Need to replace manifold--what to expect?

[Chris Simenstad]

I just completed a six week, 913 NM cruise from San Francisco to Southern California and back, and had to rely on the motor a lot. It ran like a top, but on the way back the boat took a pounding and my vapor detector went off. I couldn't find a gas leak, but after feeling around the aft end of the manifold I felt hot exhaust, and looked at the spot with a mirror. The manifold is really corroded, and needs replacement. (I was able to stifle the leak with a ball of tin foil and wire, and the engine ran fine for the remaining 20 hours home. I ran the blower and stayed out of the cabin to avoid carbon monoxide poisoning).

So now I need to pull the manifold and replace it. How tough a DIY job is this? Should I expect that I can pull the old studs out? This is the original engine (1975), but access to the manifold is pretty good. Any advice on this one?

Best,
Chris

[ghaegele]

Yeah, if you haven't had the manifold off ever the studs can be beastly (even if you have!). Take lost of time and use lots of penetrating oil. Once you get the manifold backed off a bit (you might use a putty knife as a wedge to get in the space between the manifold and block occupied by the gasket and rip out the old gasket) then you can spray the studs closer to their threads. I found a torch, a hammer and PB Blaster eventually worked. And unless you have lots of work space around your engine don't break them off. If you do you might have to lift the engine to drill out the stud and oversize it.

Also, expect the hot side pipes leading to your muffler to crumble when you do this. Outfitting replacements isn't that hard at your local plumbing store. (DON'T USE HOME DEPOT PIPE!!!!! The Chinese steel they use is garbage and the threads never match up well.)

Deciding how much force it too much when removing studs reminds me of a Woody Allen quote: "More than any other time in history, mankind faces a crossroads. One path leads to despair and utter hopelessness. The other, to total extinction. Let us pray we have the wisdom to choose correctly."

Good luck, Greg

[msauntry]

I had the same thing happen and I didn't have a hard time with replacing it. The studs stay in the block and the manifold slides over them, so you shouldn't have to remove anything other than the nut. Hopefully that will go well... You'll need a few inches of clearance to the side of the engine, so see what cabinetry you have in the way and remove it.

I'd not waste my time trying to salvage the old fittings, just order a new manifold, new gasket, new exhaust flange and bolts. Check the condition of the hot exhaust section. $30 worth of galvanized pipes can easily be installed at this point, unless you know what you got is good. Its one of those "while I'm back here" projects. Don't forget new wrap for it.

[ghaegele]

That's a good point. When I had the beastly problem removing the studs was after I removed the engine and was taking everything off the block. One of the studs had frozen in the manifold. And now that I think about it, the stud didn't break in the block but stripped when I was replacing the manifold. That's when drilling and retapping was such a nightmare. Whew, now I remember why I nearly wiped that from my memory.

[blackdove]

Today, I took my old and corroded exhaust piping off. I had been putting it off for a while but today was the day it came due on my list of action items.
A couple of days ago, I sprayed the bolts on the manifold fitting with a mineral oil based product called Bolt Off (Home Depot)/let it sit and came back today.
Slight tapping of the wrench with the hammer and bingo, the bolts freed upon almost instantly. A skeptic could argue that they were not properly tightened, but trust me...before the Bolt Off, I tried and could get any movement and I was afraid I would snap the bolt off or strip the head.

As Don has said in other posts, patience and persistence. Thank you.

Blackdove

[dcneuro]

I took my exhaust manifold off this weekend. There was no need to remove the studs as the manifold easily slips over them. However, upon putting the new one back on, there was a size difference in width of the new manifod by almost half an inch. This difference caused the studs to barely make it out of the exterior surface of the exhaust manifold. As such, the nuts only fit on threaded up about halfway. And, there is supposed to be a throttle linkage bracket mount on two of them as well. With this in place, the studs don't even come out enough to thread the nuts at all.

Anyone ever encounter this? Apparently, the aftermarket exhaust manifold is not made by Universal, and it is obviously not the same.

I forced water through my old manifold and a bunch of stuff came out, and have been soaking it in vinegar over night and now intend to try and re-use it.

Thoughts and suggestions appreciated.

Dr. S.

[Greg]

Chris,
Just ran across your post. It's a pretty easy pull on our boats. Disconnect the water lines, 2 bolts at the manifold flange on the aft side .. then the 3 nuts off the manifold studs. A stiff putty knife as I think was mentioned, maybe some persuasion with a rubber mallet and it should slide off. Once I had mine off, I double nutted the studs and they came out easy. If they're tough, you can soak a bit with pb blaster or kroils. If they look sound you also could chase the threads and call it good till re-build. I got the new studs from Moyer. I also bought a new manifold flange from them and the new bronze ell from Svendsen's. You may consider having it boiled and see if a welder can do his magic with it .. unless it's real bad ?

Good luck, Greg

[Greg]

http://www.moyermarine.com/forums/showthread.php?t=3191

might be worth shipping and a bottle of Napa Valley juice ..

Greg

[keelcooler]

I ran into the same problem.With only a few manifold stud threads showing,I ended up stripping a stud.
I went ahead and replaced all three with new longer studs from MMI. A snug fit manifold to block is a must have item.

[hank]

I pulled my manifold yesterday, pretty straight forward - soak the two exhaust flange bolts with penetrating oil before you remove them. Remove the carb, then the 3 nuts on the manifold. On mine, the front two nuts came off the studs, but the 3rd stud came out. Mine was a tight fit, so I removed the fitting from the manifold for the copper air line to the carburetor for that extra 1/4 inch and just made it.