Valve clearence adjustment

[northwind]

Originally Posted by Well Oiled

........or if you get a fatigue failure of the valve stem (we test engines at work and I've seen a few of these) the valve head will drop off and rattle around in the cylinder. Very nasty !! I still have the souvenir of a mangled piston with a piece of valve head embedded in the top.

Heh, I saw pics a while back of a Corrado G60 that had the standard supercharger fall to bits and drop a hail of bearings into the heads... Never seen anything like it in my life, every surface was cratered like the face of the moon. The guy replaced the valves and carried on

[Sid Squid]

Originally Posted by hitmanip

why is it that the SV has all this shim BS and my 250 you adjust it with a screw driver

Swings and roundabouts, screw and locknut much easier to adjust it's true, but will need doing far more often as the mechanism is simply less resilient, shims are less convenient it's true but require less frequent adjustment. The shims are under the buckets in order to make the system less prone to failure, some older Suzukis had 2p sized shims on top of the buckets, at extreme revs if valve float occurred it was possible for the shim to be dislodged, not pretty.

Originally Posted by minifun

What happens if they are out and you just keep using it? Does it do any damage?!?

Yes, it can do:

Originally Posted by I Previously

Every time the inlet valve opens it receives a nice cooling rush of incoming gas, and when it's closed it dissapates heat through the valve seat, even though that's a small area for conducting away heat - every little helps - in short the valve itself has an easy life, and thus wear in the opening mechanism commonly outweighs the wear to the valve - thus the clearance often opens up a bit. Exhaust valves however don't have such an easy time, they get and stay very very hot, their primary way to dissapate heat is the thin ring of the valve seat, and a little up the stem, everytime the long suffering exhaust valve opens it gets fried with gas at/near combustion temperature - typically 300-700C - thus in the case of the exhaust, the valve tends to wear more than the opening mechanism, hence the clearance reducing.

Also we have a nasty Catch 22 - if the clearance becomes significantly reduced, (or worse still if there's no clearance and the valve never fully closes), the valve spends less of the already small amount of time that it should do closed, thus it never disspates the heat it should do and can literally melt, this is called burning a valve, no surprise there, and you really don't want to get into that.

A round of applause for your exhaust valves please - the hardest working bit of your bike, full stop.

Originally Posted by minifun

My friend used to be a suzuki mechanic and said they very rarely needed doing!

True, but:

Originally Posted by I Also

the SV is well known for not requiring much adjustment, but as an unscientific example of how random it can be I've adjusted nothing at all on many 15,000 mile bikes but just recently did one, (that I've known from new, so can be certain of the mileage), at the same 15,000 that needed three shims changing. Another SV, just on 95-100,000 miles now, has had only three valves adjusted in all that time - five have never moved at all, but the 45,000 check on another late last year revealed four needing attention.

Go check.

[Spanner Man]

Morning all.
Ditto the Squids findings and advice!..........I've found that around one in three bikes need shimming at 15k. As stated checking the clearances isn't too difficult, but changing shims is a touch fiddly, with expensive consequences if not done correctly.
Better to cough up and have it done, than ignore it, for if the clearances are tight your engine will eventually burn out a valve or two.

Cheers.