Destroying pistons in 1.4s? Maybe stock ring gap is the issue.

[Nataphen]

Many of the pictures of broken stock pistons I’ve seen looked like the ring gaps could’ve pinched shut. The ring lands being weak is commonly thought to be the culprit, but I wanted to check into this. I looked for the stock ring gap specs, and they’re way too tight for even stock boost in my opinion. The only specs I could find show top ring gap specs to be .0098” to .0157”. Bottom ring gap specs are .0157” to .0236”. The ring lands may not be quite as bad as people think, and the rings may just need to be ground down a bit.

Has anyone tried regapping the stock rings before turning boost up to 20psi+? I feel like it may be almost necessary. Even in the loosest spec for the top, you’re only at .016”. I’m thinking it needs to be more like .021” top and .023” bottom. Blow by would be pretty minimal there, and you’d have a lot safer ring gap for a more performance oriented application. Any thoughts?


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[Italianjoe1]

This is an issue in almost every production engine nowadays, the emissions requirements necessitate small gaps, and the tuning compensates by limiting boost/timing where it would overheat the pistons. When we push them, absolutely the gaps are too small. Nobody is pulling down stock engines just to re-gap, but you are correct in saying it would help.

 

[Nataphen]

I did some more reading, and it appears that GM changed the spec of the top ring gap to be the same as the bottom ring gap in later production. I’m guessing that this is what helped reduce the frequency of blown pistons in the early 1.4T motors.

Looking at some calculations from Wiseco based on the stock bore size, they recommend that this engine’s rings for modified street use should be gapped at .0143” top, and .0157” bottom. It seems that the issue may be fixed now, and that the issues I’m seeing are mostly early models.

Sorry I didn’t make the connection before posting. I’m trying to solve a problem that’s already been solved apparently.

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[skurtov]

Big reason for the cracked pistons was oil blow by buildup in the cylinders. It would cause uneven heating on the walls.