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  #1  
Old 02-08-20, 07:43
Mike Kelly's Avatar
Mike Kelly Mike Kelly is offline
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Default CMP alloy pistons

These dome top pistons will fit the CMP engine

https://www.ebay.com.au/itm/1937-194...IAAOSw5r5e0BbI
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1940 cab 11 C8
1940 Morris-Commercial PU
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  #2  
Old 02-08-20, 14:07
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Hanno Spoelstra Hanno Spoelstra is offline
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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?
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Old 02-08-20, 14:55
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Mike Kelly Mike Kelly is offline
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Default yes

Quote:
Originally Posted by Hanno Spoelstra View Post
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.
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1940 cab 11 C8
1940 Morris-Commercial PU
1941 Morris-Commercial CS8
1940 Chev. 15cwt GS Van ( Aust.)
1950 Land Rover signals replica
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  #4  
Old 03-08-20, 08:52
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Hanno Spoelstra Hanno Spoelstra is offline
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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...
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  #5  
Old 03-08-20, 13:07
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Phil Waterman Phil Waterman is offline
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Default 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


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Last edited by Phil Waterman; 03-08-20 at 16:12. Reason: Add photos
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  #6  
Old 03-08-20, 13:48
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Mike Kelly Mike Kelly is offline
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Default Standard

Quote:
Originally Posted by Hanno Spoelstra View Post
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.
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1940 cab 11 C8
1940 Morris-Commercial PU
1941 Morris-Commercial CS8
1940 Chev. 15cwt GS Van ( Aust.)
1950 Land Rover signals replica
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  #7  
Old 04-08-20, 08:43
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Mike, Phil, thanks for all the info!
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