www.zxrworld.co.uk

why do you have to have valveclearences done ??

to stop the valves and pistons catching up with each other and making a horrible mess.

there is a stunning thread about here that tells you exactly how to do it. well worth checking out.

viewtopic.php?f=55&t=8002



simply amazing i tell thee.

hatatfatcat wrote:to stop the valves and pistons catching up with each other and making a horrible mess.

Not really 'hatatfatcat'...even on 'tight' race engines the inlet valve is 1mm from the piston at its closest and the exhaust 1.5mm...the valve clearances are set to give optimum performance from the camshaft and adequade lubrication...too slack and they will rattle and lose performance and too tight they will stop the valve seating and lose performance and retrict the oil film between the rocker and the cam which can damage either or both.

too slack and they will rattle

and then the collets fall out and you have a blown engine.

Here is the result from a CBR400 engine, one exhaust valve was broken off and jammed in the port and the other went through the piston and out through the bottom crankcase.

hatatfatcat wrote:

too slack and they will rattle

and then the collets fall out and you have a blown engine.

Here is the result from a CBR400 engine, one exhaust valve was broken off and jammed in the port and the other went through the piston and out through the bottom crankcase.

please tell me that isnt a piston

hatatfatcat wrote:

too slack and they will rattle

and then the collets fall out and you have a blown engine.

Here is the result from a CBR400 engine, one exhaust valve was broken off and jammed in the port and the other went through the piston and out through the bottom crankcase.

Its getting worse this analasis of valve failure
Collets dont fall out unless i suppose they havent been put in correctly in the first place.
Two causes of valve failure...component failure...as we all know? oem valves are a two piece weld valve and this can fracture.
The most common is 'valve float' which is over revving and the valve springs cant cope with the revs and dont return the valves to the seats quickly enough,the piston catches it up and bang! either use race springs or shim the original springs to suit...when the piston does come in contact with the valve it usually bends..then breaks the head off the valve and ...then! the collets are 'shocked' out of the retainer...many people think the collets 'fall out' not so. ..'what came first the chicken or the egg':smt003

The most common is 'valve float' which is over revving and the valve springs cant cope with the revs and dont return the valves to the seats quickly enough,the piston catches it up and bang! either use race springs or shim the original springs to suit

That makes sense, and that is what has happened here then, (definitely over revved oops)

So are race springs longer or do they have a different spring rate? I had been told that the shims were needed (after the event!) but assumed that just changed the valve gap? Obviously not.


Oh and yes that was the remains of the piston.

To be honest the zxr 400 comes with various strength springs as standard and i shim the bottom retainers on the strongest spring...maybe HRC do race springs for CBR's ?....but a slight draw back is ..'a stronger spring may stop valve float or bounce' but it takes more 'pushing'... more...drag...more friction.! Win a bit lose a bit ?
Another cause of 'dropped valves' usually exhaust valves...is cam chain wear which most 'Racers' dont even think about.
On race engines when clearances(valve to piston squish ect) are set to a minimum there is very little room for valve timing to move before the valves get dangerously close to the piston...When a camchain wears it retards the valve timing...on the inlet side this isnt a problem as it brings the valve further away from the piston..ie if your original setting was say 105 LCA
it could move to say 107LCA with a bit of chain wear..this wont affect performance. But on the exhaust what was say 105LCA could come back to 103LCA... reducing your valve to piston clearance...say from a minimum of 54 thou to 48 thou...Most tuners would play on the safe side and give it plenty of clearance to start with to allow for this,but inturn you are sacrificing power! on our own race engines i check the valve timing as regular as i check the clearances...this usually pays off and we can keep it round the 80bhp all season and as safe as a race engine can be.

I can understand the reasoning behind the valve timing being important, but why shim the springs? All that does is preload the spring, are you saying that the preload stops the valve rattle because the tension in the spring is not fully released? and what sort of thickness shim are you talking about.

Yes I am in the middle of rebuilding the head on my zxr.

The other reason is going to be better fuel economy and better performance.

Okay so i've already sorted the valve clearances on my KLR as its meant to be the main killer of KLR's and i understand all about the valves n pistons n all that.

However i dont understand all this shimming business.

Can sumone explain what it is please?

I've had a look on the internet but it mentions passive shimming and allsorts of other stuff.

The shims are whats used to adjust the valve clearances i.e bigger shim gives you a smaller clearance, smaller shim gives you a bigger clearance.

Shims look like small watch batteries.

How did you do the clearances on the KLR??
Or does the KLR have adjustable tappets?

Yeah the tappets are adjustable, u just undo the locknut and either tighten the vale clearence or give it more, its a bugger tho as it takes a few tries as they have a tendancy to tighten as u try to lock the nut, even if u hold it with a flat head, had problems kicking it over when i first got it and once the clearances were sorted it kicks first time every time