CMP alloy pistons

[Mike Kelly]

These dome top pistons will fit the CMP engine

https://www.ebay.com.au/itm/1937-194...IAAOSw5r5e0BbI

[Hanno Spoelstra]

What’s the advantage of alloy pistons? Lighter weight so higher revs, eh?

Were these an aftermarket item, or were they factory fitted in some cases?

[Mike Kelly]

Originally Posted by Hanno Spoelstra

What’s the advantage of alloy pistons? Lighter weight so higher revs, eh?

Were these an aftermarket item, or were they factory fitted in some cases?

These are Aftermarket Hanno . Yes, less mass moving up/down = less force on the rod bearings and longer life , and higher revs are possible but I would not like to test that theory myself. I think they are about 25% lighter than the iron pistons. The CMPs had the heavier iron alloy pistons fitted at the factory.

The iron pistons , I've heard the top section can fatigue and break off One advantage of the iron pistons is, the top ring groove doesn't wear like the alloy pistons suffer from.

[Hanno Spoelstra]

Thanks Mike. And is the some top standard or are these pistons meant to increase compression too?

I have a lot to learn about Chevs still...

[Phil Waterman]

Hi All

Just a reminder with the Chevrolet engine used in CMPs that have domed pistons use a different head than other Chevrolet engines of the time that used flat top pistons. The domed pistons will not work with the flat topped heads. They hit the head.

I would suspect that if you put flat topped pistons in an engine with the domed piston head the engine would run but with a significant loss in compression.

Will post picture of the different heads.

Cheers Phil


Added Pictures these are all related to my 1945 HUP overhaul a few years ago pictures are from http://canadianmilitarypattern.com/H...May%20Work.htm

[Mike Kelly]

Originally Posted by Hanno Spoelstra

Thanks Mike. And is the some top standard or are these pistons meant to increase compression too?

I have a lot to learn about Chevs still...

Hanno, the dome tops are standard for their matching head . From memory the flat top pistons and revised head were released in 1941 but the CMPs kept on with the earlier design pistons til the end of production.

[Hanno Spoelstra]

Mike, Phil, thanks for all the info!