head crack of doom ??!!

[Vincent Waldon]

Busy rebuilding another AAZ as a winter project... doing the teardown and so far so good... until this crack to the prechamber:



The wet stuff is just brake drum cleaner.  The head is in really good shape otherwise...very straight with great guides and lifter bores.

We know that small cracks between the valves are normal... and in comparison the crack to the prechamber doesn't seem worse... but... :?:

I'd interested to hear some experienced opinions on the viability of re-use... AAZ heads don't grow on trees, but I'm not one to knowingly park my family by the side of the road.

[jtanguay]

i wonder how far that crack goes???  :shock:

did you pull the head from a known good running motor??? i'd say that its on its last legs for sure.  you could nearly cough on it and it would have a leak.

[Smokey Eddy]

:cry: *sniff*

[handedyourhat]

anyone ever put one of these heads in a bandsaw and cut it in half to see how thick the area is where the cracks are ?

[Vincent Waldon]

anyone ever put one of these heads in a bandsaw and cut it in half to see how thick the area is where the cracks are ?

Aha !!  That's *exactly* the question I meant to ask !!  If the metal is the same thickness in that region, and cracks between valves are known to be fine... this one should be fine as well.  But it all depends on the profile of the metal behind the crack.

'Twould be an interesting bandsaw experiment for sure.

[saurkraut]

In my experience, cracks emanating from the swirl chamber are always fatal.

I've had them slow leak, and give you some time to get it home, and some that go big-time; take the burp bottle cap off and idle it home.

There are some photos on this forum in a post about IDI Improvements from the early days of this forum with some cross sections done by RedRotors.


Link to RedRotors' orginal post: IDI engine, there IS a future...

[Vincent Waldon]

Great cross-sections... thanks for posting !!

[dillenger1]

The area in question definetly looks meaty enough,but lookj how far the valve crack goes in.I never thought it was like that!

[dieselweasel]

I don't have any wisdom from experience to share, but I don't think I'd reuse that head Vince.  You could have it pressure tested and it would likely be ok but the crack may get deeper over time and extend into the cooling system.  Also I have heard of pre-cups coming loose and falling into the cyliner...that crack may increase the chances of this?

[zukgod1]

If you had the time and the equipment I would think one could repair it. Knock out the precup and race of the offending port then get a small bit for your die grinder and notch it out. Tig it up and have it machined flat. New valve seat and off to the races.