[jlaskowsky73]

G'Day! I bought a 1980 PY26 last July and have been slowly bringing her back to life. I had the freshly rebuilt Yanmar YSM8 placed back in the engine compartment and the mechanic and I had a meeting this morning. He told me he wants to move the exhaust mixing elbow 10-12 inches above where it sits now because the previous owner had the problem of salt water siphoning back into the cylinder head 3 times in the last few years. He recommended I do a little research to see if this was a problem/flaw in the boat design or if it was the previous owner. The last setup was 1 3/8 exhaust hose all the way. I have changed the muffler to 1 3/4 with 1 1/2 from the mixing elbow with an increase to 1 3/4 to mate to the muffler. Out of the muffler I used a reducer to 1 3/8 to mate to the exhaust port. Any info would be helpful.

 

[Rockter]

If your siphon defence siphon break is working OK then it should not be a problem.
It should not matter what size the exhaust pipe is, if the siphon break is working.
The siphon break detects that the pressure inside the exhaust has dropped below atmospheric, and simply opens to equalise it, so killing the siphon effect.
Do you have a siphon break device fitted?
They are not expensive and it is easy to test them if you suspect the one you have is malfunctioning.
.

 

[Faster]

You say the engine is freshly rebuilt.. if it had been hard to start in previous years the water may have come from prolonged unsuccessful start attempts with the RW intake open.. pumping the exhaust system full, but never 'expelling' it.. if enough water got in there it would backflow into the engine once they quit cranking.

 

[Rockter]

Yes, if you are cranking for a while, or think you might have to, shut the engine intake through-hull for the cooling circuit. You can always open it again when the motor starts.
If you crank and crank and the motor does not start, you can fill up your exhaust and from there the water gets in to the exhaust valves. You can even bend a crank if you get unlucky.
.

 

[aa3jy]

G'Day! I bought a 1980 PY26 last July and have been slowly bringing her back to life. I had the freshly rebuilt Yanmar YSM8 placed back in the engine compartment and the mechanic and I had a meeting this morning. He told me he wants to move the exhaust mixing elbow 10-12 inches above where it sits now because the previous owner had the problem of salt water siphoning back into the cylinder head 3 times in the last few years. He recommended I do a little research to see if this was a problem/flaw in the boat design or if it was the previous owner. The last setup was 1 3/8 exhaust hose all the way. I have changed the muffler to 1 3/4 with 1 1/2 from the mixing elbow with an increase to 1 3/4 to mate to the muffler. Out of the muffler I used a reducer to 1 3/8 to mate to the exhaust port. Any info would be helpful.

Marine Engine basics..

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[jlaskowsky73]

Thanks for the replies everyone. I don't know how the previous owner treated the last engine the one I installed came from a different boat that ran real well and was overhauled prior to being installed on my boat. I don't have an anti siphon devise just a loop way above the waterline. I was just wondering if this was a design flaw that was known but unknown to me with the AMF/Paceship. I posted the same question on another forum that shares the name of my boats manufacturer, but nobody has chimed in as of yet. Thanks everyone!!!

 

[Capt Len]

You see that high loop on the cooling water hose? At the highest point jab it with an ice pick. That will let air in when the engine stops.It also lets water out when it's running so maybe better to install an anti syphon device at that point. This rocket science has been masticated on 'I hate boats' thread which may be informative .If long cranking ,you're pumping water in to the exhaust and it will fill the engine. Either shut the seacock or open a valve in the bottom of the muffler to bilge . Persoally I prefer both,particularly when leaving the vessel for any period.

 

[RichH]

Discuss with your mechanic to install a 'heat riser' ... a 1-2ft. vertical rise of black iron piping from the exhaust manifold to the relocated injection elbow. This will also require changing the path of the rubber exhaust hose to the water lift. On boats where the injection elbow is near or below the boats waterline will promote 'back siphoning' of water into the engine at shut down (and requires a well working siphon break) Having the injection elbow at well above the waterline will prevent such 'backflow' from the waterlift into the stopped/cooling engine (although it still needs a siphon break but then such is not absolutely required to work 100% of the time).

A dry-stack heat-riser is simply black iron piping screwed together with close-elbows and 'pipe nipples'; most engine dealers will have the 'conversion' - flange to NPT screw adapter flange to fit up to the exhaust manifold. Such will be hot and therefore is typically covered with 'lagging' to attempt to contain the heat of this non water cooled 'dry stack'.