CMP alloy pistons
 

These dome top pistons will fit the CMP engine

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

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?

yes
 

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 :confused One advantage of the iron pistons is, the top ring groove doesn't wear like the alloy pistons suffer from.

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...

Remember the head used with domed piston is different.
 

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


Attachment 115253 Attachment 115254 Attachment 115255 Attachment 115256 Attachment 115257

Standard
 

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.

Mike, Phil, thanks for all the info!