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Piston ring gaps too big before filing

Practical Engine Building

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B6ZE (mx5 1.6) Rebuild

My piston rings came with a spec sheet of recomended ring gaps for different applications.

Their recomendation that suits my current build, (High Compression Naturally Aspirated) is

Multiply Bore Diameter in inches by a factor of 0.0045

My current Bore is 79mm or 3.11024"

This comes out to 0.01399608" so 0.014", awesome!

But the first top ring I measured comes to 0.017"

A little disapointing as I have been told that these engines do like to be tight (but I'm not going to push any boundaries)

It isn't too much wider, but now should I:

Make my to ring gaps consistant with the largest Gap that I measure?

I.E. 3rd cylinder top ring measures 0.019" So I file all 4 top rings to 0.019"


Do this cylinder by cylinder?

I.E. 1st cylinder top ring measures 0.017" making bottom ring 0.022"

3rd cylinder top ring measures 0.019" making bottom ring 0.024".

(bottom ring gap = top ring gap * 1.25)

Initially I cant see any issue with the 2nd method besides each cylinder having a slightly different compression & VE

(maybe this would also make the engine run rougher)

This is a street engine for a friend

So smoother is probably better

less oil consumption is better

I'm leaning towards the first option for saftey and smoothness

But I am still curious as the 2nd option still sounds viable

Thanks in advance these forums are amazing!

That is a minimum clearance, while it may be preferred to have it at that value, 3 thou' is going to make little difference. You don't need to make the others the same, as long as they are at least the 14 thou' required minimum.

sSme with the second ring, use the minimum value for the clearance if you can - if using that formula it would be 0.014"* 1.25 for 0.0175. "Don't change it for different actual top ring clearances on diferent cylinders.

If you are really wanting that last tiny little bit, you may be able to source file-to-fit rings (maybe a better material or design) or, failing that, ring sets for the next bore oversize.