So, I took the top end of my 1971 r75/5 apart to have it examined and measured by a local BMW pro and machinist (San Jose, actually, not totally local) Robert Grauer. What started with just cylinder removal turned into discovering lots of pitting on the cam lifters and the camshaft itself. So, this is an account of removing and replacing the camshaft and putting it all back together.
My last blog entry about starting this is linked here. I'll try to include photos or links to the various trouble areas I hit.
First off, when I took my heads down to Robert, I also brought a set of Nikasil-lined r80 cylinders and pistons that I had bought a few years ago on craigslist. The valves were a definite rebuild, and when he measured the piston clearance on my r75s, he told me I'd need to size up the pistons to the first oversize from stock (must be common, as they make two oversize steps). So, when we measured the r80 clearance, he said it was great and suggested I use those, and have him turn (grind) down the base to fit into my engine casing. More info here on Robert Fleischer's page.
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| that is probably 40 years worth of carbon buildup in combustion chamber |
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| Robert checking some specs |
So, with the heads being machined in San Jose, it was suggested I pull out the lifters and check their condition. Which was pretty bad:
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| in the words of friend Blaise: dogshit |
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| this is good, am actually using this one again |
So, the worst of it was that I discovered I needed to get in and pull out and replace my stock camshaft due to really ugly pitting on one of the lobes.
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| and... those are two of the lobes on my camshaft (the surface these lifters ride to push the pushrods) |
| From where I was at this point, cylinders removed, some other stuff out of the way, it seemed possible to continue this project on my own. I was told I'd need to remove the flywheel and push the camshaft out the front, but would need access to the back in order to line up putting the new one in. I just did it slowly and will highlight some of the harder areas. To start, the front cover and then rotor and stator, points, etc, etc (it's been a few months, sorry) all need to come off in order to pull the timing cover off. There are seals around both the camshaft and the crankshaft, in addition to a timing cover gasket, which all need replacing. Pulling the timing cover was pretty straightforward. I heeded advice to heat the crankshaft bearing to help the seal slide off. Hairdryer for maybe five minutes worked swimingly. On the backside, getting the boot out of the way of the drive shaft housing was almost more difficult than removing the four bolts holding it to the transmission. At first I thought the bolts were going to require a special tool, but they are a ten-sided 10mm metric wrench fitting. I got these loose without too much trouble and then pulled the driveshaft out of the way enough to remove the transmission. Transmission The bolts and nut holding the transmission are kind of varied. There's one long post that comes out of the engine to mount it on. This helped greatly with reassembly and when I used the transmission to help center the clutch (I'll get to later) There's a long bolt and then a nut for the bottom rt side, then a shorter bolt into the engine at both the top and bottom left. Top bolt also holds a metal shim to help fit the air filter housing. I taped them together and kept all the fittings in the same plastic bag. Note on organization: Every time I removed a part, I'd put all the bolts, nuts, screws, etc in a plastic ziploc bag and label what the heck I just disassembled. I'd done this with egg cartons in the past, but now swear by ziploc baggies. No error if you drop the egg carton ;-) I seem to have lost a bunch of photos I took around this point, but will describe to the best of my memory.. Clutch Next up for removal was the clutch. A tad scared I'd sent springs flying everywhere, I was tentative. The way the Clymer book tells you to do this is to remove three of the six bolts holding it in place. Every other one. Then in their place screw in three long (2") bolts with oversized nuts on them to slowly decrease the pressure on the spring. There's one diaphram-type spring putting pressure on the friction plate. It probably would not come flying off, but it might damage or warp something if you didn't do it slowly and evenly. Timing chain One doesn't have to go in this order, but I chose to cut off my timing chain after clutch, before flywheel. I used a dremel and ground away. I had an awesome photo of sparks flying, but seem to have lost it. Anyway, definitely plug up all the holes to keep debris from falling in. And then order a new chain with a master link! I replaced the new camshaft along with an attached sproket. Also chose to keep the crankshaft sprocket and bearing on. (covering both from dremel dust) Flywheel Next up, flywheel removal. In many, many different accounts it is made known that when you remove this the crankshaft will be able to move forward. This is bad!! Thrust washer movement described here. We used a series of tight zipties crossing the front bearing to hold the assembly in place. See below  (timing chain is removed here, as is camshaft, but it shows tiedowns) For the flywheel to not spin, there's a tool or way to fabricate a piece of metal to fit over the transmission mounting bolts and then use a clutch bolt to hold it to the flywheel. Thanks to pal Blaise for the loan. These flywheel bolts need to be replaced with new ones, as they stretch when tightened down. Flywheel off, the camshaft came out pretty easily, after taking two screws Once I got the camshaft out it was officially time to celebrate the "rebuilding" part of the project. Here's the two camshafts getting friendly:  So, ready to swap in the new one, I realize that the flanges take different screws! The old one had counter-sunk allen heads, and the new one takes two bolts I still needed to order.. for $8.49 each. Ugh. A few days later I get them (thanks Hucky's!) and try them out, and find that the clearance sucks. The bolt tops were hitting the sprocket as it turned.  After some emails to Hans at Hucky's, Rober Grauer and a visit to David Benda at local shop Bavarian Cycle Works, I was given the option of either replacing the flange and using the old-style bolts, or grinding the new ones down a little to clear the sprocket. I opted for the latter and used some red locktite to put it in the casing and lock it down. The rest of it's been pretty easy. Flywheel with new bolts, back on. I did color in the OT, F and S timing marks on the side with white crayon, per the Clymer book's recommendation. Attaching the new chain master link SUCKED. I ended up being wired after band practice Tuesday and decided to tackle it at midnight. When ordering the new chain, I decided to get a second masterlink with the fish-looking double connector (stock it has two tiny, tiny circlips. Disaster if they spring away into the engine..) I did struggle with it for a good hour. Make sure to block all ports of entry to the engine. That clip piece is small. I ended up using some clean engine oil to help it stick to the chain and eventually learned that tapping it on (wrench on a very small screwdriver) fit it on there snug and safe. Made triple-sure my timing marks lined up and double checked that the closed end of the link was travelling into the rotation. New tensioner and spring:  that's 83,000 miles of rubber-eroding chain! With the new timing chain tensioner and spring in, I have to wait now for the new seals and timing chain gasket. So, I moved back to installing the clutch. Redoing a clutch has always seemed like a really scary and intensive job. I did have mine replaced maybe 8,000 miles ago by Dave Gardner, so I knew it should be still in decent shape. I did lube the two areas on the spring, and did have to seek out the coveted Honda Moly 60 grease (SF Honda on S Van Ness, only place). Sf BMW shop said they use it now, as the Staburags lube is too hard to find.? Or they don't carry it at least. Interesting trivia about Staburags, it's a cliff in Latvia with an interesting back story.   Next step was to get the clutch on. Basically it's just backwards from the installation. Put the three long bolts in and gradually tighten them evenly until you can get the shorter, stock bolts in. There's a BMW part you're supposed to order to line up the friction plate, but I followed Duane Ausherman's advice on using the transmission spline itself as a guide, see line L. Basically you tighten just enough to be able to shift the friction plate a little and get the transmission mounted as it will be attaching, to know it lines up smoothly. I used the external transmission-mounting bolt sticking out, as well as lining up a second bolt on the opposite (lower left) side. It took me two tries before it felt like a smooth fit, going in and out, but I got it.  The above photo shows it installing, and a crescent wrench fits in between the fitting so you can tighten it down before removing the transmission. An interesting way of doing it, but Duane A recommends it, but I'm all for not having to order a tool I won't need for another decade or two! Once that was done and torqued to spec, I attached the transmission, still eying the fit. Also lubed the splines with Moly 60 and a paintbrush. Last on was the driveshaft. Pretty basic. Put bike in gear to torque then neutral to spin each bolt around to the top. This was also rebuild by Dave G in the past decade, so I didn't pay too much attention to the condition. Tried hardest to keep both ends clean and wrestled a bunch with the boot. That's it for now, I hope to have it running again in the next two weeks. |
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