Alpha 1 Exhaust 4-cylinder

[stephensackro]

Just bought my first Mercruiser I/O and would like to know how the exhaust on a Alpha one drive unit (1986) works. I always thought that all of the exhaust gases and cooling water all went out threw the center of the prop. When the engine is at idle, the exhaust appears to come from the bottom of the yoke/transome area. There are two holes about one inch in diameter on the bottom of the yoke where the exhaust and water seem to come out. When I saw all the bubbles rolling up the transsom, I thought that maybe my bellows came off or had a tear in it but it appears to look ok. Is this normal and how is it suppose to work?

 

[jimh1626]

Re: Alpha 1 Exhaust 4-cylinder

I believe that is correct, but you should have some coming out the prop also. I have an 88 and it comes out each side at the top of the drive and a little out the prop. But there are more knowledgeable people than me on here.

 

[ziggy]

Re: Alpha 1 Exhaust 4-cylinder

There are two holes about one inch in diameter on the bottom of the yoke where the exhaust and water seem to come out.

yep, those are idle relief ports. when at idle,
exhaust gases and water exit through these holes + out the prop hub.

this is a mc-1 drive. a pre alpha, your's will be the same. water exits 4 places. the prop hub, the pee hole and both sides of the transom via the idle relief ports.

 

[thumpar]

Re: Alpha 1 Exhaust 4-cylinder

Yep all normal. I was concerned when I first got mine also.

 

[stephensackro]

Re: Alpha 1 Exhaust 4-cylinder

yep, those are idle relief ports. when at idle,
exhaust gases and water exit through these holes + out the prop hub.

this is a mc-1 drive. a pre alpha, your's will be the same. water exits 4 places. the prop hub, the pee hole and both sides of the transom via the idle relief ports.

Is there some sort of flapper relief valve in there that routes the exhaust gases either down the drive leg or out at the bottom of the gimble mount or does it simply work on a back pressure basis ? At idle the exhaust gasses would have to exert more force in order to push the gases two feet under water and come out threw the prop so they would exit at the bottom of the gimble instead. When your underway the ventury action of the prop hub acts to suck the gasses out? Does that sound right? Also mine does not have a pee hole, or I can't see it because it might be plugged up ??