cam chain & sprockets?

[montmil]

Quoting Steve Mcqueen in Sand Pebbles, "I was almost home."

Was about to button up the timing chain case after replacing the chain -plus the part that was causing the racket (story and pics later).

Put the trans in high gear and turn the rear wheel to check for any problems. UhOh. Felt resistance, backed down and tried again. Still got mechanical contact. Suspect valve to piston interference.

Pulled the new chain off and both valve covers. Release tension from the chain tensioner plus removed the chain guide rail.

So here's where I am with this... The large cam sprocket has a dimple mark. It is at 6 o'clock just as it was when I removed the original chain. However, I have rotated the cam to bring the right cylinder to TDC with the flywheel mark at OT.

Need some guidance on correct position of the crankshaft sprocket. No marks visible due to the large bearing in place. I think I was a tooth off?

Looking for some experienced hands that can help me wrap up this job. What have I missed or failed to do? Been taking lots of pics for a post. Can ya help a brother out?

Thanks!   Monte



Cam sproket with dimple at bottom, six o'clock. Cam tensioner off chain.

[Bob_Roller]

Monte,

The BMW manual is pretty vague on this, it states ; 'When installed the marks on both sprockets must be aligned' .

The best I can remember, is the dimple or mark on the crankshaft sprocket should be at the 12 o'clock position, and the camshaft sprocket mark should be at the 6 o'clock position.

If you look at my posting on your original topic on replacing the chain, I mentioned that I marked both sprockets and case front with a dab of paint to make sure if any movement of the sprockets occured, you could determine it before proceeding with the chain installation .

[Justin B.]

That's the way I remember it.  I thought I had a pic maybe showing the marks, but no.  I did, however, find a pic that shows the solid upper diode board mounts some people swear by.  There are suppose to provide additional grounding and won't rot like the two lower ones in the pic...

[montmil]

...The best I can remember, is the dimple or mark on the crankshaft sprocket should be at the 12 o'clock position, and the camshaft sprocket mark should be at the 6 o'clock position...

I can easily rotate the cam sprocket to 12. Any thoughts on positioning the crank sprocket? Will TDC on one cylinder or the other determine correct position?

I'm half way there. Need the last half and I'm rolling. Thanks, J.

[Bob_Roller]

About the only thing I can think of here is, loosen up all 8 nuts holding the rocker arm shafts down, to close all of the valves, rotate the crankshaft sprocket to where it is supposed to be.

Then tighten the nuts down again, and then rotate the cam sprocket to the correct position.

[montmil]

About the only thing I can think of here is, loosen up all 8 nuts holding the rocker arm shafts down, to close all of the valves, rotate the crankshaft sprocket to where it is supposed to be.

Then tighten the nuts down again, and then rotate the cam sprocket to the correct position.

That's the nut to crack! Finding the correct crankshaft position without having to pull the bearing.

Is there no relationship to a cylinder at TDC for positioning? I hate to yank the bearing unless it's the last resort. My bad.

Monte

[Bob_Roller]

I don't think you need to remove the bearing, can you use a small mechanics mirror, and get a look between the bearing and sprocket ??

I don't know if this will work or not, but if you have a set of ignition feeler gauges, the round wire type with a 90 degree 'hook' on the end, if you can get it in between the sprocket and bearing, and 'feel' for the mark on the sprocket.

[montmil]

Been trying the mirror idea but no joy yet. Need to replace the batts in my R65.org flashlight. Will see if I can find the keyway slot. Thanks, Bob.   Monte

[Justin B.]

But, won't the bearing slip off if heated to a couple hunnert degrees?  I don't know as I've never had to remove one but that might be the quickest and easiest thing to do...  

[nhmaf]

Both my Haynes and Clymer manuals say that the timing sprocket (lower) has an engraved mark that must be exactly lined up with the engraved mark on the crankshaft sprocket (upper).  So, this would entail putting the top sprocket's mark at 6 0'clock and the lower large sprocket's mark at 12 'o'clock.   Haynes shows a small photograph of this that I could try to scan and email if you need it.   Haynes also indicates if replacing the sprocket to put the crankshaft at TDC first - but I don't know if this would put the mark on the crankshaft sprocket @6:00 or not - still, it seems that if they align as indicated when the engine is at TDC it would be easiest to get the cam/rockers/valves set accordingly.

[montmil]

Got 'er done!  Some data from the Airheads organization was a large help. Now what was that about paint dots? I'll try and remember next time.     Monte

[Bob_Roller]

Monte,

What did you finally do to get the situation 'unconfused' ?

[montmil]

Monte, What did you finally do to get the situation 'unconfused' ?

Ah, I've set the hook...

Watch for the soon to be released "Timing Chain Tales" playing on your favorite Wiki site.
 
• Starring a 1981 R65
• Directed by Justin Don't Be A Wuss Bowser

• Photography & Script by Three-Card Monte

First gotta get it all back together, install the freshened carbs and see if it makes steam.
Don't rush me... I'm an artiste   Monte
 

[Bob_Roller]

Spill it 'drama queen' !!!

[Justin B.]

He, he, he...