Bent Valve Woes

[Uber E30]

So i popped the head off my s50 and it seems 2 of the exhaust valves are toast. My plan is to get a new head, but thats not my concern. What im curious about is that the bent valves hit the piston head a few times before the engine was shut off and left # 4 and 5 a bit marred. The damage is just to the top of the pistons and isnt that close to the sides where it obviously has to be a perfect surface.

I was thinking i would just smooth them out with some fine grit sand paper and call it a day. Does this sound viable or crazy?

[FredK]

It sounds viable to me. My friend did something similar when he had light valve-to-piston contact on his 95 M3. Really all that happened was just a little depression at the valve pockets, just enough to remove the baked on carbon.

After getting his head rebuilt, he made sure the rough edges on the little dimples were smoothed out, and he installed the head again.

[gazellebeigem3]

I see this all the time. If they just kissed, theres no harm in grinding everything smooth so that no detonation occurs. Post pics and ill tell you for sure.

Ive probably done it 4 or 5 times by now on race cars that moneyshift like its their jobs.

[Uber E30]

Ok will get some pics up here soon... any recommendation on how to grind them? I have it on a stand so i was just gonna flip it upside down and hit it with some sand paper so all the shavings just fall to the ground

[gazellebeigem3]

Ok will get some pics up here soon... any recommendation on how to grind them? I have it on a stand so i was just gonna flip it upside down and hit it with some sand paper so all the shavings just fall to the ground

Yeah sandpaper will work fine. Just rotate each piston that youre working on to top dead center so theres no chance of scuffing up the cylinder walls. Also, that way youll be able to clean any shavings out easily with out them getting down into the rings.

[e30this]

pull your oil pan and check to see if you bent rods. Sounds weird but I had a buddy who had piston to valve contact and it didnt do anything to the piston but put some nicks in it. he put it back together to find out it was running shitty and a rod was bent. I will try and find the photos..

[lifeiskaos]

i would think you maybe able to tell if a rod is bent by comparing piston heights at tdc?

[jrdeamicis]

4 and 5 are pretty gnarly. More on the head side rather than the piston side.

[Uber E30]

This is the worst of it, the other ones just have a small grove

[SiGmA_X]

Clean the carbon off, finely sand it, and see how it looks. Don't go too deep, but do make sure its smooth.

[matt]

That piston looks done to me.