Brielle Cosworth Venturi LM600 works piston

You don't need (or want) to copy an 'unknown' piston.

I'm not sure how much clearer I need to be on this - it's a genuine LM600 piston from bona fide LM600 engine, lent to me by the owner *of the engine* (and several others!). He says (and he'd know) that it was made by Cosworth.

.....

Oh well

Maybe it's because Cossie make slugs for a lot of OEMs ??? I seem to remember reading in the Skyline world that they make Jun's pistons...

But that pic you have is a cast piston, not forged..

A forged piston will start off as a cylinder of forged ally, say 95mm in diameter, and then machined down to the 93mm that you want, so all the faces etc will be ultra smooth, ie a machined finish, almost polished.



The pic you have is a piston with tiny pitting all over it (like a blasted finish) which is typical of a cast piston. Even if you look closely at the ringlands, it has fine pitting on the edges. You do not get this on a machined forged piston.

If it really is a '600LM' piston, then its sh*t..., but that doesn't matter because your not actually going to use those pistons anyway.

Hmmmmm.................. looks more like a post-op finish to me .You wouldn't/shouldn't/couldn't cast the ring grooves in .You can see the beading goes over the machining marks on the gudgeon pin relief ...................................

Yes, you don't cast in the ring lands, but the edge of the land where it has been cut isnt a very clean edge...

I did a bit of reading on forged vs cast and what the two actually mean.

Basically most small/single batch forged pistons are indeed machined from a lump of billet of the alloy used to make forged pistons. But medium production runs use pressed molds to create a forged blank from a heated slug of alloy, and this is where I think you'll find this piston hails from, given Cossie use the same diameter, it makes sense to me that they simply used one of their own blanks and modified it slightly.

A fully cast piston (which this definitely isn't) will only come from a very high production run, typically only the large manufacturers producing thousands at a time.

As to the finish.... I don't know, I'll ask. I'm sure it's not there because it's a sh!t piston!

Have you got a pic of inside the piston? I can get a pic from Ferry of the pistons they produced for the 600LMs and see if it looks similar...

End of the day, the finish on the piston is not a final 'machined' finish so its either a cast or a plug. The only pistons Cosworth do in 93mm are for Pintos. By todays standards, those pistons are very low spec, no skirt or ringland coatings, and the top ringland is the same thickness as a standard PRV piston..