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Exhaust manifold bolts?

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1-8-4-3-6-5-7-2

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Hey all, I was removing my exhaust manifolds on my '94 K1500 with a TBI 350 and a few of the bolts were real hard to turn the whole time they were coming out. Once removed, the threads on the bolt looked like they are sort of cross-threaded.

I'm guessing my next move would be to run a tap into the hole to clean the threads, but what size tap do I need? Do I need a tap that is flat on the end, or would the standard pointed end tap work fine? Would grade 8 bolts from the hardware store work fine for replacement bolts?

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What you want is a threadchaser...

if you have no choice, a starter tap, then finish it off with a bottoming tap...

Threadchasers are cheap tho, and the appropriate avenue to explore first if you can...

iirc, they are 3/8 - 16
 
I'll bet the manifold has shrunk and you'll need a manifold spreader in order to reinstall the manifold. The tap size is 3/8" x 16 and a standard tap will work but it's notthe threads in the head that are bad. It is the fact that the manifold has shrunk and that's what made the bolts tight while coming out.
 
Ok, I tried to find some grade 8 bolts locally, but nobody had any that are 2.25" long. I did find the bolts I need in the HELP! section at AutoZone, but they are of unknown grade.

Will the bolts from Autozone work fine? I was thinking the grade 8 bolts may be better (stronger and not twist off in the head) for in the future if I need to take these manifolds off again. Maybe I'm thinking about it too much... :rolleyes: :D
 
Forget the bolts "of unknown grade". If a bolt head is not marked, it is a grade three. Not good enough for any automotive use.

If you need to replace the bolts, I would buy them from someone like Summit or Jegs. They will be the correct lenght, have the correct amount of thread, and be the correct grade. Exhaust manifold bolts are not torqued to a high spec, so if you have access to a cabinet media blaster, blast them, check the threads and if not damaged, reuse them.

Anytime I work on cast iron, I always chase the threads. If the threads are not damaged, a bottom taps works best. If they are damaged, you may not be able to safely start a bottom tap without possibly cross threading. In that case you will have to start with a taper tap and finish with a bottom tap. You can get taps at any industrial supply house or good hardware store. After repairing and/or cleaning the thread, blow out the hole to remove any trash.

When reinstalling bolts use a good antisieze to make future removal easier. I use antisieze on any bolts going into anything other than steel. Also, antisieze will work as a thread sealer in case the bolt goes into the water jacket.

As for the possibility of the manifold shrinking, I normally use a die grinder to elongate the holes to fit. That way the manifold is not in tension and I feel will be less likely to crack. If you do have to modify the manifold in any way, it would be a good idea to use a manifold gasket.
 
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Ok... how far will the manifold spreader spread my manifolds? The rear bolts look to be off by about 3/16" (about half the diameter of the bolt hole). Are the manifolds trash?

Anyone know anything about the Summit Racing shorty headers? They bolt to the stock Y-pipe, and I'm considering them as an option instead of putting these manifolds back on.



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i bet it's hard to maintain proper sealing once the manifolds have warped like that even after bendin them back.

looks like you could make one of those expanders out of a bolt, washer, and nut, sort of like a homemade balljoint press.
 
1-8-4-3-6-5-7-2 said:
Ok... how far will the manifold spreader spread my manifolds? The rear bolts look to be off by about 3/16" (about half the diameter of the bolt hole). Are the manifolds trash?

Anyone know anything about the Summit Racing shorty headers? They bolt to the stock Y-pipe, and I'm considering them as an option instead of putting these manifolds back on.



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Click to expand...

As I recall -- it's been a few years and a divorce -- the cast manifolds will move A LOT with those spreaders. Figure each side has to go 3/32" to make your 3/16", which isn't really that much.

I would avoid cheap headers. I've heard too many bad things about them.

-- A
 
Ok, the manifolds also have some serious pitting on the mating surfaces, so I ordered the cheap ($153) headers from Summit and put them on. They fit the stock Y-pipe real nice and have a 3/8" flange, so hopefully they'll hold up for a while. I plan to SAS this truck within a year and then I'll go with some nice full length headers and dual exhaust.


Just a FYI, if you need a plug for an oxygen sensor bung and can't find one locally, a spark plug will work just fine. It's the same thread and has the crush gasket for leak-free installation. Champion number D21.



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