7.4L MPI manifolds (rusty underneath)

[Shaun78]

All big block manifolds get heavy rust underneath as they don't have the water jackets like the small blocks.(they get hotter) They bolts get really rusty FAST. What is the best way to remove the rusted manifold bolts? Some the heads look almost rounded.

 

[Don S]

Re: 7.4L MPI manifolds (rusty underneath)

I set the engine on the floor, on blocks. Get the Oxy/Act Torch out, and burn the heads off the bolts. Have done it many times

 

[Shaun78]

Re: 7.4L MPI manifolds (rusty underneath)

You pull the engine out? You don't worry about damaging the head gasket with all the heat? Head gasket is pretty close.

 

[Don S]

Re: 7.4L MPI manifolds (rusty underneath)

You pull the engine out?

You don't for a minute think I'm going to take a blue tipped wrench to manifold bolts with a 100+ gallon GAS tank only a foot or two away, rubber gas lines, fuel filters etc. do you?????
I may be crazy for working on these @#%&*#$ boats to begin with, but I am NOT stupid.
As far as the head gasket goes, it doesn't get that hot!. You are only burning the head off the bolt, then move to the other side, take your time.
Once you burn the head off the bolt, and get the manifold off, simple vise grips removes the remaining portion of the bolt or stud.

 

[Locke]

Re: 7.4L MPI manifolds (rusty underneath)

Interesting timing on this question, I just took a rusty manifold off tonight. I'm the new owner of a 2000 Sea Ray 270 Sundancer that had some rust on the starboard side 7.4L exhaust manifold and none on the port side. So I thought why not take it off and investigate. The back 5 bolts came right out but the front three no go, they had deteriorated some from rust. I ended up trying 1/2" and 13mm 6-point sockets and banging them on to fit after an overnight soak with WD-40, a little finesse and lucky me they came off.

Turns out the rust is caused by leaks from both of the plugs that are in the back of the manifold. Is this a common problem? Now I have to pull the plugs out and see if the manifold is salvageable. My guess is that when the manifold was prepped to install on the engine the threads on this one were not treated correctly. Anybody know the correct way to do this?

Locke

 

[Don S]

Re: 7.4L MPI manifolds (rusty underneath)

Start a new thread with your question Locke, don't just add on to someone elses question.

 

[wire2]

Re: removing rusty bolts

Re: removing rusty bolts

File the surface flat, locate the middle, and center punch.

Drill a small pilot hole, then go up to 3/8 drill bit.

Stop when you get to the manifold, and slide the manifold off the studs.

Turn studs out with vice grips.

No flame, no heat, no sparks.

 

[Shaun78]

Re: 7.4L MPI manifolds (rusty underneath)

the boat is a 1998 with only 265 hours. I pulled the plugs and they are all PERFECT!. They are all burning the same. no white smoke when running and boat doesn't heat up. Manifolds underneath are rusty and chunks falling off. Should I replace manifolds & risers or wait until I get some symptoms that its time to replace (hard starts, white smoke, higher temps) What should I do? If I just pull a riser off then I will probably just replace everthing. ????