36 replies to this topic

[fikus01]

oh dear!! so it actually dropped inside!! :S:S you could bolt it all back together and hope for the best but id go with takeing the engine out and removing the piston to give it a good inspectin or even replace it!! also check that theres no bore damage!!

if you're going that road a full re-build mite as well be done too!

otherwise chuck it all back together and hope for the best!!

Edited by fikus01, 25 October 2006 - 06:52 PM.

[Big_Adam]

i exspected much worse.

[mini93]

i realy would make sure that everythings ok ie bore wise, think how strong the valves have to be and thats snapped so i would check over the bores to make sure it hasnt gouged chunks out of it. might be an idea also to clean the piston top as much as you can it looks quite bad also remember that the sharp points can gather heat alot quicker which might cause pre ignition and also runnings on, preignition can also bend your conrods aswell so be careful abotu that
did you say you had a new head to go into it? because there could be damage to that aswell

also check the crown depth because if the valve has been stuck in there the piston could have already bent the conrod

Edited by mini93, 25 October 2006 - 07:04 PM.

[topcat]

The annoying thing is the engine has just been rebuilt. I'd only done 200 miles!!! Shame I put an old head on. You don't really expect a spring to snap though. So annoyed. I think I'll try just putting my other head on and hope for the best. Should I just try and smooth the dents out with wet and dry?

There's no visible damage to the cylinder wall

[mini93]

might need somthing a bit more abrasive than wet n dry, try getting a dremmel attachment and clean up the metal filings a best as possible

[miniboo]

i take it on the rebuild new pistons weren't used?

looks fairly mangled to me. but try it and see it may be ok

[topcat]

I'm not sure, They looked pretty new when I put the head on. I was told it was a new engine (not the head) but I think its pretty unlikely.

Edited by topcat, 25 October 2006 - 08:07 PM.

[Bill USN-1]

You need to try and move the piston back and forth and see if the top ring is moving. It appears the valve stem got smashed right on the edge of the piston which is the ring lands...If the ring is pinched you will either break the ring and score the cylinder or it will blow compression by the rings and pressurize the crank case....oil leaks.

Edited by Bill USN-1, 25 October 2006 - 09:24 PM.

[Big_Adam]

think of it like this.

can't really break it any more. stick the head back on. .. .. after checking the bores that is.

if their mangled then your boned. ... .. royaly boned.

[topcat]

Lol, well I've checked the bores and there isn't a scratch! Supprising really. Checked for any movement in the piston and it seems to be OK. Well the same as the others. There is very small visible movement, I can just see the oil squidge slightly as the piston pivots slightly, same as on the others.

So I need to re-lap the valves in my other head, clean it and paint it, get another head gasket and try again. I'll report back in about a week to let you know if it works! Thanks for your comments.

Edited by topcat, 25 October 2006 - 08:54 PM.

[che]

Good luck, I've just had to fork out a lot for a rebore due to a broken valve. I had a new set of valves only about 3 months ago, and I'm still mad about this happening!

Hopefully my engine will be reassembled at the weekend.

[The Matt]

OK so here's the damage:




What's the verdict?

Yer valve's knackered!

You need to try and move the piston back and forth and see if the top ring is moving. It appears the valve stem got smashed right on the edge of the piston which is the ring lands...If the ring is pinched you will either break the ring and score the cylinder or it will blow compression by the rings and pressurize the crank case....oil leaks.

I'd tend to agree with that, I'd be concerned about where the valve stem has banged into the edge of the piston and put that nice trough into it, it could have deformed the piston enough to pinch the ring slightly, which could lead to bore damage.

I'd also say that I wouldn't go using a dremel to clean it up unless you take the piston out! You don't want loads of little pieces of ground up alloy floating around in yer ring!

If there are no visible signs of bore wall damage, and the ring seems OK, and you can get all the little deposits out of there. I would personally put the head back on and give it a go.

At the end of the day though, it's probably better to do a strip down and you can at least do a proper inspection of it all.

It's a real shame that a mini has the gearbox in the sump. in alot of other cars you could just whip the sump off and remove the rod from the crank and push it out to fix it/inspect it.

But that's why we all love minis!!!!

[supermotolee]

the sharp edges that are now on the piston could cause hot spots and overrunning and pinking maybe but to clean it up properly it would be complete strip down think if it were mine i'd stick the other head on and give it a go haha

good luck...

[Jammy]

Yep, you gotta replace that piston!!

[TimS]

How do you come to that conclusion jammy?