Broke a piston...are the heads fixable?

1slow95 · Oct 11, 2009

My last trip to the track a couple weeks ago didn't turn out too good... I missed 4th somehow and over revved it to 6800 rpm. I'm not sure if that's what caused it to break, but I'm sure it didn't help...

Anyways, I pulled the motor and tore it apart yesterday. Here's what I found

It appears a chunk bounced through the intake over to cyl. #4

Full size HQ pics here -> http://www.mustangaddiction.com/images/10-10-09/

My question is can that head be fixed? Any idea how much it would cost? And who would be able to fix it?

Dino Dino Bambino · Oct 11, 2009

Looks like the 6800rpm overrev floated the valves and they got smacked several times by the piston (the semicircular grooves in the piston give that away). Since the piston is softer, the valves gouged pieces out of it and those pieces got between the piston crown and the head, damaging the head.
Since the head is aluminium it should be repairable but it'll take a lot of work. I hope the cylinder bore is OK so you'll only have to replace one piston instead of needing a rebore and replacing all eight.
Good luck with the rebuild.

revhead347 · Oct 11, 2009

That's not too bad at all. I had a friend how cracked the front end of his block off, and was able to fix the heads when they dropped a valve. I can't tell from the pictures if the cylinder wall got any serious grooves. It looks like you could rehone that cylinder, change the piston and redo the valve job on the head for good measure. If there isn't too much damage to the block, it's not going to be that expensive.

There is no way to get rid of all the combustion chamber damage to that cylinder head, but if you can get it smoothed out, it will work ok. The biggest concern is carbon deposits building up inside those little pockets creating hot spots. I've seen people run heads in a lot worse shape than that.

Kurt

Pokageek · Oct 11, 2009

I dont understand how you could float a valve with those heads that are top notch?

revhead347 · Oct 11, 2009

If the valves floated, they would be bent on the sides. The valves were working fine.

Kurt

1slow95 · Oct 11, 2009

Those marks on the pistons were already there. It was a used short block that had the valves smack the pistons when the previous owner had it. I'm not saying that didn't happen this time, but I don't see any damage to the valves....

revhead347 · Oct 11, 2009

That may have been what weakened the piston in the first place.

Kurt

divit250r · Oct 12, 2009

revhead347 said:
There is no way to get rid of all the combustion chamber damage to that cylinder head, but if you can get it smoothed out, it will work ok. The biggest concern is carbon deposits building up inside those little pockets creating hot spots. I've seen people run heads in a lot worse shape than that.

Kurt

Don't you think you could TIG the pits once you clean the head up and then face mill it to clean up the whole surface? Time consuming, but not as expensive as a new head I would imagine.

On a side note, you should be able to repair them no matter what. Aluminum is very friendly in that respect, unlike cast iron.

Good luck!
Scott

revhead347 · Oct 12, 2009

I'm not a machinest, so I'm not sure what kind of repair you could do to fix that perfectly smooth again. I suppose what you are saying is very plausible. I'm just saying that I've seen people reuse cylinder heads that were damanged like that before.

Kurt

nmcgrawj · Oct 12, 2009

My heads were worse than that, and they were fixed. Brian at @adperformance fixed them for me. He had to weld em up then smooth them down. Cant remember the exact cost, but it was cheaper than buying a new head!

Dino Dino Bambino · Oct 12, 2009

Low-5.0 said:
Those marks on the pistons were already there. It was a used short block that had the valves smack the pistons when the previous owner had it.

Ah OK, that explains things but it did leave me confused 'cause your valves look fine. You might want to check them anyway 'cause they could still be slightly bent and you might not notice it while they're in the head.
If it's not the valves, some other solid objects damaged your piston and head (might have detonated and broken a piston ring land).

tealstang67 · Oct 12, 2009

My tfs heads looked like that when i went lean on the bottle and burned the whole end off of the plug. All i had to do was have .010 takin off the heads they were like new. I would however have the valves checked and also find out what got in the cylinder. What did the plug look like that came out of that cylinder?

revhead347 · Oct 12, 2009

You can see where the piston came apart, that's what got in the cylinder.

Kurt

Broke a piston...are the heads fixable?

1slow95

Dino Dino Bambino

revhead347

Apparently my ex-husband made that mistake.

Pokageek

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nmcgrawj

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