valve shim

[Bibio]

who has had the valve shims done since owning an SV. i'm not talking about a valve check i'm on about an actual shimming to get back into spec. also at what mileage was it done?

thanks.

[yorkie_chris]

Me.

15k, all correct. 29k 6 shims replaced, all too tight by 0.05 - 0.1mm.
I put this down to some periods of running lean while jetting for various mods eroding the valve seats faster than normal.

I had a fair few shims, and ordered some so as to put the clearances towards the top end of their adjustment. E.g for the intakes, I aimed for 0.175mm clearance. I reckon I got it near enough spot on.

A further check at 37k showed no change.

[Bibio]

cheers Chris...

anyone else?

[jambo]

I re-shimmed my SV when I got it, clocks said 25,000 miles, but the engine is not orginal so there's no real way to know how many miles were on that. From memory I think 3 clearances were out.

Every SV I know with any extended milage has needed re-shimming at some point. The clearances seem not to move as fast as they do on some other bikes (hence checks are only every 15,000 miles or so, VS 8,000 for my ZX6R) but they do move.

Bottom line is they need checking as per the manual, sometimes you get lucky and everything's in tollerence, sometimes not. But the consequences of an overly tight clerarance on an exhaust valve are not minor.

Jambo

[Bibio]

cheers jambo...

iv never understood all this worry about clearances, please explain as that the way i can see it in my head is that no matter how worn the valve seats get, the distance between the cam and the crank shafts doesnt change, neither does the length of the valve or the conrods so surely the worst that can happen is poor running?

i arent being a clever **** here either, i just want to know if im missing something?!

[yorkie_chris]

The exhaust valve has still-burning, incandescantly hot gas going past it at well above it's plastic temperature. If it does not close fully it cannot dump this heat into the cylinder head casting and thus into the cooling system.

Held open by a too-small clearance, the exhaust valve will either burn away, leading to loss of compression and power. Or will act as a hot-spot, acting like a glowplug and starting off destructive preignition which will do further damage, like melting the piston.

aah right, cheers for that, learn something everyday and all that!

i read a post somewhere and they were making out that it would cause valve to piston sex and go pop!

[yorkie_chris]

An engine detonating itself to death is just as destructive, if not so instant, as valve-piston crunchiness.

My raptor was similar to YCs bike, OK at 15,000, reshimmed two( exhaust valves) out of 8 v/vs at 30, 000.
As a general rule exhaust clearance gets used up with miles ( the valve seats wear down).
Cheers
Pod