Irish Mini Owners Club

Need some advice on what would do this to a piston. I have asked the same question to many a mechanic and mini expert. All of them have never seen this before and are stumped to how the person who had the car at the time managed to cause the damage. As you can see from the pictures the damage is all to the side of the piston. If anyone has come across something similar the info would be greatly appreciated, as i'm at a loss to know what this person did to get this end result. You will be glad to know that the engine is being stripped and will be sorted within the week

Detnation has caused this over advanced ignition.
Regards,
Paul

Yep, second that one Paul, defo detonation and not a valve issue.

Thanks for the input lads, much appreciated. Is there anything that would contribute to the detonation/advanced ignition? the guy that built the car is disgusted and convinced the person who had it did something to cause it and jokingly said "he must hae put NOS in it or something"

How long was it built? Did you not hear it pinking under load? I have seen this before, not on a mini but it will eventually hole the piston and the bits will drop in and screw everything . just aswell you pulled it apart

It was built a good few months, car was borrowed by a person and thats the way i got it back. Brake cable snapped aswell so we reckon he was driving the crap outta it and might have added something to the fuel. The lads have come accross damaged pistons but not along the side of one in a mini.

Octane boost?? Have seen holes in the middle of the piston, never round the edge, I take it the cyclinder lining is distroyed??

oel159 wrote:so we reckon he was driving the crap outta it

That wont cause that problem if it was correctly set up in the first place. As said already , incorrect timing can cause pinking. Also wrong spark plugs or a weak mixture can cause it too.

Deadly Dave wrote:

oel159 wrote:so we reckon he was driving the crap outta it

That wont cause that problem if it was correctly set up in the first place. As said already , incorrect timing can cause pinking. Also wrong spark plugs or a weak mixture can cause it too.

The engine set-up was grand, was driving for months without any issues. I wouldn't be surprised if he put octane boost in it.

If he put octane booster on it would reduce this problem no make it worse the problem was caused by the fact the engine was setup wrong with to much advance full stop,
regards,
Paul.

oel159 wrote: The engine set-up was grand, was driving for months without any issues. I wouldn't be surprised if he put octane boost in it.

What spec was the engine. If it is running a high compression ratio then it would probably need octane boost to prevent the problem.Octane boost wont cause problems in an engine but is a waste unless you have a highly tuned engine.

Did you ask him what he did (that's if you are still talking to him!)?

DaveC wrote:Did you ask him what he did (that's if you are still talking to him!)?

Don't think ill be doing that anytime soon Engine is out and should be sorted by the weekend. Looking better now that it'll be sorted soon. Appreciate all the comments and input. Will get pictures up soon to see the end result whens shes tidy.

Good to hear you got it sorted Happy motoring!

I would agree ignition timing could have been the problem but here is something to think about ??
Opened an engine before that was ran on on avation fuel and had burned the piston we were also questioning the exhaust system as there was a flap on it for back pressure.It might be an idea to drain the fuel tank and give it clean petrol.

Aviation fuel, wouldn't put it past him. He could have been tinkering around with the engine aswell. Lets put it this way, when its back on the road, its not leaving my sight. Fuel tank was drained, and the lines cleared out just in case.

Was the engine rebuilt with new pistons, if its only one piston damaged and the others are perfect could be a faulty piston disintergrating. How is the combustion chamber?

Thanks to everyone's input, car sparked up there the other day! Few bits and bobs to be done and she'll be back on the road. Fresh respray is on the cards too.

Your piston was damaged because your fuel mix was to lean at the top end of the rev range.

I have seen this before if it was timed wrong you would put a hole in the centre of the piston and the pistons would whip on the side wall of the barrel as it fired close to top dead centre this would wear the barrel at the top end of the stroke.
The reason you got it back damaged is because whoever borrowed was driving the stones out of the motor and with the lean mix the engine temp would increase and the aluminum piston started to melt on the side were it would hottest against the other piston and there is less cooling as the water jacket is on the other side of the piston.
If you wish to contact me I will explain it better to you my no is 087 6563916

Again, why only one piston? Possible air leak at the inlet on that cylinder? I assume all new gaskets will be used so may never know.

Air leak on inlet still equals a lean mix at top rev range that's the problem what ever the cause

That was my point. It might indicate why only one piston was affected.