7 replies to this topic

[gazza82]

What does everyone use as the tolerances/gaps on pistons and rings?

 

It's a 1275 overbored by .060" to 1330. Pistons are Minispares Mega.

 

Just wondering what the gap needs to be on piston to bore (without rings) and ring gaps (Haynes says .012 to .028 for top ring, etc). Am I best going for min, max or median (eg 20thou)? Hayes also assume 4 rings, but Mega's only have 3.

 

Car will be used for road, and mildly tuned with 266 cam, etc.

 

Thanks in advance!

Edited by gazza82, 29 September 2014 - 09:17 PM.

[Gr4h4m]

I presume you are using new pistons? If so you are best to ask the manufacture, mine came wth instrutions that way you are installing them as designed.

[ACDodd]

Ring packs with megas usually come up on the large side 0.018 up to 0.025" etc. if rebuilding I fit omega rings this pulls the gap down. What cam and rockers are you using?

Ac

Edited by ACDodd, 29 September 2014 - 09:41 PM.

[gazza82]

Probably a 266 AC. Not sure about rockers yet ...suggestions? Fitting a 12G940 Cooper S head with 1.4" inlet valve.

I'll check a set of my rings tomorrow to see what they come up as.

Edited by gazza82, 30 September 2014 - 10:02 AM.

[ACDodd]

I machine mine to 0.003" bore clearance with that cam.

AC

[gazza82]

I've got about 4thou between piston and bore.

 

Ring gaps are top: 23thou, middle: 20thou (didn't try oil ring) which are way bigger than Haynes suggest.

 

Omega rings aren't cheap though are they?!?

 

I've emailed MiniSpares for their input ...

[ACDodd]

No point contacting minispares, the rings are all like this. Your bore size is adding to the end gap issue.

Ac

[gazza82]

So is the gap ok or should I look for some with smaller gaps?

 

I would have thought the rings would be slightly longer where they are for oversized bores or is that not the case? Only rebuild standard engines before.

Also with a 266 should I go for roller rockers, 1:3 or 1:5, or ok with forged Cooper rockers, sintered or pressed (welded up)?

Edited by gazza82, 03 October 2014 - 01:31 PM.