Triple valve shims

E

eabergman

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I've been having trouble adjusting the valve lash on my Jarama, the kind of trouble where you measure everything, calculate the shim sizes needed, put them in, remeasure and discover some of them are wrong, but not in any consistent way. I think I have discovered the problem: some shims have longer sidewalls than the clearance from the top of the stem to the collet. I'm worried that some or all of the valves have been tipped by unknown amounts, but I suppose it could be an issue with the production of the shims. I'm not sure if this was a problem with any of the shims that came out, as I wasn't measuring this and they were filed away in a small parts bin. So I have a couple of questions:

1) Is it normal for the (untrimmed) valve stems to be lower than the face of the spring retainer? I'm seeing about 0.7 mm gap on the two I have measured so far (right side intake and exhaust), and values around 3.5-3.7 mm for the distance from valve tip to collet. In one of those two cases the shim I was getting ready to install would have seated on the collet, not the valve stem.

2) Is it common to encounter shims with sidewalls that need to be trimmed before you can get a correct adjustment with them?

3) I'm going to have to go back to the beginning, refit thin shims that have had their sidewalls checked for length, put the cams back in, torque the nuts, measure clearances, remove cams, select new shims and refit cams. Can I do all this without bothering to reconnect the cam chain?
 
I have been advised by those who know more than I do that measuring the gaps with chain connected and tensioned is the way to do it. The clearance with tensioned chain is likely to be different to the clearance with no chain or the chain un-tensioned. It does make sense if you think about it. Hope that helps a bit. Someone far more knowledgeable than me will no doubt be along in a minute and give their own view on your trimming questions which i am not sure I am able to understand let alone answer.
 
A common source of error is measuring the shim with a micrometer - where the spindle diameter is a bit too big and rests on the internal radius formed within the shim. So the shim measures a bit fatter than the true face-to-face thickness. HTH
 
TheWrongTrousers said:
I have been advised by those who know more than I do that measuring the gaps with chain connected and tensioned is the way to do it. The clearance with tensioned chain is likely to be different to the clearance with no chain or the chain un-tensioned. It does make sense if you think about it. Hope that helps a bit. Someone far more knowledgeable than me will no doubt be along in a minute and give their own view on your trimming questions which i am not sure I am able to understand let alone answer.
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Even in 'good' conditions it can be very frustrating trying to find consistency between what you calculate the new clearances should be, and what you measure afterwards. Unlike many other engines I have worked on. I find that pushing the camshaft hard down at the nearest bearing block while measuring can help. One school of thought is not to re-measure after shimming. Just work out and fit the correct new shims, and your only check afterwards is to make sure all valves have clearance (in case you made a significant error).

I haven't ever really considered it, but I have noticed my shim kit has shims of various lengths now. Probably due to re-shimming engines with a mix of shims of other makes, maybe? Could be very dangerous as Paul says so I will pay attention to this in future! Good you are fixing this issue and thanks for raising it.

If you have the pistons set around mid-stroke I reckon you could do your check with the cam chain disconnected, while pressing down on the cams to take up bearing clearance.
 
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Indeed, early days of reshim had me going, precise calculation of new shim, tap crank shaft with non impact hammer or handle, install cam cover and ride the bike for maybe 100kms, provided no sounds that alarm... recheck, by and large the correct lash is established. Total waste of time in installing new shim and then measuring the lash afterwards immediately, just saved you 100 hours of worry...j.
 
Wise Words from Piet. With many thanks to him, I hope these help.

"When measuring the clearances:

1. The cam chain should be fitted AND tensioned.

2. You'll do your head in trying to get them "spot-on". The clearances in the cam bearing blocks alone can throw many measurements/adjustments out the window. So …

3. Press down on the cam lobes. This eliminates any play in the bearing, with the result that you will measure the lowest value of valve clearance.

Don’t let either inlet or exhaust go less than 0.15mm - have found both inlet and exhaust valves get burnt. Adding the bearing play to the valve clearance gives you a slightly larger margin of error. The tappets only start getting noisy with more than 0.80mm clearance!

The bastard in the shimming process is re-fitting the cam bearings in the head. Once the slot in the head is knackered, it is difficult to repeatedly align the bearings exactly the same. The slightest deviance throws the previous measurements out the window."
 
How are your cam bearing blocks positioned? For example, if they aren't positioned as they should be, e.g. on older heads, they can move around a little and this will influence the valve play significantly (DAMHIK).

This is explained in this post: Dowels or no?
 
I have billet cam blocks too - but it depends what eabergman has in his Jarama. As Piet is stating in the link above, early heads had hollow dowels placed over the 8mm studs to locate the bearing blocks - this has to be considered regardles if factory cam bearings or billet ones are used.
 
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