Do you remember what gap you set the rings at?

Its been a while but from memory it was 0.35 mm

That sounds about right, I erred on the larger end of spec just to be safe.

I wish I could offer definitive advice; I'm with some of the other guys on detonation, my experience with it has always been melted pistons and busted ring lands.

Note I also use a ring spreader tool to install them.

I had a closer look at the rings and the broken ring has a concave wear patters on the axial face of the ring and you can clearly see the sides are shiny (high spots) compared to the center were ist not being touching the piston as is darker (carbon)

The good rings are not as severly worn as broken one but show slight concave wear.

Piston grooves dont show any wear though.

Not sire what would cause wear as such besides being hammered by detonation? Rings rotating to much or to fast? Never realy heard of this or why it would happen.



Rings maybe have maximum of 10-15000km so the wear seems quite excessive

Also confirmed rings gap and its 0.42 mm so seems plenty of anything on the high side

Something I have come across is that over the years people cook the engine and some numb nuts machines the head which has bowed from the overheating and surprise not they lift up in the centre and with overhead valve engines you do not come across the warning sign something is not right the cam shaft does not turn freely like for instance in an L series engine.

Where it becomes an issue is the chamber sizes now vary with the end chambers being smaller and more likely to detonate simply because they machined a head instead of getting it straightened and then skimming it.

You need to cc the chambers and even a syringe from the vet will give you an idea if that is the problem,The correct method involves a burrette a plexi glass plate to seal the head gasket surface with a light smear of grease to make it seal and some kero to fill it and measure the volume.

Unfortunately whilst I have a burrette etc to do this job most do not so you have to ask around to see who can measure it accurately that along with detonation it causes are the most likely culprits that will need investigating I bet the issue started with the flat tops and increase in compression that pushed the end cylinder over the top compression wise so that cylinder alone detonated much harder to hear than all doing it together.