Cracked head - options or paperweight?

purplehaze · 09:56 AM

-> Hairline crack between the valves, 930 heads, alloy RR350

Any options? Is there a way to tell if it's topical, or doesn't it matter?

This is how it came back from the machine shop and I plan to call Monday. I just wanted to hear some feedback or options. Without seeing it, I've had another Porsche mechanic say it's junk and to have them re-do it.

I had one half of the long block done, and went to install the heads for the other side. On closer inspection, noticed the crack, and I know the machine shop had seen the same thing; there were rotary grinder marks over/near the crack, I'm assuming for closer inspection. No other heads are marked in this manner. The heads went to them free of visible cracks, and they were paid to do an inspection/disassembly as well.

There was a lot of machine work done to the stock 3.3 heads; twin plugged, flame ringed, ported for 3.2 intake and headers, welded/extended intake flange for 3.2 gaskets, new valves, guides, seals, valve job. Then I installed all new intake and exh studs. The kicker is that I got these 'new' 3.3 heads because several of my 3.2 heads were cracked.

What do you think?

Now where did I put my bourbon!?!?!?.....

3.2 CAB · 01-27-2008, 10:40 AM

If it is actually a crack, and not a tool mark artifact, my first reaction would be that it would make a great looking EXPENSIVE paperweight. But, without doing further testing to really see what the deal with it is, I would have to say that the autopsy results, would be inconclusive.

purplehaze · 01-27-2008, 01:15 PM

Unfortunately it is a crack. Just using a 10x magnifying glass you can see it connect the 2 seats. Depth is not determined.

My guess is it was caused by pressing in or the removal of the guides.

Come on, a little JB Weld, and good as new! Right?

cgarr · cgarr's Garage

If this was caused by installing guides and they went in that hard to crack that part of the head you are going to have some guide bosses cracked too. This is common on 912 heads between the plug hole and seat, caused by excessive heat. The shop should have caught this.

purplehaze · 01-27-2008, 04:39 PM

Thanks Craig. I may just remove a valve to inspect.

It's a guess on the guide install - but I don't know what else would create the stress necessary for a crack there.

Steve@Rennsport · 01-27-2008, 05:15 PM

Glenn:

Its a paperweight,....

One can Zyglow it to confirm but if its cracked, its a trophy of sorts. Cracks in that area are generally not caused by guide removal & installation. This one represents a thermal issue,............

911quest · 01-27-2008, 06:21 PM

Did you use a machine shop that specializes in Porsche? The reason I ask it is pretty common to have that on other types of motors and not be a big deal, now if it is between the plug and the seat that's another story. I guess what I'm getting at they may not thought that it would be a problem but still should have told you.

purplehaze · 01-27-2008, 06:29 PM

Steve and Tony - Thanks.

Yes, they specialize in Porsche work.

I can understand cracking from high heat - but I don't think the crack existed before the machine work. I do appreciate the honesty.

dyerkes · dyerkes's Garage

Glenn,

I'm sorry to hear of your dilemna. I'm assuming that you're confident that the crack didn't exist prior to the machining? Is the shop not willing to assist you in rectifying this? You might want to check with Ted at German Precision to see what he thinks, and see if he has any options for you. Good luck!

David
1986 911 Turbo

Crashly · 01-28-2008, 04:36 PM

It may be able to be repaired. I was at a machine shop the other day that is doing my rebuild and I saw a VW head that the owner had welded and was repairing. The cracks were from the valves to the spark plug. Everything has to be remachined once he is done but at least he is saving the head. Sergio is the owners name that was doing the welding and the name of his shop is Motor Works in National City, California. Give him a call he has over 50 years in these oil air cooled motors.

purplehaze · 01-28-2008, 04:52 PM

David - Thanks for the support. Yes, I'm confident the cracks did not exist prior (photos as well). I spoke with the machine shop, plan to send him another used head and he said he'd make it match. I'll confirm it's no cost, but he's trying to make it right. It's going to be a 2-week delay, but at least I'm catching it now (instead of exploding mid-season). Thanks again for everything!

Crashly - Thanks. I might look into getting my old set of 3.2 heads repaired, so I'll check into it. For 'normal' use I bet the repair would be fine. I track mine so it sees frequent boost, so I'm trying to build for durability. Thanks again!

Glenn