smooth and stiction free; if that work is done make sure you reap benefits! There is no adjustment besides shimming.

Perfect time to install milled upper triple plate to replace that flimsy stock thing, if it has not alreeady been done.
 
Thanks guys. I will look at those forks later in the year as they are working great. During the winter I can take my time and service the forks properly.

Thanks about the locktite, I got the right one now.

I'm only using this bike to tool around town for vintage fun, so I'm not going to invest in a new triple clamp. But, it does have a strong fork brace as noted.
 
Things are progressing.

I got the new bearings from Autozone for the rear wheel. I used my kerosine heater to get the hub hot, at least 200 degrees F, and the bearing assembly, held together with a long bolt, was put in the freezer. It dropped right into the hot hub w/o issue, and locktite glue was used to hold the outer race in place. New bearings were a good idea. The new bearings are just so nice and smooth. I should be able to completely assemble the rear wheel tonight and adjust the bearing preload.

The swing arm is about the only item on the bike that was in good condition. The bearings are great, and they were clean and lubed. They'll be going back in with new seals.

I also got the transmission out. The good news is that all the clutch parts look fine. At least good enough to not replace anything now. Clutch parts are not cheap, so this is good news. Also, the friction disc was very sticky on the transmission input spline, so I'm confident a good cleaning and spline lube will help with the shifting issues I was seeing.

Here' s one thing that drives me mad: poor quality, lazy workmanship. The last person to service the clutch put in one of the clutch bolts and stripped it badly. There was no way to get it out with an allen wrench. The internal hex hole was at this point almost round. The bolt was too tight (and seized?) for vise grips even though I had a decent purchase. I might have been able to use an Easy Out extractor, but the most simple solution was to use the MIG welder as the space was tight and the other bolts were REALLY tight and needed a lot of torque to break loose.

I got a proper sized bolt and MIG welded it to the exposed head of the stripped bolt and then it came out quite easily. I am thinking that the heat of the welding made the bolt easier to get out than the others. I have ordered 6 new bolts. I don't know if I will ever be in this area of the bike again, but at least the next guy who is won't have to deal with any poor workmanship on my part.

Here's a few pics:

This is the neutral switch on the trans. The wires are cut, which explains why the neutral light was not working!
033neutralswitch.jpg

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Whoo hoo, the trans is out!
032transout.jpg

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Here is the allen bolt on the clutch that is completely stripped:
034strippedbolt.jpg

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And the bolt I MIG welded to it to easily extract it. All six will go to the trash.
035weldedbolt.jpg
 
Good weekend for the R90. I made a clutch centering tool and got the clutch and transmission back in. I installed new seals in the swingarm and back it went. Finally, the final drive and wheel. The seals are VERY difficult to get started into the swingarm, even using a press. I almost messed one up beyond usage but I was able to salvage it.

Since I put new bearings in the wheel hub, I had to set the spacing and bearing preload. This was new to me, probably not for Airhead gurus on this board. This is done with an inner and outer spacer. The outer spacer sets the distance between the bearing races and is fixed. The inner spacer sets the distance between the center of the bearings (the part that spins with the axle). You change this distance with thin spacers until you have the proper preload. This is determined by rocking the rear wheel while a buddy (in this case, Brian!) tightens the axle. Once the wheel has no play in it, you check the torque. If it is around 25 ft-lbs, you're done. It took several tries to get it right, but we got it.

I still don't have a front brake (the master cylinder is being re-sleeved at Apple Hydraulics) but I still went out for a few miles. It's running great, just a few more things to wrap up, like the seat and hinges and the front brake. Once that is done, it's time to enjoy it for a while and then later in the year I'll take the front forks apart for a servicing and the steering head bearings.

Here's a picture of the parts of the wheel hub, spacers, bearings, etc. Everything but the grease seals. There's a hell of a lotta parts in the rear wheel hub!
stack.jpg


Here's the centering tool I made on the wood lathe:
036clutchtool.jpg

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Here it is ready for use. The size fits snugly into the clutch disc and the center tip falls into the dimple on the pressure plate. That centers the clutch disc so the transmission will go in properly.
037clutchtool2.jpg

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Here's the clutch back together, and centered. You have to use longer bolts, seen with the wood blocks, to compress the clutch spring disc. Then you can put in the proper smaller bolts and torque it down. It all worked really well.
038clutch.jpg
 
You have to use longer bolts, seen with the wood blocks, to compress the clutch spring disc. Then you can put in the proper smaller bolts and torque it down. It all worked really well.

I didn't use wood blocks but used nuts and oversized washers run down to the back of the clutch pack. Then, using a wrench, I turned each nut about the same amount in succession. I went round and round the three nuts to evenly pull the spring down. Without the nuts/washers, you have to know rather precisely how thick to make the wood blocks. But in the end, it does the same thing.
 
The only reason I used wood blocks was because when I bought the bolts, I forgot to measure the correct size. I got 2.5 inch bolts to be safe, then had to make up the difference with the wood blocks. Would have done it your way if I had planned better!
 
I got the re-sleeved master cylinder back from Apple Hydraulics in New York today. They did a fine job. You can see the nicely fitted and honed brass?? sleeve they inserted. I got it all back together and the front brake works quite well now. I'm quite happy with the braking for the first time since I bought the bike.

All I have left now is to install the new points, set the timing, check the carb balance one last time, and she's ready to go. I'll still work on the seat and lubricate the center stand and some other things here and there, but she'll be pretty much ready to ride on Saturday.

I'll give it a good wash and take some final pictures, then it's time to put on some miles.

Oh, yeah, maybe I'll get a license plate....

Here's the re-sleeved master cylinder. It was $90 to have this done.
039brakemaster.jpg
 
It's done! Took it out for a ride today and it runs well. The down shift from 3d to 2d is a bit tough, but unless it becomes more serious, it's fine. It fires up perfectly from dead cold and has good strong power. It got a wash today and joined the seraglio. I'll get a plate tomorrow and get some good miles on it next week.

IMG_0122.jpg

IMG_0123.jpg

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All four of the sisters:
IMG_0118.jpg
 
I've been riding the bike but the issue with shifting from 3d to 2d is just too annoying. I removed the trans to have a look. Here's a shot of the transmission. You can see the gears look great. I'd like to do the rebuild myself, all the information and special tools are available, but I decided to send it out. At this point, wanting to ride wins out over wanting to wrench. Plus, I figure I'll get back a tranny that will last as long as I do and I will be done with it.

The only thing 'wrong' I could find was that NONE of the three shafts had end play shims. That can't be right!

trans_apartl.jpg
 
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I decided to rebuild this transmission myself. The special tools are available and I have this kind of knowledge and a well stocked shop with all of the common tools needed (and now many of the special tools). Transmissions are much simpler to rebuild than engines I will say.

Firstly, I had a VERY NEGATIVE experience with Tom Cutter of Rubber Chicken Racing and I do not recommend you use him. Although I have no doubt that his workmanship is flawless, his business ethics and customer skills are horrible. I emailed him and asked for an estimate of turn around time before sending my transmission to him, and he replied "6 to 8 business days minimum." After a month, I emailed to ask how it was going. His reply was curt and rude, and so I had him return my transmission to me untouched. He was, to be blunt, a curmudgeon. I found out that a fellow MOA member sent him a trans in February and still does not have it back. I don't begrudge him being busy, but he just outright lied to me about how long it would take. If you choose to go with Tom, send him your work in the Fall so that you can use the Winter down time to your advantage, and don't expect any warm and courteous emails.

The good news is that I decided to do it myself. I wanted to anyway, but I felt I didn't have the time and wanted to ride the bike. But, given the circumstances, I'm doing it.

I bought the most excellent DVD from Cycle Works that goes through a transmission rebuild; this is a great video. Between that, the Clymer manual, and online resources (such as Snow Bum) I felt ready to dive in.

The nice thing is that all the bearings, shift forks and gears, etc., look great. So I don't need expensive parts. Just new seals and gaskets. As I said earlier, there are no shims for shaft endplay in this transmission. Whoever did it last time skipped this important step. I ordered shims and will correct this problem.

But here's what I found. To refresh your memory, the transmission was getting stuck in 3d gear when down shifting to 2d gear. I had to keep hitting the shift lever repeatedly to get it go shift, applying a lot of force. This problem was reproducible on the bench.

What I found was that the shift cam slot was too tight, and was binding on the shift fork (just for one fork). I'll show some pictures. The one shift cam was fine, and the forks would glide effortlessly in the slots. The other shift fork and cam were bad. The fork was completely getting bound up. It was as if the cam had shrunk, but yet it looked perfectly fine and straight so I don't get it.

I used my Dremel tool to grind the slots where they were binding and got enough freeplay so the fork slides well. I put it back together and it shifts perfectly now. So once I get the new seals and gaskets, etc., I'll put it back together and I'm good to go. If I ever have a transmission problem, I know this thing inside and out now and have no fear of failure in the future.

Pics to follow.
 
Here's some pics.

This is the shift cassette. You can see the two cams with the curved slot races that the shift fork ball goes in. As the cam turns, it lifts and lowers the shift fork (and hence the dog gear). The fork on the left was binding badly in the slot, it was not wide enough, and I widened it with the Dremel until the fork ball traveled smoothly from end to end.
cassette.jpg

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Next it was time to drop the shafts back in the case. The case needs to be hot (above 200 F) to expand the bosses to receive the bearings. You can see the bearing on the bottom of the shaft, and the corresponding hole or boss where it drops into the case. I set the case on the kerosine heater for 5 minutes to heat it and the shafts went right in. Let me tell you, it's hot here today and running the kerosine heater was no fun.
hottrans.jpg

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Here's the shafts and one shift fork (the problem one) in the case. Once the case cools, the bearings are locked in place.
gearintrans.jpg

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And finally, the shift cassette in place. You can kind of see how the shift fork rides in the slot of the cam. It no longer is binding and shifting really well on the bench now for the first time.
forksintrans.jpg
 
Thanx much for the great pics, my '74900 when under hard throttle will sometimes miss third going up. In future I definitely will consider prying it open myself.
 
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