Pulled head studs on fresh 3.3 build

gumba · 07-13-2015, 10:28 AM

Just finished a complete rebuild on a 3.3 turbo motor. Did the 20 minute break in @2,000 rpm with no issues, and let the motor cool over night. Drained the oil next day, adjusted the valves and re torqued the heads to 36 lbs. Two of the studs won't torque down, so I'm assuming they are starting to pull out of the case. The rest of the studs either held the original torque, or were within a couple of pounds. I used ARP head studs and installed with red locktite.

What are my repair options? I would like to either install, or have a machine shop install time certs or helicoils in all 12 stud holes. Hopefully (and this could be wishful thinking)this could be done to the short block without splitting the case.

The motor is a '79 3.3 stock bottom end, and stock 7:1 p&c's.

cabmandone · cabmandone's Garage

Most seem to favor case savers over timesert from the research I did. I installed a timesert in my engine by myself without splitting the case. I used timesert because they offered a kit with bit, tap and everything else necessary. I leveled the block on a drill press and then checked to make sure the bit was square to the block. It really wasn't that hard but I only had to do 1 and I was NERVOUS doing that one.

Btw, the thing that worried me most was I didn't remove the rods and that made plugging the holes a bit difficult. I pushed paper towels down into the bores then used Gorilla duct tape to seal the holes and around the rods that were up. I then used Gorilla duct tape to cover the rods that stuck above the bores. Since I did my own, I had my son there with a shop vac sucking up the shavings as I drilled the hole.

Henry Schmidt · Henry Schmidt's Garage

CaseSaver for sure and I would rethink the 36 pound torque number.
They are steel studs and because of the difference in expansion rates the clamping force will increase with heat. 28 to 32 lb would be my recommendation. The issue with ARP bolts in the past is that they tend to loosen after heat cycles so there may be times when you will need to re-torque your head studs.

gumba · 07-13-2015, 11:37 AM

Thanks. Any particular brand or kit of case savers?

gumba · 07-13-2015, 12:07 PM

I was looking at this time-cert kit. Universal m10x1.25 head bolt kit #6250

Henry Schmidt · Henry Schmidt's Garage

Quote:

Originally Posted by gumba

I was looking at this time-cert kit. Universal m10x1.25 head bolt kit #6250

First the head stud threads in the case are 10x1.50mm.

The Timesert is structurally weaker than the CaseSaver. Powdered metal / sintered metal casting vs. solid steel. The design of the CaseSaver uses courser threads which translates to better holding power in a soft metal like aluminum or magnesium.
As far as I know, no one is offering a kit. The CaseSaver below is 14x2.0mm od and 10x1.50mm id.

gumba · 07-13-2015, 02:28 PM

Thanks for the clarification. So a m14 x 2.0 tap, 15/32" drill bit and some type of jig to locate the hole.

Henry Schmidt · Henry Schmidt's Garage

Quote:

Originally Posted by gumba

Thanks for the clarification. So a m14 x 2.0 tap, 15/32" drill bit and some type of jig to locate the hole.

yes
We use a mill but in lieu of that at home, a jig will be important. Even a slight variance in drilling leave you with "porcupine stud syndrome" Studs going in every direction. This can make cylinder installation incredibly tedious if not impossible.

gumba · 07-13-2015, 04:14 PM

Can you tell me the center to center head stud spacing. I have a mill and can make a 2.250" thick jig.

chris_seven · 07-16-2015, 12:01 AM

It all sounds a bit too close for comfort.

All things being equal a change from 32 lbsft to 36 lbsft torque will only increase the static preload by around 12.5%.

This well within the expected scatter in the relationship between torque and static preload - typically 30% and should have been taken into account at the design stage.

The increase in force on the thread caused by expansion will add directly to the static preload and this will further reduce the percentage difference between the preload values due to the difference between the two torque values to less than 5%.

I would worry if small differences at this level are significant as if this were the case we should be seeing many more failures that seem to be reported.

I would certainly look for other causes as this doesn't seem to be an issue due to studs and the arithmetic says that there may be another issue which has caused an excessive static preload.