New hot section: Do I need to remove exhaust flange?

[ernst]

This is probably a stupid question but I have never been known to be shy to ask. So here goes:

I discovered today a hole in the hot part of my exhaust system. All the way at the top, where the nipple meets with the 90deg elbow.

You may be surprised but I was actually happy to find that! I had noticed increasing amounts of exhaust fumes in the cabin and had the 'fumes' detector in the engine room going off after running the motor for more than 15 minutes or so. I was getting concerned that this was due to blow-by (even though I have the Indigo PCV installed) and that my good old A4 was on its last gasp. Compared to that scenario, replacing the exhaust seems a very desirable option!

I actually had built the whole system myself, according to my records in 2004. I don't have pictures but it is very similar to many others that I have seen here: a close nipple into the exhaust flange, then an elbow, up for 5", another elbow, horizontal 3" nipple (this one has the hole), final elbow pointing downwards, and then down to water injection and Vetus muffler. All in black iron, except below water injection where I used galvanized.

I already was at Home Depot and bought identical replacement nipples and elbows. When I started to plan mentally the steps, it struck me that I am not sure why I even have to remove the exhaust flange.

Can't I just unscrew the short nipple from the flange, and leave the flange itself untouched and on the manifold???

This would have clear advantages: I would not risk breaking any bolts, and more importantly, I would not need a new gasket. I know it is easy enough to buy one from MMI but having to wait for it means no sailing next week.

So, what am I overlooking? What is wrong with the idea of grabbing the short nipple (to be replaced anyway) with plyers or something and turning it out of the flange?

Thanks!

[67c&ccorv]

It is going to depend upon the degree of rust built up on the threads of the flange and the hot section.

I am assuming you used cast iron pipe and therefore there is likely a lot of rust build up?

Pics would help greatly.

And you will need a propane torch (being mindful of the danger of fire due to gasoline)...and a large pipe wrench...not pliers to do the job.

[romantic comedy]

I would be amazed if you could unscrew that pipe. As far as I know it would be iron pipe, and not cast iron. I guess it would not hurt to try though.

[ernst]

I would be amazed if you could unscrew that pipe. As far as I know it would be iron pipe, and not cast iron. I guess it would not hurt to try though.

Yes, it is black iron.

Well, I am expecting that it will be difficult to unscrew but don't I have to do it anyways?

[ernst]

It is going to depend upon the degree of rust built up on the threads of the flange and the hot section.

I am assuming you used cast iron pipe and therefore there is likely a lot of rust build up?

Pics would help greatly.

And you will need a propane torch (being mindful of the danger of fire due to gasoline)...and a large pipe wrench...not pliers to do the job.

I used black iron pipe from Home Depot. My understanding is that it is just steel, not cast iron, right?

Yeah, there is some rust, obviously at least one location so much that the pipe is entirely rusted through.

Propane torch, eh? I suppose in that case the question becomes moot. If I have to heat the flange, the gasket will be, ehm, toast anyways and I have to take it off. Hm.

[romantic comedy]

I redid my exhaust this year. I had to take the flange off and put it in a vice. I ground off the pipe off with two inches sticking out of the flange.

I heated it very hot with MAPP gas, but no luck. I had to put a hack saw thru the center, then reassemble it, then cut the pipe to the threads. I then used a chisel to collapse in in on itself. It worked well, and the flange threads were not damaged.

I would suggest that you at least try to loosen the manifold bolts. You never know. This is also a good time to freshen up the studs, or bolts. Worrying about the gasket is a luxury. I keep all engine gaskets as spares. Not the head gaskets, but I should. That is not much help for you now.

You can also wait a bit, right? If the hole is small, can you can make a patch with a hose clamp?

Remember that things always take at least twice as long and cost at least twice as much.

Good luck!!!

[romantic comedy]

My understand is that black and galvanized are the same ductile iron. I could only find some black iron locally. I needed a custom length nipple, and had it cut in galvanized. I just sanded of the galvanized finish.

Actually the black iron was not black, but unpainted. It looked like bare iron. I sanded it and coated everything in heat resistant paint. If you use another coating, you need to sand to bare metal anyway.

[hanleyclifford]

I've never had much success unscrewing those nipples from the flange. Usually you have to get it all off and start from scratch. Be careful putting a lot of torque on that nipple. If you break a flange stud you have increased the job a lot. I think it's best to use the opportunity to upgrade to a new flange from Moyer Marine, which flange will have the pressure test port. If you're not already using studs on the manifold to flange this is a good time to change over.

[ernst]

I've never had much success unscrewing those nipples from the flange. Usually you have to get it all off and start from scratch. Be careful putting a lot of torque on that nipple. If you break a flange stud you have increased the job a lot. I think it's best to use the opportunity to upgrade to a new flange from Moyer Marine, which flange will have the pressure test port. If you're not already using studs on the manifold to flange this is a good time to change over.

OK, I get it!

In theory, it can be done.

In practice, after 8 years the threads will be so heavily corroded that it is unlikely I will be unable to unscrew them. And if I apply too much force, I might break a flange stud which would be Bad News.

Indeed, considering whether or not to replace a gasket is a luxury, compared to that alternative.

So I will dismantle the whole thing, starting by taking off the flange from the manifold. And then put an order to MMI for whatever parts I need.

Oh, and a question: why are studs preferable to bolts? I believe that MMI ships bolts with the new flange (http://www.moyermarine.com/cgi-bin/s...rebuilder.html), although they also sell studs (same link).

Finally: is there anything that can be done to make it easier next time? I realize that pipe dope is not going to survive 8 years of exhaust duty. Graphite on the threads?

This group is amazing! It is barely 12 hours that I asked a somewhat stupid question on a somewhat elusive topic, and I already have a half dozen highly useful answers. THANK YOU!

[ernst]

I redid my exhaust this year. I had to take the flange off and put it in a vice. I ground off the pipe off with two inches sticking out of the flange.

I heated it very hot with MAPP gas, but no luck. I had to put a hack saw thru the center, then reassemble it, then cut the pipe to the threads. I then used a chisel to collapse in in on itself. It worked well, and the flange threads were not damaged.

I would suggest that you at least try to loosen the manifold bolts. You never know. This is also a good time to freshen up the studs, or bolts. Worrying about the gasket is a luxury. I keep all engine gaskets as spares. Not the head gaskets, but I should. That is not much help for you now.

You can also wait a bit, right? If the hole is small, can you can make a patch with a hose clamp?

Remember that things always take at least twice as long and cost at least twice as much.

Good luck!!!

I did not realize how difficult it will be to get the pipe out of the flange and I will surely not muck around with MAPP in the back of the CAVE! So the flange comes off.

Patching with a hose clamp won't work, it is corroded right where the nipple meets the elbox. Muffler tape might work. I may try that.

Thanks!

[ernst]

OK, some more browsing in this great section gave me answer to at least one of my questions: "why are studs preferable to bolts?" Don Moyer himself answered this in his response to someone else's question:"Studs tend to be a little friendlier to the threads in the manifold than bolts do."

Duh, makes perfect sense! Not turning the bolt inside the threads under load is surely preferable. So, I suppose I will order the studs.

Still not clear if I should put some kind of anti-seize, graphite or something during reassembly.

[67c&ccorv]

I prefer to use studs.

The only way I could get my original exhaust out of the boat was to remove the exhaust manifold and pull the entire assembly of 4 feet of welded nipple and water jacket exhaust forward into the galley!

[ernst]

I prefer to use studs.

The only way I could get my original exhaust out of the boat was to remove the exhaust manifold and pull the entire assembly of 4 feet of welded nipple and water jacket exhaust forward into the galley!

Well, I think I got VERY lucky (see below).

I went to the boat today with two goals:

1) to take pictures, since some people here wanted them,

2) to take off the exhaust.

I did (1) but I cannot upload them to this page. I tried to 'attach' them but I am getting an error message, "The connection to www.moyermarine.com was interrupted." I don't know why. Sorry guys!

EDIT: I think I found a way to get the pictures across: Picasa. So, if you are really interested in viewing a hunk of rusted iron in high resolution, point your trusted browser towards https://picasaweb.google.com/ernst.n...4ExhaustRepair
I hope I set the permissions correct to allow public viewing.

About (2):

Much to my relief, the exhaust flange bolts moved after just the tiniest shot of PB Blaster! I remember that I put some high-temp composite on them (and all the other threads) when I built the thing in 2004, maybe that helped. Now the scary part: when I had both bolts off, the pipe broke in two at the crack . It was not just a small hole, as I originally thought, but it went all around the pipe. I had played with the idea of using muffler tape to get in some more sailing but I am very glad that I decided to do the right thing!

When I got the beast home, I tried to turn the first nipple in the flange (in a vise). No joy. I looked closer at the flange and noticed that it has a crack, too! I cannot be sure but I am pretty sure that it looked the same way in 2004 (funny what you remember). Nevertheless, I will order a new flange. This will also save me the chore of getting out the old pipe.

Other observations: Everything that was in contact with the hot exhaust gases (before water injection) is, ahem, toast. Not broken (other than the one place) or crumbly but welded together with no hope of getting it apart. However, I was able to unscrew the reducing piece (from 1/2" water to 1 1/4" exhaust TEE). Likewise, the piece _under_ the Tee (which was already cooled) came out nicely. The goo I had smeared on the threads may have helped again.

I also found that there was basically no corrosion in either of these two parts. There was maybe 1/4" of rusty deposit immediately where the water was injected but it was soft and I just scraped it off with a screwdriver. I will re-use both of these parts.

So, I will send my order for a new flange, a couple more gaskets as spares, and exhaust studs tonight, with the hope of getting it this week and putting it in next weekend. I saw Don also sells a high-temp coating and I will order that too. Maybe it helps, although the corrosion clearly came from the inside of the pipe and not from the outside.

So far so good.

[Al Schober]

This may be too late to help in this case, but my technique for removing the pipe from the exhaust flange is as follows: a) cut the pipe off about 1/8" from the flange, b) using a sawz-all, put two cuts on the ID of the remaining pipe about 1/4" apart, c) using a screwdriver and a hammer, remove the piece of pipe between the cuts, and d) collapse and remove the remaining piece of pipe.

[edwardc]

... when I had both bolts off, the pipe broke in two at the crack . It was not just a small hole, as I originally thought, but it went all around the pipe.

This is a very typical failure in the hot section. The nipple is exposed to some of the hottest gases, and the bottom of the thread grooves in the nipple are the thinnest point of the whole system. And its under the worst stress from the weight of the system.

I've seen three hot section failures on other boats, and they all played out like this. It's one of the reasons I went with stainless pipe when I rebuilt my hot section. Hopefully it will hold up better.