Piston Ring End Gaps - Not so crucial after all.

[MattH]

This cropped up on an e-mail recently and makes interesting and not too boring reading.
Its all to do with the myths of ring end gaps and gap stagger.
http://www.diagnosticengineers.org/jour ... 20Gaps.php

[Demon James]

Right, that's it.............. engine's coming back out!! I've been too precise with my piston rings

Seriously though, as I'd never rebuilt an engine before, I did wonder as I installed the new rings "what are the chances of these things actually staying where I put them with 5 odd thousand explosions a minute?"

As a novice I guess I look at things with a less knowledgeable eye but I did genuinely wonder how the rings would stay put in a slippery and violent moving environment.

The ring gaps on the other hand, I did think seemed important. I thought "too small and things will tighten up through heat expansion" and "too big would not seal well"

Interesting read

[Blue]

Whilst I accept most of that article is probably true, it's worth questioning. I assume that's a standard production engine doing standard production stuff in the article. We often confuse standard engines with racing engines when it comes to the rights and wrongs of how you should build them, and there are times when perfectly acceptable practice on a standard engine spells disaster on a racing engine. I think this is one of those cases. Too small a ring gap would prove disasterous in either case, where as too big might just lose some power.
In a case such as high compression or boosted, the rings will expand more so a bigger gap than standard is needed. In a racing engine ring seal is everything, you want zero blowby if you can achieve it, so you don't want the gaps lined up.
I don't think staggering the ring gaps is a waste of time, yes I know they are all free to rotate as they wish but I've always assumed the forces acting on the rings causing them to rotate, would be more or less equal on all the rings. If that's true they would rotate at much the same speed so if they weren't lined up to start with, they wouldn't line up for long if at all. I'm not going to build my next engine without setting the gaps and lining all the rings up just to see if I've been wasting my time all these years...

[Dave999]

I would say it also makes sense not to have the join in the oil control expander at the same point as the joins in the rails
or indeed any of them at the point where their land goes through the end of the piston pin bore (on some pistons)

My original post on demon James thread after his lovely diagram basically said

who cares, they all spin round anyway.
Based on what I'd found after stripping mine TWICE.....I was looking at everything....I had to....people were starting to say get some who knows what they are doing to build it

but I didn't want to pass on my Good luck

so I deleted it and said something more sensible

it just seemed a bit contentious.

every 2 stroke has a pin i.e a bloody big gap....

Dave

[MattH]

I would still stagger on install, as having them lined up is just asking for them to leak by if they DON'T rotate in the grooves.
I definitely agree with Blue that too tight is a problem.

Quite an interesting article though.
The most important thing I gleaned from it was not to confuse large ring gaps with a worn ring which has reduced its outer diameter, I think that is what the author meant.

[Blue]

Yes that's right, a worn ring will lose tension and eventually fail to seal at any point.

[shovelheadrob]

2 strokes have to have a pin to prevent rotation as you wouldn't want a ring end catching the transfer port. Small gaps is a big no no on anything as with heat expansion the ends could meet & be the start od a seizure. Although like Blue I'm always meticulous when building a motor, we did once throw a motor together for Gary's Picnic a good few years back, we had a destroked BB Chevy that was campaigned in Super Mod & wanted to run in the Outlaw class, we had a bigger crank & some well used rods already & after a raid on Andy Robinson's old parts bin we had enough pistons & rings to nail it together albeit with ring gaps you measured with fingers rather than feeler gauges! 3 stages of nitrous later we were running 6's all weekend, no issues in nearly 20 passes & when we tore it down no signs of blow by.