I have a 1988 seafarer with a merc half block 3.7 ..3 of the cylinders have 170lb pressure 154 lbs 150lbs but one has 65 lbs. Is it worth running till it dies or is it worth putting new rings ? Don't have tons of money to sink in and very little knowledge with I/O and the costs involved. Also need to change the outdrive.
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Mercruzier 3.7 half block bad cylinder
- Thread starter TomHigg
- Start date
VeroWing
GreatGrady Captain
You should get a borescope (camera) and check cylinder with 65# pressure to see if there are gouges in it. If so then block will need bored out if specs allow it. May no be worth it, especially if you need outdrive also, then you have to consider "project creep". I know those 3.7s had problems with generator/alternators that were located on tip of crankshaft, and were prone to magnets coming loose and causes havoc. They need to be changed out for modern alternator. Also the water pumps were prone to start leaking after a while, and they were located on tip of camshaft, and actually would wear a groove in camshaft ends causes water to enter engine mixing with oil and causing damage. There used to be a kit available to place a sleeve over end of camshaft correcting this issue. If your block has many hours on it, plan on fixing those issues when you do engine work. You're sure to run into more issues once you pull engine and take it apart. You would probably be better off finding a more modern engine/outdrive and swap everything out. If you have room in engine compartment a good 4.3 setup would be a nice upgrade, and there are usually good used ones available if you look around. May have to change mounts around to accommodate this change though, but maybe not, and 4.3 will be a better setup for the Seafarer. If cylinders look good and you want to just do a ring change, those blocks were like half of a Ford 460 block and use the pistons, rings, etc from it. You could get a inexpensive cylinder hone tool ($20-30) and clean-up cylinder surfaces, and install new rings and bearings. Lot of work, and not sure if parts are still available, but the 3.7s were good engines when all is right. You have to decide if what is best for you.
DennisG01
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Has the engine been sitting unused for a while before doing the test? Was the engine cold or warm when you did it?
Yes it sat at least a few months....The engine was cold, actually we never got it started yet we just turned it over with starting fluidHas the engine been sitting unused for a while before doing the test? Was the engine cold or warm when you did it?
DennisG01
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I wouldn't worry about anything, yet. There's a good chance a ring is stuck simply from sitting and being cold. Wait till you get at least a few hours of running before doing the compression test, again. Wouldn't hurt to squirt a little de-carboner like the stuff Merc has - or even some Sea Foam, ATF or Marvel Mystery oil into the cylinder through the plug hole and let it sit. If you have a camera, like Vero mentioned, wouldn't hurt to take a looksee - but I wouldn't go out and buy one at this point.Yes it sat at least a few months....The engine was cold, actually we never got it started yet we just turned it over with starting fluid
What's wrong with the outdrive?
Had lots of water in it so probably seals.....I will probably just get a used one and replace.....Thank you for your helpI wouldn't worry about anything, yet. There's a good chance a ring is stuck simply from sitting and being cold. Wait till you get at least a few hours of running before doing the compression test, again. Wouldn't hurt to squirt a little de-carboner like the stuff Merc has - or even some Sea Foam, ATF or Marvel Mystery oil into the cylinder through the plug hole and let it sit. If you have a camera, like Vero mentioned, wouldn't hurt to take a looksee - but I wouldn't go out and buy one at this point.
What's wrong with the outdrive?
If I decide to just run it local in the bay do you think the engine would just seeze or slowly die ? I ask because I was thinking running it through summer and do a engine replacement offseason.You should get a borescope (camera) and check cylinder with 65# pressure to see if there are gouges in it. If so then block will need bored out if specs allow it. May no be worth it, especially if you need outdrive also, then you have to consider "project creep". I know those 3.7s had problems with generator/alternators that were located on tip of crankshaft, and were prone to magnets coming loose and causes havoc. They need to be changed out for modern alternator. Also the water pumps were prone to start leaking after a while, and they were located on tip of camshaft, and actually would wear a groove in camshaft ends causes water to enter engine mixing with oil and causing damage. There used to be a kit available to place a sleeve over end of camshaft correcting this issue. If your block has many hours on it, plan on fixing those issues when you do engine work. You're sure to run into more issues once you pull engine and take it apart. You would probably be better off finding a more modern engine/outdrive and swap everything out. If you have room in engine compartment a good 4.3 setup would be a nice upgrade, and there are usually good used ones available if you look around. May have to change mounts around to accommodate this change though, but maybe not, and 4.3 will be a better setup for the Seafarer. If cylinders look good and you want to just do a ring change, those blocks were like half of a Ford 460 block and use the pistons, rings, etc from it. You could get a inexpensive cylinder hone tool ($20-30) and clean-up cylinder surfaces, and install new rings and bearings. Lot of work, and not sure if parts are still available, but the 3.7s were good engines when all is right. You have to decide if what is best for you.
VeroWing
GreatGrady Captain
It's hard to tell, but all things are possible. If you are leaning towards that, I would do what Dennis has recommended and pouring a little Sea Foam, ATF or Marvel Mystery oil into the cylinder through the plug hole and let it sit for a day or two, then change oil and let engine run for a bit. Then while still warm check compression again.