7 replies to this topic

[KRM_Simon]

Morning all.
I am currently building a 1330 (1275 +.060) engine for my rally car and I'm having problems with some piston rings and I was hoping I could rely on the experience and advice of TMF.
Firstly I have had the block rebored to suit the pistons and I have measured it at 72.07mm which is just under what a 1330 should be. However when my new rings arrived for AE 21251 +60 pistons all looked fine the boxes were marked up correctly the rings themselves were all the right profile but when it came to gaping them I have pushed them into the bore nice and square and the end gap is already 17 thou where as I am after 12 thou. The rings are made by goetze who manufacture for AE and are sold by the likes of minispares and minisport.
Has anyone else had this experience of rings that have gaps too big out of the box? Is this potentially a batch issue? I have tried 2 out of the 4 sets of rings and got exactly the same measurements on each. Are there any other after market ring suppliers I can buy from?

Thanks, Simon.

[Cooperman]

It does seem as though ring gaps have increased over the years and even when correctly bored I've seen gaps of up to 0.020" which, IMHO, is too big for a new engine.

Ideally the gap should be 0.003" to 0.005" per inch of bore, so for a 1275 block with a bore approaching 3" a figure of 0.009" to 0.015" is acceptable. Yours at 0.017" will be OK, but make sure the gaps on alternate rings are 180 degrees separated and are on the non-thrust faces.

A guy I knew who built a lot of competition engines used to use a set of rings for the next size up, then shorten the ring circumference until he got the 0.003" per inch gap. It's an expensive way to do it and won't work at maximum nominal over-bore and unless it's a race/rally engine it is really not worth doing.

[ACDodd]

Just import a set of total seal top rings from the states.

Ac

[Cooperman]

Just import a set of total seal top rings from the states.

Ac

+1. The total seal rings have a 'gapless' second ring.

My friends in air racing in the USA use these rings.

I've used them with Karl Schmidt pistons and they are truly fantastic.

[KRM_Simon]

Thanks for your help cooperman and AC, I know 17 thou isn't a million miles and if it was a mild mannered road engine I would probably go with it. But given the amount of money going into this build and it is for rallying even if it isn't the highest spec thing going, I like things to be right especially the details as they tend to be the things that make the difference.
I have heard total seals mentioned before, they sound like what I need then. Had a look on their website and they only advertise up to +40, will get in touch with them see what they say.
Thanks again.

[ACDodd]

Also try www.calverst.com

It is annoying problem for me too! You can also look at omega pistons and rings. In most cases the rings come up smaller in end gap.


Ac

Edited by ACDodd, 16 August 2014 - 04:58 PM.

[racingbob]

my mates got these rings and his is 17 18 thou as well on a 1293

just been bored

hes doing it now, when his mate checked the bore size was 1 thou over size

[Cooperman]

One thou over size is about 3 thou extra ring gap.