20v pistons ring differences

[Sam_Q]

After a lot of searching I can't seem to find the real world difference between the different 20v engines and 7afe rings. They all have different part numbers and all are meant to have a 1.2/1.5mm top ring combo and a 3mm oil control.

Assuming that no one knowns the answer is there a way to visibility tell the difference without taking them to a metallurgist?

I would assume that if they are dimensionally the same then the blacktop rings would be the best because they where the last revision of the available materials and had the highest piston speed of the lot.

[oldeskewltoy]

After a lot of searching I can't seem to find the real world difference between the different 20v engines and 7afe rings. They all have different part numbers and all are meant to have a 1.2/1.5mm top ring combo and a 3mm oil control.

Assuming that no one knowns the answer is there a way to visibility tell the difference without taking them to a metallurgist?

I would assume that if they are dimensionally the same then the blacktop rings would be the best because they where the last revision of the available materials and had the highest piston speed of the lot.

Sam... often times the compression rings will have different tensions. Low tension allows for less drag... etc. My guess is before a metallurgist... you might try checking them for how hard they are.... (Rockwell test)

[Sam_Q]

oh ring tension, I didn't think of that one, it's a smart idea.

I wouldn't take it somewhere to get tested but rather likely use blacktop rings for all 20v engines.

[beerhead]

Soft rings do have one purpose, that's dry sump engines. If you want epic ring seal in boosted engines modify the piston to take an NA Diesel ring designed to hold 20:1+ comp. Remember the principle of diesels running is detonation, so these rings are a flexible alloy and take huge abuse.

[Sam_Q]

what I could never figure out is how diesel engines last for so long considering the load they're under.

[trdee]

have you seen the internals of a diesel engine? they're built like tanks due to the high cylinder pressures they need to withstand, which is also why they cant rev all that high, the lower revs and better lubricating properties of diesel help too

[Sam_Q]

oh I should of been more specific, why the rings don't wear out quick

[rolleraction]

Beerhead, Ive never considered that. What a cool idea.

[bermy]

bluetop ring are 1.5mm 1.5mm for both compression and 2.8mm for oil, red top and 20v are 1.2mm, 1.5mm and 2.8mm and 7A are 1.2mm, 1.5mm and 3.0mm and early 4A-F are 1.5mm, 1.5mm and 3.0mm

My guess is that they are pretty similair in fabrication, just that not one engine has the same combination hense the diffirence in parts number...

[Sam_Q]

where did you get those numbers because I beleive they are incorrect. Unless I measured them wrong both black and silvertop pistons here are 3mm oil control. They are brand new oversize genuine.

[bermy]

where did you get those numbers because I beleive they are incorrect. Unless I measured them wrong both black and silvertop pistons here are 3mm oil control. They are brand new oversize genuine.

Hmmm that was "on top of my head"... I do believe that all 4A-G use 2.8mm oil control rings... opposed to the F that use the 3.0mm I'd have to measure a set again since you make me second guess here

[Sam_Q]

It also depends on how it's measured, a 3mm slot on the piston for 0.2mm clearance?

[bermy]

It also depends on how it's measured, a 3mm slot on the piston for 0.2mm clearance?

I have no idea on vertical gap, but when I measure ring thickness I alwasy measure the ring

Anyway, shuffled through boxes and all I have laying around is a couple set of bluetop pistons and 7A-FE one... sorry

[beerhead]

No worries man, I got lucky and met a very cluey bloke who taught me some cool tricks. On completely stock pistons in a 318i taken to 2L with modified rings he made 580hp atw on 30psi. The engine is still running as far as I know, and has been seen shaming race bikes at lakeside.