Seeking opinion on damaged piston crown

[eandrade]

(this is a repost from bimmerforums...I figured with all the 24V experience on here, someone might be able to provide an informed opinion)


Car is a 1998 M3 (S52B32) with 140K miles.
A nut and washer got sucked into cylinder #4 (don't ask)
We pulled the head and saw that the piston top was heavily gouged from hammering the nut into the head. Luckily no damage to the cylinder wall. The head is toast and will get rebuilt.

I searched and found this thread on bimmerforums, but the damage there seems minor compared to ours.

We're seeking honest opinions from experienced builders: is it safe to simply ball peen the high spots down (or dremel) without removing the piston? Or is replacing a piston absolutely a must in this case?

BTW, the owner is seeking to get at least another 4 years/50K miles out of the car as a daily driver. We definitely don't want to have to pull a piston unless we absolutely must, since the cylinder is still good.

Photos of the carnage:






Thanks in advance!
-Ernie

[Exodus_2pt0]

I'd pull it, hone the cylinder, and throw a new piston in there. That is more than just a nick.

If you put it back together with that piston you risk doing the job again.

[jrdeamicis]

I just went through the same experience on my own personal car. A bolt had fallen onto my intake before I was working on the car. Pulled the intake, tumbled in. Chomped up my piston also along with destroying my head.

Had the head repaired and I am swapping the piston. Just swap it, that thing is DEAD. To the max, don't even ball hone. Just pull it, transfer rings, plop in, take off.

Measure the cylinder bore and check some end ring gap. You can make the decisions from there on how long the engine will last.


Hey ernie! Didn't realize it was you until I re-read the post.

[M-technik-3]

Agreed replace it. Not worth the future aggravation down the road.

[eandrade]

Hey Julian! Yeah, it's my brother's car. We're discussing options.
Transfer rings, eh? Hope I could pull 'em off without breaking 'em.

Thanks all for the quick feedback, it confirms what I suspected (dreaded).
Love this forum...got a much better response than the other one :)

[Ryann]

Piston must be replaced. The largest gouge is at the edge of the piston and could've collapsed the upper ring land enough to pinch the ring. If so the ring will wear quickly there and blow by will ensue.

[eandrade]

Ah, good point, didn't think about that. Thanks Ryann.
Well, the car needed a new oil pan gasket anyways...and would give us a chance to secure that oil pump nut.

[Mr.SWISS]

Ouch, that's toast. Butter?

[jrdeamicis]

As far as pinching the rings, just inspect and see what is up.


On a side note.

Ernie, BUY THIS TOOL! Its what I use at the shop and seriously ring transferring is mindless now.

http://buy1.snapon.com/catalog/item.asp?P65=&tool=all&item_ID=635926&group_ID=675643&store=snapon-store&dir=catalog

[Rugbyfan]

I had a piston that wasn't nearly that bad. We junked it.

[eandrade]

Ernie, BUY THIS TOOL! Its what I use at the shop and seriously ring transferring is mindless now.

http://buy1.snapon.com/catalog/item....re&dir=catalog

Mmmm...shiny.
Thanks for the tip, just placed the order. Especially seeing as how freakin' expensive rings are (and not wanting to have to hone the cylinder).

[eandrade]

Ouch, that's toast. Butter?

I prefer Nutella.
Yum.

[jrdeamicis]

Mmmm...shiny.
Thanks for the tip, just placed the order. Especially seeing as how freakin' expensive rings are (and not wanting to have to hone the cylinder).

That tool is amazing and cheap.

Ball hone is easy however its very messy and requires the crank to be out to properly clean it. (EEK)

If you want to borrow my cylinder bore gauge I can mail it to you.