The Triumph Dolomite Club - Discussion Forum

Can someone explain the difference between F and G grade Sprint pistons?

I have a Sprint engine with pistons that are stamped with G on the crowns. Two of these pistons are damaged. Number 1 has broken under the top compression ring and has pre detonation damage on the crown. Number 2 just has pre detonation damage on the crown. Number 3 and 4 pistons seem undamaged and suitable for re-use.

I've been looking for some second-hand pistons as I just want to repair this engine without spending a lot of money. I've been offered some F grade pistons but am unsure if I can use these to replace the damaged pistons.

I'd appreciate some advice.

I'd reuse the best of the spare F grades and try to balance them with the rods weight wise.

But I'm a known cheapskate...

More important is: Is your bore damaged?

This is showing the dangers of BL's decision to weaken Sprint needles in the later cars and how its compounded
with modern fuels.



Jonners

With my anorak firmly zipped up the difference in " F " and " G " grade pistons is in terms of diameter, and is about 1.5 thou. So not a lot.
The actual differences are in the Sprint workshop manual.
But after a reasonable mileage these differences will be lost in general piston / ring / bore wear.
Tony.

Like Tony says after a fair bit of running it shouldn't make much difference anyway. I would be more concerned to find four that all weigh more or less the same.