Exhaust Manifold Bolts

[eldplanko]

I'm removing the exhaust manifolds for the second time in a few years, and again sheared a bolt. Long story short, engine is a '74 ford 302 on a Mercruiser 888 i/o, used in saltwater and has freshwater cooling. Two years ago, I pulled the engine out of the boat to replace the transom plate and Y-pipes for the exhaust. While the engine was out of the boat, I pulled the exhaust manifolds off the heads, and the heads off the block to fix a few burnt valves. While pulling these, I had one bolt shear flush with the head (one in the rear, where it's the hottest and where it looked like a bit of wet exhaust was leaking out of the risers). I had a machine shop remove the sheared bolt, and helicoll it. The exhaust manifolds / risers are the older "log" style, and at the time looked like they would need to replaced soon. I surface painted them, reassembled and ran these for two summers with no problems.

A few notes on reassembly, I used grade 8 bolts to reattach the manifolds to the heads. I didn't use anti-sieze, and put the exhaust gasket on dry.

Two years have passed, and I picked up some new (used) risers and manifolds to replace the old corroding ones. In pulling everything again, the same bolt sheared in the back. I also noticed that after only two years, the grade 8 bolt heads had some serious rusting... had I waited longer, I'm sure I would have had more problems pulling these bolts.

My questions, should I use stainless instead of grade 8 to bolt the exhaust manifolds to the heads? Should I use anti-sieze?

Thanks in advance!

 

[dingdongs]

Re: Exhaust Manifold Bolts

anti seize is the way to go and keep with steel bolts .

 

[Bondo]

Re: Exhaust Manifold Bolts

Ayuh,.... Anti-seize is fine,... SSteel bolts, No,... SSteel bolts are pretty soft,...

Stop sprayin' saltwater on yer motor will help the most,...

 

[Scott Danforth]

Re: Exhaust Manifold Bolts

never seize is a good idea here. however going into the head for exhaust bolt, I coat the threads in maalox. I would also put some tefgel under the bolt heads. the heat turns the maalox coating into a dry film that resists high temp burn off and the bolts come out easy after years. The tefgel works to slow the corrosion from wicking down the fastener

 

[eldplanko]

Re: Exhaust Manifold Bolts

Thanks guys... I figured stainless would be too soft also. I'm hoping the new risers will cut down on the corrosion problems. Anyone every try mounting a few studs on the head? I plan to temporarily use some to get the gasket and manifold alligned while I button everything up. I was thinking to leave a pair on the last aft cylinder on each side, as these seem to always be stuck the worst.

 

[Scott Danforth]

Re: Exhaust Manifold Bolts

you put the end bolts thru the manifold loosely, then drop the gasket over the bolts, then put in the rest of the bolts.

the two end holes on the manifold gaskets are slotted for that reason.

 

[eldplanko]

Re: Exhaust Manifold Bolts

Well why didn't I think of that ! Thanks.

 

[Bt Doctur]

Re: Exhaust Manifold Bolts

And should you get a gasket with holes, just notch the 2 end ones.

 

[NHGuy]

Re: Exhaust Manifold Bolts

My motor is down low and my back isn't great so I use 2 headless bolts to hang the gaskets and manifolds. Then I start 2 normal bolts, then I swap the headless bolts for regular ones.
I think I'd change the bolt that fails often, like yearly, if it's easy to reach. Loosen the other bolts first in case it's crooked and binding when the others are snug.
When you tighten them start in the middle with about 1/3 of final torque. If it's a 4 bolt manifold do #2, #3, #1 and then #4. ie. Circle your way to the outer bolts for your tightening sequence.
So 1/3, of total, 2/3 of total, and then final torque. It's an extra step but could save you trouble later.