Technical Piston Ring Gap

[myoshik]

Hello - apologies if this was already asked and answered. May I ask if there are any suggestions on the appropriate gap for the piston rings? My manual shows recommendations on clearances of the piston groove, but not the distance of gap on the ring.

Engine is a 126A 000, with 73.5mm bore. Grateful for any advice.

Thanks in advance!

 

[bugsymike]

Hello - apologies if this was already asked and answered. May I ask if there are any suggestions on the appropriate gap for the piston rings? My manual shows recommendations on clearances of the piston groove, but not the distance of gap on the ring.

Engine is a 126A 000, with 73.5mm bore. Grateful for any advice.

Thanks in advance!

I was always taught 3 thousands of an inch per inch of bore on water cooled engines (which never gave a problem on all the engines I have rebuilt over 50 years in the motor trade) , as air cooled generally run hotter slightly more, so possibly around 12 thou gap on your piston size as a suggestion , hopefully you will get a definitive answer for your model here on the Forum.
There is more information on the internet from piston suppliers.
Allegedly pistons come pre gapped, but I always checked them myself on every ring, inserting the ring down the bore about an inch, then pushing a piston upside down on top of it to make sure the ring is square in the bore before checking the gap. That and positioning the gaps equally away from each other (not all in line as I have seen) along with a lightly honed bore with plenty of oil around everything always did the job.
Just looked at an old Citroen 2CV air cooled twin manual with piston similar size to yours and it says 12-14 thousands of an inch gap.

 

[fiat500]

The information I have from Autobooks is that gapping is as follows:
top ring: .0098 to .0157inch
second ring: .008 to .0136inch
bottom ring: .008 to .0136inch
It's a while since I did this so it would be wise to verify elsewhere.

 

[Toshi 975]

The information I have from Autobooks is that gapping is as follows:
top ring: .0098 to .0157inch
second ring: .008 to .0136inch
bottom ring: .008 to .0136inch
It's a while since I did this so it would be wise to verify elsewhere.

Gospel according to Haynes confirms the .0098 To .0157 (0.25 to 0.40mm) etc
Good tips there as ever Mike

 

[myoshik]

Gospel according to Haynes confirms the .0098 To .0157 (0.25 to 0.40mm) etc
Good tips there as ever Mike

After reading your response, went through my Haynes Manual again and just realized it's clearly shown under the "Specification" section! Completely missed it

Thank you everyone!