89 5.7 mercruiser inboard no start, compression all over the place

[dmohring]

I just bought a project boat with an 89 merc inboard 5.7 liter. Boat apparently ran within the last year or 2 but story I got was one day it just wouldnt start. no start but turns over with spark. Checked compression and got the following.

cyl 1 140 psi
2 0
3 30
4 40
5 60
6 40
7 90
8 120

I was wondering if the timing chain jumped a link would I see this kind of variation? Then I started seeing blogs about leaking risers. I pulled all plugs and some have a little rust. So could be that water has be leaking down through valves? the oil does not appear to have any water in it. So... what next? thanks.

 

[andrewterri]

The experts will chime in tomorrow but if I remember correctly the 5.7 is an interference engine which means the valves open into the space where the pistons travel. What all that means is if you jump a timing chain, say by over revving without a load on the engine, it would put a valve into the combustion chamber when the piston is entering the same space thereby striking the valve. I have never heard of a timing chain jumping a tooth and causing six values on six different cylinders to impact the piston. I don't think that is even possible, but might be. You could have a stuck valve or two but on six cylinders it would be very unlikely in my opinion. A warped head(s) or blown head gasket(s) would explain what you have going on. Only thing I would think that would cause that is an overheating issue. Have you looked at the intake manifold, if so, how does it look? A cracked intake manifold would cause this but it would have to have a crack running from one side to the other to explain the lose of compression on both sides. If the engine was ran very hot it could have destroyed the rings but I would think you should see it on every cylinder at that point and not just six. It would have to be really hot to cause that. I would ask if know if your compression gauge is accurate and the conditions of the test but with that much variation none of that would explain it. When you asked about the leaking riser you have to remember to look for a solution/reason you lost compression on both sides of the engine. Your absolutely right that a leaking riser can cause you problems but to see both fail at the same time is highly improbable. I am sure a lot of people will give you much better information tomorrow but I know what its like waiting for an answer so wanted to give you my thoughts. Also, the light rust is probably from moisture in the cylinders from not being fogged. One that note, do you know if the engine was winterized or if the engine was at least drained by the previous owner after it would not start? You stated it sat for a couple years before you bought it. Please forgive any spelling or grammar errors, it has been a very long day.

 

[andrewterri]

I completely forgot to say welcome to the forum dmohring. There is a lot of knowledge on this forum with great members to help you. They have kept my boat running for years.

 

[Bondo]

I was wondering if the timing chain jumped a link would I see this kind of variation? Then I started seeing blogs about leaking risers. I pulled all plugs and some have a little rust. So could be that water has be leaking down through valves? the oil does not appear to have any water in it. So... what next? thanks.

Ayuh,..... Welcome Aboard,.... Rather doubtful it's the timin' chain,..... More likely detonated to death, or possibly rusted cylinders,.....

I suggest ya pull the motor, 'n work on it on the floor,.... easier to get at,.....

Yer gonna end up replacin' the long block, or doin' a full on rebuild on it before ya go boatin' anyways,....
There's No simple fix for numbers like those,....​

A leak-down test will tell ya whether it's the valves or rings,....​

 

[Scott Danforth]

As bondo said, either water entering thru exhaust manifold rusting the valves and rings or pistons gone from detonation.

Pull the drive, pull the motor, fix or replace motor, reinstall motor, go boating

 

[Scott Danforth]

The experts will chime in tomorrow but if I remember correctly the 5.7 is an interference engine .

nope, stock motors are free running. Big cam motors with aftermarket pistons are a different story

 

[dmohring]

To answer Andrews questions, I did not see signs of overheating. I used a brand new compression gauge that held pressure after the check. Intake manifold looks fine from the outside. Not to sure about how it was left either as winterized or not. Boat has a registration sticker on it good till next year so it has likely been used within the last few years. Now that I am thinking about it, a jumped timing chain would likely cause all the cylinders to lower compression the same since they all have to follow the same increment. I am leaning towards the riser leaks.

 

[dmohring]

If I decide to get a reman, how do I know if its a short or a long block?

 

[Scott Danforth]

Short block is block with its crank, rods, and pistons (no heads)

Long block has heads

 

[Bondo]

If I decide to get a reman, how do I know if its a short or a long block?

Ayuh,.... You'd want a Long block, which is a short block, with the heads included,....

 

[andrewterri]

Thanks for the correction Scott Danforth. Is it common to see the exhaust risers on both sides fail at the same time to allow water in?

 

[Lou C]

Also make sure your original intake manifold is not rotted out under the thermostat housing and the sealing surfaces where the front water passages mate up with the cyl heads are not eroded. The none Vortec cast iron intakes for carbed engines are not that easy to find in good shape and this will not come with a reman or new long block. Also you will need your old flywheel. I found a good spare marine 4 bbl intake for my old non Vortec 4.3 on eBay....

 

[dmohring]

Yep, the right side had definitely been leaking. Pulled the right manifold and head off. # 2 had broken exhaust valve from small chucks of the top edge of the piston beating against the valve and head. signs of water everywhere. Long block time... The intake manifold is in good shape though. Does anyone know if I could upgrade to a vortec block with what I have? I have a 4 barrel intake and carb that are good as well as the distributor, alternator, water pump. I have an inboard.

 

[Rick Stephens]

You can upgrade to Vortec, you will need a Vortec intake though, they are different.

 

[Lou C]

Vortec will take a different intake manifold and if the carb used an exhaust passage heated choke, it will have to be changed to an electric choke since there is no exhaust crossover passage on the Vortec intake. No reason not to update to a Vortec set up they put out more power and parts are more easily available.

While you're at it, see if you can up-grade to the Merc dry joint exhaust system, its a much better set up at avoiding water in the cyls due to a leak at the riser/manifold gasket. They cost more but are worth it.

 

[dmohring]

ok thanks I will consider those options. Just to make sure I am not confused, my motor turns counterclockwise when viewed from the flywheel side (rear) so that means it is a standard rotation motor correct? The tag on the motor says RH but this is obviously from the front of the motor.

 

[dmohring]

Scratch my question about the engine rotation. the dude I got the boat from had put a new starter on it because he thought it wasnt turning over fast enough (I now know this is because of the water that got into cylinders). Just so happens he put a CCW starter in. The original was a CW which turns the motor RH or clockwise looking forward from the flywheel side. So this motor IS a opposite rotation RH engine as the motor tag says. Why would they put this opposite rotation single motor in the boat? I thought for single motors they would have just used the normal std rotation CCW motor?