Repairing exhaust stud hack, ideas ??/

[yelcab1]

I am repairing an exhaust leak on a 1972 911S (magnesium case). It's cyl4, one of the two exhaust studs has pulled out of a case due to a very bad job by the previous engine rebuilder. The hole was improperly drilled, a helicoil was used instead of a Timesert, and now it has pulled out of the head. The hole is oblong, and is too big for an M8 Timersert.

This hole is the stud where the barrel nut goes on to, not a hex nut.

Ok, what are my options?

1. next size up metric, helicoil, time sert ? With a allen head bolt?
2. Next size up standard size, helicoil or timesert? With an allen head bolt?
3. Welding, brazing, glueing in a stud? I can't weld magnesium ...
4. Tow the car to a welding shop? Remove the head and bring it there
5. Replace the head

?????

[Mixed76]

Isn't it just the case that's magnesium, and all the heads are aluminum?

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[yelcab1]

pix,

The timesert fits loosely into the too big hole.

You may be right, the head is aluminum

[Marc Bixen]

Check into "Big-serts" they are oversized on the O.D.

[john walker's workshop]

It's aluminum, so welding and redrill is an option. We used to get 8/10 step studs to use on vws with the same problem, but the timesert is probably that big already. A case saver is even larger OD, but not enough meat toward the outside for it. Welding I guess is your only hope. Make your own sleeve from a 12mm bolt and drill down the middle and tap for 8mm? Still maybe not enough meat.

[yelcab1]

Welding means removal of that one head.... does it not? The hole is pretty big and there does not seem to be enough meat toward the outside.

The long side of the hole is ... 12mm. That is 50% bigger than the stud.

Damn, what "professional" left this mess for me to clean up.

[TimT]

Yes, a big-sert.. that is if the hole is still on center.. If you don't have one, try and borrow one of those fixture that locates on the port, and remaining stud, and drill for a big-sert...

If the hole is still effed... this is what I did once, because I wasn't going to let a po's poor repair slow me down... I don't remember the dimensions of what I made but here goes.. The repaired hole was hogged out way off center.. so

I drill it out to clean it up
Turned down and then threaded a steel plug
Tapped the head
installed the plug w /red loctite (i know it softens at high temps..)
mounted the headers,
transfer punched the location..
remove headers,
drill and tap installed plug (loctite so plug would not rotate during drilling or taping)
Install stud,
Install headers..

And it was all done with engine in car..

[john walker's workshop]

A welding shop should be able to weld it in situ, if it's upside down. They do have to clean it and heat it beforehand and probably drill out the hole to make it cleaner. Aluminum welding and oil don't get along.

[356911930]

Yelcab,

You could drill then thread the head the next size tap up. Then get an Al rod and thread it to the new tap size. Drill the center of the AL rod and tap to the exhaust stud size. Cut the Al rod to correct length to fill the hole in your head (engine head Loctite, JB weld or weld the threaded AL rod in head and then install the exhaust stud.

Rahl

[john walker's workshop]

[47silver]

That hole looks too big on closeup to just put in a plug snd tap, a good welder who knows his metals as opposed to someone that dables can fill that hole like new and then you can tap it perfectly and know it was done right, if you leak there you could fry a valve. Weld and tap.

[356911930]

So I had you until the JB weld

The OP said he wanted options. You already mentioned welding and drilling, so here are some more options. Threaded in and held in place JB weld has a very good chance of success, especially if he lives in an area where there are no experienced AL welders.


Rahl

[yelcab1]

I presented the choices to the owner and he approved removal of engine, disassembly of bank 2 to the heads, removal of head and taken to machine shop to be welded, drilled, tapped for timesert, and install an M8 timesert to the correct height. I am not equipped to do TIG welding at home, I can drill and tap.

This hole is going to be hidden by the header (where the round barrel nut goes) and header cannot be used as a template. Where do I find / buy a template / jig for locating the hole?

[fred cook]

Originally Posted by yelcab1

I presented the choices to the owner and he approved removal of engine, disassembly of bank 2 to the heads, removal of head and taken to machine shop to be welded, drilled, tapped for timesert, and install an M8 timesert to the correct height. I am not equipped to do TIG welding at home, I can drill and tap.

This hole is going to be hidden by the header (where the round barrel nut goes) and header cannot be used as a template. Where do I find / buy a template / jig for locating the hole?

How 'bout using an exhaust gasket as a template?

[356911930]

I think that Stomski (sp) Racing makes a jig to drill out the stud and thread the hole.

Rahl

[911pcars]

JB Weld/Wikipedia says:

"J-B Weld can withstand a constant temperature of 500 °F (260 °C), and the maximum temperature threshold is approximately 600 °F (316 °C) for 10 minutes. J-B Weld can also be used inside a microwave oven, exposed to microwave radiation instead of infrared radiation (heat)."

At that temperature, any bond will separate. Here's a temp. reading at a heat exchanger/exh. tube under the lower valve cover.

Test condition:
Objective: to measure radiated heat at lower valve cover
Idle speed (approx. 900 rpm)



Notice the Thermax test strip I used maxes out at 309 deg. F. Under full throttle, I have no doubt there's a chance a regular J-B bond might be compromised. J-B Weld ExtremeHeat (37901), Loctite (235579), Permatex and many other companies have high temperature epoxy products.

Since the exhaust port is not conveniently accessed, I'd suggest welding or mechanically restrain/stake whatever insert-type used.

Sherwood

[john walker's workshop]

You could save the guy some money if you built a quick cart that mounted the engine upside down. Just roll it into the welding shop as is.

[yelcab1]

Originally Posted by john walker's workshop

You could save the guy some money if you built a quick cart that mounted the engine upside down. Just roll it into the welding shop as is.

I would need to build a cart which I will never use again, and have no storage for. And I would need to buy a pick up truck to move the engine and cart to the welder...

I think it is better to remove the head from the engine. I'm 80% there anyway this morning.

[yelcab1]

John,

What is your opinion on taking out just one head while leaving the nuts on other heads untouched. Will there be undue warpage on the case? I can certainly get to the head nuts but judging from what I have seen on this "rebuilt" engine, I rather let sleeping dogs ... just lie there.

[jjeffries]

Wait a second ... call a mobile welder to come to your shop. Pull the motor, rotate it upside down, welder shows up with a TiG on his truck .... Bob's your uncle. Don't go thru unnecessary motor 50% teardown.

John in Conn