exhaust gases, where do they go?

[boat_crazee]

Hi Boaters,<br /><br />This is a question regarding exhaust gases and where they go in a Mercruiser stern drive setup. The boat has an Alpha 1 drive with the thru the prop hub exhaust. So I would expect to see lots of bubbles at the aft end of the prop during idle, right? What I'm seeing is alot of bubbling near the transom and maybe even some exhaust gas. Any thoughts on this? Do I even have a problem? Already have other problems, don't need to go looking for more, but don't want to destroy something either.<br /><br />The setup is a 1979 Mercruiser 260 with the GM 350 and an Alpha 1 outdrive.<br /><br />Thanks

 

[MFG197]

Re: exhaust gases, where do they go?

This is how I believe A1 od exhaust works. Gasses leave the combustion chamber and go into the manifolds, after the riser it mixes with water from the manifolds and travells down to the Y pipe at the transom plate, through the exhaust bellows and out the prop hub, some if not most of the exhaust/water at goes out through the two approx 1" holes on either side of the transom assebly. you can see these holes if you look at the transom area from underneith. When running the engine on muffs out the water you can really get a good look at how the system works. this is on a boat without thru hull exhaust. Anyone feel free to correct or add....

 

[Buttanic]

Re: exhaust gases, where do they go?

WWYCna7<br />You are correct, without the two bypass holes in the transom assembly there would be too much back pressure from the water at the depth the through prop exhaust is when the engine is at idle.

 

[outboardguy]

Re: exhaust gases, where do they go?

I agree the exhaust is designed to exit from the transom at idle. If the exhaust were allowed to exit the prop at idle you would overheat the motor every time you put the shifter into reverse as the exhaust gasses would then be getting pushed right past the water pick-ups

 

[imported_wildcat]

Re: exhaust gases, where do they go?

I just flushed my Alpha 1 sterndrive with Salt Away and noticed most of the exhaust coming out the 2 one inch holes on the transom. I am a newbie who has really studied the manuals to become knowledgeable about the engine. Some exhaust still came out the prop, but most was out the one inch holes with the engine at idle (500 rpm). I was really concerned until I read this thread.<br /><br />I would now like to know how the exhaust reaches these 2 one inch lines. Do these lines come off the Y-duct? I have really studied the engine and outdrive manuals and can find it nowhere.<br /><br />Thanks for any assistance. I am learning and would be totally lost without this forum.

 

[tommays]

Re: exhaust gases, where do they go?

everything happens after the y if you look at a manual picture of transome assembly it may be clearer<br /><br />how do you like the salt away<br /><br />tommays

 

[imported_wildcat]

Re: exhaust gases, where do they go?

Tommays,<br />I looked extensively at the service manual through the exhaust system and cannot find these hoses. I will look through the transom assembly section.<br /><br />The salt away works great. I just feel that if I am going to flush with water, it might as well be done with the Salt away container connected.<br /><br />I understand that the Salt Away does not hurt the environment in any way.

 

[imported_wildcat]

Re: exhaust gases, where do they go?

Tommays,<br />I give up. I searched the entire engine service manual for the two one inch exhaust lines and cannot locate.<br /><br />Did you intend for me to look at the sterndrive manual? I don't have one yet.

 

[tommays]

Re: exhaust gases, where do they go?

i have a brand x manual that does not show it but all you have to due is look at the stern and you will see the vent holes in the plate<br /><br />tommays

 

[Don S]

Re: exhaust gases, where do they go?

Wildcat, look at the bottom of the transom shield, not the manual. They are not specifically mentioned in the manual because there is nothing to repair or go wrong with them. They are just holes cast into the transom shild.

 

[imported_wildcat]

Re: exhaust gases, where do they go?

But how do the two holes in the transom shield connect to the exhaust duct? My only logic tells me that the Y-duct is connected to the transom shield and the transom shield is connected to the sterndrive via the bellows. Logic tells me that the two holes are vented from the transom shield between the Y-duct connection and the bellows connection. Please verify that I have this correct.

 

[tommays]

Re: exhaust gases, where do they go?

thats how it works its cast into the shield<br /><br />tommays