Re-using perfectly serviceable piston rings - yes or no ?
Turbo Mini Forums

Hi guys.

As some of you will know, I'm in the middle of an engine rebuild on the van after blowing the ring lands and disintegrating No 4 piston at the TM RR day in April. My own fault !

The long and short of it is that I'm replacing the 8cc Omega pistons with a set of 10cc Omegas in order to drop the compression.

This means replacing all 4 pistons, so with Adam's help, I have a new set of 10cc Omegas going in.

Luckily, the bore on No 4 didn't get zapped and is fine so I'm putting a new piston in, with NEW rings, but a light hone to the bore so that the new rings bed in.

However, the bores and rings on the other 3 are still spot on, and dont need doing.

The old pistons were Cast Omega +.020's and having only done about 1300 miles since the engine was built, the rings remain absolutely fine and are of course, a match with each of their respective bores.

The new pistons are again, Cast Omega +.020's with exactly the same ring groove and ring land dimensions - the same rings are used, even down to the ring part numbers.

I don't see the need to fit new rings on these three new pistons when the outgoing rings are fine and the engine is nicely run-in on them otherwise I'm going to have to re-hone and then run-in the whole motor all over again when I could just be doing that on No 4 on its own.

Dont get me wrong, I'm not being tight, I have two sets of new rings available but my theory is that if I was going to drop my original 8cc pistons back in, then I wouldn't be taking the rings off and replacing them so why do it just because I'm fitting new pistons ?

Maybe a stupid question but has anyone ever re-used their piston rings under similar circumstances ?

Cheers

Richard.

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u

I dont see any problem with this.

Its not ideal, but I have used a mixture of rings from different pistons/bores in the past and, as long as the components are not badly worn,I cant see that this matters either.

If I was building an out and out competition engine its a different matter.

Seem ok but guessing other ring lands/rings are ok,if you overheated them they have loosen tension.whatever you clerly destroyed one piston, assuming all others are cmpletely ok is a bit risquy

I wouldn't take the risk , and would hone each bore a go from new...too much headacke in the future,
if their's any trouble you'll don't find where to strat and will have to start from scratch.

i agree fab ,but if they feel the same as the new ones tension wise and look fine , id use the old ones.

Medusa + injection = too much torque for the dyno ..https://youtu.be/qg5o0_tJxYM

Ask yourself this how much extra to hone all 4 and fit new rings. On the other hand If 1, 2 & 3 are all ok and as you say its only done 1300 miles, and you know what caused the failure you can make an educated decision.

But and we all know this to be true if you thought this was a no brainer you would not be asking us for our opinion

Own the day

I'd use the new ones and keep the old useable ones as spares. It's very easy to snap a modern brittle ring.

Remember a 4% leakage in the cylinder is 4% less power.

for the sake of not having to pull the engine again, I would just re-ring all 4 and have done with it. Having seen how busy your engine bay is I would do that, it is just to easy to scratch and damage stuff if it had to come out again.

Thats not to say I have not taken my chances. A couple of years ago I pulled a piston from an engine that had covered just 16 miles since a rebuild, to check something. As the rings were no longer available had no choise but to stick it back in.

Compression was dead on across all cylinders, and it used no oil.

Many thanks for all the responses guys.

Am gonna do a full detailed survey of the rings on 1-3, particularly for over temp and cross section dimensions then make a decision on whether to re-use on 1-3 and just fit new in 4.

Let you know how I get on.

Cheers.

Richard.

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u