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Valve shimming question on modified bike

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So I am doing a valve check on my bike that I bought heavily modified. Has hot cams, lightweight rotor/flywheel (I think), big bore, other things. So problem number 1, there is no timing mark on the rotor/flywheel, so I am not 100% sure I am at TDC. (it also doesn't help that the stupid plastic drive shaft cover is stripped so I'm turning the engine by leaving it in 5th gear and turning the wheel). This makes it tough to stop the cylinder exactly, but I get it to a point where the piston is near the top and the cams are at the ~9 and 2 oclock positions. So it seemed right.

I can't guarantee if the timing was changed, the cam gears have some marks on it but there not aligned to anything when the cylinder is at TDC.

So on to the shims, the exhaust was fine but I could not even get a 0.004" gauge under the intake cams. Swapped the original 2.85 shim for a 2.8 (actually measures 2.82 with calipers) and I still can't get a 0.004" feeler gauge in there. So either it is so damn tight that I've been running it near zero intake clearance for who knows how long, or I am measuring this wrong.

Any suggestions before I just keep changing shims, perhaps incorrectly?

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I think it was TrailTech that was making a light weight flywheel that didn't have a TDC mark on it? There maybe others. Stupid in my opinion... 

2.85 is still a pretty thick shim. Why not go to a thinner shim, till you get proper clearance? The valves recede into the head and tighten up as things wear over time anyways.

If you are really paranoid or get crazy results all you can do is get a degree wheel out. Or setup a dial indicator on the piston to find TDC through the spark plug hole. (Maybe easier)

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Don't you have a smaller gauge?
I have to ask are, you sure your reading the feeler right?

Did you measure the shims? If your clearance was .002 and the actual shim size difference was only .001 smaller then a .004 isn't going to fit. You need to know the actual clearance to select the correct shim, or guess like you're doing.

I have the same flywheel. I found TDC with a dial indicator and marked the flywheel with a sharpie. The mark has been there for years. I still use the indicator when the cams are out though. The line is good enough for checks.

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My feeler gauges only go down to 0.10mm.

The original shims were marked 2.85mm but actually measured 2.87mm. The new ones are 2.80 but measure 2.82, so a true 0.05mm change. So regardless of my feeler gauge, my intake valves were REALLY tight. At the maximum, I am at 0.09mm. Previously I was anywhere from ZERO to 0.04mm. So either I was WAYYY to tight, and am still too tight, or I am not really at TDC.

If I indicate the top of the piston (I have the tools for this), then as long as both cams are pointing at ~2 and ~10 oclock, then that is true TDC, correct?

cam cap fastener position.jpg

Edited by joey stalin

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Yes, when you find the high spot of the piston with the cams at 10 & 2 position you are at absolute TDC on the correct stroke. It's also a good way to look at the error in timing due to a worn cam chain.

 

 

 

 

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On 5/21/2017 at 6:12 PM, joey stalin said:

My feeler gauges only go down to 0.10mm.

The original shims were marked 2.85mm but actually measured 2.87mm. The new ones are 2.80 but measure 2.82

 

I'm willing to bet that the shim manufacturer has calibrated instruments and your Harbor Freight calipers are in error. Good that they seem to be linear in the area your measuring.

Unfortunately, it would seem your ingesting something on your intake that is destroying your valves.

Edited by Bermudacat

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31 minutes ago, Bermudacat said:

I'm willing to bet that the shim manufacturer has calibrated instruments and your Harbor Freight calipers are in error. Good that they seem to be linear in the area your measuring.

Unfortunately, it would seem your ingesting something on your intake that is destroying your valves.

Actually no, there a pair of Brown and Sharpe calipers that I've measured against calibration gauge blocks at work.

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1 hour ago, joey stalin said:

Actually no, there a pair of Brown and Sharpe calipers that I've measured against calibration gauge blocks at work.

Swiss?

What does your mic read? :)

That is my Fowler mic. Brown & Sharp's Chinese made line. I don't use it at work. :(

20170603_085139.jpg

20170603_085154.jpg

Edited by Bermudacat

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