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wiseco pro lite to namura


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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

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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

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  • 1 year later...

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).

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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.

 

 

 

Mull Engineering

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