14k rpm 0 deck

[bentvalves]

at 14k rpm is an .030" headgasket going to be enough to keep the piston from kissing the quench pads on a single piston cylinder head?

surely things are going to be stretching and moving at these kinds of RPM.

will be run on race fuel to keep chamber temps in check, not sure if that is pertinent information so just going to put it out there.

honda had it .030 in the hole. I put it at .005" in the hole but when you rock the piston at tdc, she goes 0.

please advise fellow gear heads.

best,

bent

[Tuner]

LOL Run it up to 8000, pull the head and check it, repeat up to 9000, check it, 10,000, 11,000 +++ etc. Depends on how heavy the piston is.

[bentvalves]

ok, excellent idea tuner. Im going to poke a camera in the bore rather than remove the head however and look at the top of the piston.

do you think I might be able to feel or hear the piston thumping the head if they are indeed kissing? I guess things are pretty rowdy up at that point and likely the answer to that is no, huh?

[MadBill]

Someone would have to confirm, but a sudden increase in blow by at 'X' RPM could signal that the shock of piston/head contact is unseating the compression ring.

[bentvalves]

another excellent train of thought.

Im not sure the the ring would be getting unsettled however, I think it would get pinched in the ring land and I will see a loss of compression...

In all honesty, I can't see the connecting rod stretching .030" even at those revs. The race gas will keep the piston cool and keep thermal expansion to a minimum. Prolly won't want to moon rev it in neutral however like Mitch and the boys.

bore is 3" stroke is 2"

[Tuner]

I doubt without some instrumentation, such as a knock sensor, you could hear any mechanical contact and pick it out from all the other racket an engine makes. Perhaps with a direct acoustic link listening device like the gizmo with a length of pipe bolted to the engine with a 3/8" or larger hose leading to earmuffs. As RPM increases and it approaches actually touching the head the first indication will be witness marks in whatever carbon deposits there may be before it actually makes metal to metal contact, and even then if it does "kiss" a tiny bit that won't hurt anything but leave tiny impressions in the piston top of the machine tool marks on the deck surface of the head. (if there are such flat areas that can contact), otherwise, a close examination for localized points of contact.

Somebody must have some motorcycle engine experience with high RPM like this. George Bryce? https://www.facebook.com/george.bryce

[bentvalves]

ooohh det cans. have a set hanging on the wall.

[modok]

I think .030" should be just fine.

The amount of clearance needed is proportional to the engine dimensions and materials.

[bentvalves]

hey man, I was waiting for you to pop on in here!

I'll let you all know how it pans out.

[englertracing]

If this is a roller bearing motor run 0.040

[Momus]

030" will probably be ok. I have a couple of 2 valve Honda engines, single compression ring, short skirt. 62 mm bore on a built up roller big end crank that run to 15000 with about 020" minus rock.

You will need to run it- static tests with plasticine, clay, solder, cameras are very approximate.

Not sure what squish clearance the std engines have, but the professionally modified 250 Kawasaki MXGP engines Cosworth developed in 2014/15 and possibly beyond, were run to 16500. One of the things the high rpm units have is a thicker than standard crankpin with more insertion length.

[mag2555]

So your for some unknown reason counting on race fuel to keep cylinder / combustion / Exh temps in check?

[MadBill]

Maybe if it needs to be retarded from MBT spark to quell detonation, absent race fuel..

[Momus]

The current 250 MXers are all around 13.5 - 13.8:1 compression ratio, rev to 14000 and run well on bowser premium fuel.

[bentvalves]

So your for some unknown reason counting on race fuel to keep cylinder / combustion / Exh temps in check?

nah man, going to run it on 87 octane pump gas then run it hard in deep sand and see what she tells me.