Mercruiser compression OK?

[pckeen]

Hi Everyone,

I had started a thread over in the non-repair IO forum - but this question is best placed here.

I've been looking for a donor boat with an Alpha Mercruiser 5.7. I found one, and had it inspected by a marine mechanic, who spent an hour and half going through it. The motor is in a 1989 Sea Ray, Mercruiser 5.7, engine number 0C605284. The motor was tested in a 'fake lake', but wasn't taken for a test run - and a test run isn't possible. The mechanic advised that a full inspection was done on everything mechanical - and it all tested good. The compression numbers were:
1 - 145
2 - 150
3 - 140
4 - 155
5 - 150
6 - 170
7 - 140
8 - 140

The only cylinder that give me pause is number 6 - the 170 reading. The mechanic I spoke to said the motor was good, he wouldn't be concerned about the 170 reading, and that this motor was pretty much bulletproof. What are your views on this?

Also, do I understand correctly that this motor is the 260hp 5.7L 350 MAG, a model which was used from 1983-1993?

 

[NHGuy]

Yes they are pretty bulletproof. And I wouldn't sweat the compression figure either.
You aren't near the salt water right?

 

[Bondo]

Ayuh,.... I wouldn't shy away from that motor, if it's a fair deal,....

Maybe pull the riser off the manifold over #6, 'n see if the gasket is failin',...

 

[pckeen]

Yes they are pretty bulletproof. And I wouldn't sweat the compression figure either.
You aren't near the salt water right?

No salt water anywhere near us

 

[pckeen]

Ayuh,.... I wouldn't shy away from that motor, if it's a fair deal,....

Maybe pull the riser off the manifold over #6, 'n see if the gasket is failin',...

I'll do that...after I've bought it. Unfortunately the boat is quite a drive. Hence the paid inspection.

 

[pckeen]

Thanks for the advice everyone. I've made the deal - and will pick it up in September....which makes two road trips, one to pick up the Chief, one to pick up this.

 

[achris]

0C605284 is just a garden variety 1989 Alpha drive 5.7L engine. It's not a Magnum.

I also would not be too concerned about those compression number. What I would do when I got it home is treat it as if the PO had never done a service. Start out doing and checking EVERYTHING. That gives you a baseline to start from. Once you do all the things needed, you know where you stand.

Good luck.

Chris..........

 

[pckeen]

So what would be the list of things to do. I was planning on a bellows replacement, oil change, spark-plug change, trim unit oil change, lower unit oil change before storing it for the winter. I'll check all fuel lines, belts and hoses, and will replace anything that looks like it needs it (bearing in mind that the mechanic just gave it a clean bill of health). The lower unit looks like it could use a repaint. I was thinking of doing a gimble bearing replacement as well, while I have the drive apart, but I don't know if that is overkill. What do you think? Anything else that should be done?

 

[achris]

HERE is a list of things I gave another guy. Start with that list. As far as replacing things like unis and Gimbal bearing, only if they need it. Unless the bellows have had water in them unis and gimbal bearing should last well over 2,000 hours/25 years.

Chris.....

 

[pckeen]

What is a unis?

 

[fishrdan]

U-joints

 

[achris]

What is a unis?

Universal joints. Exactly the same as the ones in your car on the tailshaft, between the back of the gearbox and the input of the differential. There are 2 of them on the drive yoke between the back of the engine and the front of the drive. Have a look at my videos, the one on removing the drive and you'll see them.

Chris......