slate blue

Tuomo spot on but there is another option and that is to have the rings ground down, Total seal will do that and they have done it for me before, so no need to pay through the nose. I will put that info up on the 928 racing website as I never knew why the GTS rings were different to all the others.

Greg

ptuomov

Total seal will grind down the rings for 54 American pesos?

RKD in OKC

944 is Alusil bore just like 928.

Vilhuer

Good idea but what will happen to skirt coating? Will it start to peal off?

ptuomov

I am not sure, so take the following with a grain of salt, caveat emptor, bull**** detector on, etc. But here's what I think.

First, it was my impression that cutting the ring grooves is always the last operation that you do with a piston. The ring groove has to be controlled extremely closely, and other machining operations etc. are done before that. Just a safety factor. Based on this impression, I suspect (but do not know) that the ring grooves were cut after coating. I don't have a piston at hand so I can't check.

Second, suppose that the pistons are coated after the ring grooves are cut. I think the second ring bangs up 6000 times per minute when the engine is running at 6000 rpm. Would the coating survive in the groove?

I guess someone could send an email to that Rebco guy, he would know, since he apparently machines a lot of weird old pistons.

Shark_Week

RKD, thanks for the info.
greg interresting option, will look into it

namasgt

I have cleaned 3 sets of S4 pistons, looks like the machining of the ring grooves was done after the coating since after cleaning you only see shiny aluminum, no sign of coating.

S4ordie

Don't forget to drill an oil passage hole in the GTS pistons while you have them out.

ptuomov

In case someone is interested, I just spoke to Eric henke at Rebco who said that there should be no issues with cutting the groove on the iron coated piston without hurting the skirt coating and that the price is $54 for eight pistons. Beats paying an extra grand for GTS rings.

Shark_Week

what is the 928 racing wesite?

Shark_Week

wondering if any of you guru's had the actual dimensions of the gts piston rings. or an idea where to find them. looked through all my technical material and cannot locate. i know the earlier engines have ring dimensions of 1.5, 1.75, and 3 mm.

Rob Edwards

Martin-

Here are the measurements I made a while back on GTS rings, subject to wear and my ability to use a caliper and a scale. Yell if there are any other dimensions you need.

Ignore the thread title, they were GTS rings, not S4:


https://rennlist.com/forums/928-foru...ton-rings.html

Shark_Week

just thought i would update the thread for those interested. the set of rings that i was sold p/n 94410390282 will not work. the first ring had an end gap of about 1/4 to 3/8 of an inch, the 2nd had a similar end gap and is actually too Thin not too thick. altogether wrong

thanks Rob!

slate blue

If you search 928racing at yahoo message groups you should find it. It has 100 members but is racing focused and not general repair stuff etc. If you can't find it I will look it up for you. Adrian928se on this forum runs it.

Greg

Shark_Week

ok thanks