924Board.org

[Mkol]

Hi folks, i need some general advice about piston rings and honing on my first 'engine job'...

Having removed the pistons and rings in order to check and clean clean clean..
my question is should i:

A) use new rings and give the bores a hone, cross hatching is very faint.

or

B) simply put the engine back together with the old rings given it did have good compression prior to strip down.

as always the info out there is contradictory!

[924RACR]

A, new and fresh.
_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[Carrera RSR]

Depends on your expectation and longevity of the engine post rebuild. Speaking to an engine builder who’s done fast and dirty repairs/rebuilds at race meetings and seen these engine run on for many a race mile, but they always expected to pull the engine again in the near future to properly and methodically rebuild to a high standard. If you’re happy to pull the engine again in the not too distant future, reuse old stuff. Any longevity in its life is a bonus. If you don’t intend to pull the engine any time soon, do it right, do it once.
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
Now www.924board.org/viewtopic.php?t=34690
Then www.924board.org/viewtopic.php?t=31252

[Mkol]

[Karlio]

If they are standard size pistons,86.5mm you can get new rings faily easily( if you need some i have some in stock here in UK) If the pistons are oversize,87mm/87.5mm then your going to have fun finding new rings.
To see if your original rings are within spec you need to measure the ring gap. Pop the rings into the bore, about 25mm down and measure the gap between the ends of the ring.
The new when installed gap is 0.3 -0.5mm with the wear limit 1mm. You can measure the ring gap with feeler gauges.

If you need valves,crankshaft bearings and big end bearings I have them in stock.

Cheers karl

[Mkol]

[daniel]

Yes you can reuse rings provided there is minimal wear on rings and bore and you hone out the bore.
_________________
Over the top of skyline, total brake failure.... hit the wall at over 200 kp/h at the dipper, so anyone who has to brake for the esses is a pussy.
1977.5 Race Car, CAMS Group S Spec
1989 944 Cabriolet

[safe]

The important questions are:
Are your ring grooves worn out or not?
Are the cylinders out of round?
Are there lip from the rings in the cylinders?

New rings are a no-brainier.
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/Magnus, Stockholm Sweden
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Porsche 924 -79 NA, EFI and Turbo.
Porsche 931 -79
Porsche 911 -77, 3.2 Targa
Porsche 911 -69, 3.6, Coupe

[Beartooth]

My take is it couldn't hurt, but I'd want to have a good idea of the health of the engine before I made any decision. My 931 gave acceptable compression numbers, but the leakdown results were terrible (possibly some rings broke apart between when I did the compression check and the leakdown after I'd put some miles on it; it'd sat a long time). Without some measurements, it's a complete guess as to what you'll get: new rings might make it run like new, or might not make any difference.

I just bought a bore gauge and micrometer so I could get solid numbers on the snowmobile engine I'm rebuilding after finding premature wear on the work I did just a year ago, but half the reason I bought it is because I'm going to tear into my 931 soon. $500 will get you all the diagnostic tools you'd need (or you might rent or borrow them). Of course, your expectations, budget, and reasons for tearing into it all factor in. I know it was all a bit overwhelming for me the first time I took an engine apart, so I don't want to come across as saying you're just wasting your time if you don't check out the bores and pistons - just that it's a roll of the dice without that. As long as it's not a car you're going to be relying on for transportation, there's nothing wrong with putting new rings in and you get what you get. Good luck with it!
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1980 931 diamond in the rough