psychodoc

So I was having a slight coolant loss that I couldn't trace. Pressure tested the cooling system; held 10lbs. Went for a drive and when I came back, popped the hood and noticed some steam from the rear of the head. Reached back there and noticed the rear most head stud was just sitting in the hole, probably broken. Is this a common occurrence?
I know I'll have to pull the head to replace the stud.
Questions:
1) Is this safe to drive to the shop (approx. 50 miles)?
2) What is the preferred method of repair if the threads are stripped (heli-coil?)?
3) What are the common pitfalls in doing this job?

Stats:
1984 n/a 944
100k miles
No coolant in the oil, no white exhaust.
Thanks for any replies.

Van

I don't know how common it is, but is it possible it's been like that for a while?

It's probably safe to drive 50 miles... Have you noticed a performance decline? I'd think you might. Or, pull the #4 spark plug and see how it looks? Is it rich, have there been misfires? Or has coolant gotten in that cylinder?

The repair method is going to depend on the failure mode. If the stud is broken, it might be possible to just heat up the block, remove the 1/2 stud and replace it. If it's stripped, then you can look at a helicoil or timecert (timecerts are stronger), or, perhaps, a new block.

I'd say the biggest pitfall is that, while you're in there, you'll spend $3-4k on fully rebuilding the engine.

psychodoc

Not sure, but it seems like a recent issue (just noticed it in the last few days)

No decline in performance, #4 plug looks fine (tan, dry), cylinder appears dry.
Ok, timecert it is....
Hopefully I won't need to.....Is that 3-4k doing the work myself?
Thanks Van..

krystar

so the head nut is still on the stud. but the stud is just wobbling?

remove the IM, take the wobbling piece out. see where it is. if it's snapped in middle and half of the stud is still in the block.....that's gonna be interesting and expensive to try to fix. take a picture and post it up.

psychodoc

That is correct. I can pull the stud up until it hits the IM....Doesn't want to thread back in.
Will have to wait until the weekend, but will do.

psychodoc

Does anyone know what size the studs are?

krystar

M12 x 1.5 i believe.

psychodoc

Pulled the IM and found the bolt was broken. Here are some pix. For reference, the bolt is 6 3/16" long. Looks like I will do the top end. I plan to do the following:
Replace:
-TB/BB belts
-water pump, gasket, thermostat
-vac lines
-intake, exhaust, cam tower, head gaskets
-camshaft seals
-spark plugs/wires
-head studs (What's recommended? OEM Porsche set is $80.00 and Raceware is over $300.00)

Am I missing anything?
Also, does anyone know of a good shop that can check and mill the head (if needed) in the southern Vermont, western New Hampshire area?
Thanks for any response.

psychodoc

Anyone?

Van

Before doing the other work... I'd make sure that broken bit of the stud can be removed. Otherwise you'll need a new block. Which might give you other options.

It's interesting to see that the nut is threaded so far down the stud. That's not normal. Either the bottom wasn't threaded all the way in or else the stud stretched.

I bet the block wasn't threaded properly or something and the stud wasn't fully installed - or maybe even stressed because it stopped turning before the operator thought it should.

psychodoc

Thanks Van, I'll check that first.

dontnow

Wow, someone bottomed the nut out on the stud. Looks like it has been broken for awhile like Van said. Hope the other part is not too deep.

psychodoc

I hope so too...Seems strange that it has been like that for awhile. I have driven the car almost 4,000 miles since I bought it and there was no indication of an issue until a few weeks ago.....I will dive into it this weekend and pull the head.....Does anyone know what the length overall should be?

krystar

dunno about stud length. i'll have to measure a spare when i get home tonite. but deck height to tip of stud height when installed is suppsoed to be....62mm...or was it 52.. something 2

TexasRider

I have not done any real engineering in about 15 years, and not that it matters all that much now, but that full slant fracture surface in the range of 45 degrees is evidence of a tensile fracture and is characteristic of an overload.

There may have been some irregularity right there in the stud, but when it got mongo-ed on, as has been identified by the bottomed nut, it started cracking. It may have been felt by the mongo-er.

Then when the other loads such as heat and vibration and combustion were applied over time as you drove it, the final fracture occurred.

So while it was there for a while, it wasnt really completely through and there waiting for you to find it. Only Mongo knows for sure LOL. This is more commonly known as twsited the **** off.

I raced motorcyles in the 1970s and 80's and 90's with crap fasteners so I know first hand about these things. I too resembeled mongo until the bolts got better and I got some torque wrenches. And then came Harleys. Make it up tight - real tight. My engine guy and I built up a Harley motor and I never saw him pick up a torque wrench except for the crank. Made it up tight too !