GregBBRD

This is a "loaded" question, but I'm wondering what you guys that have redone early engines with head studs have done regarding the studs.

While I almost always use new head bolts...I've re-used head studs, in the past...mostly because they are a real pain to remove from the block. I've got a really nice, fairly low mileage '83, in the shop, that has really nice looking studs, except for a few that were attacked by the water seeping past the head gaskets (which is why we pulled the heads off...the heads leaked both water and oil.) When I went to get 6 new studs to replace the ones with corrosion, I was intriqued that they only existed in Germany...which means that not many get replaced!

I installed the 6 new studs yesterday and installed the heads. I then proceeded to angle torque the heads....wow, that was an eye opener!

I've got a couple of those really trick Snap-on digital torque wrenches that reads the angle and then tells you what torque it took to achieve that angle. That might seem like too much information, but it really tells the story about how much torque is actually on each stud.

I used the "standard" 20nm plus three 90 degree series of angles. That's when my eyes got opened. The "majority" of the used studs finished up at about 75 ftlbs. The new studs finished up at about 105 ftlbs. Three to four of the used studs barely made it to 50ftlbs.

This was obviously a huge range...and there was no way that any head could be happy with this amount of torque difference, so I began looking at the problem. If you look back and see what torque specification was used, by Porsche, before they changed to the angle torque method, they called for 66 ftlbs. So, I guessed that this should be approximately where the torque should be after angle torquing the heads. So, the "average" reading of about 75 ftlbs on most of the used studs seemed pretty good. The over 100 ftlbs of the new studs seemed really high. The ones that could not make much more than 50 seemed very low.

The next thing I did was to increase the angle on the studs that read around 50 ftlbs. No amount of turning would increase this number and you could feel the stud "yielding". I removed the heads and checked the studs that would not torque above 50 ftlbs. They were stretching and were "necked" down below the top, in the threaded section. Junk.

I've now ordered 14 more new studs....however, I think that the 105 ftlbs that these studs achieve is too high and plan on reducing the angles used in angle torquing these new studs.

What have you guys found out/done?

AO

Very interesting. I always wondered about the change from tq to degree spec.

Mark Anderson

When I use to build my own engines I just set my impact gun to 3/4's max. Since then I found a really good engine builder and I let him figure this stuff out.

AO

I don't think he's figured it out, quite yet, but he sure seems to be on the hunt!

BC

I found that the 2V studs are available since the 944s use the similar lengths? IIRC.
Except for the two or three short ones at the edges.

I found the same yielding issue with rod bolts. So the last two times I have replaced both sets with new.

Why is 105 too high?

svp928

Might want to ask Mike Simard what he did to come up with his stud specs- we used to measure stretch along with torque- you got a sample of this with the low-torque ones. On head studs, there is a little more leeway as compared to rod bolts.

BC

But Geez, I like those tools you mentioned Greg.

danglerb

Were the heads ever off before? I"m thinking maybe the previous mechanic was Mark with his rattle gun?

Should we be thinking about switching to a fancy new stud like ARP?

danglerb

BC expensive toys ....

http://buy1.snapon.com/catalog/item....re&dir=catalog

TECHANGLE, Flex Ratchet, 12.5 to 250 ft. lbs., 1/2" drive Stock#: ATECH3FR250 $499.95

blown 87

The only thing that makes any sense to me is that on the new studs there is less stretch, and that yields a higher torque figure.

You would think though with new studs and nuts that there would be more friction on the initial install that it would end up being less final torque.

IE more friction to get to the first torque reading before going to a + angle.

But yes, that is a huge difference in the amount of torque, 105 FT/LBS does not seem like much to me for a head stud.

blown 87

The only thing from Snap-On that is cheap, is the free air conditioning you get from standing in the truck while waiting for you bill to be printed.

mark kibort

that could be, pre stretch, dont you think. did you do it twice to see after a few hours? If not, thats kind of scary. You know me, if I have a good looking block, I just re-use the bolts or studs and have been ok out of my massive experience with building about 7 motors. But, certainly, if you have to change a few as I did one time, (but those were torque driven, not angle tighten), and you find there is a descrepancy, i guess its a good idea to change them all out. With one of scots motors, we had to really wrench on the block to get two of the studs out. I always wonder if that is riskier than putting a new stud in.
With the S4 heads, we used the cometic gaskets and did the angle torque only to find that the end torque was only 20-30ftlbs. after doing it again, it jumped up to near 80ft-lbs. (cant remember, but it was way differenent than the first pass)

too many variables! let us know how it turns out!

mk

GregBBRD

Not a snowball's chance.

I was unfortunate enough to be building 944 Turbo engines when ARP started making studs for those engines.

The head gasket problems got much worse, when using those studs, than the original studs ever were. On top of that, they insisted that you re-torque the studs once the engine got ran through a heat cycle. Pulling the cam carrier off a 944 is not much fun, just to retorque the hardware. Pulling both cam carriers off a 928, to retorque the head nuts, isn't ever going to happen, in my shop....I can barely stant to do it once, per engine.

The Porsche hardware stretches, by design. This keeps the head "clamped" to the block as the engine warms up and cools down...it is always clamped. The ARP hardware is very high quality and doesn't stretch much. The "clamping" doesn't work as well. The result is more blown gasakets...not less!

I've got huge box of ARP hardware that I've removed out of 944 engines, around here, somewhere. Scrap metal.

ptuomov

I have solid lifters, MLS head gaskets, and ARP head studs that I want you to install in my car. ;-)

Jokes aside, if one builds the engine in a way that requires taking off the cams after running it for a little while, one might as well go all the way. Kind of like in one of the early scenes in the movie "Heat."

GregBBRD

After years of working on these and the 944 engines, I'm used to seeing torque numbers that are 65 to about 80 ftlbs. That 105 number scares me...especially thinking about what it grows to when the engine gets hot. I envision studs pulling out of the aluminum block.

I'd initially guess that the current batch of studs has slightly different material and takes more torque to yield. I'll play around with them, while I wait for more studs to come from Germany, and see if they get "softer" with multiple torques.