12 replies to this topic

[riderofthestorm]

I recently busted a skirt on one of my wiseco's and decided to try the namura piston kit just for shits and giggles. With the wiseco's i was at about 135-140 psi, when the skirt broke one was still 135 and the other was 120 psi. When i put the Namura's in i got 120 psi on both cylinders, and yes they were honed. This just don't make any sense to me, anyone else have the same issue or know why this happened? thanks in advance for the info HQ oh and yes i did clean out the crank case

[okbeast]

Did you check your squish with either set?

[riderofthestorm]

Did you check your squish with either set?

no i didn't, whats the easiest way? wouldn't think they would make pistons that different from one another?

[okbeast]

Take a piece of solder and bend it 90 degrees where it will go into the spark plug hole and u feel it hit the side of the dome. squish it, take it out and measure it.

[endofitall9]

unless whoever you took it too honed the shit out of the cylinders(seen this done) then your compression should be close, also you should have done a review on the Namura pistons which are cast..the skirts supposedly bust off really easy on them...

[XxMeltIcexX]

With past experiences it is best to have the pistons on hand when honing so they are in tolerances, getting them honed and then buying a set of pistons is just asking for trouble im opinion.

Eric

[riderofthestorm]

unless whoever you took it too honed the shit out of the cylinders(seen this done) then your compression should be close, also you should have done a review on the Namura pistons which are cast..the skirts supposedly bust off really easy on them...

I honed it myself, and i didn't hone it alot, just enough to get the glaze off, the namura's seemed to fit tighter than the wiseco's did, i dunno, whats the squish supposed to be? i'll have to check it i guess,, thanks again guys

[okbeast]

I think anywhere from .040 to .050 or something like that.

[dajogejr]

Um...what caused the skirt to break in the first place, that's the first question that needs to be asked.

Did you check hot or cold? Cast pistons and forged heat up and expand differently.

Did you bother to check ring end gap?

[notsed]

what about the fact that pro lites need a .004 clearance and namura needs .002

[sleeper06]

I run .oo3 on wisecos,look on the package check ring gap,but there is a reason that skirt cracked,out of round cylinder,collapsed skirt from piston cocking in bore,I would pull it down again find some one with a bore guage and check it good

[FireHead]

Um...what caused the skirt to break in the first place, that's the first question that needs to be asked.

Did you check hot or cold? Cast pistons and forged heat up and expand differently.

Did you bother to check ring end gap?

Two things (Dave noted both):

1.) The piston skirt broke for a reason. Most likely, the bore is out of round or not square to the crank (providing nothing else is wrong with the engine.

2.) You can't put a cast piston in a hole machined for a forged piston and vise versa (The machining spec. / tolerances are different).

[blowit]

I am in total agreement with above but not sure if the difference in bore sizing would be causing such a drop in comp. I wonder if the holes are egged. Round rings in an oval hole never works out too good. However, the old rings would have worn to this egg shape.

I would certainly want to look closely at the squish clearance. Probably a good idea to pull the topend and get a more thorough QA inspection. As mentioned above, skirts don't just break for no reason.

Also keep in mind that that gauge is NOT a bible but merely a tool. Tools can fail.



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