TR4/4A Exhaust manifold missing stud

[Sierra65]

Yep, it's missing. No stud/bolt in the lower middle hole of the exhaust manifold on the front right hand side of the engine. I'm not a mechanic, so what does this mean? What should I do about it? Is my world coming to an end? Could this explain the popping/very minor backfiring I hear coasting down hills? Opinions and recommendations greatly appreciated!

 

[Geo Hahn]

By lower middle it sounds like one of the two under the manifold - but you also say 'front right had side of the engine'.

In any case, this thread describes the studs:

https://www.britishcarforum.com/bcf/showthread.php?32419-TR3-Intake-Exhaust-Manifold-Studs

The Roadster factory & others have them though it doesn't specify length:

https://www.britishcarforum.com/bcf/showthread.php?32419-TR3-Intake-Exhaust-Manifold-Studs

They are possibly available at any local parts stores -- I have bought them in the past but it was the distant past. If it is one of the middle pair there is also a bridge piece that would be under the nut that secures the flange of both manifolds -- examine the other lower middle hole and you should see it.

Bit first thing I would do is examine the hole closely to verify that the remains of the old stud are not in there. Broken studs can happen, completely AWOL seems less likely but hopefully that is the case.

To install it one would double-nut the end and wrench it in. If it is one of the lower middle pair -- this may be possible with the head an manifold in place but much easier if the manifold is off or just undone and pulled back. If it is the forward one the task is much easier.

A more ghetto fix would be to substitute a bolt until such time as the head has to come off.

As for popping and backfiring - that sounds like a lean mixture which I suppose could be a manifold leak but perhaps more likely to be a carb mixture adjustment.

Oh, and welcome to the Forum!

 

[Geo Hahn]

Okay - which one is gone?

 

[Sierra65]

Thanks for the response! The stud hole is easily visible looking at the right hand side of the engine. It's the most forward one. Is the head of the stud on the inside of the manifold thus requiring removal of the carbs, exhaust and intake manifolds?

 

[Sierra65]

Ha!! You are good. The most forward bottom one. Very accessible!

 

[Sierra65]

Forward stud missing!​

 

[TR3driver]

If it is leaking, then very likely it is the cause of your popping noise. The leak will also continue to get worse (the escaping hot gases act like a cutting torch and erode the cast iron) and if you let it go long enough, ruin both head and manifold.

Unless it just happened to fall out (very unlikely IMO), any repair is going to involve removing the manifold and trying to get the broken end of the old stud out of the hole.

With the manifold out of the way, there are various techniques you can try. Personally, I have never had any luck at all using "Easy-Out" type extractors. For me, they usually snap off before the stud starts to turn, leaving you with a much worse problem! (The easy-out is much too hard to drill out.)

I have had fairly good luck with center-punching and drilling, starting at about half size and gradually stepping up until the threads just start to show on one side. (Impossible to get the center punch perfectly centered, so you're always off a little bit.) With care, you can then use a dental pick and tap to clean up the original threads. Or if not, install a Heli-coil.

What I plan to try next time is this:
https://bbs.homeshopmachinist.net/threads/54076-Removing-broken-stud-by-welding-on-nut

From what I've heard, the heat (and perhaps current) from the welding tend to loosen any rust, making it come out easier.

But since you are "not a mechanic", you'll probably want to take it to a shop instead.

FWIW, although not original, I've had a lot less trouble with those corner nuts after I started putting an extra heavy "setup" washer under the lockwasher. You can see the washer on the rear stud here

 

[Geo Hahn]

You may still get off easy -- stick something in that hole (small screwdriver, bamboo skewer, nail etc) and see how deep it is. That should tell you if the stud is just missing or if it has broken off in there.

Sometimes the studs comes out with the nut when removed (nut rusted on) so it is just possible that the whole works backed out at some time.

If the depth of the hole is shallow (say the thickness of the manifold flange) then it is broken in there -- but if it is deep (say more than an inch) then it may simply be missing and you should be able to just thread a stud in there.

In the latter case you would want to get the correct stud, double-nut it and use some Loctite on the threads. Run it in, remove the double nut and finish up with the washers, nut and anti-seize.

I also use an extra flat washer on those corner studs.

 

[TR-3rg]

Hi,

I worked my way thru college in an engine shop. I always got stuck with broken exhaust manifold bolts. Try using a left hand (counter clockwise rotation) drill bit to remove broken studs or bolts. Grainger and MMC sells them. About 3/16 diameter should do it. Check the depth and compare it to the other holes to see how deep you are. Typically the drill would go in about 3/8" deep and fastener will spin out. Spin the drill slow with a lot of pressure.

I put a helicoil in the rear hole on my TR-4 head. The helicoil drill & tap broke into the water jacket. I installed the helicoil and sealed the stud with Aviation Permatex. No issues in 5 years,

Good luck, Roy