Tips for replacing exhaust manifold on old v-8?

**Patches** · 10-22-2009, 04:01 PM

I just bought an '89 ford van (351 engine) that has an exhaust manifold crack. I was going to replace it, but I'm worried one of the studs will snap off. Any tips for keeping that from happening?

The thing actually runs OK, rough idle when cold, but it won't pass emissions- O2 is sucking in the crack and the sensor thinks the car is running lean so it compensates by making the mixture too rich. I don't have to pass emissions but it bugs me, and its probably wasting gas and wearing things out.

The engine in the van has 50K miles in 7 years. It is a rusting heap of shit but I like it. Reminds me of the one I had to sell to pay for my wife's engagement ring lo these many years ago... but its a 4x4. It would be nice to get it all dialed in before the snow comes.

**khakis** · 10-22-2009, 04:08 PM

replacing manifolds can really suck. Maybe you will be better off just plugging the crack with J-B weld?
Otherwise hit the studs with P-B Blaster frequently over the course of a couple of days, then when you're ready to try and break the nuts free, hit them with a propane or MAPP torch to get them good and hot then the first attempt you make to turn them, make it hard and fast. Slow and gradual tends to break/strip stuff

**karpiel** · 10-22-2009, 04:11 PM

Pay someone a set price to do it. If the studs break or the threads get fucked up, it's their time and money.

**Norseman** · 10-22-2009, 04:22 PM

Seconded on the PB Blaster. That stuff is gold.
Buy two cans and spray the shit out of the exhaust studs for a week prior to touching anything.

**vanisle** · 10-22-2009, 07:15 PM

You can weld a cast manifold with the proper rod.If you know where the crack is and can access it without pulling the manifold that might work...

**Pow4Brains** · 10-22-2009, 07:24 PM

Heat the nuts with an oxyacetylene torch. Just before they turn redhot they'll come off rather easily.

**Patches** · 10-22-2009, 09:06 PM

Thanks fellas, I'll get some P-B Blaster and a torch. It'll be a trick to get a torch up in there (all kinds of crap in the way) but I'll try.

**lemon boy** · 10-23-2009, 07:53 AM

ExMs are easy!

First, spray the everlovin shit out of the nuts with some PB Blaster, then drive down the road a bunch in a low gear getting the thing just as goddamn glowing red hot as you possibly can, stuff your hand down next to the thing and whack that hand with a ball peen hammer (whichever side) and take to an exhaust shop.

couldn't be easier.

**bmg97** · 10-23-2009, 08:04 AM

Did you try JB Weld on it ?

**XXX-er** · 10-23-2009, 08:14 AM

Originally Posted by bmg97

Did you try JB Weld on it ?

I was gona say ,try and stuff it down in the crack so there is a wad of it on the inside

SB · 10-23-2009, 10:22 AM

take it to the shop if you are worried about snapping a stud off

**refried** · 10-23-2009, 11:15 AM

I have a '79 (460) with the same problem, I should replace them before it starts snowing but I've been putting it off because I know I'll break at least one stud getting them off (I'm going to do both). Ford never used gaskets on the manifolds and they dont leak when new but will leak (or crack) eventualy because of the heat. Fel-Pro makes a steel gasket for use in service vehicles that's not supposed to leak or blow out like paper gaskets, I'm going to try them and see if it works.

**khakis** · 10-25-2009, 10:13 AM

Originally Posted by lemon boy

ExMs are easy!

First, spray the everlovin shit out of the nuts with some PB Blaster, then drive down the road a bunch in a low gear getting the thing just as goddamn glowing red hot as you possibly can, stuff your hand down next to the thing and whack that hand with a ball peen hammer (whichever side) and take to an exhaust shop.

couldn't be easier.

there's a man who's played this game before! You forgot to start by turning the timing waaaaay back to help heat 'er up

**jon turner** · 10-25-2009, 10:50 AM

penetrating oil (P-Blaster) and heat will get those bolts moving almost every time. An impact wrench would be nice too, but could be hard to get in there. I think the last time I pulled an exhaust manifold on an old car, it took several hours just to get everything out of the way and the bolts off. It ended with me standing over my car triumphantly with exhaust manifold hoisted overhead. It only took maybe an hour to get it all back together again. Exhaust manifolds are a pain if they're all rusted up, but as long as you take your time and give the P-blaster enough time to work, you should be able to get it done. Don't get frustrated, pissed, and break something (been there many times)...

**Patches** · 10-27-2009, 04:25 PM

Piece of cake, I didn't bother to torch the studs since the bolts came out so easy. Most knuckle skin still intact. P-B Blaster is good stuff.

So now an engineering question... the manifold was held on with a combo of studs and bolts. Why a combo? You'd think it would be all studs or all bolts.

**bmg97** · 10-27-2009, 04:43 PM

Originally Posted by Patches

Piece of cake, I didn't bother to torch the studs since the bolts came out so easy. Most knuckle skin still intact. P-B Blaster is good stuff.

So now an engineering question... the manifold was held on with a combo of studs and bolts. Why a combo? You'd think it would be all studs or all bolts.

Probably so you can place the manifold on the studs then secure it.

**Pow4Brains** · 10-27-2009, 05:29 PM

Or because you can't get a bolt in due to lenght and the curve of the manifold.

Glad it worked out easy for you, wanna come do mine now?

**Patches** · 10-27-2009, 05:34 PM

Originally Posted by Pow4Brains

Glad it worked out easy for you, wanna come do mine now?

Heh. I'll be a traveling manifolder. Like Swayze in Road House

Pow4Brains: Your file says you've got a degree from NYU. What in?
Patches: Philosophy.
Pow4Brains: Any particular discipline?
Patches: No. Not really. Man's search for faith. That sort of shit.
Pow4Brains: Come up with any answers?
Patches: Not too many.
Pow4Brains: How's a guy like you end up a manifolder?
Patches: Just lucky I guess.