R60/5 rebuild nears completion – with some puzzles. . .
I’m approaching first phase completion of what has been an unremarkable, although lengthy, restoration of my airhead. In fact, this is probably the longest rebuild in the history of this forum and is possibly the only thing that distinguishes it from many other restoration projects here.
A little history – I bought the 1973 bike in 1984 and vaguely remember riding it home. It looked like it had been through a war and had obviously seen a rough life in Ontario by the PO who racked up about 87,000 tough kilometers (54,000 miles). He was clearly not mechanically inclined nor was he a big fan of preventative maintenance. In a final leap of faith, he rode the bike from Sudbury to Vancouver, a distance of about 2000 miles, and left it with a buddy who ultimately sold it to me. I think I paid 800 bucks for it.
I immediately dismantled the bike with the intention of rebuilding it back in the 1980s but two marriages, parenthood, a career and a couple of house renovations intervened. By some miracle, the boxes of parts survived mostly intact despite several moves. Every now and then, I would grab a random part and clean, polish, paint or otherwise refurbish it but never with the benefit of an actual shop manual and mostly prior to the invention of the internet (stupid is what stupid does). I stopped short of dismantling the engine but did replace some key gaskets mostly to keep the garage floor clean – the transmission was treated to new gaskets and seals as well. Over time, I began to run out of parts to clean/paint/fix and a year ago realized I could actually start the reassembly process so I dug up the paperwork and transferred the title (I know, I know. . .)
Despite the abuse the bike suffered in the hands of the PO, many of the parts were relatively pristine since it only had about ten years of use. In a sense, the almost three decades it spent disassembled in boxes prevented further deterioration and preserved it in almost a time capsule-like state. In my opinion, these relics are a portal into mid-20th century engineering and should be preserved in their original state or as close to it as possible.
Using almost all original parts on this project turned out to have been a good idea – I’ve been checking the market for used parts and whole bikes from this era and it’s clear to me the old slash fives are becoming highly prized – of course, you already knew that. Too bad I threw out the chrome toaster panels on the gas tank in ’84 (couldn’t possibly understand why anyone would want them back then!) I have had plenty of time to examine each part closely and am often struck by their beauty (yes, I really said that). The factory used slide rules, intuition, imagination and process of elimination to refine their designs – I guess that’s why lots of kids like these old bikes.
Anyway, even though this project could be called a sympathetic restoration, I’m not beyond using non-period parts such as stainless steel mufflers for /6 models just because I got a great deal on them. I’m actually a cheapskate at heart. In fact I shot the frame, tank, fenders, headlight and other parts with black metallic polyurethane paint that has no authentic merit at all. I’m not even going to put the pinstripes back on – I don’t like them and don’t care what the purists say. The next owner can correct these abominations if he is so inclined.
I won’t bore you with details of the rebuild process but will be pleased to share with you the final phases, some of which are proving to be problematic. I’d be grateful for your input so feel free to make recommendations and point out areas where I’ve screwed up – I know you’re a tough crowd and I welcome constructive criticism.
First, a few photos documenting the state of the project then I’ll describe the first puzzle and I think it will entertain you (there will undoubtedly be many more to come). Some of you have already seen some of my photos on Photobucket but this thread will put them into context -
Here's the first puzzle -
When I GENTLY torque the ATU nut, the camshaft tip turns but the crankshaft and valves do not move.
When I turn the crank, the valves function correctly and the camshaft tip turns along with the ATU. The threads on the camshaft tip are fine and I have verified that the tip does, in fact turn while the cam sprocket does not. This would indicate the Woodruff key is possibly sheared but why would the entire camshaft and tip turn when I manually turn the crankshaft? The last time I checked, the camshaft is one piece - unless mine is fractured. If anyone is interested, I will post the next series of photos showing what I found when I removed the duplex chain cover.
Sounds like a bit of slop in the chain. Sounds normal or it could be getting to the point the chain and associated parts need replacement.
There is also a small amount of slop in the position of the ATU on the D shape at the tip of the cam shaft. This need to be taken into account when timing the engine but once the timing is correct and the nut is tightened it can be forgotten about till the next time the ATU is taken loose.
The gears on the ends of the crank shaft and cam shaft are not loose enough that they can rotate.
Maybe what you are seeing is the ATU rotates a certain amount independent of the cam tip? This is how it Advances the timing. It is the advance Unit. As the rpm increases to ATU advances the moment the points are opened. With the ATU bolted in place on the tip of the cam shaft grab the top portion of the ATU and rotate. You can see the points cam underneath moving to open the points sooner. It is most properly called a "mechanical advance unit".
Diston, you're right about the chain slop although it's actually severe enough to chew into the bearing carrier -.
You can see how slack it is here -
I was kind of anticipating a worn chain and/or sprockets. But that's not the immediate problem.
What I can't understand is why the camshaft tip can be turned independent of its sprocket. And I mean turned completely, not just a little bit. Like the woodruff key is sheared.
It still doesn't explain why when I turn the crankshaft, the camshaft lobes turn and engage the valve lifters. Something's not adding up. Replacing the timing chain and gears, tensioner, etc., would be pretty straight forward but I'm sensing a bigger problem. I was hoping to avoid an engine tear down for a while. Any ideas?
Replace the chain and crank sprocket-- they're worn.
The camshaft tip is machined from the same casting that the camshaft is. The cam sprocket is a good press fit with a key to the camshaft, and (in the unlikely event) it was loose you'd see all manner of destruction around the keyway.
Thanks for the response, Bill. Agreed, the camshaft is one piece. So turning the camshaft tip should cause the valves to open and close. This is not the case. I'm still perplexed.
I believe what you are seeing as a problem is not a problem. Lets try to divide this thing into several parts to make explanation more easy to digests.
We can see the timing chain is in need of replacement. This can wait but should be taken care of sooner rather than later. When the timing chain is done you will need the chain, small gear on the crankshaft, bearing in front of gear, tensioner parts. We do not normally change the large gear on the cam shaft.
The cam chain and it's gears is the connection between the crankshaft and the cam. The small nut on the tip of the cam shaft is holding the advance unit on the end of the cam shaft. The advance unit operates the ignition points. You must be careful with this small nut and not over tighten it. The small piece of thread on the end of the cam shaft can be broken.
Once the advance unit is on the end of the cam shaft and the small nut is tightened the advance unit can be rotated. It does this in operation. It is how it advances the timing which is what we want it to do. It will only rotate a certain amount and I forget what this is. It is the number of degrees that the ignition is advanced in operation. A total of 26 or 28 degrees or there abouts.
You are rotating the advance unit, not the cam shaft.
Don't overthink this.
And especially don't go anywhere without replacing the timing chain. It very loose and has been replaced once, but the a master link was used and the keeper clip installed in such a way that it could be dislodged with the chain rattling against the front main bearing housing. Major headache if that master link parts company.
BTW, it is not uncommon to see timing chains loose enough to rub in the fashion that yours has. Not uncommon but not pretty either. This really needs fixing right away.
Turns out I'm not crazy after all.
Thanks fellas for your comments. Did some research the last couple of days and the results will likely shock you. First, I made absolutely sure of the following:
1. The camshaft tip definitely turns independently of its sprocket. It's somewhat stiff but doesn't cause me to over-torque the nut.
2. The camshaft tip can be made to turn by its nut without activating the cam lobes.
3. The camshaft and lobes can be made to turn correctly by turning the crankshaft.
How can this possibly be true? Turns out, the camshaft tip and the camshaft are actually two pieces (the tip is press fitted into the end of the camshaft.) For some reason, mine apparently wasn't machined to the right tolerances. If you tighten the nut on the ATU, the entire ATU moves clockwise relative to the camshaft.
How the previous owner managed to set the timing is anyone's guess.
I confirmed this today by visiting our local BMW shop and told him my dilemma. He thought I was nuts. He brought out an old camshaft and to his surprise, determined that it is a two-piece unit. He tells me he has never seen a cam tip slip in his 30 years in the business and he's changed a lot of them.
While I was there, I bought a shop manual.
You're joking , right?
Cross my heart.
In all my years... :huh:eek1:huh:eek1
I still am convinced that the /5 camshaft (including the point cam shaft--AKA "the camshaft tip") has to be machined in one piece. This is the simply most reasonable manufacturing process since the D-shaped end determines the ignition timing.
I'm not saying your observation is wrong. It's been years since I've looked closely at at camshaft and I don't have one I can look at here, so I may have had the misimpression all these years.
Anton?? BMWrench? et al? :deal
At any rate, unless we can thing of some way to re-index that points cam tip in the engine, you'll need to replace the camshaft... :(
Yes, there's no question the camshaft is unusable. I had already resigned myself to a new chain job - might as well go all the way and change out the camshaft while I'm at it. If the camshaft sprocket is worn, I would have had to pull the camshaft anyway - could be a blessing in disguise.
I'm betting the PO never discovered the slipped cam tip and couldn't figure out why the timing was always off. Must have driven him absolutely nuts.
Yes, the end of the camshaft the auto advance is attached to is an interference fit into a ground hole in the end of the cam. The end is known as a drive quill. I was at the Pennsylvania Airheads SuperTech last weekend and talked with a guy whose quill first slipped, then pulled out. This amazed me, because I have had cause to remove them. They didn't come willingly. However, the ones I removed were from /7s-it may be that the fit had to be improved.
During a conversation with Tom Anderson (of Anderson Cams) some years ago, he told me that they had slotted the quill so air would not be trapped as it was pushed in. BMW did not do this.
Live and learn.
How is the drive quill indexed to the camshaft/cam sprocket? That D-shaped end of the quill has to be oriented precisely for ignition timing.
This explains the reports we've heard/seen over the years about the timing being off so much that the points plate couldn't be turned enough. I've usually assumed a stretched timing chain.
|Times are GMT -7. It's 09:16 AM.|
Powered by vBulletin® Version 3.8.5
Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Copyright ADVrider 2011-2014