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Discussion Starter #1
My first time doing valve clearances and almost all of them are on the tightest end of spec, with a few too tight (maybe the new cams). I was under the impression that I was supposed to shoot for the middle of spec. I've read on here that they get tighter over time, anyone recommend setting them to the loose end of spec so they won't need replaced as soon?
 

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There's a spec sheet that shows the range and does the math for you out there (the T595 forum IIRC). I tried it when I did mine last spring. The specs work such that it is hard to do just that -- they either need more clearance or they don't, not enough range to go looser. I have had bikes I could set to the loose side. Moslty, just means a bit less valve overlap, and a tiny bit less performance. May add some valve noise.

Just check your valves each winter when you aren't riding anyhow and you'll be good to go.
 

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Shoot for the middle of the spec. The range of the spec is actually a set of limits that should not be exceeded.

There are separate specs for the intake and exhaust, so pay attention and don't confuse the two.

The valves will 'grow' in length as the engine heats up so if you set them too tight you'll start to loose lubrication between the cam and shim or (worst case) the valve won't seat fully. An un-seated exhaust valve will burn and an un-seated intake will cause backfiring through the carbs -- and maybe a fire.

If you set the valves too loose, the acceleration ramps on the cam lobes won't make contact. The accel ramps provide a gentle transition from lobe contact to lift and without that transition the valve train starts to slam the valves open and closed which causes lots of stress on the system.

Jim
 

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middle towards loose is usually best - but try to avoid the extremity. Often your choice os shim will be dictated by what you already have in hand unlkess you have a full shim set. So long as they all fall in the spec range then dont sweat if they end up towards the tighter or looser end of the scale.
 

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If you've got the bike apart it makes sense to replace the shims now rather than wait. Especially since you have to remove the shims to check the size so you know which replacement shims to buy.

0.03mm is like 1/1000 of an inch so it's not going to cause any damage if you have a desperate need to ride for a couple of weeks or so... :-D

Jim
 

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Discussion Starter #7
Thanks for the replies! I managed to get all but four to the middle of spec by swapping shims around (and measuring each about four times).
 

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Most shops will swap you even-steven shim for shim if they are still readable (some will do it even if unreadable). Most of the Jap brands use the same shims.
 
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