1972 Mercury 650

[shipfloats]

Hello,

I have two merc 650's one a '72 and the other is a '76....basically I put the two together to create a good one....the lower unit (gears) on the '72 was already bad and now it's done so I am going to switch it out with the '76. everything appears to be identical and mounts perfectly. the only difference is that the cooling flow runs on the inside of the exhaust tube within the midsection on the '76, but is sprayed on the outside of the '72.

Does it really matter how the water leaves the power head...will it all drain the same whether it's leaving inside the exhaust or not within the midsection?

I did check the '72 over many times to ensure that a component wasn't missing causing it to diver the flow to the outside of the exhaust, but it appears that's the way it is suppose to be.

any advice would be greatly appreciated...

thanks

 

[Laddies]

Re: 1972 Mercury 650

At the time it was manufactured the 72 had a tube in it to, I have seem several in late years without them it don't seem to hurt them. Heres a parts breakdown for the 72. http://www.mercruiserparts.com/Show...54&bnbr=15&bdesc=DRIVE+SHAFT+HOUSING+ASSEMBLY

 

[Starppy]

Re: 1972 Mercury 650

I do know that the two used a different exhaust plate. 72-75 took one exhaust plate (last revisions was 74007A1) and the 76 took a different one (last revision 73712A3). I have not actually compared the two different designs so I can't say for sure what the differences are. The lower units should be the same though and they should vent water and exhaust the same. Could it be that you have a blown gasket either between the powerhead and exhaust plate, or a crack in the plate?

 

[Laddies]

Re: 1972 Mercury 650

The lower units on both motor use the same exhaust grommit so the two will interchange as the old and new exhaust tube will plug into same grommit.

 

[Starppy]

Re: 1972 Mercury 650

Agreed that they are the same (I believe they use the same exhaust tube as well), but they should be expelling the water and exhaust in the same manner, through the exhaust tube and out through the prop. It could be that the water spray he is seeing outside the tube could be coming through a leak in the pressurized inlet side of the water jacket.

There is a reason why there were 6 different revisions to the exhaust plate from 72 through 76. 1972-75 58909A4, 64965A4, 65354A4 and 74007A1. 1976 72268A1, and 73712A3. Mercury had a problem with them cracking and leaking around the gaskets. When they did it would "spray" the water at a pretty good volume. The bigger issue is that once they start to leak, the water jacket loses pressure and water doesn't get to the top cylinder which could cause a scorching. So when shipfloats says it is "spraying" water onto the outside of the exhaust tube I can't help but wonder if it isn't an issue with the exhaust plate or gaskets.

 

[shipfloats]

Re: 1972 Mercury 650

thank you kindly for all the feedback. I had replaced the exhaust gasket between the midsection and the powerhead, the gasket plate is not cracked. It is visable where the water comes out of the powerhead and is diverted thru chanels on the top of the midsection to flow water to the outside of the exhaust tube. The way the channels are, the water can not reach the inside of the exhaust tube. That is what is confusing me. What I should have done in the beginning is take the power head off of the '76 to see how the water is being channelled to compare the two. The tell tale on the '72 sprays water well so I don't think I have low water pressure with respect to cooling the powerhead. I hope anyway.

thanks again,