Euro startup sounding like a diesel engine

**EUR003act** · 30-01-2009 03:25 PM

Originally Posted by JohnL

Then is that a problem with low spring stiffness or with inadequate spring pre-load. I'd suggest it's an issue with preload and the spring needs to either be longer or shimmed at it's base (so long as you could shim it without risking coil bind).

I'm all for using the weakest springs reasonably possible for the red-line the engine sees (+ a bit for safety), stiffer springs use power and cause greater cam wear etc.

It seems to me that so long as any clearance exists then the spring will be pushing (or pulling) the valve shut just as hard no matter what the clearance might be.

you may be right, it was just interesting to me that the engines which have the lower redlines/weaker springs all have slightly looser clearances...

and true, hard spings to use up valuable power

**JohnL** · 31-01-2009 08:05 AM

Originally Posted by EUR003act

you may be right, it was just interesting to me that the engines which have the lower redlines/weaker springs all have slightly looser clearances...

I suspect it might allow more time to safely ignore the valve clearance?

Sometimes valve clearances open up with wear, sometimes they close up with wear, depending on what surface is wearing the most quickly (i.e. wear on lobes / followers / valve stem tips causes clearances to open up, wear on valve seats causes them to close up).

My gut feeling is that it's probably safer to allow the clearances to get too big than too small, hence a larger clearance on a lower perfomance engine with a longer clearance service interval(???).

Or, maybe one engine model wears the lobes / followers etc faster (than the seats) and can tolerate smaller spec clearances because they tend to get bigger in service, but the other engine model tends to wear seats more so the clearance tends to get smaller in service, thus requiring a larger spec gap...???

Dunno, just thinking out loud..

**Type R Positive** · 01-02-2009 04:06 PM

Originally Posted by JohnL

My gut feeling is that it's probably safer to allow the clearances to get too big than too small, hence a larger clearance on a lower perfomance engine with a longer clearance service interval(???).

Nah, you can create too much force smacking the valve cap.
One of my good mates lunched the head on his 450 dirtbike, as valve clearance was out of spec (too large) on one valve. I used to help him with all that stuff, as there is nothing to doing cam swaps and valve clearancesw in these things.
He never got around to replacing the shim that was out of spec, and guess which cap smashed to pieces, in turn dropping the valve into the cylinder and making a mess of things?

My theory is you could throw the valve open, insted of just pushing it open with loose clearances.

I guess that's why they have a lower and upper limit to valve clearance specs.