exhaust manifold to downpipe leak

[micbrody]

I have a 1981 FI. I removed heat shield and started engine. I see small wisps of smoke from union of exhaust manifold and downpipe.
Reading around board and internet, I think there is no actual gasket for this union. I assume one piece is slightly recessed into other and tightened down with 6 bolts.

In any event, upon inspection of bolts, one of the heads have be sheared off. I am wondering if previous owner tried to disassemble and sheared head off. I am a little leery of trying to loosen others in fear of more shearing.

My first thought: Is there an outside sealant I can use to seal leak? I have some permashield gasket dressing and sealant that is rated to 500 deg F, and remains flexible. Can I just smear a few applications around joint? Does joint get hotter? will it burn?

If the consensus is no, then I need to disassemble.

1) any tricks in loosening these bolts
2) any idea how to replace the broken one?

[AriK]

Unfortunately, gasket sealant is always a short term remedy and you'll never get satisfaction out of it. Applying high heat to the broken stud (red hot) and grabbing it with a vice grip will usually get it out like butter.

[riverdadd]

ive seen videos on you tube where a nut is welded to the broken bolt, allowing removal..... ive never done it my self but next time i wring off a bolt, i will try it

[micbrody]

I finally started to tackle the leak issue:

I used an impact driver to remove 5 of the bolts. I LOVE THIS TOOL!!!!

The 6th bolt head was broken from previous owner. The downpipe and manifold separated easily. What has not been easy is: removing the remnant bolt from the manifold. The following is what I have tried (all unsuccessful).
1) PB Blaster
2) propane heat
3) propane heat followed by paraffin
4) prolonged propane heat (4 minutes)
5) medical cooling spray

I have used a 10 inch vise grip on shaft of bolt. It just won't budge.
I have done all this with manifold still attached. Very awkward and tight space;however the only downside I see is that PB blaster cannot use gravity to penetrate. I was hoping that "capillary" action would draw it up to threads......no idea if it will .
I have sprayed again with PB blaster. Will repeat everything again tomorrow.

So here is my dilemma: what to do:
1) I remove manifold so I can get better access; maybe even figure out how to attach the impact driver to the broken bolt. Also will be able to just get better access to try all the things I already tried.
The downside: I screw up something else; lots to disconnect to get manifold out; potential for more frozen bolts/studs . AND If successful with all of that, I still might not be able to get broken bolt out.
2) just reassemble again; but add the high temp copper gasket stuff. Some people on the board have used it with success; but not sure with missing bolt if it will still leak. Leak is small; but enough to smell in cabin when stopped for a minute. The bolt that is missing a middle bolt on one of the sides of three bolts .
If it still leaks, I might have room to tap two new holes for bolts on each side of stuck bolt; but not sure if it's a good idea (crack flange?) the new bolts would definitely be smaller diameter
3) buy a new header/down pipe (Vicks?). The previous owner removed catalytic converter and replaced with test pipe; however everything is welded; I don't own nor have experience with welder.

Any suggestions appreciated.

[Nanonevol]

Someone may correct me but I think the easiest thing to do would be to reassemble with a gasket and see how that works. More likely I think you should remove the manifold and take another try at removing the broken off stud. If that fails you could drill it out and put in a helicoil. In some cases you can drill all the way through and use a nut and bolt with washers.

[micbrody]

The FI models don't use a gasket; There is a metal gasket for 4 bolt down pipe (pre FI models) that supposedly could be modified. However, I think because of the heat, not sure if synthetic would hold up; and if I use metal gasket, still have same problem of how to deal with part of downpipe that does not have functional bolt clamping it.

[kmoses]

Have you checked with a automotive machine shop or a machine & welding shop? I'm sure they could get it out by welding a nut on the stud close to the casting. That high heat really can make even the most rusted threads let go.

[grrrdot]

Impact guns are great, they really speed things up. Since you have an impact gun I would suggest buying a stud extractor and pulling the mainfold
Stud Extractor:


These things are awesome for old stuff ownership! Only studs I cant get out with my extractor on the impact gun are really short or recessed, when I run into those I weld a nut on the stub.

With the manifold off you can check manifold and downpipe surfaces to make sure they are flat and smooth. From memory the FI downpipes were higher quality but I have seen exhaust leaks warp pieces and accelerate corrosion. If they are messed up you might be able to use a piece of glass and some wet sand paper to true it up again.

Oh, you might want to check the support under the car that goes from the transmission to the downpipe. That support helps prevent leaks by taking some weight and strain of the exhaust system off the manifold downpipe joint.

-G

[micbrody]

I was wondering if they made a tool like that!
Also interesting you mentioned the support from transmission to downpipe . I read about it and realized my car does not have it. Does anyone have a diagram or photo of what hanger looks like, and where it's suppose to attach?

[carl]

I think you were incredibly lucky to get the other five nuts off without breaking those studs too. Really, the best solution is heat and a propane heater is not nearly hot enough. Find someone or shop with a proper torch and get that manifold red hot around the stud. I have drilled out busted studs that were flush with the gasket surface and drilled and tapped the hole but never got the hole drilled perfectly perpendicular to the mating surface. Another thought is to look for a used manifold with all six studs in good order, should be tons of them floating around.

[micbrody]

I finally just removed manifold to work on it on the bench with a vise.
I again tried previous stuff. In addition, I bought a broken bolt extractor. It's hollow with teeth on inside of hole; it digs into outside of bolt shaft as your impact driver unscrews. All it did was dig into shaft, and with the help of impact driver, dug into shaft and shaved off extra metal. I did this after hearing with propane to red hot: took about 8 minutes. Still didn't budge. Tried it with candle wax; pbblaster . Still no movement. I drilled a hole from opposite site and heated , adding wax, pbblaster overnight.... stilll no movement. I dremeled flat slot and tried impact driver with flat bit. The bolt slot broke. Made two cuts to make a Phillips slot; those broken. I dremeled bolt off and drilled hole ; and then used bolt extractor ..... no movement....... . I took successive bigger drill bits; eventually the integrity of bolt remnant was low enough that a small section peeled away from hole!!!!!
I worked that with a screw and fine pick. Eventually got it out; though about 30% quadrant of hole has no threads...... but enough to grab screw

[So Cal Mark]

is there enough material left for threads?

[micbrody]

It appears so.
I threaded a screw. It seems to grip very well.
Obviously the only way to know is to re-install and see if I can get tight enough to prevent leak.

If threads don't hold, I can install a small anchoring bolt on on the other side of hole (probably would have to drill out a little extra manifold to fit in bolt).

[micbrody]

Just re-installed.

Everything looks tight. Ran car for 15 minutes. No exhaust leak noted at the union!

[AriK]

Way to go!