Exhaust Headpipe Studs

Well, I made it back home safely, and now with the cold weather have got to get this fixed. The exhaust donut at the headpipe flange is leaking. At first, I thought it was the manifold but no, its the gasket. For this one, I am taking it to the muffler shop and having them do the gasket and make a whole new headpipe. My question is: Should I expect them to have a hard time with those 2 studs?? I let them sit for 3 months with PB blaster. If they snap off, are they difficult to replace?? The entire exhaust is new from the cat back, it only makes sense to me to do the rest.

Is this the joint from the exhaust mainifold to the down pipe? The nuts are usually an interference lock type and are virtually impossible to undo. It is normal to cut them off and replace them. ( those are not studs but bolts, so maybe we are talking about a different joint?)

First of all - Welcome Home! I'll bet you're glad to be back.

Now, I think you're talking about the join at the end of the header, where it bolts up to the pipe going to the catalytic converter, am I right? You can service that join yourself quite easily, moreso since you've done the "PB Blaster" thing. Just go get a couple 3/8" UNC brass machine nuts before you get started, and be ready to throw away the steel ones. Why brass? You'll be able to take it apart later without spending a week preparing (trust me - I've been using brass on exhaust hardware for a number of years, and it's always done well for me...)

If memory serves, a gasket there is not strictly necessary. In fact, none of my three XJ's (87, 88, and 89) have it - it's just a "ball and flange" joint that seals on the metal surfaces. Each time I think I've sprung an exhaust leak, it was quickly remedied simply by tightening the nuts - so check that first.

It is also fairly common for the manifold bolts to work loose over time (steel + heat/cool cycles = gradual loss of temper, dissimilar metals being clamped + heat = bending loads, and the bolts literally "unscrew" over time.) It may also be prudent to check torque on all your manifold bolts and see that they're still tight, and if it hasn't been leaking too long you can do the job without tearing it all to bits. If the gasket is shot, order a batch of silicon bronze bolts from Fastenal (if memory serves, you'll want a batch of 3/8"-16x1.25" hex heads) and use those to reinstall.

Why do I suggest brass? Two main reasons:
1) Brass is "springier" than steel - that's the same reason it works so well for ammunition cartridges. Brass won't have as much trouble with the bending loads and expanding aluminum intake manifold as steel eventually will.

2) Unlike steel, brass actually gets slightly harder with heating/cooling cycles. Since we're not going to "red heat," it's not going to be a critical point, but the steel will eventually loosen because you are annealing it each time you run the engine. Annealing will reduce the hardness of the metal - which reduces its tensile (pulling) strength over time. It's the merest fraction of a percentage point, but the effects are acumulative over time. Even as the brass hardens, the inherent "springiness" of the metal will compensate for the gradually increasing hardness. It is not unreasonable to expect a service life of 20-30 years from brass exhaust hardware.

Oh - and use LocTite #272 to retain your exhaust fasteners - NOTHING ELSE. 272 is designed for exhaust heat, and most better supply houses will have it or can get it for you.

5-90

Yes, the gasket at the header collector itself. I thought it was the manifold itself, but from underneath I can see it when its cold leaking. That headpipe is original and in pretty rough shape, I left it when the exhaust was done just for the $$$ involved. My plan is to have the muffler shop bend a whole new downpipe from the collector to ahead of the cat. My big concern is if those studs snap, they will have to drill the manifold collector and more $$$ involved. But they are actually bolts? So, if they snap no big deal, right? Great idea with the brass hardware though, I will have to ask them to follow that route. I know I can undo the collector, but I want that whole pipe replaced and working outside in this cold is a killer to me right now.

Unless they changed them in later years, they're studs, pressed into the flange on the manifold with splines, similar to a wheel stud. When I last did this, I just punched them out and used 3/8 inch bolts, which worked fine even though the holes in the manifold flange are a little bigger than the bolts will be. I just used washers. I would still try to get the nuts off without shearing them if possible, and perhaps use brass nuts to replace them, mostly because it's a difficult reach to get up there and hammer out the stubs if you shear them, but I wouldn't worry too much either way.

I just changed my header last weekend, on my 94. There were bolts holding the header to the downpipe. I removed a Hedman Hedder, but I would think they would use stock style hardware. I snapped one of the bolts, the other came off ok.

I think the manifold was different on the 88 though. As long as you folks dont think it would be much for a competent shop to handle if the snapped off. For worse case, I am planning on them breaking and considering they are 17 years old they probably will. I will tear into anything else, but I hate messing with exhaust.