Ring gaps and gap-less rings

[SteveK]

Can anyone tell me (from experience) what the acceptable piston ring gap should be on an L28 with standard sized pistons

Have read all the books (How to rebuild, Haynes etc) and it varies from 9 thou to 18 thou, however I am just installing new rings on some dished pistons and without gapping them I am seeing 20 thou on both top and bottom sets. The bores look good (86.02 - 86.03 mm max and practically no taper) with cross hatch honing marks clearly visible (engine has only done 5K since last rebuild) old rings show 22 thou and car made 158 Bhp at the wheels when last dyno’d.

Moving on from this has anyone used total seal (or such like) gap-less rings ???

Phred it would really be nice to get your input here if you are around

Regards

[240ZX]

Have you talked with the ring manufactures tech reps about your issue?

[SteveK]

Have you talked with the ring manufactures tech reps about your issue?

Yep, first phone call I made and the answer was "I should be OK" hmm didnt like the word "should" kinda lacked conviction.

[Phred]

This is an area that can have more than one right answer. So you will always be able to find various specs. First I'll be general, then specific.

The ring needs clearance between its ends (end gap) when installed in the bore. This is to allow for expansion of the ring when it gets hot. There are various sizes and designs of rings, and they will expand more, or less, depending on there mass, material, and location. Even the type of induction, and jetting, will affect ring gaps. So when you see a recomended gap of .017 for an L28, you know it will be safe for all models of that engine. This is based on a very simple formula of .005 (gap) per inch of bore. SteveK said he measured .020 in his L28. This would indicate a bore .001 larger than stock. This has to do with the formula for circumference/bore and Pi (3.1416). Just know that for every .001 inch of bore dia. changed, the end gap of the ring will change .003. So in answer to his question, yes those gaps will work fine, even though they are a bit on the wide side. Just for reference, I found that end gaps can be reduced to .014 on certain race engines without butting the rings. The reason you hear such a fuss about ring gaps is because they can be a race engine builders friend or enemy. Too wide, it runs ok, but a slight amount of compression is lost. Tighten them up, more compression and horsepower. too tight, the ring gap is lost, the ring is forced into the cyl, and damage occures. Enter gapless rings. TotalSeal provides sets which include a conventional top ring, and a modified two piece second ring which uses a "rail" (like on on oil ring) to stop compression gas from leaking past. I have used these rings on many engines, and have not had any problems with them.

Phred

[SteveK]

Phred

Thank you for a comprehensive answer to my questions. I am certainly more comfortable now with the 20 thou gap than when I first saw it.

Incidentally I spoke to Total seal yesterday who are willing to make a gapless chrome moly top ring set for me --- not cheap though -- I am just deliberating as to which direction I should take.

.

[NovaSS]

As for the Gap Less rings, they show low STATIC leak down numbers but in dynamic operation the difference is slight compared to a properly gap standard ring. The gap less are showing great results in alcohol fueled engines due to the extreme rich conditions they are run in.

On the street? Go for it you have the money but don’t expect a whole lot.