Importance of tightening heads after rebuild?

[JohnJL]

Hi Guys,

I understand the logic to checking and re-torquing the cylinder and head bolts after break-in. I was just curious if the factory/dealerships actually do this? Seems to me most cars were sold and put on normal maintenance regimes...unless the dealership maintenance regime included tighting head/cyl bolts during the first maintenance?

[Eagledriver]

I don't know of any manufacturer that does this including Porsche. That being said, I always do this on my air cooled motors. We especially have problems with all the different studs out there and with the alloy cylinders. I wouldn't bother with doing this on a water cooled car. They don't have as much of an expansion problem.

-Andy

[Steve@Rennsport]

Andy is right: head gasket technology has progressed to the point where this procedure is unnecessary and OEM's don't do that. The only ones that still do are engine builders using annealed copper head gaskets under very high boost conditions.

Generally speaking, I don't re-torque Porsche heads since we use late Dilavar head studs (everything but early, small engines) and they do not change.

[JohnJL]

Thanks guys. Did the factory every specify that, early on? The winter project list includes an oil change and valve adjust on the supercharged motor and the carbd engine, so I'll be curious to see if either loosened up.

[KTL]

Glad to see this question come up, as I recently tore down my 3.2SS engine and found my head nuts to be not all that tight (I do realize the torque spec is quite low, however they're usually resistant to break free) and inconsistently so.

Also my 24 dilivar studs were not well secured into the case. They were easy to remove by hand with a normal length socket wrench and no heat. Instead of loctite, a non-hardening gray paste was used, which has a distinct strong solvent-like smell to it.

The point being is that my engine showed some significant leakage between the case-cylinders-heads at each cylinder, and I think it was due to the lack of clamping force, as well as some use of sealants in places not needed.

[Dan J]

When I worked at the dealer in the 80's this was part of the 2500 mile check up on the air cooled cars it also included checking valve clearance and torquing rocker arm shafts. I think they stopped with the 964. I still do it on air cooled motors. Old habit I guess but every once in a while you find a lose one

[haycait911]

I tend to run a torque wrench over them when doing valves. more looking for a broken/pulled stud.

[village idiot]

Originally Posted by haycait911

I tend to run a torque wrench over them when doing valves. more looking for a broken/pulled stud.

I do the same

[vulcan300]

Sorry, I know this is an old thread. What torque value do you use as a check when doing valves?

[Eagledriver]

You should use the original spec for your headstuds. I think it's 25 ft/lb for steel and 29 ft/lb for dilivar.

-Andy

[vulcan300]

The vehicle is a 1990 964. I believe the head studs are stock, so would that make them Dilivar? Is there an easy way to tell the difference between the two?

[boyt911sc]

Originally Posted by targamaniac

The vehicle is a 1990 964. I believe the head studs are stock, so would that make them Dilivar? Is there an easy way to tell the difference between the two?

targamaniac,

Dilavar studs are non-magnetic and steel studs are magnetic. The problem is finding an exposed section of the dilavar studs to test on your engine (installed).

Tony

[afterburn 549]

I understand the "No need" as far as head gasket
.But -Maybe cause the whole thing has been ran and "needs to be relaxed" a little?

[larrym]

yup -

had the nuts get loose on my 2.7 some yrs back after a rebuild followed by a hard-charging race weekend

heard an unsetttling rattling noise in the last couple laps at very high rpm (7500+) - so i retired

- teardown revealed #6 cyl "way too loose" - insignificant damage - just worm tracks which were curable - found a few other nuts also "too loose" on other cyls

running oem steel studs all around cuz that was the experts' advice at the time i built it

local Sac'to porsche shop said they'd seen it before - had no idea why such loosening happens

replaced the #6 CE ring and surface-plate honed the cyl edge - retorqued everything

engine has run 5K street miles since with no issues - recent Compression test on all cyls = about 165

there is another fairly recent thread about this same issue

.

[Arrowhead]

I am rebuilding my 3.6 engine and on tear down I noticed it has the newer 993 dilivar head studs. They are the heavier full threaded non magnetic and look like new. I looked them up and to replace them it would cost $1,000.

I know I will probably get beat up for this question but has anybody ever reused these studs with success. I know the factory manual does not mention "replace" as they do for other fastners.

Also, I hear mention of using a lubricant and some use locktite on head stud nuts. I know the factory states oil.

[afterburn 549]

Studs---I think i would follow a builders advice on what is the latest best deal..Maybe Henry
or some others here that do it every day.
They have to back up their work and are not going to use anything less then the best

[Eagledriver]

The 993 headstuds are very good. If they look good (no corrosion) then I wouldn't be afraid to re-use them.

-Andy