What would you do? '74 merc 650

[jbjennings]

So I own 2 merc 650's, one running good but with JB WELD holding the water jackets together on all 3 cylinders but great even compression on all 3 cylinders, the other as of today not running good, with 2 out of 3 rings bad on the middle cylinder but having no cracks in the block/water jackets. The compression on the latter is 140, 140, and 130 on the bottom. The bad middle piston/cylinder makes more compression than the bottom cylinder! The lower unit on the bad running motor with 130 on the bottom is great.
Anyway, I was thinking I might take the good running motor with good compression apart, put the crank and pistons and such on the "good" block and make one motor that's reliable out of it. New rings and break the glaze on the cylinders.
What do you guys think? Strangely enough, when I took the exhaust cover off to look at the pistons since the motor was hotter than I expected even though it was pumping lots of water out of the tattletale, it had no thermostat or poppit valve. I have run a lot of tanks of gas through this motor never knowing it didn't have the thermo or poppit valves in it. I just rebuilt the carbs and put new crank seals in it today, and it ran perfect for about 2 miles before I came back to the launch and stopped idling nicely and at that point would fall on it's face with the slightest throttle so we went home and I found the bad piston rings on the middle cylinder.
JBJ

 

[jbjennings]

Re: What would you do? '74 merc 650

Waste of money?
rings (25$ for each piston)
Powerhead gasket set $75

I hate to junk 'em.

Just curious what you think.
JBJ

 

[MARV1]

Re: What would you do? '74 merc 650

A new or good used 4 stroke is much more reliable and will use less fuel day in and day out.... Sell them as parts.

 

[mercurymang]

Re: What would you do? '74 merc 650

A new or good used 4 stroke is much more reliable and will use less fuel day in and day out.... Sell them as parts.

Agreed but you're looking at several thousand dollars for a comparable motor.

 

[jbjennings]

Re: What would you do? '74 merc 650

I never troll---just WOT to my fishing hole, so I think the fuel savings would be slim. Also, I just don't have the money for a new motor of that horsepower or I'd do just that. Trying to hold out as long as possible. I actually like my old mercs and would like to get one right. I've priced all the parts and if my cylinders are good in my good block, and the pistons are not too scuffed in the block with perfect compression, I'm going to be out about $180 in parts. You may be right, it's probably better to just put it into a newer motor so it doesn't nickel and dime me to death trying to keep it going.
Thanks for the comments,
JBj