Shim Dilemma

[2manycrashes]

Ok guys,

I will try to explain this one the best that I can. I am new to motor work and have a friend that is showing me how to re-build the engine.

I am installing a new piston. I had the head ported and polished. I believe they also did a 3 angle valve grind. Anyways, here is the scenario.

The problem or question deals with the exhaust shims. The prior exhaust shims were 2.18 (218) shims. After installing the cam and torqueing it to spec, the following issue arose. The required shim is now 3mm, per the honda service manual, that is the highest allowed shim without refacing the valve seat.

Keep in mind that the Intake Valves are perfect with the old shims.

Honda has looked at the head, dis-assembled the exhaust side, said everything looks perfect, but is unable to tell us why there was such a drastic change in the size of the required shim for the exhaust side.

The 3mm shim will put the clearance at exactly .28 mm per the service manual on page 4-11. This was measured by 3 different people at honda and so far no one can give an explanation as to why this is happening.

I've been told it will work okay this way, but honestly I am not 100% comfortable with what appears to be a drastic change in machine tolerances.

Let me know if I can provide more info, once again I really appreciate the help !!!!!!!!!!!!!!!!!!!!!!!!!!

[MIKE400EX]

Is that after you changed the cam too? If so then maybe the exhaust side is ground with a smaller base diameter than the old cam.

[2manycrashes]

Had the hrc cam installed from when I bought the quad In February.

[chad502ex]

I would suspect the exhaust uni-rocker arm being slightly bent. Sunken valve seats would not cause wider valve lash measurements. If your valves seats were pounded into the head that would cause your lash to get smaller- not bigger. A leak down test would show if your valves were not "seating" correctly- if they aren't. If your valves were not seating right, then your valves would be partially open. Because Honda heads are typically soft, the valves tend to pound into the head over time and cause the valve lash to eventually close.

It could be as simple as your cam carriage not being torque down or installed correctly. Good luck. Let us know what you find.

Were the valve seats altered in any way?

chad502ex

[2manycrashes]

Had the guy who did the head work doublecheck it. Multiple people have said that it would be just fine. Should have the motor complete tonight. I'll let ya know how it turns out.

[2manycrashes]

Update-
ok, bend your mind around this, the parts guy at honda said that the clips for the retainer need to be replaced. Of course the old ones looked fine. The head guy, puts it back together - I just put the cam assembly on the head and now the original shim is just a bit 2 snug.

Not making alot of sense, my friend is going to check it tomorrow. Sounds like I will need a slightly smaller shim instead of the huge 3mm shim. Anyways, going to have someone look at it that knows what they are doing tomorrow.

The smallest feeler gauge that I have is .203 mm and it is prettty close, but to tight. The honda spec is .28 +- .03mm, this tells me I will need a slightly smaller shim to make the gap equal to the .28 honda spec.

[chad502ex]

sounds like your getting closer and your on track

smaller

good luck

[MIKE400EX]

Get somebody other than the dealer to look at it. The retainer clips/keys should not have any effect on the shim thickness needed. Sounds like maybe the bucket is binding on something (retainer, spring) or the shim is not seated correctly.