Shim size from the factory

[SuperTanker]

Has anyone kept record of the size shims they take out of their In and EX? If this motor is put together all with the same specs wouldn't the shims all be the same size from the factory? How do they know if they are tight or loose without tearing each engine down and checking and then putting in the correct shim? All of you that have checked and had to change shims should have the same size shims from the factory or am I way off base in thinking that, or is that way to easy? That way, we would know the size shims without checking the size and could figure out the correct shim before we pull the cams with shim sizes from all of you that have had to change shims. Also, when you change shims to get into spec, do you use only one shim or do you put in a couple shims to get it into spec? I know that is a wierd question but I really don't know the answer to that.
thank you
Al

 

[wjbertrand]

I don't think all of the shims on a new bike are the same size, I've found different ones on machines where I am checking the valves for the first time. Honda makes pretty precise motors, but I don't think they're so good that all the parts when assembled always results in the same clearance! Never stack the shims, use a single replacement of the correct thickness. I don't think you could get two of the thinnest ones available in there anyway.

 

[Blue STreak]

What Jeff said. There are a lot of individual parts that fit together to get to the final valve clearance: heads, valves, valve seats, gaskets, buckets and the cams, at least. Each of those parts has a tolerance range. Once engine could have all the parts at the ends of the tolerance range that causes the widest gap, another all the parts that lead to the narrowest. In practice, they'll vary, some parts toward one end of the range, some towards the other, some in the middle. But no two engines, nor any two valves in one engine, are likely to be exactly the same.

 

[sirepair]

As stated, the valve train is measured during assembly and the proper shims are installed at that time. Company I work for makes a differential assy for Honda cars and each one is measured, proper shims installed, assembled and tested.

 

[BigBadblue]

The ST used the same diameter shims that virtually all 250F motocrosser/enduro bikes do (7.5 mm), (450's use 9.5mm shims). If you have buddies that ride dirt maybe you can collectively invest in a shim set.
OR- during your first valve check, record all the shim sizes and their locations on the bike, from then on when you check valves you can just pop-off valve covers do a quick check and if there is a problem you can just put the covers back on, order/get the shim you need and pull the cams at your leisure having the shim you need on hand.

BTW My Yamaha WR426F is the only bike I have ever seen with all (3) intake valves requiring the same size shim, extremely rare.

 

[ST/SV]

I got a question. If you have one on the loose side, say .011 on the exhaust, on the next check should that be tighter or more loose?

 

[wjbertrand]

I got a question. If you have one on the loose side, say .011 on the exhaust, on the next check should that be tighter or more loose?

Because of the phenomenon of valve recession, i.e. the valve tends to seat further into the head as the seat and valve perimeter wear over time, clearances tend to tighten with wear. I've noticed this is true for virtually all the shim and bucket type valve arrangements I've seen. The only systems I've seen that wear toward greater clearance are push rod and rocker arm configurations with a screw and lock nut adjustment.

I would leave that 0.011" exhaust alone, likely it will wear toward the middle of the spec.

 

[ST/SV]

Because of the phenomenon of valve recession, i.e. the valve tends to seat further into the head as the seat and valve perimeter wear over time, clearances tend to tighten with wear. I've noticed this is true for virtually all the shim and bucket type valve arrangements I've seen. The only systems I've seen that wear toward greater clearance are push rod and rocker arm configurations with a screw and lock nut adjustment.

I would leave that 0.011" exhaust alone, likely it will wear toward the middle of the spec.

That's good to know because mine were either right at or loose side, none were on the tighter side of spec.

 

[saaz]

I asked about the half size shims at the local Honda shop. It seems they are factory only (at least in Australia, so you can't order then in). I just go down the local Honda workshop with the shims I have taken out and specify what clearance I want. They measure the shims they have and I swap them for no cost.

 

[BigBadblue]

A correction on my previous post, a good buddy just let me know the KTM 450's use 7.5mm shims, I guess the 250/450 rule only applies to Japanese bikes. Oh, just to clarify the shims are actually 7.48mm and 9.48mm in diameter, but are generically known as 7.5 and 9.5.

 

[wjbertrand]

For less than $100 you can buy a shim kit from Hot Cams. First time you use it (as opposed to a dealer) it'll pay for itself.

http://www.hotcamsinc.com/index.cfm?fuseaction=cProducts.view&productid=508