.040 Pistons for Mazda

[JohnW8]

Making some off season plans for a new engine build with .040 pistons. Mazdaspeed says they don't carry them anymore. All the aftermarket pistons I've looked at online are forged and I don't believe in line with what the rulebook states. A forged piston will likely be lighter than a stock cast piston.

What are the options when a factory oversize piston isn't available anymore? Cu$tom?

[joeg]

Smaller oversize?

[chuck baader]

Forged pistons are legal. You must specify stock dimensions and usually send them a stock piston to copy. JE, Mahle, etc. all do custom pistons. Chuck

[mossaidis]

Add CP and Wiseco to the list. Pistons must be the similar shape and dimensions (less overbore), must not have any coatings and must weigh the same or greater than the OEM piston.

[RacerBowie]

RPM Machine, in Utah I believe.

They are stock replacement cast pistons. Cheap. Quick shipping.

http://www.rpmmachine.com/engine-rebuild-kits.shtml

.040 in stock, at least they were a month ago.

[Andy Bettencourt]

Or just go with the .020 from Mazda. Cheap and available and it gives you some room for a second crack at the block.

[RacerBowie]

Or just go with the .020 from Mazda. Cheap and available and it gives you some room for a second crack at the block.

Which comes in awful handy sometimes.

<--- on his second crack at this block.

[JohnW8]

The block already .020 over but the rings don't seem to be sealing real good. 12-14% leakdown on all four cylinders. That doesn't seem like much until you consider 5-6% is what it should be.
At Barbers I had to empty the oil catch can twice. Lots of blowby, but no nasty debris left on the plugs.

They say you can't polish a turd but maybe you can rebore one.


Thanks for the input.

[Z3_GoCar]

If there's too much wear in the cylinders the rings won't seat correctly and the motor will drink oil. If you've changed the rings you need to have the bore measured for wear, specifically for roundness through out the bore.

[joeg]

Jim is correct but a worn bore/ring will make the engine act more like the Exxon Valdez (push oil out into dump tank or just plain leak more so than burn it).

If you are filling the dump tank, that is classic blow-by from rings/worn bores.

[joeg]

It can also run a long time in that condition but you will need shorter races and a bigger dump tank!

[JohnW8]

The engine was rebuilt over the course of most of last year.
I finally, (long story) got it all back from the engine builder September/2010 where it was rebuilt and bored .020 over.

It has 2 hillclimbs, and 3 SARRC races and 1 Time trial event on it.

In my opinion that's too short of an interval for rebuilds but this thing has been a thorn in my side for a while now.

[joeg]

Yes--too short, but if the rings were never seated in (or if the motor ran hot), that stuff can happen.

[JohnW8]

I plan on doing alot of the work myself. I've turned wrenches for a long time but never got inside and rebuilt an engine. It's something I need to learn to do myself.

I wonder though if it's like the guy who decides to be his own lawyer, he has a fool for a client.

Anyway, I pulled the rod caps off last night and to me it looks like the low oil pressure wasn't a figment of my imagination.

[joeg]

John--Those bearings do not look all that bad.

I have re-used worse with no ill effects.

[JohnW8]

Thanks Joe. To me it looked like the surface was wiped away from low oil pressure. It's a learning process with a whole lot to learn.

[joeg]

They would be badly scored (blue and distorted also) if run dry of oil--as would the crank journals.

Bearings are designed to be a bit sacrificial--the crank journal condition is the real test.