9 broken studs - a record? Can I repair head?
 

Finally got the engine from the 1981 SC apart and found no less than 9 broken dilavar studs! This car ran brilliantly for the first 10 years I had it. Good power, no oil leaks. Then I didn’t use it so much - and then I got the dreaded clattering noise under acceleration. I regularly checked the valves and didn’t notice loose studs so they must have all let go pretty much at the same time.
Anyway, most of the cylinders and heads look ok, but one of them shows some damage where gasses have escaped past the gasket. I’m wondering...

- Can you machine off a few thou from the damaged surface so the gasket can sit flat (and add a shim to the back?)
- Can I just replace one barrel and head? Second hand an option?
- Do I have to get a whole set of barrels and heads?

Will go off and scour the forums but was wondering mostly about the machining route as the engine was otherwise fine. Thanks for any help.
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Wow!
Sorry no help on the machining but someone will chime in soon.
You could most likely find a head and a matched cylinder for it on the classifieds.
Nikasil or Alusil?

Was the car stored outdoors? How many KM?

Joshua Gregorio could probably repair that damage. He has been doing 944 turbo heads for a while, and does some pretty impressive aluminum repairs. look him up on facebook (that's how I communicate with him)

The head can be resurfaced to remove the damage. Of course the best solution is to have all of them done so they all match up in height. You don’t say if the cylinder is damaged, but if it is, a machine shop could resurface the cylinders as well. You have to make sure that any repairs you do result in the heads matching in height so that the cam towers will fit without warping.

-Andy

After machining, just use thicker base gaskets. Machinist should take off the thickness of the stock gasket, or a multiple if needed.

What you do to one head, machine wise, you need to do to the others. Otherwise you will have camshaft problems (among other things). Yes you can buy a single cylinder - you need to find a supplier who has/will break a set - post a WTB. You need to specify the group height (number in triangle on base of cylinder). A 5 or 6. You should get the piston as well - they are matched to the cylinder. But then the group weights will probably be different too - you will likely either be taking weight out of 1 piston assembly (best scenario) or if unlucky taking weight out of the other 5 (if your newer one is the lightest weight). There are some tolerance allowances with group weights - will depend what you end up with. I had the bad luck of purchasing a low end range weight 6th piston/C. And my other 5 were high end weight range. A LOT of work to get the 5 several gms down in weight.
But is all possible.
Alan
Edit - you can get away with just doing 3 heads on one bank.

I broke 12 on a 3.0 turbo and suffered very similar head damage. In the end I was able to get it machined and rebuilt.


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That’s brilliant, thanks for all the helpful replies. I’ll see if I can find a machinist with 911 experience here in the U.K. it’s good to know that it’s possibly an option.

You can machine the other five if you want, but you will then need to shim them all to keep the cams and clearances and CR at what they were. Extra shimming of just the damaged head would seem a better choice. Mark the short head so it is easy to keep track of it and its extra shim.

There is a .50mm head spacer ring you could use. Take off .50mm from each head, install the ring then you are back to stock with no extra base gaskets etc


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They made different height group sizes for the cylinders. If you go the route of replacing one of them, be sure to get one that is the same group size. I want to say the cylinders have either a 5 or a 6 inside of a triangle to denote which height group it is.

Craig,

What is the part number for this spacer? I searched for parts by that description and only found a 996 part: 99610549170.

This spacer would go between the cylinder and head, right?

Thanks,
Steve

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Yes


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After machined the heads, don't you have to change the spring high for the valves?

Spring height is dictated by the camshaft profile. While valve clearance is certainly a concern with respect to the valves contacting the pistons, spring height shouldn't be altered on account of the head machining. The reduced head thickness is typically corrected by a thicker base gasket under the cylinder. Or, one could use the 964 turbo spacer/gasket as mentioned by cgarr above. Here's another mention of that spacer gasket

http://forums.pelicanparts.com/911-engine-rebuilding-forum/949083-88-3-2-cylinder-head-gasket.html