Pulled stud when meant to remove nut on thermostat housing.

[StephenGwyn]

Hi,

I removed my thermostat housing over the weekend to sort out some cooling issues. One of the nuts holding the housing down came off fine, but when I turned the other, the stud turned instead of the nut. When I pulled the stud out, it came out with a bit of oil on the bottom end. When I put everthing back together, I put the stud back in and tightened it firmly, although since I couldn't get a socket and my torque wrench on to the nut, I can't say for sure if it's exactly 35 ft-lbs.

My questions are:
1) What's the oil on the bottom end of the stud?
2) Should I pull the stud again, replace it and put on a shoulder nut so I can get my torque wrench on it?
3) What's the proper way to install a stud?

Thanks,

SG

[BunnyPlanet169]

Stephen -

Oil would be surprising - apparently oily organic goo maybe? The block cooling passages is where the bottoms of most studs reside.

Studs go back into the block firmly finger tight with the sealing powers of Permatex gasket goop (see cooling water, above). The MMI replacement studs are sized to go up to their shoulders and stop - note different lengths for different places on the block. ALSO note 3/8-16 thread on the block side, and 3/8-24 on the nut side.....

Torque should be applied to a well lubricated head nut, not the stud directly. Note these are different than regular 3/8-24 nuts in that they're usually case hardened to match the strength of the studs (roughly grade 8).

[StephenGwyn]

Oily organic goo? Possibly. I have a second short block with the water jacket off and I can feel that the stud in question bottoms out in the cooling passage. And there's no oil running through the head right? The other possibility is this stud was accidentally pulled before by a previous owner, who lubed the stud rather than buying a new stud and a new nut. See attached picture.

So when I re-install this stud, do I need to drain the block of coolant, and carefully clean out this hole of coolant and oil? Do I need locite/JB weld/Permatex/something on the the block threads?

I'm guessing the reason the studs (normally) stay put in the block is because the thread pitch in the block end is coarser than the thread pitch at the nut end. Is that right?

Thanks,

SG

[BunnyPlanet169]

That's a really long stud, and I'm a bit alarmed by the length of the coarse thread (which will allow it to go too deep), and the lock washer which simply shouldn't be there.

If you look at the studs for sale here, you'll see the coarse threaded ends are only about 6-8 threads long ~ 1/2". They bottom out in the block on the threads, not on the opposite inside wall of the casting.

I'd get a stud the correct length from MMI and install with Permatex into a dry (as possible) hole. And drop the lock washer.

[Al Schober]

Is that a collar around the stud you're holding? If so, it's the wrong stud. The proper stud has no collar - just a straight stud. It goes hand tight into the block (with sealant), through the head and t'stat housing, and then gets torqued. Keep in mind that the thermostat studs secure the head too, so their torque is sealing the head gasket. The thermostat nuts get torqued just like the other head nuts.

[StephenGwyn]

That's the locked-on nut and lock washer your seeing. It was definitely long, protruding
quite high above the block and thermostat housing on the top end. No idea about thread length on the bottom end.

I wasn't able to shift the nut, so I'm buying a new stud no matter what. I guess I'm also removing the lock washer I found on the other thermostat stud. I'll try pulling a stud from my dead block to get the size right. And then to find some shoulder nuts.

Once again, I'd happilly buy from MMI, except shipping to Canada+customs+brokerage fees doubles to triples the cost.

I'm assuming that it's not worth pulling the other thermostat stud, which is probably also slightly wrong. Based on feeling around in my dead block, although it may be sticking too far into the water passage, it's not hitting anything, or impeding water flow much it's stuck in the corner. And the possibility of messing up is non-zero.

[StephenGwyn]

About sealing the head gasket, it would be better to raise the nuts a little higher so the socket on the end of the torque wrench seats better. Short of the fancy shouldered nuts sold by MMI, can I get away with some sort of 1/4" long, loose-fitting collar?

[Al Schober]

All my thermostat studs take a different socket than the other head nuts. The usual head nuts are 'heavies', while the t'stat studs take standard nuts - to fit the recess in the t'stat housing.
I see no problem with a spacer under the t'stat studs - if the studs are long enough. When torqued, you want a thread or two showing through the top of the nut. Perhaps just a couple of washers?

[BunnyPlanet169]

How about grinding off a bit of the stud? Also - you may be able to source better nuts locally, or with someone like McMaster Carr (do they do Canadian distribution?). Look for 'heavy nuts' for pressure flange applications.

[StephenGwyn]

I'd rather not grind off the bottom of the stud. Doing it wrong means leaving burrs which might damage the threads in the block. I was going to track down a new stud. Or are they unusual items? Does anybody know the dimensions? Over all length, coarse threaded length and fine threaded length for a thermostat stud where the thermostat has an extra spacer?

[sastanley]

A simple file will solve the burr problem. I have had great success using a Dremel with the "EZ-lock" metal cutting wheels.

[BunnyPlanet169]

I agree with Shawn - it's pretty easy to clean up threads.

Thermostat mounting holes- measured on my block and parts this AM....

You have ~ 5.0" down from the top surface of the block before the stud hits anything.

Head ~1.63"
Unmodified* thermostat housing ~0.69"
MMI thermostat spacer 0.25"
2x Head gaskets compress to ~ 0.06" ish, add another ~ 0.03" for the 2x Tstat gaskets....

Stacked thickness (length) ~= 2.65"
You'll want working threads ~ 0.5" above the stack, and for argument, 0.25" below....

For replacement, the only magic is that the unthreaded body length can't be more than 2.5"

Lower thread = 3/8-16UNC
Upper thread = 3/8-24UNF

Perfect world - you're looking for a 4" stud with 0.75" at both ends, or 4.5" with 1" at both ends... etc....

* MMI makes a modified tstat housing with counterbores and special nuts that allow for the use of original length studs. It would seem likely that a P.O. used locally available aftermarket studs instead when they added the MMI spacer to your engine.

[sastanley]

One more thought since I am up on my soapbox. 10 years ago, someone recommended a "thread chaser kit" to me..I found one at Sears and cannot tell you how great a tool it is to have handy. It is similar to a tap & die set, but it is designed to clean up burred or damaged bolt/stud/nuts, as opposed to cutting new ones.

http://www.sears.com/craftsman-48-pc...p-00942275000P

[BunnyPlanet169]

Get a thread file - these are the bomb if you have room.

[StephenGwyn]

This is all extremely helpful.

The reasons I'm reluctant to cut and dress the existing stud are:

1) The nut is currently seized to the stud. I used heat (although maybe I could have used more head), penetrating oil (the good stuff, not WD40). I've slightly chewed up the sides of the smooth part of the stud, but the nut didn't go anywhere.

2) While I have successfully cut bolts and then cleaned up the mess, my success rate is less than 100%.

This is not to say someone with a better tools and skills couldn't do it properly. I want one of those thread restorers and/or thread files. Which of course are not available from Sears Canada.

The MMI manual section on thermostats just says, essentially, "put the thermostat housing back on and tighten up the nuts" with no mention of the fact that these nuts are in fact holding on the head, which might be worth a mention. I assume I need to follow the full procedure in the overhaul section, tightening the bolts in stages until I get to 35 ft-lbs?

[hanleyclifford]

The stud in the picture looks a little suspect. Make sure it isn't some metric substitute. Get a new clean 3/8x16 nut and check the threads. There is no harm in going in a little deeper on the block but be sure to use permatex #2 (the goo) to seat the stud. It is ok to use regular 3/8x24 nuts on the two housing studs - never use lock washers. Use 9/16 socket on nuts.

[BunnyPlanet169]

Originally Posted by StephenGwyn

1) The nut is currently seized to the stud. I used heat (although maybe I could have used more head), penetrating oil (the good stuff, not WD40). I've slightly chewed up the sides of the smooth part of the stud, but the nut didn't go anywhere.

The MMI manual section on thermostats just says, essentially, "put the thermostat housing back on and tighten up the nuts" with no mention of the fact that these nuts are in fact holding on the head, which might be worth a mention. I assume I need to follow the full procedure in the overhaul section, tightening the bolts in stages until I get to 35 ft-lbs?

I would not reuse it unless I could loosen it up.

IMHO, the use of the head studs for thermostat housing mounting is a design weakness. That said, it's been working for 40 years or more. I've always just tightened them, and frankly, not always with a torque wrench....

[StephenGwyn]

I'm not going to reuse it. I bought a new one at an autoparts store and pulled an old one from the "spare" block sitting in the shed. Back to the boat on the weekend. Also, at the autoparts store, I bought a socket with slightly thinner walls which fits just exactly between the thermostat housing and the nut, so I don't need to spacers or shoulder nuts.

SG