M20 valves hitting...

[Yakker]

Well i guess i've been lurking this site for a little while but and now finally posting... But anyways I just bought a 1990 525i for a really good price, and it had a bit of a head gasket leak and from the sounds of it valve contact. I got the head off today and noticed exactly what i suspected, the valves have hit the pistons. Its not terrible but what do you guys think about running with pistons like this? I've got a new head already built ready to drop on there.




hopefully a little tech to add to the board for my first post.

[Yakker]

Here's a pic... from a cell phone unfortunately but something...

http://images14.fotki.com/v388/photos/1/112285/421739/020207_1856c-vi.jpg (http://public.fotki.com/yakker333/misc/0202071856c.html)
Hosted on Fotki (http://www.fotki.com)

[winfred]

no problem i just dress down the sharp bits with a chisel and slap the head on, done dozens of heads like that

[632 Regal]

can I help? lol... Winfred got me on this

new head make sure you dont have oil or anything in the bolt holes before doing this.

[shrike071]

I think it should also be stated that it would be an exceptionally good idea to replace the rod bearings and the wrist pins - as well as the required valvetrain parts. Contact like that can wreck them in short order. Also - check the sidewalls for scoring. Your pistons DID pitch a little in the bores when contact was made.

[winfred]

id leave the bearings alone that small amount of contact won't hurt them, i am not talking out of my ass here, i have some motors over 100k miles after a broken belt still running fine some well over 200k miles total

[gale]

Ditto to what Winfred said, smooth out any sharp edges of the dings & put the head on. My former e28 m20 chucked a belt at 75 mph, bent 5 intakes & 2 exhausts (or visa-versa) & put a few dings in the pistons. Had the shop rebuild the head & manually debur the tops of the pistons & she ran great for many 10's of k-miles afterwards. In fact it ran much smoother than before. The shop didn't see any need to mess with the crank.

[Bill R.]

I would use more than a chisel though to knock off the raised area where the valve smacked, i'd use a file and some abrasive to make sure there aren't any sharp edges. Any edges left will lead to preignition or detonation, what you hear as ping or knocking. So don't leave any burrs or sharp edges sticking up.

[Yakker]

Ah, great thanks ya'll. I'm gonna go ahead and clean up the sharp edges a bit and smooth em out and call it done.. thanks alot!