Mercruiser 3.7 (470) wont turn all the way

[Scott06]

Horrible advice. The engines, if maintained, are fine. And the power is closer to a V6 than a 3.0

Seriously just asking this not looking for an argument, then why did you take your 3.7 out ?

 

[nola mike]

Seriously just asking this not looking for an argument, then why did you take your 3.7 out ?

Needed a rebuild, and thought that a newer powerplant with with (allegedly) 50+ hp made more sense. Plus I'm a glutton for punishment. It's more powerful mid range, and much smoother (again mid range), and overall a better engine, but the 3.7 performs very well and is easier to work on/more accessable. The 3.0 is a significant step down imo. Nobody is happy by bumping down power, and parts for a 3.0 are nearly as pricy as the 3.7

 

[Bt Doctur]

Couple of options

remove the pushrods and see if all the valves are the same height.a low one is the sticking one.

 

[Scott Danforth]

The 3.7 was an OK concept, however Mercruiser fell down with the execution. We can all agree on that

Half a ford 460 with a gm flywheel and custom crank and cam, great midrange motor a step above the 2.5/3.0, and a step below the 5.0

The floating bores of the open deck block should have been addressed durring the design phase and the iron Ford head should have been aluminum from day 1. These two issues are the major downside of the motor

The heat exchanger should have been 4" from day 1.

The other shortfalls of the non-hardened cam snout and the outboard charging system can be dealt with.

Hoewever if the head gasket went and the motor sat for more than a week, (and it sat for years based on thr first post) there will be rust on the cylinder walls.

The OP has a 470, our job is to give him answers to his questions, not argue among ourselves.

Since the drive is off, the motor still wont turn, time to pull it and tear into it

Merry Christmas y'all

 

[Scott Danforth]

And if you pull the rockers, pushrods, or lifters. Label them. They must go back in the exact same location.

 

[nola mike]

The 3.7 was an OK concept, however Mercruiser fell down with the execution. We can all agree on that

Yes

Half a ford 460 with a gm flywheel and custom crank and cam, great midrange motor a step above the 2.5/3.0, and a step below the 5.0

The floating bores of the open deck block should have been addressed durring the design phase and the iron Ford head should have been aluminum from day 1. These two issues are the major downside of the motor

Yes, although i don't recall any of us on here in "the 470 club" blowing a hg. And in the grand scheme of engine repair that isn't a huge deal. Wondering how the open bore would have fared with an aluminum head

The heat exchanger should have been 4" from day 1.

Yes, but plenty of reserve with the 4"

The other shortfalls of the non-hardened cam snout and the outboard charging system can be dealt with.

Yup. I also never had to do the cam seal, and the original regulator was 30 years old when it failed. And nobody would have complained about the system if not for the price of a replacement VR

Hoewever if the head gasket went and the motor sat for more than a week, (and it sat for years based on thr first post) there will be rust on the cylinder walls.

The OP has a 470, our job is to give him answers to his questions, not argue among ourselves.

Since the drive is off, the motor still wont turn, time to pull it and tear into it

Worth pulling the head first imo

Merry Christmas y'all

You too, I'll be in your neck of the woods next week

 

[QBhoy]

Seriously just asking this not looking for an argument, then why did you take your 3.7 out ?

Not sure many won’t have had their mounts undone at somepoint

 

[Scott Danforth]

Yes

Yes, although i don't recall any of us on here in "the 470 club" blowing a hg. And in the grand scheme of engine repair that isn't a huge deal. Wondering how the open bore would have fared with an aluminum head

Yes, but plenty of reserve with the 4"

Yup. I also never had to do the cam seal, and the original regulator was 30 years old when it failed. And nobody would have complained about the system if not for the price of a replacement VR

Worth pulling the head first imo


You too, I'll be in your neck of the woods next week

If your in FL...... Swung by for a beer

 

[QBhoy]

Needed a rebuild, and thought that a newer powerplant with with (allegedly) 50+ hp made more sense. Plus I'm a glutton for punishment. It's more powerful mid range, and much smoother (again mid range), and overall a better engine, but the 3.7 performs very well and is easier to work on/more accessable. The 3.0 is a significant step down imo. Nobody is happy by bumping down power, and parts for a 3.0 are nearly as pricy as the 3.7

Must admit…I do admire guys like yourself, who keep these things running and running well. Fair play. I’d be inclined to do similar myself perhaps. But thinking about your average fella who might find himself owning one of these…the type of fella who just wants to turn up and turn the key every weekend…gets it serviced every year by a dealer because he has no interest or the ability to self maintain…it’s certainly not a good engine for these guys. My good friend had a boat with one of these in it. He was the type I’ve mentioned above. No interest in lifting the hatch to check over things before starting etc. He had a disaster of a time with it. The usual things happened. (Turns out not for the first time and had happened with the previous owner too). Had to get it rebuilt. Then it happened again. He then had to get another 3.7 put in it that a local dealer had in the workshop. Same thing happened again. This was all over a 2 year period. I had to cut short family days out dozens of times to tow it all the way home with my boat. Could just never trust it. Eventually he put a brand new 3.0 in it. Ran great since. Lost a little grunt out the hole. But not as much as I thought it might. Was down on top end by about 3/4 mph at most.
Anyway…no doubt they have a bit of power behind them. But that’s when they are running well. Just a shame that’s not often…unless your committed to go above and beyond the usual level of spanner work that your average and common GM Mercruiser requires. Merry Xmas !

 

[Thomas1981]

So I took off all rocker arms and now the engine can turn all the way. So a piston was hiting a valve. I added some oil to every valve and place back the rocker arms. Engine can still turn freely, so problems was a stuck valve.
No I have to get the starter to operate, the solenoid is stuck.

 

[Scott06]

So I took off all rocker arms and now the engine can turn all the way. So a piston was hiting a valve. I added some oil to every valve and place back the rocker arms. Engine can still turn freely, so problems was a stuck valve.
No I have to get the starter to operate, the solenoid is stuck.

you maybe able to take starter apart clean and lube it and get it working

 

[kenny nunez]

First with the piston down in the cylinder try to raise the umbrella valve seal with a small scribe or screwdriver and spray some penetrating oil over the valve stem. Get a brass flat punch and hold it over the valve stem then tap the punch with a hammer to see if the valve will move. If it moves tap it a few more times and quite often the valve spring will pop the valve back up. This has worked for me many times. If it does not want to move then the head has to come off.

 

[nola mike]

Also, remove the pushrod and make sure it isn't bent

 

[Scott Danforth]

If you have to replace the push rod, you need the exact length

 

[Thomas1981]

Happy New Year.
Engine is turning on the starter so I could do I a compression test:
1: 115psi
2: 125 psi
3: 130 psi
4: 90 psi

This is done with a cold engine, so not very reliable, just for indication.
I will replace fuel and oil so I can start the engine and do a proper compression test with warm engine.

My question. I dont like to lower compression on the last cylinder. From your experience, I this are really bad sign. Or too early to say for an engine that rotated first time after 5 years?

 

[Scott06]

My question. I dont like to lower compression on the last cylinder. From your experience, I this are really bad sign. Or too early to say for an engine that rotated first time after 5 years?

I would start it up and see 90 is normally a dead cylinder, and the 115 is pretty low too... Hard to say if rings will get freed up or if there is corrosion of valve faces or seats that prevent a proper seal. Bottom line as long as it turns freely start it up and see.

 

[kenny nunez]

The valve and seat probably have a build up of rust. Just get it running and there is a good chance that the valve seat area will clear up. If it does not then the head needs to come off.
Was it hard to free up the stuck valve?

 

[Thomas1981]

The valve and seat probably have a build up of rust. Just get it running and there is a good chance that the valve seat area will clear up. If it does not then the head needs to come off.
Was it hard to free up the stuck valve?

No, the moment I took off the rocker arm it completely closed. And after putting back the rocker it didnt hit the piston any more.

 

[Scott06]

No, the moment I took off the rocker arm it completely closed. And after putting back the rocker it didnt hit the piston any more.

I would think that means the lifter for that valve may have been stuck in the bore. Not sure if it it is an interference engine or not

 

[jhamblett]

Mine from the other day, hope the valves loosen up, cold engine