Weeping exhaust manifold studs

[Pope1]

Guys, I'm sure you're getting pretty tired of my constant questions but I have another I'm afraid. What the best way of dealing with weeping exhaust manifold studs? I've got oil leaking from the two short centre ones. Engine is out of the car at the moment and the manifold is off already so everything is accessible. I'm sure I saw something on this before but I've done a search and have not been able to find it again.

[Wallace]

Remove studs and Loctite them in ! Or use expoxy type glue - make sure it's all degreased first though - and I'd fit new studs (stainless Will ? :wink: ) because you might find it difficult to get them out again . .

[Pope1]

I assume that they're just screwed into the head? Didn't have much success trying to remove the first one so thought I'd ask for advice first before buggering them up.

OK they're on the move now so please ignore that question. Many thanks.

[Wallace]

They are !

M8 by 1.25 - just screwed in - just as long as they don't shear off when you try to remove them . . (been there, seen it, done it . . . )

[Pope1]

They are !

M8 by 1.25 - just screwed in - just as long as they don't shear off when you try to remove them . . (been there, seen it, done it . . . )

All sorted now thanks. Sounds like I was lucky, they turned quite easily once I applied a little more force. I used exhaust paste on the threads as I figured it would seal well, would withstand heat yet would still allow the studs to be removed in future if necessary. Only time will tell whether my theory was sound.

[Skufy]

....been there, seen it, done it . . .and still doing it!

[Will]

...I think nearly every Lancia owner runs across this problem at some point. There are a few things we should all know regarding this:

a) The studs don't actually seal on the threads, but on the "shoulder" where the thread stops and the stud is thicker.

b) The studs are assymetrical and need to be pointed in the right direction (really applies only to studs that you are reinstalling).

c) Many of the OEM studs have a triangular stamp on the end that goes into the cam box.

d) It's the upper two studs that go into the cambox, and they leak either because;
1) they were cranked down so tight that expansion of the exhaust flange actually stripped them or
2) thermal expansion of the flange and head worked them loose or
3) the motor mouints are weak or
4) the exhaust spring-clamp setup where the headed joins the main exhaust has been overtighted, and the exhaust can't move with the engine torque twist. (Beta Spider and Coupe)

Loc-tite would be great except- it's removable by heat, and guess what part gets really hot? The loc-tite will work temporarily, but it softens up once your exhaust gets to temp and the washer/nut makes a good heat-sink for your exhaust flange :(


Likewise, Nyloc nuts are useless because it'll just melt the locks out of them.

Knowing what I know now, after going down that road a few times, I would put an internal star lockwasher on them. Nord-locks might be nice, but it's not like I have them laying about, 'specially in 8mm.

Anything that has a little give, like the shallow cup washers FIAT is famous for, would probably suffice. What you are trying to do is hold the part secure and from rotating even when it is repeatedly heat-cycled.

Of course, if you really want to do it right, the BEST way would be to safety wire them- that will definitely solve the problem! Safety wiring is the only method (that I know of, anyway)that allows fixing the fasteners relative to each other to prevent rotation absolutely.

You CAN also heli-coil the head, but now you need to rely on a sealant since you have cut away the shoulder bit where the stud normally seals. A Mapp gas torch and some of that "Alumaweld" rod solder would be my pick there- the stuff makes amazingly good bonds to aluminum, but is not really hard enough to actually cut threads into, and welding up the aluminum and then cutting threads into the weld gives you (at best) what you started out with.

OK sorry for the long dissertation, but this problem is so common I thought it a good idea to share everything I learned about dealing with it.


Regards Lancisti,

-Will

PS> All IMHO of course, even though I've been through it several times, atmospheric conditions in your garage may be different. There are also about sixty different formulations of loc-tite if you really want to experiment, you can get most of them them from Techni-tool. I stick to the standard red and blue, and after that I resort to mechanical fasteners.

[Wallace]

But Will - if the studs in the head - then it's going to be at the head's temeperature - which shouldn't be that hot . . . ! (we're not talking about the nut on the end of the stud . . .) :lol:

In the UK, you can get "deformed" nuts from Halfords that are pretty good for exhaust manifolds - as you said - the plastic in the loctite ones would melt !

Anyhow - I'm off for a few days. Have a nice Christmas everyone.

[Wallace]

But Will - if the studs in the head - then it's going to be at the head's temeperature - which shouldn't be that hot . . . ! (we're not talking about the nut on the end of the stud . . .) :lol:

In the UK, you can get "deformed" nuts from Halfords that are pretty good for exhaust manifolds - as you said - the plastic in the loctite ones would melt !

Anyhow - I'm off for a few days. Have a nice Christmas everyone.

[tbalon]

Because the oil is actually under pressure for at least one of the studs (the center one I believe). I would utilize high temp, non hardening thread sealer on the studs. As noted in other posts, crimp or deformed type lock nuts work great and don't melt. Another trick from the DSM cars (eclipse, talon) which have a lot of problems with broken exhaust studs from manifold expansion is to use two flat washers between the manifold and the lock nut so the manifold can expand a bit. This may require longer than factory studs.

[Will]

Wallace;
Try appling your same logic thus; the stud is also in the exhaust header, then should it be the same temp as the header? If so, then it would reach over 1400F!
In actuality, it will be somewhere between the two, How hot exactly, I can't tell you, but I can attest to the fact that both brass and stainless steel nuts will discolor, which I think you'll find requires somewhere in the neighborhood of 600-800F minimum. I know it's higher than 500F because that's what I post-heat my stainless welded parts at in the oven and they don't discolor. Granted aluminum may be a better conductor of heat, and the surface area is high in the thread, but at least the "other" end of the stud gets pretty hot. It definitely gets hot enough to make the nylon locks completely disappear from the locknuts, BTDT. oops!
For this reason, I would not trust loc-tite in the commonly available formulation to seal AND fix the thread, and as I posted earlier, the thread isn't really the sealing surface. Of course, one could choose to make a note of that or not, as one desires. I'm just sharing what I've been through. I thought the thread sealed at first, too.

Tom;
The center stud's at the bottom, at least on the regular 1.8 and 2L's, and it should be just a blind hole. If it were drilled through, I'm almost certain you'd find it intersected the cooling gallery rather than the oil gallery since the stud is off-center in the length of the flange, but I'd have to double-check by looking at a head before I'd bet my first-born on it. The Vx heads have two studs in place of the one, but again I think you'll find they pass either side of the oil gallery and thus, if drilled all the way through, would end up in the coolant galleries.
Of course, you may be referring to a 1600 or some motor that I'm completely unfamiliar with.

Regards all, and happy wrenching!
-Will

[tbalon]

Will,

I would put the head itself at about 300F to 350F given that both oil and coolant are both relatively close to the rear of the head and if the head temps were much higher than this, the car would overheat (spot boiling) as soon as you turned the car off. I have a head temp gauge in my 78 911 and it seldom runs above 300F.

1400F for the manifold is very high, I would hope it is closer to 800F to 1000F on the high side under load, maybe a bit higher in a turbo applicaiton. If you are at 1400F you have other issues like burning fuel in the manifold instead of the engine. Maybe in a race cam application.

Pyrometer testing (infrared thermometer) on the dyno indicates 500F to 600F at the exhaust (in this case a BMW 2.0, with pretty agressive cams), about the same for my turbo cobra.

I believe we all agree that only the crimp/distorsion lock nuts will work. I wouldn't even trust a nylock on the intake manifold, they are made for swing sets. I don't recommend lock washers as they can lead to stud failure from manifold expansion working the bolts back and forth. I always use a pair of flat washers as they are cheap insurance.

It has ben a long time but I remember starting an 1800 beta coupe one time with one of the exhaust studs missing and there was oil everywhere. I don't have a spare head around so I can't verify. If someone can verify it would be useful information. If I read the original post correctly the exhaust stud is weaping oil so it is either an oil feed or oil drain gallery penetration.

The whole original question of thread sealant is a tough one. Thread friction (which holds the stud in place) is usually enough to seal the stud and the seat of the stud will also seal against the head. You need both so the stud will stay in the engine when the nut is removed. I personally don't recommend lock tight (although I think it might work) as the temperatures encountered are in the phase change range so the lock tight is shifting from solid to liquid all the time. There are several viscous, non-hardening thread sealants out there that will help seal the threads without any adverse effects.

I guess my only question here is are you recommending that no thread sealant be used to resolve the issue, or only a vote against lock tight.?

Just trying to get all thoughts documented.

Merry Christmas,

[Will]

Warning:long post follows-

The upper exhaust studs that go through into the cam box oil drain area will DEFINITELY leak if they don't seal, and in fact, in a Beta, oil "spurts" out of these right onto the exhaust manifold. Enough so that I had a Zagato instantly fill the driver's compartment with smoke, and when I say instantly, I mean maybe two seconds to white-out conditions. I found in that case that poor motor mounts, not much in the way of chassis engineering, and overtightening of the four spring-bolt flange underneath the car were the culprits, plus a bit of additional torque from my newly-installed nitrous rig on that car. Unfortunately, that car subsequently ended up going to Shaun's FIAT boneyard because it really wasn't economical to fix.
I 'll add that I also had welded the upper and lower cast manifold sections together, and if I hadn't , then they MIGHT have popped apart and saved the motor- I can't say.

As far as exhaust temps, I'm not going to argue that point, because I don't know. My Autometer probe setup in the cat box reads up to around 1450 under certain conditions (which is NOT full throttle or high revs, remarkably) but it is probably reading catalyst temperature. If the exhaust stud nuts are only getting to 300 degrees though, what do you offer as to an explanation of why stainless nuts (or brass) discolor so?
I have a cheap-ass $100 Minitemp IR gun I bought a few years ago that's handy for finding the coldest beer in the fridge, but sometimes just gives trotally errant readings, so I distrust it. I went to get the temp of my fish pond the other day with it, and it was reading (repeatedly, mind you) nearly 1000F off of the patio surface! I changed the 9v battery, but still the same, so I assume it's completely broken now. When it was new, I was impressed by it, but even then it was a bit twitchy regarding the angle you held it at- I don't think I could rely on a reading from the exhaust header as definitively accurate. You may well have a better unit, granted.

Thread and/or stud sealant:
OK, you are asking for opinion here? My preference would be PTFE paste on the stud, for several reasons.
a) It is virtually immune to heat (well, almost)
b) It's one of only a few sealants that are rated for both threads and seats (the stud shoulder is essentially like a narrow-angle flare seat)
c) I might be the only guy on the planet that feel this way, but I'm not sure I WANT my studs to stay in the head all that well. Sure, you don't want them backing out, but the lockwasher, etc. should take care of that. Meanwhile, if the nut does freeze on, you DO want to be able to get the stud out of the head so you can replace it. And, if you are using stainless studs, then you'll need an anti-spall anyway, which PTFE paste does a good job of. Because I do a fair amount of plumbing work, and we stick with what we know, my second choice would probably be Megaloc thread sealer, which is rated for high-pressure steam lines. I'm sure there are better race-car/aeronautical esoteric gooies available- I just haven't had to resort to any of them. There are a lot of guys who swear by the Permatex aviation (brown), but I have not tried it. I'd like to, though- can't find any.
BTW- kind of agree on the Nyloc nuts- but I had used them as the outside of a pair of nuts that were backed against each other. On the flat washers you recommended, take a close look at the "flat" washers that FIAT used, if you take two of them back to back you will notice that they are very slightly convex. I assume that this is to provide that little bit of expansion room you describe, since the cup shaped washer would effectively act like a (very strong) spring.

Lastly, what I will do on my next head with a stripped exhaust stud is to use an insert on the hole (allows the depth of the stud to be slightly less) and then weld the hole over from the top of the head. That should solve that engineering problem forever IMO.


Regards,
-Will

[tbalon]

Thanks Will,

First, I agree that the outer ends of the studs would have to be roughly equal to the exhaust flange temperature of up to 1000F (turbo car normal), more usually 600F with the head closer to 300F to 350F. The interface bwteen the studs and the head could be in the 500F to 600F range but probably a bit lower. Definately get a new IR unit and get one with the highest spot ratio you can. Some IR units, even good ones, have to be within inches of the target to measure accurately.

We all appear to agree that loctite, or more specifically thread lockers, is a poor choice and does not facilitate stud removal when they break.

PTFE is a good choice and is good to about 500F and widely available. My personal favorite for thread sealing is Hylomar which is a non-hardening silicone sealer good to about 600F. Honda and Yamaha have their own versions that are purported to be superior to Hylomar but I have not tried them. Copper Anti-gall coatings are good to 1800F but they are not good sealers.

Also, you mention stainless exhaust studs and it is worth reinforcing the point that stanless studs have come a long way and should be used. Not all are created equal so shop around.

I hope this helps the original poster, who has been mysteriously quiet.

[Pope1]

Yes, I have been quiet of late but please check my post of December 18. Since then a wealth of additional information has been posted for which I am most grateful. Apart from the usual Christmas distractions, my e-mail notification of new posts stopped arrriving for a few days so I've only just discovered that several other items have been posted recently. My apologies if anyone took my temporary silence to indicate a lack or interest of gratitude on my part.

I'm inclined to leave my studs alone now that I've put them back with the exhaust paste, but will look at the washers again. I think the washers are the split ring variety that were used before. The engine and gearbox are still out of the car as I'm waiting for a new gearbox oil seal to arrive, so I can easily have another look at the manifold.

[tbalon]

Sorry, was not hunting for gratitude, it appears I need to use the emoticons more often it seems. :lol: Actually just trying to get some discussion back onto the board as well as get some useful information in the database. I tend to drift away for months at a time as my Scorpion is currently dead and I have other distractions of late. I apparently missed the your December 18th as I picked up the thread from the front page of the site. My Bad. :(

Enjoy.

[Pope1]

No problem, I can see how my apparent silence did seem strange. :D

[Wallace]

I've found spring washers NBG as the heat tends to knacker the temper of them . . . tab types might be better . . . or deformed nuts.

ps. I'm still going to use loctite on my engine !!!!

[Pope1]

Yes I'm going to go back and look at the whole thing again including those washers. At the moment I don't like the way the manifold is fitting, it's almost as though there is a gap between the manifold and the gasket in a couple of places at the top. I guess it's the metal bits around the bores that really need to seal properly but even so it looks odd to me. The other thing is that the two studs that were leaking are shorter than the others for some reason. With the manifold on, there is only just enough thread left to get a couple of washers and nut on. :roll: