Thread: piston ring grove clearance - how much is too much ?

Originally Posted by Taz

8.13:1 3.5 EFI. Bores and piston skirts look good (std size) and diameters are within spec. Ring gaps are excessive (around 0.9mm compared to max spec of 0.55mm) so planning to replace rings plus a lite hone. However the piston ring grove clearance is also excessive on the top compression ring (between 0.1 to 0.2mm compared to max spec of 0.1mm) and slightly better on the second compression ring. The groves look nice and square and undamaged.

Trying to avoid a full rebuild - the rangie probably wont see a lot of use. Hence is it worth forking out for new new pistons ?

Is that clearance measured with the old rings or new ones?

Ring gaps being excessive points to bore wear, If your cross hatchings gone thats the second pointer. with a .4mm inrease in the ring gap you have a .1mm increase in bore diameter and thats likely to be at the end of the acceptable tolerance for the bore clearance.

All that said, IF it was running before it'll run again with the same clearances and tolerances with just new rings it just wont last as long

Grove gap was measured with original rings on the piston. I re measured today after removing the ring from the piston and then feeding the ring (outer edge first) back into the grove (along with the feeler gauge). This measurement method yielded better results (0.1mm - ie just within spec). It is plausible that the grooves have a very slight taper however there is no visible wear on the groove lands.

Original cross-hatch hone marks are quite visible in the bore. Although most are glazed. However I'm starting to doubt my previous bore diameter measurements - I was using a telescopic "Tee" gauge and then transferring to a micrometer - but I couldn't get a consistent and repeatable 'feel' on the telescoping gauge. I need to get myself a proper bore gauge.

Cheers

Originally Posted by Taz

Grove gap was measured with original rings on the piston. I re measured today after removing the ring from the piston and then feeding the ring (outer edge first) back into the grove (along with the feeler gauge). This measurement method yielded better results (0.1mm - ie just within spec). It is plausible that the grooves have a very slight taper however there is no visible wear on the groove lands.

Original cross-hatch hone marks are quite visible in the bore. Although most are glazed. However I'm starting to doubt my previous bore diameter measurements - I was using a telescopic "Tee" gauge and then transferring to a micrometer - but I couldn't get a consistent and repeatable 'feel' on the telescoping gauge. I need to get myself a proper bore gauge.

Cheers

thats uaully only good enough for a bold indication, where abouts are you?

Hi Dave

I'm in the Perth hills

Cheers