mk1-forum.net

I have just pulled down a 970S motor, and found that the top ring on 3 of the pistons have broken into about 6 pieces.
What would have caused this?

Thanks for your help,

James

A broken top ring can be caused by not removing the ridge at the top of the cylinder when re-ringing an worn engine.

Tim

Hi James, some suggestions...
a)worn piston lands from years of revving, or overfueling washing any oil off.
b)Detonation, caused by shite fuel, too much compression, incorrect ignition timing.
c)Overheating the engine causing rings to end butt
d)incorrect gapping of rings causing rings to end butt
e)too much piston/bore clearance

Foggy

Hi James,
The fact that it could have been broken when the piston was fitted shouldn't be overlooked either, although not so likely with three broken. Doesn't sound good

Regards
Al

foggy wrote:Hi James, some suggestions...
a)worn piston lands from years of revving, or overfueling washing any oil off.
Foggy

Hi James,
Is it this engine?

http://www.youtube.com/watch?v=ykqi1CY5jY0

Al

That will be the day you revved the tits off it so much it tried to empty the sump of oil
Good video, who's car is that then

Austincostin: Yes that was the day after you put about 8 litres of oil in the sump

66s: That youtube vid is on the day of the Okains Bay Cooper run, Me driving Pauls CCC rep with the 970s engine that i have now bought from Paul. How in the hell did you find that piece of incriminating evidence?

Did Paul make you buy it afterwards then James?? Have you still got the nos 970 block?

Gray: Yes i still have the NOS block, and a NOS crank, the crank in this one is 10/10, which is good, but it is out to +60.

Ok, so i'm just interested in why the rings broke, and how to stop it happening again,i guess i just need to use good fuel, make sure the timing is right, and cc the head before i use it. I don't have the head that was on this previously, so i'm prepping another. Should i also measure the piston ring groove, as it may be too wide?

Is detonation the same as "pinking"??

J

James,

Ridges + worn ring groove might be the reasons!
I had encountered +20 thou on a worn S pistons' top ring groove, machined them and fit thicker rings cure the problem!
Wrong fuel hardly broke the rings, but the piston crown damage instead, hope your motor rebuilt going smooth!

Al