Dorsetgem

Hi All
Just about to install the pistons and upon checking the gap, can't find a measurement in the Porsche workshop so does anyone know the correct gap for each ring please.
They are ranging from 0.15mm-0.5mm ?
Thanks
Glen

GlenL

From the 78-80 Tech Spec booklet:
Top 0.20 to 0.40mm
Middle 0.20 to 0.40mm
Bottom 0.40 to 1.40mm

What year is the car?

Dorsetgem

Thanks for quick reply (again)
4.7L 1984 M2822

Ad0911

I always feel uneasy to take off the rings to measure the ring gap and than putting them back on the piston. Fear of breaking the ring or bending them. Also when using the proper tool. But I guess this is what needs to be doen right? You can not measure the ring gap while the ring is still on the piston using some tool like a ring compressor

GlenL

The M28.21/22 engine has the same gap specs.

Rings are gapped off the pistons and by sticking them into the bores. Put the rings into the cylinder they'll be used in, one-at-a-time, and then even them up an inch down. Then check the gap with a feeler gauge. Remove, file and repeat.

To start, I put them all into one bore to find relative sizes of rings and then put the same ring into each bore to find relative sizes of the bores. Then assign each ring in size order. Reduces filing work.

Ad0911

Thank you very much for this writeup. It is for new rings I understand. Do you take old rings off to see if the ring gap isn't too big due to wear and if ring gap is within spec, put them back? Or always renew?

GlenL

It varies based on situation. If the rings are original then I'd think about replacing them especially if the compression test results were suspect. If the rings are newer and the compression is good then I'd leave them alone and not take the pistons out of the bores. I wouldn't replace them just because I could.