M20 885 head crack (but not where you think it is)

[G-man55]

Cleaning off a new head today to swap in when I found a crack in the part of the casting that the rocker shafts are pushed through. My questions now are these: How did this happen, and is there any way to jb weld (or something) it back up, and continue running it, or is the head completely done?

I want to post a picture but I can't figure out how.

Joe

[SkiFree]

I would do something better than JB weld, like say some actual welding. But really it's a matter of how much risk you're willing to take.

As for photo posting....

http://www.bmw2002faq.com/topic/110075-posting-pictures-a-six-step-tutorial-with-pics-of-course/

[ttrousdell]

how did it happen? there is a ton of stress in on the parts of the head every time the engine is in motion. The engine heats up and cools down, thermal stress. Springs and cams push on the rockers which then exert forces on the rocker shafts and the casing. Can you run it? well its your gamble. Cracks in heads can be welded then machined back to spec. Might be easier and cheaper to just buy a new casing though.

[TobyB]

Yeah, that happens when the valves hit the pistons.

Not always, but often.

You could have it welded. I did that on one- it seemed to work fine, for a street car.
The guy who did the welding for me said it was easy to do a good job on, and he had faith in the weld.

But I never really beat on it...

t

[jlevie]

The casting can be repaired by welding. But that set of rocker shaft supports will have to be line reamed afterward and since the head will have to be pre-heated it will require surfacing. Probably be cheaper to get another head.

[jeffnhiscars]

I bought my barn find with a broken timing belt and I'm not sure if the rocker tower was cracked when I bought it or if it happened when I drove out a bent shaft. Either way aluminum is brittle and as Jim says, better and probably cheaper to get a good used head

[TobyB]

I was ready to align- bore mine- and they didn't need it. I was surprised, to say the least.
Even made up a bracket to do it in the Bridgeport...

My welding was done by a good friend, who is a good welder, but he's not a professional
by any stretch.

just what I did,
t