exhaust back pressure

[jpian0923]

Can excess exhaust back pressure cause hard starting?
Lately I have been having trouble with hard starting, also with overheating. I have narrowed down the overheating to past the point where water is injected into the hot exhaust. I know this because I removed the hose from where it enters the exhaust, ran the engine, let the water run into bilge...engine runs cool til I re-attach the hose to the exhaust. Also, it was so easy to start the engine without the hose attached to the hot exhaust. I think I just answered my own question but what next?
I think I know what next but am not sure I want the truth!

[roadnsky]

Can excess exhaust back pressure cause hard starting?
Lately I have been having trouble with hard starting, also with overheating. I have narrowed down the overheating to past the point where water is injected into the hot exhaust. I know this because I removed the hose from where it enters the exhaust, ran the engine, let the water run into bilge...engine runs cool til I re-attach the hose to the exhaust. Also, it was so easy to start the engine without the hose attached to the hot exhaust. I think I just answered my own question but what next?
I think I know what next but am not sure I want the truth!

The short answer... YES!!

The longer answer is a quote from Don...

"The Atomic 4 likes a quite low exhaust back pressure of 1 to 1-¼ psi. Our tech service experience indicates that much of the Atomic 4 fleet (my guess would be at least 70%) is suffering some impairment in performance or reliability due to some amount of elevated exhaust backpressure. Symptoms include chronic sootiness of all four spark plugs, one or two cylinders failing to work with otherwise good compression, engine refusing to accelerate accompanied by a “gagging” sound from the carburetor, engine running better with any one of the four plug leads removed (yes, believe it or not), and eventually failing to start.

Being able to read your exhaust back pressure won’t in and of itself cure the problem but given the difficulty of working on the exhaust system, it would be good to know before starting that gruesome work that you do indeed have a blockage. Difficult access on some boats can make even this suggestion a bit difficult, but the reward will be worth the effort.

In the event that you can remove the two bolts retaining the exhaust flange, some folks have diagnosed elevated back pressure by removing the bolts, propping the flange away from the manifold a fraction of an inch and running the engine for a few seconds. If your symptoms are quite profound, you should notice a definite improvement in running for just a few seconds.

If you can remove the two flange bolts, you may also be able to remove the entire hot section of the exhaust and replace it as a preventative maintenance measure without ever testing the back pressure."

Sounds like you're up for an exhaust rebuild.
The forum is full of good threads on it...

[jpian0923]

I've read thousands of them! I knew that was going to be the answer so I already got started on it. Had to remove carb and manifold to get exhaust off. My hot section is this weird elbow shaped thing though. Not sure how severe the blockage is so I'm soaking it in vinegar in hopes to salvage it. Dreading the task at hand was much harder than the actual task itself.

[hanleyclifford]

If you have gone thru all the trouble to disassemble you owe it to yourself to replace it with new black iron components, possibly incorporating an upgrade.

[jpian0923]

This is what was there. Feels heavy and looks solid and expensive. That is why I want to keep it alive. I owe it to the part!
Does anybody recognize that thing? Know it's name? Know what's inside?
I plan on removing the fittings, putting it on a bench vise, and hammer and chisel out and gunk or calcification...restore it to it's original glory.

[Kurt]

I believe that is just a type of exhaust mixing elbow - pretty sure that is the correct name. That is where exhaust gasses mix with cooling water. Hence, the exhaust gasses moving through the wet exhaust and out the back of the boat are cooled.

[ndutton]

Kurt's right, mixing elbow.

Inside it's a water jacketed elbow with the water injected in the exhaust near the discharge port. They are known to rust internally and salt encrustation can be an issue.

Due to the weight, supplemental support would be a good thing. Without it you're asking a lot of the two exhaust flange bolts.

[hanleyclifford]

Kurt's right, mixing elbow.

Inside it's a water jacketed elbow with the water injected in the exhaust near the discharge port. They are known to rust internally and salt encrustation can be an issue.

Due to the weight, supplemental support would be a good thing. Without it you're asking a lot of the two exhaust flange bolts.

Two good reasons to retire it to the "someday bin".

[jpian0923]

Well, I'm gonna give a try at restoration since I have a few hours to kill anyway. It will be good practice at rust removal, salt encrustation removal, fittings removal and bench vise usage. I should weigh it before and after. I'm sure somebody out there would want to know how much calcification weighs before a serious blockage occurs. Might even become a measuring stick for diagnosing whether a mixing elbow is good or not. Xray vision would be a better measuring stick but I haven't invented it yet.

[thatch]

jpian,
While there is nothing wrong with using this style of riser, it is considerably heavier than our normal "assembled" units, as Neil pointed out. After a thorough cleaning (both acid and prodding) it is imperative that the uphill part of the riser be checked for leaks. To do this, since we really can't see inside, connect a garden hose to the water inlet fitting and with the unit in an upright position check to make sure that water is not comming out of the engine side port. If it is, this is an indication that the riser wall has a hole in it and the unit should be disgarded.
Tom

[roadnsky]

UPGRADE!
Lighter, stronger, better, faster, etc...

[sastanley]

thanks jerry..>i had thought about posting earlier, but didn't want to come off as a jerk...glad I wasn't the only one thinking that way.

jpian - here is my setup that I built a couple years back...based on discussions since this was built, I'd recommend going all black iron...galvanized has some off-gassing issues that can be a health concern.

[roadnsky]

thanks jerry..>i had thought about posting earlier, but didn't want to come off as a jerk...glad I wasn't the only one thinking that way...

Well, didn't mean to sound smarmy or be a jerk. (:o)
Sometimes posts can come off sounding that way.
Truly, what I mean is...
You can improve your exhaust with a better, lighter fitting.
The re-build is not a bad job if you have access, AND it will last a long time.

[jpian0923]

Great advice, not jerky at all. I went to 5 different stores to try to locate all the parts for the rebuild. Finally found all I need at a Lowe's but some of it is galvanized, not all. How long will it off gas? Should I wear a respirator every time I motor??

I'll take pics when I dry fit it, for forum criticism. Will post tomorrow.

Also, I'm soaking the inside of the old setup in muriatic acid overnight to see if I can salvage it. I will try the garden hose test after that. I can hear the acid eating up something in there. Sounds hungry.

[jpian0923]

I read the "acid flush procedure" which I plan to do after installing my new exhaust. Is anybody letting this stuff flow directly into the ocean/bay? Is it dangerous to do this? I know it says to "try" to catch it in a bucket.

[hanleyclifford]

Just for future reference the best place to buy pipe is Plumbers' Supply if you have one in your area.

[sastanley]

jpian, Lowe's is where I found most of mine too. The galvanized pipe off-gassed for maybe 15 hours. I made sure to have the boat's hatches open & the engine compartment open too..I also used Permatex #2 to seal the threads, although that was probably overkill..that could have been some of the smell too. :confused:

Here's a picture of it assembled. I've had zero trouble with my replacement.
http://www.moyermarine.com/forums/attachment.php?attachmentid=1283&stc=1&d=1237686890

[Administrator]

McMaster-Carr (http://www.mcmaster.com/#) is a good option if you're forced or prefer to shop online.

Bill

[Kurt]

jpian0923 -- regarding letting the muriatic acid flow out the back of the boat into the bay ----- I'll be the bad guy here and say that I used to flush my block with acid (this is the same type of acid used in pools) at least annually when it was raw water cooled. Yes, I let it go out the back of the boat into the bay and never bothered trying to catch it in a bucket. I actually thought that exercise would be a bit more dangerous as I didn't want to get splashed with the stuff. I used to have a 25,000 gallon pool and treated the water periodically with muriatic acid. The acid would become diluted quickly in that much water and swimming could resume in 15 minutes max. So, sending a gallon of the stuff into the vastness that is a body of sea water, lake water, etc. was not a concern to me. I know the Coast Guard would not agree with this. If a fish was hanging out right at my transom when I did this, he/she might not like it either and might get a little acid burn, but probably nothing fatal as I have splashed this stuff on myself many times and washing it off with water takes the slightly uncomfortable sensation away very quickly. My theory may be flawed here as that poor fish would end up drinking the stuff - although diluted, probably not too tasty. Of course, I'm also the guy that puts 1" chlorine tabs in-line (in one of those little in-line canisters) on the head plumbing so I never have bad smells there. This is also supposedly not as "environmentally friendly" as the blue tabs they sell at the marine store (that don't work very well in my opinion). So, there you have it --- I'm bad and do these things, but I really don't believe they have any adverse consequences to the natural environment I love and play in. After all, I swam often in that pool I used to have and there was chlorine and acid in there.............

[Baltimore Sailor]

My problem with dumping the muriatic acid flush into the creek was not from the acid, but from the pure nastiness of the water coming out of there. Our bays and rivers get enough filth from runoff -- I don't see the need to add to it by putting the dissolved contents of my engine in there as well.

When I did my flush, I was easily able to run a line to position the bucket under my exhaust outflow and catch all of it. I just shut the engine off while switching buckets (one bucket in made two buckets of filth out), and there was no difficulty.

[jpian0923]

Here is my new exhaust. Hopefully the out gassing won't be too bad for too long. I'll motor with all hatches open for a while.
For the most part I did not use any tools to assemble it. I did use my body weight and some leverage to tighten the fittings. They all seem pretty tight. It was somewhat difficult getting everything tight and aligned just right at the same time, that's why I didn't use tools. Anyone think I should do otherwise? I didn't seal anything either. I read in another thread that rust will come soon and seal any leaks. Thoughts?

[JOHN COOKSON]

When I rebuilt my hot section I put a union right after the manifold. It made lining up and instillation a lot easier because I could remove the plumbing to do just that.

It doesn't look like your instillation has room to add a union.

TRUE GRIT

[hanleyclifford]

Nice job. I like the "street" coming out of the flange and the water injection setup is superb. No sealer is good in this instance and hand tight is just right.

[Laker]

Baltimore ,

What did you do with the discharged stuff after you captured it ?

[sastanley]

jpian...looks good...:cool:

if you still have the pieces off the motor, I may recommend trying to remove as much of the rust off the manifold as you can, and giving it something (Rustoleum or that grey stuff you paint on to change rusty metal to primer) as a rust inhibitor. Blocking the rusty & bare metal from oxygen is key to reducing the rust cancer.

[jpian0923]

I don't have alot of room to play with where my engine is. Basically, I brought the old setup with me into Lowe's and replicated all the critical dimensions to almost exact. This way I didn't have to do any math or science related to proper exhaust systems etc... I'm putting alot of faith in the PO in this area.
It's upside down but, you get it. How important is wrapping it? I'm not planning on it.

[roadnsky]

Baltimore ,

What did you do with the discharged stuff after you captured it ?

He gave it to the water treatment facility. Post #23 in another thread... http://www.moyermarine.com/forums/showthread.php?p=32311#post32311

[jpian0923]

Still have the pieces at home. Going to boat in a minute to install it. I thought about painting the manifold but I'm sure the rest of the engine would be jealous. And, besides, I know if I paint one thing my brain will be nagging me to do the rest.

[roadnsky]

How important is wrapping it? I'm not planning on it.

Uhhh, you gotta wrap it.
I got a temp reading on mine this summer of 520º! :eek:
AND, mine was wrapped.

[sastanley]

jpian, don't worry about the jealousy...give the rest of the motor some love in due time. I hate to see old rusty parts put back on the motor still rusty..they never get any better without TLC...even if piece by piece.

The wrap is mostly about heat absorption I think..In the C-30 like I have my 'hot stack' is 1/2" from the bottom of the galley cabinet..

I have plenty of wrap left (Moyer sells it at a reasonable cost also) from the huge roll I bought at my local NAPA...I'd be happy to send it to you.

Here's a 'dry-fit' pic of my exhaust to show why I chose to go ahead and wrap it with the enclosure so close.

By the way - the lower the 'injection point' the better..any chance you can swap the short and long pieces in the three manifold pics to get the water injection point down a little (my understanding is the farther away from the cylinders?? ) :confused:

[ndutton]

If your wrap is the old material, kinda like coarse canvas (don't ask what it really is), soaking it in water before application will make the process much easier - and safer.

[jpian0923]

I finished the installation, went well. I did see a little leakage but I'm hoping rust will seal it. The only flaw in my design was the water injection hose was touching the hot section and I could smell it burning. I twisted the fitting away a couple inches and that resolved it. I reconsidered the wrap because of your advice and, It did get really hot. I do have a couple inches of clearance all around the hot section but for piece of mind...well, you know. I will do it but I want to give the galvanized a chance to off gas first. I kept the water injection at the same level as the old setup so I wouldn't have to do any math or science. Seems to be at the right level. Pipe is cool only past that point so I figure it's not going towards the engine. I will get around to painting the engine but was so excited to get the thing back together to see if it works...you know the feeling. And, besides, I'm in San Diego, it's still sailing season here and I don't want to miss it!
Thanks for all the help.

Last question: How do I get the engine temperature up now? I don't have a thermostat.

p.s. My name is Jim

[hanleyclifford]

Jim - If you don't want to have a thermostat a good alternative is a three way valve bypass to return coolant to the water pump intake. The issue of running the exhaust system dry while warming up must be addressed (in the case of a raw water cooled engine). Hanley

[ndutton]

Jim,
Looking at your manifold I'm pretty sure you have a late model engine with the thermostat housing in the head. If true, you can control your temperature with a manual bypass valve and never have to worry about a dry exhaust.

The valve kit is available from Moyer here (http://www.moyermarine.com/cgi-bin/shopper.cgi?preadd=action&key=CSOT_01_61)

The more the valve is closed, the cooler the engine runs. It acts somewhat like a manual temperature control.

[jpian0923]

I was thinking about restricting the water flow through the engine using the thru hull. Sound reasonable?
I think the moyer kit reduces temperature. I want to increase it a bit. It's at 100 or less now with the new exhaust.

[ndutton]

I was thinking about restricting the water flow through the engine using the thru hull. Sound reasonable?
I think the moyer kit reduces temperature. I want to increase it a bit. It's at 100 or less now with the new exhaust.

I've got problems with that idea. Reduced flow could damage the water pump impeller and worst of all, could dangerously decrease the cooling of the exhaust system after the water injection.

Have you considered FWC? It has benefits well beyond higher operating temps.

[jpian0923]

I have not considered FWC yet. I have only pondered spending $163 on a thermostat that still requires a valve in the by pass loop. I"ll give it some thought.

[jpian0923]

I field tested it tonight on the San Diego Bay. Went from Harbor Island Yacht Club to Coronado Bridge and back in two hours. For the first hour the off gassing was bad but I sat on the bow and steered with a long boat hook. It ran at about 120 the whole way. Problem is I can see exhaust leaking from the manifold. The gasket looked pretty good when I took it off and it stayed on the engine so I kept it there. Not sure if I tightened the manifold bolts enough but half way through the trip I tightened them some more but could still see some exhaust leaking. Would it be ok to seal it with a liquid gasket designed for high temp? Or should I just bite the bullet and spend for a new manifold gasket...plus shipping and handling?

[ndutton]

My opinion is go for a proper repair with a new gasket. The gases that are currently leaking can be deadly. You don't want to fool around with this.

[jpian0923]

Will any quality exhaust wrap do?

[jpian0923]

Good, sound advice Neil. Found a new gasket locally for $6. Also, heavy duty exhaust wrap from an autoparts store.

[Crash]

Just sounding off here...I LOVE this thread and so glad to have read everything as I intended to do the same thing to my exhaust!

Thank you guys!! :)

[ILikeRust]

This is what was there. Feels heavy and looks solid and expensive. That is why I want to keep it alive. I owe it to the part!
Does anybody recognize that thing? Know it's name? Know what's inside?
I plan on removing the fittings, putting it on a bench vise, and hammer and chisel out and gunk or calcification...restore it to it's original glory.

I was just spending some time clicking on all the many links in all these many threads about exhaust systems. I saw this posting with pic and then a few minutes later read this page:

http://www.yachtsurvey.com/exhaust_risers.htm

About halfway down the page is this picture:

http://www.yachtsurvey.com/RiserSail.JPG

Accompanied by this text:

Here's a picture that would make any surveyor's blood run cold. This cast aluminum riser is guaranteed to wreck this engine when it fails, as it inevitably must. In addition, combined with engine vibration, that long lever arm (pipe between aluminum riser and manifold) is bound to break the mount or pipe. The insulation on the down side indicates that the exhaust hose is getting too hot, so they wrapped it with insulation!!!

So you might want to reconsider the possibility of re-using that device, ever...

Of course yours appears to be cast iron or steel, rather than aluminum, but still looks like the same design.

[hanleyclifford]

Whatever it's made of, it should be disposed of. Much better options are available.

[jpian0923]

I've been soaking it in muriatic acid for a month now. I'm not giving up on it yet! :eek: (That's my New York wise guy upbringing speaking) I rebuilt the hot section already. Mostly black iron, some galvanized. It works well...and it's cheap. :D

[jpian0923]

After a month of soaking the wet exhaust mixing elbow in muriatic acid I brought it back to life. Check out the videos. You can see that all the water that goes into the elbow comes out where it should. None comes out of the exhaust input pipe which tells me that the integrity of the insides is still intact. I did a hose test upside down and right side up. Also did hose test on exhaust input fitting and that also came out through the exhaust/water output fitting.

http://www.youtube.com/watch?v=N_6x-vB9VDo
http://www.youtube.com/watch?v=_oN8wD3842U

[jpian0923]

I installed it tonight and it works great!

I had problems, with the hot section I made of black iron and galvanized, getting it installed and lined up correctly. It had water and exhaust leaks in several places also.

The mixing elbow install took me less time and hassle. It's smaller and weighs less overall and has less connections. No water or exhaust leaks either and it's cool to the touch.

Just my opinion.