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First Mistake; gaps too big!

Practical Engine Building

Discussion and questions related to the course Practical Engine Building


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I'm using some supertech rings for a blown mx5 build, with low compression supertech pistons aiming for c.250 whp. I miscalculated the required gap and took too much off the top ring gap! I am just after some advice on the affect if I use them in the application.

The recommended gap for my application was meant to be 0.40mm and filed them to 0.53mm; so 0.13 bigger than required.

The second ring gap I didn't mess up and is set at 0.49mm.

Will I really see a huge drop in performance from blow by, or will the 2nd ring help?

Thanks in advance.

That's about 5 thou", there will be a tiny bit more leakage and you may need to re-ring/bore it a little sooner but, unless you want every little bit out of the engine, you may not notice the difference. Remember, OEM engines and many aftermarket 'jobber' ring sets are 'preset' to significantly more than that, and they normally seal well.

That said, I'd probably pick up another ring set and redo them - you may even be able to pick up just top rings, worth a phone call?

Oh, sometimes the exact same rings are used for both compression positions, might be worth checking as, if so, you could use the tighter gapped 'second' rings in the top and vice versa.