Troubleshooting post-rebuild misfire

[Stevenph]

When installed the top of the pipe tilts aft about five to ten degrees, in order to prevent water from flowing back to the pipe and down to the dry exhaust.

[hanleyclifford]

Then the water is not being injected with a down hill path. The design is flawed and allows water back into the engine; #4 would get it the worst.

[Stevenph]

What if i added an addition two elbows to the system, like in the (crude) drawing attached?

[hanleyclifford]

The whole idea of a riser type hot section is to create a down hill path for the water and present it with maximum difficulty of getting back into the engine. The higher the riser the better. All pipe ahead of the water injection point should be wrapped. Every boat requires a custom design. This is mine:

[Stevenph]

Very helpful - thanks. I should be able to design something that will work fairly easily.

Do you have a thought on the use of the hose as a connector between the manifold and the pipe? It's only rated to 250degree F and the one i pulled off was in terrible shape (the one in the photo is a new replacement). Do most have their pipes directly attached to the manifold like in yours?

The only flexible hose rated higher that i've found at my local supply is a silicone hose that is over 150$ for the minimum 3ft section... rather not go that route if not necessary.

[hanleyclifford]

Your drawing represents improvement. But the section is cumbersome, made of galvanized pipe rather than black iron, and is probably very heavy. The soft section between it and the engine is dangerous. If there is any question about angular torque on the manifold and studs, support should be provided as you see in my picture. The section should be wrapped and never supported on a bulkhead. I recommend you 86 that system and design your own.

[Stevenph]

I'll take your recommendation - this design does all of those things wrong, too heavy, not taped, supported on the bulkhead, etc etc.

I'll come up with something tomorrow, will let you all know how it goes.

Thanks again.

[hanleyclifford]

Here is a classic design sold by Moyer Marine in the on line catalogue.

[Stevenph]

This design has a much shallower rise than mine - but it's correct that the rise needs to go above the waterline? Does the wet exhaust hose need to enter the system above the waterline?

[hanleyclifford]

Originally Posted by Stevenph

This design has a much shallower rise than mine - but it's correct that the rise needs to go above the waterline? Does the wet exhaust hose need to enter the system above the waterline?

If you can get the rise above the waterline that is excellent and means you don't need to worry so much about syphoning, but not all boats allow for that. The discharge from the water lift will typically be below the water line (hence the need for "lifting" the water up to the transom). The discharge at the transom should ideally be above the water line at cruise, but there are many boats that discharge under water successfully - I personally don't like it. But make sure the hose runs down hill from the poop deck to the exhaust thru hull so you don't get water from a following sea.

[ndutton]

You may find this thread useful, found in the Drawings and Schematics forum category.

[Dave Neptune]

Steve, use no rubber on the exhaust until well AFTER the water has been injected ON A DOWN HILL PATH!

You bought a poor patch and it need to be fixed for safety's sake!!then a couple feet more pipe then the rubber hose (exhaust rated) can be used. Your exhaust manifold runs well over 500 degrees when there is a load on the engine NO RUBBER where theres heat!

Use pipe fittings from the manifold to the injection

Dave Neptune

[edwardc]

Originally Posted by Stevenph

This design has a much shallower rise than mine - but it's correct that the rise needs to go above the waterline? Does the wet exhaust hose need to enter the system above the waterline?

If the water injection point is above the waterline, that's great. If not, it's still ok but the water line itself should then be routed to have a loop that goes above the waterline and have a siphon break valve there.

The important thing is that the water injection point should be at least 4" below the bottom edge of the hightest point in the loop. More is better if you can desigh it. When I did mine, I put it a full 12" below.

[Stevenph]

This all seems to make sense - i'm getting my head wrapped around this whole project that i had no idea i was about to embark upon (welcome to boat ownership...)

The only thing i'm not quite %100 on is when a waterlift is necessary - from the diagrams i've seen here and elsewhere, a waterlift is necessary when the manifold and its outputs are below the waterline?

I have plenty of room above the engine to go well above the waterline with piping and tubing, but am I correct in understanding that that is not enough?

[hanleyclifford]

Certainly you can run without a water lift; right now I'm working on a Chris Craft with no riser or water lift. But if you do this be prepared to start your engine against a flooded exhaust hose (bottom of the run). The water lift gives the engine a little airspace at start up before it begins the uphill battle. The 60 HP Hercules B does it ok - the 30 HP A4, not so much.

[ndutton]

Steven, please research information on this forum regarding standpipe exhaust systems and determine if your boat can fit one. Basic requirements are a clear shot from the engine up to nearly the hull and deck joint and from there a continuous downhill run to the exhaust outlet preferably near the center of the transom and above the waterline. If these conditions exist, since you're replacing the exhaust system anyway you have the opportunity for a superior system.

Well designed waterlift exhaust systems are an affordable alternative to standpipes when the above conditions do not exist or are otherwise unmanageable.

edit:
You will likely find no better information regarding marine exhaust systems than right here on this forum.

[edwardc]

+1 on the standpipe. If you can fit one in, its the best system, as it can't backflood the engine, and produces less backpressure than a waterlift.

[Stevenph]

Installed the new exhaust system yesterday, fired it up today and i'm good to go! Runs smooth and quiet, all 4 cylinders are humming away nicely. I have a few water leaks to solve but other than that i feel great. I'll post some pictures when i get the chance.

I do have a question about the off-gassing of galvanized steel - i've read about it on other threads here that it's normal for the new pipe to smoke upon the first few runs (and that it's highly toxic - i have my respirator at the ready).

I haven't yet taped the hot section yet - is there any reason to wait until the off-gassing is complete to wrap the pipe? I would think that since I need to run at high temps for quite a while to complete the offgassing i would want to go ahead and wrap it now.

[Stevenph]

Hi all, sorry for the long delay, but i wanted to send a quick thanks to everyone who helped me out with my long (3 years...) process of rebuilding my A4. I solved the exhaust issue, and the temporary water pump solution is still working great awaiting the replacement oberdorfer pump.

It's been starting up and running great, and i couldn't have done it without the help of this fantastic forum. I'm putting the boat up for sale soon - i'm moving out of the city, so i made a video of the engine running you can check out at the link below.

https://www.youtube.com/watch?v=vm82...ature=youtu.be