Exhaust manifold studs

[scherzoja]

I have a Universal M50 and replaced the exhaust mainfold studs during its rebuild.

Getting ready to test run it and filled engine with coolant. Two days later (I let it sit to make sure nothing is wrong) I saw coolant dripping from the exhaust manifold bolts.

Turns out that the holes in the head into which the studs screw are connected to the coolant passages.

The new studs are the correct thread type (M8 x 1.25), but the non threaded part has a slightly smaller OD than the OD of the threads.

The old studs have a non-threaded OD that is slightly larger than the OD of the threads. When the old studs go in, the larger OD forms a seal, preventing coolant from leaking.

Problem is that I cannot find studs that are the correct dia/thread pitch/length and also have a non-threaded OD that is slightly larger than the OD of the threads.

Does anyone know if there is a name for the type of stud that has a non-threaded OD larger than the OD of the threaded part?

Are studs just not made like that anymore (Engine was made in 1982).

If I can't find studs to fit, I'll have to use some kind of goop sealant.

Does anyone have a recommendation of some kind of thread sealer that can withstand the temperatures of the engine head near the exhaust ports?

Thanks

[tkeithlu]

The part number is 298635 and Westerbeke has them for $6.10 each.

[tkeithlu]

Let me qualify that. Where did you get the new studs? If you got them from Westerbeke, shame in them. If you used stock studs, then my information may be of use to you. If that fails, take one of the old studs to a machine shop - turning a rod to the right diameter (if it's not stock diameter) and then cutting the threads you need should not be a big job. I don't think I'd mess with goop in this demanding an application.

[scherzoja]

Thanks Keith,

I got the replacements from McMasters. The westerbeke studs are a match for the originals, but they are too short. I made a better alternator bracket adn oil pressure manifold bracket, so six out of the 8 studs need to be ~3/8" longer

I agree, the goop will be a last resort. I'll stop by a machine shop tomorrow. I had the same problem on the V drive (Walter V drive). It's studs were 3/8, but the OD of the non threaded of my replacement studs were narrower. I ended up cleaning up and reusing the old studs on that v drive.

[keepondancin]

Have you contacted Hansen Marine, the major distributor for Westerbeke/Universal, and talk to John (I think) Hansen? very helpful people. 781-631-3282

[Cdreamin]

I've done enough exhaust stud replacements to say you should ALWAYS ALWAYS cover the threads with anti seize compound. Don't know if it will seal your issue but the next time it will be much easier to remove the studs.

[Lepke]

Many engines have stud holes drilled into the water passages. It's a common problem. I found high temp silicone to work well. When you have a bolt/stud exposed to high heat or rust/corrosion, I have found almost all will come out easily with an impact tool when a hand tool will break them off. I also use Never Seize or something like it unless a sealing problem like yours. I have rebuilt or overhauled a couple hundred engines.

[jimbunyard]

If the threads go into the water jacket there will be a leak. Small block Chevys are a common example, the head bolts threads must be coated with some type of sealant. Chevy generally recommends something like this



or this


though in a pinch I too have used high temp RTV silicone... probably better to use the correct stuff if you can get it.

[Paul54]

On the M25 engine some of the stud holes run into the water jacket. Universal offered an enhanced alternator bracket along with longer studs. Not sure if the same was available for the M50. You do need some sealer on the threads to keep coolant from leaking.