"I have a 1972 650 Mercury 3cy
"I have a 1972 650 Mercury 3cyl. I got it from a guy who had the powerhead rebuilt due to a weak #1 cylinder after a boat swamping. (I later found the water output tube plugged with dried mud, which is how I think he got into problems) I got the head from him and remounted to lower unit as-is. I ran a few hours with it and it was running poorly on full throttle, so I took it to a marine repair to have it tuned. They supposedly tuned it up (last season) and I ran it for about two weeks and it seemed to run always great. I always saw what looked like a solid stream of cooling water ejecting from it, but he told me that I still needed a new impeller. I pulled a skier with my 16ft boat no problem. This year I took it out once and it ran OK for a while (half hour) then would not develop any power when pushed to full throttle. I was on vacation and could not get any marine mechanic to look at it, so I tried checking everything external to it (spark, fuel, distributor, coil, wires, etc). I was pretty sure that it was a sticking float/needle on one of the carbs because when I pumped the ball hard, gas would leak from the carb throat.
But, every once in a while over several days, it would all of a sudden start running fine for a while at a time. (hence I still thought carb, but wasn't about to remove them in the water, and I didn't have enough tools with me.) It did sound slightly rough, and was still rather low on top speed power.
So I took it to him for a checkup and he informed me that #1 cylinder was again low in compression. The $1200-$1500 for the rebuild he quoted me was more than I was interested in, so I took it back and decided to work on it myself. I've rebuilt many car engines, but this is the first time I've done any major engine work on a boat. I ran a compression check myself and found 1-2-3: 35-135-145, so I guess I believe him. I squirted some 80weight oil into #1 and got 150psi out of it. I am wondering if this means that the cylinder is probably not too far gone for a rebuild if some oil (heavy oil I realize) got me that much increased pressure. I hate to tear it down if it is probably hopeless.
I'm afraid if it was rebuilt or rebored once ( I have no way of finding out what the first mechanic did to it) I will not be able to get another rebore out of it, and I assume that the blind bore design cannot be sleeved by any machine shop. I looked through the exhaust port and the rings had no spring and were pretty well stuck to the piston. The engine never seized while I ran it. I don't know why this problem happened again, unless it was the few hours I ran it with the old impeller, although it looked like it was squirting OK to me. Is there any marine machine shop I can send the bare block to that will not gouge me?
Also, how can I remove the flywheel without the "special Mercury flywheel removal tool"? Or how can I get one? Do I need any other really strange tools, or are my basic engine overhaul tools all I need? I just ordered and bought the Merc. factory service manual.
Also, should I replace all pistons, or just the one that's bad? Do I need to rebalance it, and what's the best way to remove any weight from the piston/rod assembly?
If anyone is still awake after reading all this, I appreciate it. You can either post, or send me email at: [email protected]
Thanks,
John
Rochester, NY"
"I have a 1972 650 Mercury 3cyl. I got it from a guy who had the powerhead rebuilt due to a weak #1 cylinder after a boat swamping. (I later found the water output tube plugged with dried mud, which is how I think he got into problems) I got the head from him and remounted to lower unit as-is. I ran a few hours with it and it was running poorly on full throttle, so I took it to a marine repair to have it tuned. They supposedly tuned it up (last season) and I ran it for about two weeks and it seemed to run always great. I always saw what looked like a solid stream of cooling water ejecting from it, but he told me that I still needed a new impeller. I pulled a skier with my 16ft boat no problem. This year I took it out once and it ran OK for a while (half hour) then would not develop any power when pushed to full throttle. I was on vacation and could not get any marine mechanic to look at it, so I tried checking everything external to it (spark, fuel, distributor, coil, wires, etc). I was pretty sure that it was a sticking float/needle on one of the carbs because when I pumped the ball hard, gas would leak from the carb throat.
But, every once in a while over several days, it would all of a sudden start running fine for a while at a time. (hence I still thought carb, but wasn't about to remove them in the water, and I didn't have enough tools with me.) It did sound slightly rough, and was still rather low on top speed power.
So I took it to him for a checkup and he informed me that #1 cylinder was again low in compression. The $1200-$1500 for the rebuild he quoted me was more than I was interested in, so I took it back and decided to work on it myself. I've rebuilt many car engines, but this is the first time I've done any major engine work on a boat. I ran a compression check myself and found 1-2-3: 35-135-145, so I guess I believe him. I squirted some 80weight oil into #1 and got 150psi out of it. I am wondering if this means that the cylinder is probably not too far gone for a rebuild if some oil (heavy oil I realize) got me that much increased pressure. I hate to tear it down if it is probably hopeless.
I'm afraid if it was rebuilt or rebored once ( I have no way of finding out what the first mechanic did to it) I will not be able to get another rebore out of it, and I assume that the blind bore design cannot be sleeved by any machine shop. I looked through the exhaust port and the rings had no spring and were pretty well stuck to the piston. The engine never seized while I ran it. I don't know why this problem happened again, unless it was the few hours I ran it with the old impeller, although it looked like it was squirting OK to me. Is there any marine machine shop I can send the bare block to that will not gouge me?
Also, how can I remove the flywheel without the "special Mercury flywheel removal tool"? Or how can I get one? Do I need any other really strange tools, or are my basic engine overhaul tools all I need? I just ordered and bought the Merc. factory service manual.
Also, should I replace all pistons, or just the one that's bad? Do I need to rebalance it, and what's the best way to remove any weight from the piston/rod assembly?
If anyone is still awake after reading all this, I appreciate it. You can either post, or send me email at: [email protected]
Thanks,
John
Rochester, NY"