964 3.6 studs failure(( its normal?

[dan67]

hi! i want to rebuild my 964 3.6 C4 1990 early style((( if unmount i look 2 studs failure((( 5°cilinder right, its normal?
the cilinder/pistons/cams its perfect (i not open the case)
the "small" solution is new studs (993tt or brand aftermarket)
not exsist the liquid gasket for head? (loctite or other?)

[KTL]

In my opinion, with that much filth on the engine, it possibly indicates years of neglect. I think it'd be foolish not to open the case and check all the bearings, inspect/replace if needed, then reseal.

964 head studs have been known to break. It's not unheard of for your #5 cyl. to have a broken stud. Unfortunately it broke flush with the case, so it's more difficult to remove. You don't necessarily need 993TT or aftermarket head studs. The non-turbo 993 3.6 uses all plain steel studs, part number 993.101.172.02

Your heads are definitely the early 3.6 heads without the sealing ring between the head and cylinder surface. The factory fix was to machine the cylinders for a sealing ring, similar to the 2.4-3.0L engines.

Your heads also show some significant oiling and carbon buildup in some of the exhaust ports and on top of the pistons. It would be wise to have the valve guides on the heads inspected. The guides may need replacement. However the spark plugs tips that are visible in the pictures are not fouled, so the guide wear may not be that bad.

[Henry Schmidt]

The issue you have encountered is as early design flaw with the cylinder head.

The area around the exhaust port is so thin that the head actually bends when heated.
The factory warrantied this issue back in the day by machining the heads and replacing the cylinders with a redesigned version.

The best way to fix this problem now is to go one step further and replace the head studs with Supertec Head studs. The only studs guaranteed not to break.

[dan67]

hi and thanks!
yes of course, i open/split the case for full rebuild/control crankcase.
the car is stopped from 2009 for front crash and flame i have unmounted the engine+trans (and others small parts) for transplant on my 3.2.
i buy one liquid sealing/gasket head from Reinz, yes is very small solution, but whit new studs "limit" the oil leak (i suppose))
thanks All for info/tips

[KTL]

Henry,

Is the thin exhaust port an issue with only the early heads? I recall other 3.6 heads have a ceramic insert in them. This was done to address the thin casting issue?

So the bending of the head is what causes the head stud breakage and not simply axial (in relation to the head stud) stress from thermal expansion?