Holed piston! Could this be the cause?

[alanscottj]

Certainly likely you were running lean for some reason if it's a holed piston, if you don't remove the crank to check all the bearings and replace your seals your asking for more trouble down the line? also, how many miles since it was built did this happen?

Well over a thousand miles, but recently had reed valve fitted and re-dynoed, probably about 50 miles ago....

[Grumpy225]

I also think I filled up with different fuel to my normal unleaded, I used the 95 octane one, would that run hotter?

The higher the octane the slower the fuel burns (which is why you need it for high compression motors).


To answer your question though, no unless you normally run 100 octane.

Like everyone else said, strip that top end. Where do you think all the aluminium bits went?

[mick1]

You may have been a bit hasty. Similar problem with mine but before stripping it down I leaked tested it. this identified the fault as a crack in the casing, causing an air leak. Your "problem" is if it is/was an air leak caused by a leaking cylinder head/base/manifold/etc, you probably wont find it till you put it back together, then you might have cured it. Definitely worth leak testing when it's all back together.

[alanscottj]

Rebuild today, cleaned the top end last night, found a couple of bits of aluminium stuck here and there. Cleaned it all out, looks good now. When I took the cyclinderhead head off a couple of the nuts were loose. Anyhow, got new gaskets, and a torque wrench for the re-build. Goimg to make one of those leak tests out of a inner tube and test before it goes back on. Everything is going to be put back together belt and braces and everything torqued properly. And I will be pottering around until I get her dyno'd again to be on the safe side.

Which Loctite can I use on the cyclinderhead stud nuts?

[HxPaul]

I use blue loctite on cylinder head nuts.

[alanscottj]

I use blue loctite on cylinder head nuts.

Cool, I'll try a touch of that on them

[nelson pk]

Hi
Had you not been leaning the jetting in an earlier post to try and clean your low revs up??????
If you have leaned the jetting after it has been dyno'd this could well be the cause! A problem in the cooling system(ie not shifting air about efficiently) is more likely to cause a sieze and not hole a piston in my opinion.
A holed piston is more likely due to running lean or too advanced timing.
Find out why it holed otherwise its likely that it will happen again.
I also would not use any form of loctite on cylinder nuts as it will just cause issues if you need to strip it down again (pulling studs out with nuts etc). Torque the nuts up to about 18ft lb progressively and use good quality thick flat washers. After about 50 miles, retorque again on a cold engine and it wont come loose
Good luck.

Just noticed you found cylinder head nuts were loose....which if the head was blowing could well cause a holed piston.
You need to check that your head is not warped and needs refacing if its been blowing.
Thats what i would do anyway

[alanscottj]

Yeah, I dropped my pilot from a 55 to a 53, could this really be a potential cause? I don't think head was blowing as the other nuts were all tight and that includes three extra studs that the Mugello has. I thought the pilot was only responsible for idle to quarter throttle, I was not at that when I holed it?

[rosscla]

Pilot works alone up unto 1/4 throttle where the rest start to come in, pilot circuit doesn't shut off, they all are supplying fuel to some extent at full WOT

[rosscla]

See charts here

viewtopic.php?t=20873&p=149184

http://www.iwt.com.au/mikunicarb.htm