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RB25DET Oil ring Gap

Engine Building Fundamentals

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Discussion and questions related to the course Engine Building Fundamentals

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Hi everyone, I’m in the middle of building an RB25det neo with stock internals. Upon measuring Oil control ring gap, they came out as .034. Maximum Factory spec is .023 for oil control rings.

could anyone confirm if this is okay and if I should go ahead with this?

thanks!

Hey Sahan,

They came out the box at 0.034? That's quite outside of the tolerance for OEM oil control rings like you pointed out.

Are the top and 2nd rings gaps in the spec? Did the block get bored? I recently re-ringed a SR with OEM rings and all of them were in the specs.

Is this a rebuild, re-ringing the OEM pistons in a used bore, possibly with an aggressive hone job?? If so, part of the gap may be down to wear - 1 thou' bore wear is just over 3 thou' increase in ring gap. As Francis asked, what are the top and second ring gaps - and did you double check then down the bore, in case bore wear might mean they close up towards the bottom of the stroke?

Part of it may be if you're using aftermarket rings where it's common for a wider than "spec'" gap to come with the rings, because many "home mechanics" either don't bother checking and this avoids engine problems from insufficient gap, they don't have ring files and this is 'safe', or they may be a 'universal' ring set and so expected to be used in engines where that gap is common.

That said, I would have no concerns using them either way - just double check you haven't overlapped the spacer/expander ends, as that WILL cause issues.

Hey guys, thanks for the quick reply!

yes they came out of the box at .034

Block was bored and honed to use stock pistons and rods. Ring I got are aftermarket named Hastings.

1st ring was at .020 and second was .17out of the box which I thought bit weird?. Still I wanted a bit larger gap as the engine would be running a garrett 3076 turbo.

I did measure the rings at top, middle and bottom areas of the bore and it came out the same.

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