head studs

quattrorunner · quattrorunner's Garage

I recently checked my studs hoping they were not broken. They were not. I have seen pics of broken dilivar studs and they are black. Mine look to be light rust in color(as though they were raw and have been hot and time touched which is what they are). Can anyone tell me what mine are based on this idiotic description? If they are not dilivar, I assume they are steel? In which case, I won't worry about them any more. On to the next on the list to worry about? TIA

quattrorunner · quattrorunner's Garage

Bump it

88-diamondblue · 09-19-2006, 01:50 PM

If the engine is rebuilt then you may be in luck. In my 88 the dilivar studs were epoxy coated and I have not seen what the non coated dilavar look like. Hopefully someone that has will chime in. Nothing you can do until they break. I wouldn't worry and just check when you do a valve adjust.

sammyg2 · 09-19-2006, 08:02 PM

put a magnet on them. If it sticks, they are steel. If it doesn't stick, they are dilavar.
The dilavar studs from my engine were not black, they were a dull silver color with black pits from surface corrosion.

quattrorunner · quattrorunner's Garage

hummmm.

Eagledriver · 09-20-2006, 07:33 PM

If your engine hasn't had the studs replaced then they are dilivar on the bottom row. If you can see the studs the top row will look different than the bottom row. On my engine the top studs (steel) looked like a dull grey color. The bottom row looked more like silver with some rust on it. There were 3 broken bottom studs on my engine.

-Andy

quattrorunner · quattrorunner's Garage

Thanks a lot ANDY!
No really, thanks.

quattrorunner · quattrorunner's Garage

OK, what is the reason they break other than thermal expansion differances? Is there any other reason? Why are the new ones coated with epoxy? Is it something to do with rust? I live in the hot southwest, HA!

88-diamondblue · 09:52 PM

Porsche thought that the studs were breaking because of corrosion so they painted them with epoxy paint. From what I learned or read that the studs suffer from hydrogen embrittlment from the heat cycles. Stress risers from corrosion were thought to be a point at which a crack would start and the studs would break at that point. There seems to be a lot of controversy on what causes the break. It seems that it happens on cars all across the country and cars that are stored winter to prevent corrosion, so who knows for sure? Dilivar studs have broken when new being torqued down for the first time as well. No one has reorted a steel stud breaking including John Walker and a few other long time mechanics have said in past posts

88-diamondblue · 09-20-2006, 10:07 PM

Here is a picture of steel on the left and dilivar on the right. Notice the difference in color.

911pcars · 09-20-2006, 11:17 PM

Dilavar is steel, albeit a special high-strength alloy that is non-magnetic with about the same expansion rate as aluminum. The stress on head studs is not that high, even with heat expansion from the cylinder and cylinder head. Like many others theorize, I suspect corrosion and heat cycles eventually lead to a weakening of the material, moreso with the early uncoated or gold/silver-color plated studs. I also suspect the quality-control and specs of many Dilavar studs were not up to Porsche spec.

I must knock on wood every time I discuss this subject. I've got 24 of them on my engine.

So far, so good.

Sherwood