Today, 15:07 Hairline Crack in Head (w/ large pictures!)

[phredphish]

What I want to know...

Is there some tolerance for cracks in a head? My old 735i/M30 manual had several diagrams outlining allowable sizes of cracks, but I also can't imagine it had an aluminum head on it...

There isn't any noticable corrosion around or in the crack...so that leads me to believe is is a relative non-issue. I'm just trying to cover all of my bases before I put this back together.

I can get some large pictures/different angles if anyone is interested. I cropped/sized these down for people with smaller screens/connections.

Here are the pictures:




Thanks.

[Shocker]

A crack in a head is not good no matter it's size.

[ZeroG]

It needs to be repaired by a machinist.  Any crack could cause the HG to leak and result if you doing all this work all over again.

[kowalski]

i'd recomend finding yourself a used head, and getting it checked before installing it.

[scottiesharpe]

The head can be fixed by a machinst. They will bore out the crack and TIG weld it, then resurface. It may re-crack.

[gearheadE30]

My vote is get a new head. Also, get those valves cleaned off and the head steam cleaned before putting it back on.

[Vladi]

I've read before on the forum about head cracks. My 2 cent question is, why do they crack??

[Cristian G in Oz]

What I want to know...

Is there some tolerance for cracks in a head? My old 735i/M30 manual had several diagrams outlining allowable sizes of cracks, but I also can't imagine it had an aluminum head on it...

There isn't any noticable corrosion around or in the crack...so that leads me to believe is is a relative non-issue. I'm just trying to cover all of my bases before I put this back together.

I can get some large pictures/different angles if anyone is interested. I cropped/sized these down for people with smaller screens/connections.


Thanks.

The M30 was an alloy head and the early ones had a propensity to crack in the 5th and 6th cylinders.

You could get it welded and the head shaved but there is no telling how long it will last.  Once a crack has started it is all downhill.

As stated above, if you can afford it get another head, it's not worth stuffing around with old problems.  Absolute minimum is to get the head welded and crack tested.

Good luck

Cristian

[rsafier]

I've read before on the forum about head cracks. My 2 cent question is, why do they crack??

Uneven heating of the head usually due to overheating. But doesn't have to be sometimes just age and heat cycling can do it if there was a weak spot in the casting to begin with.

[ecpreston]

My vote is also for that crack being a problem. Pressurized, hot gas can pretty much get through any small crack. And then it's in your cooling system (I assume that's a water passage, yes?). Did you have any coolant temp issues or ever do a coolant pressure test before you disassembled?

[phredphish]

There weren't any discernable overheat issues, but that is assuming the temp gauge is and has been working properly.

I'm going to buy a new engine this week -- 66,000 miles on a 1993 m42 for not too much over what I've been quoted for a head rebuild, not bad!

Now, I've heard that a digital manual has been posted to this forum...is that so? I've lost my bently and will probably need some manual-based assistance pulling the old block and putting it all back together.

Any pointers from you experienced guys out there?

[D. Clay]

Digital  repair manual link. It's in the "M42 Reference" section of the User Control Panel:
http://www.m42club.com/forums/showthread.php?t=964
Also search for E36 M42 swaps. Several have been done using different approaches.