Euro startup sounding like a diesel engine

[EUR003act]

But probably not the pistons, bearings and crank?

lol no, probably not lol

although there is a guy in the states that runs his to 9000rpm for dynos...
(running K20 oil pump)

lol i think ill stick to 8000rpm however

sorry to hijack, im ashamed

[JohnL]

the main problem you might face with the tighter settings is that the valve doesnt seat properly with the weaker K24 springs, equalling loss in power

I'm having trouble seeing why that would be the case (with any springs if the only variable were the clearance), unless the clearance was so tight it wasn't really a clearance at operating temp...

The problem with weaker springs usually occurs at full lift as the valve train 'overshoots' the cam profile due to mass intertia, and perhaps a slight bounce as the valve seats, if it seats harshly (which should I think be more gentle with a lesser clearance).

[EUR003act]

I'm having trouble seeing why that would be the case (with any springs if the only variable were the clearance), unless the clearance was so tight it wasn't really a clearance at operating temp...

The problem with weaker springs usually occurs at full lift as the valve train 'overshoots' the cam profile due to mass intertia, and perhaps a slight bounce as the valve seats, if it seats harshly (which should I think be more gentle with a lesser clearance).

you said it right there yourself, with a weaker spring on a very tight clearance, the spring may not have enough pressure to push the valve all the way home...

its not going to be an issue as the AUDM K24A3 has the same spec as the K20 anyway... but if it were the K20A3 or the USDM K24A3, then yeah it might cause problems...

[JohnL]

you said it right there yourself, with a weaker spring on a very tight clearance, the spring may not have enough pressure to push the valve all the way home...

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.

[EUR003act]

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]

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]

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.

[JohnL]

Yes, it's bad thing to run with an excessive clearance for an extended period (and if you do you may end up wrecking the surfaces etc), but if the clearance tightens so much that at operating temp there is a negative clearance then the valve will be held just slightly open.

Keep in mind that the hot clearance will be significantly less than the cold clearance due to the valve expanding and getting longer as it heats up, which is why the clearances are more like 0.3mm than 0.001mm (and the hotter exhaust valves typically run a larger clearance than the cooler inlet valves).

Losing all clearance would obviously cause some compression loss, but more seriously may also cause the valve head (particularly an exhaust valve) to overheat and burn the lip of the valve head (causing more compression loss and a need to replace the valve).

This is because the hot valve head needs to seat home for a significant duration in order for heat to conduct from the valve head (through the lip) into the much cooler cylinder head. If this doesn't occur then the valve may just get hotter and hotter, and hotter.

Some heat usefully transfers through the valve stem into the head via the valve guides, but this isn't as good or direct a heat transfer pathway as the valve seat.

This is also a reason why it's a bad idea to narrow the width of the seat on exhaust valves, i.e. narrowing the seating width reduces the area of contact between the valve and the valve seat, causing a reduction in heat transfer from the valve head to the cylinder head and can cause the valve to overheat (leave it at stock width is usually the best thing).

[JohnL]

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

I don't understand your theory...?

[SPQR]

Like this: http://www.yucs.org/~rweiser/pics/balls.gif