Repairing an Uneven Exhaust Manifold

[boboskips]

Now I have two places to show my ignorance :)! Anyhow here is my question.

I read through Ratwell's article and have followed it step-by-step and found it excellent.

http://www.ratwell.com/technical/Exhaust.html

However, my left Heat-Exchanger was pulled from a salvage yard bus and the one of the manifold surfaces is pretty uneven (I'll post a pic when I get home).

I'm sure that if I filed the manifold down to be even, I would have to substantially file the ears down to make everything join properly.

My question:

Would it be ill advised to apply some JB Weld to the divot in the exhaust manifod and subsequently file that to create a clean/snug join?


Thanks~
___________

[spiffy]

Would it be ill advised to apply some JB Weld to the divot in the exhaust manifod and subsequently file that to create a clean/snug join?

I am going to say don't do it....that is one place that you do not want any leaks.

Some info on the year and engine set up would help us help you.

[boboskips]

Ahh sorry I usually have that info in my Sig (not yet setup)

73 Bus, pretty much all stock, except the PO removed the Emissions Control setup.

[boboskips]

My main concern with the JB Weld fix is that it might get too hot at the manifold/head point and cause it to break down. I think JB weld is good up to 600*F?

[spiffy]

The temp thing would worry me too, although you are in a better position then those of us with the later exhaust set up.....you may want to find a part that is in better shape...IMHO.

That manifold to head seal is mucho importante to get right....an exhaust leak there can toast your valve/valve guides.

[chitwnvw]

Why does a leak toast the guides and valves?

[spiffy]

Why does a leak toast the guides and valves?

Someone can probably explain this much better then I can...but it goes something like this....the super heated exhaust instead of going through the system and out the tail pipe just sits there and acts like a blow torch right under you exhaust valve.....the extra heat causes things to stretch more and also does not let your cooling system do its job. This extra stress over time can cause parts to move that really shouldn't be moving or otherwise creat less then optimum tolerances around your valve stem and valve seat.

[Adventurewagen]

Why does a leak toast the guides and valves?

Someone can probably explain this much better then I can...but it goes something like this....the super heated exhaust instead of going through the system and out the tail pipe just sits there and acts like a blow torch right under you exhaust valve.....the extra heat causes things to stretch more and also does not let your cooling system do its job. This extra stress over time can cause parts to move that really shouldn't be moving or otherwise creat less then optimum tolerances around your valve stem and valve seat.

It can even destroy your carbs. I had a really bad leak on #3 and you can really see it in the carb, where it was backfiring right up the venturi. Luckily I caught it without running it like that for a long time.

Exhaust leaks suck. I just got a new set of gasket material for my merged header called Remex that is supposed to be the shiznit. It looks like graphite and is super thick. You bolt it in and it compresses well over 50% of it original thickness. Some of the guys and the shop who race said it was the ONLY gasket material they've used over all their years racing that did't blow after a race or two.

I'll post some pics of the stuff and let you know how it goes. I guess the company can make up any gasket you want and maybe if we get a group buy together we could order up a bunch of the small gaskets for our heads.

[vdubyah73]

I'm not sure I understand what you mean by fileing the ears down. How deep is this divot. There is some room under the ears they don't really seat on anything. Just get a good sharp file that will be long enough to lay flat across both manifold inlets all the time you're stroking the file back and forth. Resist the urge to put all your down pressure on the munged up surface. You want to try and remove an equal amount from both sealing surfaces, it doesn't have to be rocket science perfect though.

Bill

[boboskips]

I'm not sure I understand what you mean by fileing the ears down. How deep is this divot. There is some room under the ears they don't really seat on anything. Just get a good sharp file that will be long enough to lay flat across both manifold inlets all the time you're stroking the file back and forth. Resist the urge to put all your down pressure on the munged up surface. You want to try and remove an equal amount from both sealing surfaces, it doesn't have to be rocket science perfect though.

Bill

Well I took some measurements and the manifod with the divot is already substantially (1/16 of an inch) shorter than the other one. This would require me to file that 1/16 (to match up the two manifolds), plus about another 1/16 (to remove the divot and make both sides match) off of both sides. According to Ratwell's site, if you file too much off the top, the manifolds won't seat properly. He suggests that you'll then have to file the ears down so that you have a clean join.

I called a few machine shops and they are gonna take a look at it tomorrow. If you think I can get away with just filling it down + or - 2/16 of an inch without messing with the ears then I won't bother taking it in.

[Amskeptic]

If you think I can get away with just filling it down + or - 2/16 of an inch without messing with the ears then I won't bother taking it in.

You can easily file it down with a big enough file to reach both manifold pipes. Check for true with a thick piece of mirror glass covered with 320 grit sandpaper, look for sand marks that are consistent across the entire surfaces. Then wash the manifolds out with soapy hot water followed by compressed air if you have it. You might also want to enlarge the stud holes a bit. And you are correct, you might need to file down the ears a like amount. I had to spread my pipes 1.5mm by means of a bottle jack against two breaker bars inserted into the pipes to get that EZ Slide feeling onto the head studs that promises you a clean installation.

A major leak at the manifold/port does not commonly ruin valves in a stock bus. There is a scavenging moment at the end of the exhaust stroke (more noticeable with aggressive cams) that can suck in cold outside air that supposedly can lead to thermal stresses along the perimeter of the valve, it is a very short distance from the port to the valve. That sort of damage doesn't really happen with stock engines that have minor exhaust flange leaks, they usually drop valves for other reasons.
Colin
(many of the 1700 air-injection heads started life with cold fresh air being pumped into the hot exhaust ports for hc co emission reduction)

[chitwnvw]

You might also want to enlarge the stud holes a bit. And you are correct, you might need to file down the ears a like amount. I had to spread my pipes 1.5mm by means of a bottle jack against two breaker bars inserted into the pipes to get that EZ Slide feeling onto the head studs that promises you a clean installation.

Would a failure to enlarge those holes and spread those pipes put undue pressure on the studs making them more likely to fail?

(yes, the wheels are turning)

[Amskeptic]

You might also want to enlarge the stud holes a bit. And you are correct, you might need to file down the ears a like amount. I had to spread my pipes 1.5mm by means of a bottle jack against two breaker bars inserted into the pipes to get that EZ Slide feeling onto the head studs that promises you a clean installation.

Would a failure to enlarge those holes and spread those pipes put undue pressure on the studs making them more likely to fail?

(yes, the wheels are turning)

As of yesterday's snapped exhaust stud with the copper ring that was half twisted into the port, I'd say torsional stress from damaged threads is not good and neither is being bent sideways. If you have to hammer the exhanger on, the threads get mashed, you under torque the nuts which are dragging, then a leak will compel you to tighten it some more, and you have a tight stud being pulled sideways under high heat. . .
Colin

[vdubyah73]

Enlarge the holes large enough for the manifolds to slide on with a little wiggling, but not so large that there isn't enough surface for the nuts to torque up to without trying to fall into the holes.

Did that make sense?
Bill

[Amskeptic]

Enlarge the holes large enough for the manifolds to slide on with a little wiggling, but not so large that there isn't enough surface for the nuts to torque up to without trying to fall into the holes.

Did that make sense?
Bill

Yes. Use washers under the nuts, even if they are self-locking. They will help keep the flanges clamped.
Colin