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[CapriManxr2]

So I'm rebuilding the engine on my 91 XR2 and all I have left to do is the piston rings and I can't find the end gap length for our motor. I found a thread where someone said they got the end gap "down to spec." Does anyone know the piston ring end gap for our car? Also, is there a vacuum line diagram that I can refer to when bolting everything back up?

[EShepherd]

Ring gap spec depends on what you plan on doing with the car, and what parts you are putting on the car. With a stock ring on a stock rebuild running stock boost levels, use OEM specs. They are buried in the FSM, in the engine section.

https://web.archive.org/web/20151002171537/http://techcapri.home.comcast.net/~techcapri/ServiceManuals/1991/Group%2021%20-%20Engines-Gasoline.pdf

Top Ring - 0.2-0.4mm
Second - 0.15-0.3mm
Bottom - 0.2-0.7mm

It's all on the last few pages of that link.


If you plan on running more boost, or are using fancy rings, then it gets complicated. The short answer is, you need to widen the gap. By how much...you'll want to do your own research there. Start with the ring manufacturer's recommendations and go from there. You want to avoid the ring closing up due to thermal expansion from the increased heat. This will blow the ring lands off your piston, and mulch that cylinder.


Edit- Vacuum diagram on sticker on hood of car. Can also be found in FSM

[CapriManxr2]

So for people runnin rocketchips, do they use OEM ring gaps? Because the rocketchip runs higher boost with a new fuel map and higher RPM (from what I understand).

[EShepherd]

So for people runnin rocketchips, do they use OEM ring gaps? Because the rocketchip runs higher boost with a new fuel map and higher RPM (from what I understand).

Probably. I'd assume most folks that went that route were doing it to an older used car. It's not as important then, because wear over time will likely have widened the gaps. Further, most people don't wanna tear the block down to re-ring it. It's not super important, more of a since you're already in there sorta deal. The more you plan on beating on the car at high boost. the more important it becomes (for longevity).