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Some thoughts on valve clearances...

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I just checked my valve clearances for the first time, the bike has approximately 14 hours on it.

One intake (left hand side for some strange reason) is out of spec by about 1.5 thou and the right is at the bottom end of the tolerance range (4 thou clearance.) I'm going to check at the dealer tomorrow for the appropriate shims...no big deal so far (at least I hope!)

Anyhow...this got me to thinking about how some CRF's seem to go through valves quickly and some don't. Does anybody (reliably) know how these engines are assembled at the factory?

Everything that is manuctured is manufactured within certain tolerance specifications. No two assemblies will be exactly the same even when made on the same machine with the same materials. Honda's spec on the valve clearances is 0.005" +/- 0.001. When they assemble these engines, does some guy on the assembly line put (standard) shims in every engine and send it on down the line, or do they assemble, check the clearance, disassemble and re-shim if necessary? Even if he (or she) checks the clearance on a newly assmelbed engine, is that any guarantee that this clearance will be maintained after "X" hours of initial running?

What if...an engine was assembled and had a valve that was at the "low end" or maybe even below the 5 thou clearance tolerance. (This, of course assumes that not EVERY engine is checked on assembly...perhaps they "spot check" one out of every...?...assemblies?) Wouldn't that give it a higher probability of "going to 0" quicker and "toasting" the seat? What if your bike had valves that were at the high end of the tolerance range...let's say came out of assembly at 6 thou clearance or maybe even a little higher? Wouldn't your bike's valves tend to last longer than those that came out of the factory at minimum, or (heaven forbid an oversight on Honda's QA program) below spec?

Set me straight if you think this is all crap...I'm just thinking out loud here. Lord knows that Honda is among the world's leaders in QA systems and I'm not trying to say there is something wrong with whatever system they're using for the CRF production. But even a "perfect" QA system results in a "normal distribution" of manufacturing tolerances on assembled equipment.

Could it be that the engines with valve clearance problems came out of the factory towards the "bottom end" of this distribution?

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The shims in all of the engines are different, even from valve to valve in the same engine. A valve with a tighter clearance(but still within spec) will usually last LONGER than a valve with a looser clearance.

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