Valve Clearance How-To Video

[hppants]

OK - it's Memorial Day and my back is killing me, so I'm stuck in the house longing for something (ANYTHING) to distract me. So I started thinking about this, drawing stupid pictures on napkins and ****....

And I think I've just had a light bulb moment.

What I think you are saying is that the valves do stay closed for some part of the camshaft rotation. And that part of the lobe may or may not be round. And both of those facts (if they are in fact.... facts) are irrelevant. Yamaha wants us to check the clearance when the piston is at TDC. For each bike, upon original assembly, they check it at that point, and size the shim appropriately to fit the range. Doesn't matter if the cam lobe is perfectly round there, or (exaggerated) there is a bulbous pimple at that point. What ever that gap needs to be, the simply pick a shim to fit it.

And that is what they want us to do when we check it. Simply adjust the shim (if necessary) to bring the gap to spec.

I suppose it is possible that from the gap between the shim and the valve could change slightly during the rotation of the cam until the valve touches and starts to open. It could be tighter or looser. But even it it's a LOT tighter, because the piston is no longer at TDC, the risk of damage is eliminated. By checking the gap at EXACT TDC, you are shimming for the worst possible scenario.

By Jove, me thinks me got it???

If so, then I've definitely been doing it wrong, moving the wheel in 5th gear and eyeballing the cam timing marks on the top of the cylinder head. No way that is as close as lining up the crank timing marks.

 

[Constant Mesh]

It's not critical to have the piston at exactly TDC when checking the valve clearances.

Please remember that the crankshaft turns twice as fast as the camshafts. So, a 10 degree error in rotation away from the TDC mark at the crankshaft will only be a 5 degree error on the camshafts.

More than 180 degrees of each camshaft lobe will have the same exact radius. We're checking the clearance of that portion with the lifter. There may be a slight variation around the lobe resulting from machining error but the error should be minimal.

Having it at TDC is much more important when you're removing/installing the chain after you've removed/installed a camshaft.

 

[Kaelaria]

"but the error should be minimal"

Yes, it is minimal. But when you are measuring 0.15mm as go and 0.14mm as no-go...minimal IS critical.

Yes, it's very important to do it right. I won't convince people like you that don't know otherwise, but my thoughts are for those about to do it and why you should do it right.

Believe whatever you like, I'll do things the right way.

 

[RossKean]

I think this has to be kept in perspective. Yes, there is a very close and specific "go-nogo" acceptance for minimum (or maximum) clearance and a fairly tight tolerance range and Yamaha tells you how to perform the measurements.

I don't dispute that there is value in being as close as possible within the accuracy of the measuring tools (feeler gauge increments) and ambient temperature etc. BUT there is, in fact, an acceptance range. The minimum tolerance specified by Yamaha engineers is such that there is STILL a safety factor. It is very unlikely that with the expected maximum wear between this check and the next scheduled check the valve clearance would drop below the point where engine damage is likely to occur.

Again, the correct procedure should be followed unless one chooses to take the time to verify that the cam lobes are perfectly circular in the range of positions the measurements might be made. I am defending the OP's position on this but suggesting that being a few degrees off might not be sufficiently erroneous to make a big difference. But why take the chance - do it as per the manual (it really isn't any more difficult)!!

Note: For most feeler gauge sets I have encountered, the metric versions seem to have finer gradation between individual gauge strips and therefore more accurate measurements of exact clearances are possible. While technically you can use one minimum and one maximum "go-nogo" gauge to determine whether the clearance is within spec, the finer increments are needed to assess the correct shim for replacement. Especially important if you choose to set them to 2/3 of the max so future adjustments will not be required as soon (if ever).

 

[Mad German]

"but the error should be minimal"
Yes, it is minimal. But when you are measuring 0.15mm as go and 0.14mm as no-go...minimal IS critical.

Yes, it's very important to do it right. I won't convince people like you that don't know otherwise, but my thoughts are for those about to do it and why you should do it right.

Believe whatever you like, I'll do things the right way.

That sounds like a snarky comment.