I removed the exhaust and intake manifolds tonight. I am replacing the old gasket because there seemed to be a little (very little) dusting of carbon just above one area of the exhaust manifold.
When I cleaned everything up, and examined the exhaust manifold, I noticed some lite scaling on the surface that would be facing the new gasket.
I suspect I should have this resurfaced at a local machine shop to make certain of the seal. Any thoughts? The errosion of the casting is very limited and only at one of the five exhaust ports of the mainfold (diesel). The head looks like new. I examined the manifold with a straight edge and at a single spot I could see a little light. But the majority of the surfaces look very good. Nevertheless, this must be the point of the leakage.
Has anyone else had exhaust manifolds re-surfaced? I have never done that before, usually just replaced them if problems develope, and maybe that would be the correct fix. Thoughts?
Someone posted here a while back (was it you?) about a high temp JB weld product for repairing cracks in exhaust manifolds. I'm not sure how much confidence I'd have in that application, but for what you need it might be fine. All you need is something to sit in there and take up the space. It'll be compressed in there good by the bolts and surfaces. Maybe something like that could do the trick?
If you were going to have them surfaced, I'd first have the low spot filled with brazing or something (ask a local welder about what would be best for cast iron), and then just machine off the filled area to make it level.
Just machining the face, and the resultant thinning of the flange, might be asking for cracks.
Actually, I am a little surprised that you might use JB. I suppose it is OK. Is this "The" Dave?
At any rate, I went to the machine shop, and showed the owner of the shop my concern. He said, not a problem,he could take a couple of thousands off the exhaust manifold. I than told him, whatever he took off the exahust manifold, I wanted him to remove from the intake manifold (easily measure on both) - since they use the same bolts on the head. He measured a few things but concluded that I did not likely need to do that. "The washers will compensate for the slight differences."
I went home, chatted with the only other G owner in town (also has a diesel) who shared his own tale of woe related to not equalizing these two surfaces relative to the attachment points.
So, I am headed back to the machine shop and have him consider this issue again. I really do not want to have to shim under the nuts to keep things in place, or to use even hi tech goop.
Incidently, I have no cracks, just a very minor exhaust manifold errosion at one point. A clean surface should make for a tight fit.
I just had a look at my engine. The gasket looks like a triple laminate and is fairly thick. My G came with a new exhaust manifold, gasket and bolts. There does appear to be some level of uneven pressure along the gasket. In the areas where the intake manifold contacts the gasket there is a very slight separation between the three laminates of the gasket suggesting that perhaps there is a little more pressure being applied. This may change as the exhaust manifold heats up.
The downside of milling your intake is that if you eventually need a new exhaust manifold where will you be then? I'd say give it a try with a new gasket and flattened exhaust manifold and see if it leaks(doubt it will). There must be some technical literature concerning the limit to which you can mill down the exhaust manifold. Now I wish I had ordered the engine manual with the rest of the stuff!
__________________
Greg S.
'85 300GD
'73 Unimog 416 Doka
I went back to the machine shop and considered this whole matter more with him. As I looked at the two manifolds, it dawned on me that if both surfaces are machined smoothly, I would prefer the exhaust manifold to be a little bit "thiner" (that is if it can not be perfectly the same as the intake mainfold). I can easily adjust the intake manifold position by careful grinding the softer metal where the washer meets the two manifolds. This will allow me to fine-tune the tension and make it as even as I care to achieve. I am sorry I do not have a photo to offer, but those with diesels will be able to picture what I am trying to say.
Re: Good thoughts - yes, it is a fairly thick gasket.
Why not use an exhaust assembly paste cured with a blow-lamp after assembly?
I had a cracked exhaust manifold on a 280GE. It was brazed and machined flat beautifully but, unfortunately, no longer fitted the fixing spacing properly, so I had to buy a new one anyway.
Actually I don't understand how the M110 engine arrangement is supposed to work anyway - the head is ali and the manifold cast iron so you would expect something to crack and it does.
However on OM616/7 engines in vans I haven't had a problem (but maybe only because I don't look too closely!).
Hi Seamus,
My diesel manifold just had a small leak between the manifold and the gaske...
Hi Seamus,
My diesel manifold just had a small leak between the manifold and the gasket. And the manifold is not cracked, but there is a small amount of errosion that has allowed a small amount of leakeage.
I am trying to avoid using any sealers since these parts should be made true enough to work without these items.
I think machining them into specifications, and making sure the two manifolds are fairly close in "thickness" will allow me to afix them both to the head with enough uniform pressure to remove all potential leaks. As Greg noted, the gasket is fairly thick and forgives some of the irregular features on the surface, and even the tension differences between the two manifolds. If I can avoid glue, I will.
I will let you know how this all goes together tomorrow when Hanz-the-machinist finishes the project. He had it all bolted-up in his jig this evening - with that look of determination, that it will be perfect, in his eye. [:)]
Re: JB weld!!!! I think I am having the big one...!
I don't understand your panic at the idea of filling the low area. The idea is to simply repair the defect and not engage the domino effect that you've been introduced to by others. The exhaust paste that comes with those muffler bandages is a good idea too (like Seamus said). Clean the area up with a little sand blasting, spread the paste on, bake the assembly in a 500 degree oven, and use emery paper on a flat board or stone to even up the surface.
No washers, grinding, machining other parts, chances of increased cracking or warping of thin parts, blah blah blah.
The simplest and most reliable things are all the extra things you DON'T do.
Dave, I should explain: There is a long history in my family of one brother fixing things ...
Dave, I should explain: There is a long history in my family of one brother fixing things "correctly" (me) and my brother, who likes to use glues, pastes, goop, beer cans, radiator stop leak measure sounding like alchemy, and any shortcut he might conjure up in the garage. You got caught up (without knowing it) with your JB weld suggestion, in our years of humor over our distinctly differing approaches to things mechanically.
I am sure, the JB weld is a perfectly workable approach, I am just one of those goofy folks who tries very hard to put things back the way they were when new. I am as much a restoration buff as I am a 4 wheeling driver type. I have restored everything from Model T, British sports cars, MB limo, sedans, and some Parkards with a friend. I come to this vehicle with some of those "bring it back to original" attitudes.
Does the context help to understand my comment. Hope so. I have used JB in the past on cars that I am not resoring. Good stuff.
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