1997 Mercury 40/30 jet

[rktman]

I just picked up a 97 Merc 40 / 30 jet that came with a boat hull I "needed".

The motor was reportedly low on compression and was priced accordingly (cheap).

I tested the compression myself. Cylinders 1, 2, & 4 were OK with 120, 115, and 118 psi respectively.
The No. 3 cylinder only had 20 psi, yes 20 psi.

My next step will obviously be to pull the head and see whats happening. Hopefully it will just be a blown head gasket.

If its more than a head gasket, would this motor be worth the effort to rebuild and are they fairly reliable?

 

[wmk0002]

I don't have experience with that particular motor but I would say it depends on how much you figure the motor cost you in the deal. If it was just a bad headgasket that would be awesome but either way you will have to remove the head to inspect so you might as well go ahead with that. If you have a broken ring causing 20 psi then it almost for sure has to be bored. If you have to get a machine shop to bore/hone all 4 cylinders plus buy a rebuild kit including all new gaskets, pistons, rings, needle bearings, etc then I would guess the total cost would be $800-1000 to do it yourself (if that was what you were implying you would do).

Does it run even with the dead cylinder? It would be nice to know if the ignition components were all working as those are pricey and may sway your decision.

Back to approximately how much you got the motor alone for, it may be best to part out. The jet foot is pretty valuable by itself.

 

[rktman]

It supposedly ran but not very well per the previous owner.

Gas in the tank looks terrible (water). I haven't cleaned it out and run it yet.

 

[BigTerp]

My 1994 Johnson 50/35 was purchased the same way. A buddy and I rebuilt it ourselves. Cylinders bored, new pistons, rings, etc., etc., etc. Bought the blown motor for $300 and had another $5-600 in the rebuild. Figure $1,000.00 total spent on the motor and it could sell today (3 years after the rebuild) for $2,000.00+

Figure on what you paid for the motor plus the $800+ to rebuild it yourself (if you can) that WMK suggested, which I think is a good ballpark figure. Then figure on the total spent on the motor and compare it to what you see comparable engines selling for on Craigslist. Should get you a good idea of whether it's worth the time/money to rebuild.

 

[wmk0002]

FYI, if decide to go through with a rebuild, you can buy a kit here that includes everything you will need. https://www.powerheadexchange.com/

 

[rktman]

Thanks

 

[rktman]

Well, that didn't work. This motor uses the power-chamber setup, so it doesnt do any good to remove the cover near the spark plugs. It's not really a traditional head/cylinder setup. It appears that you have to remove the whole bottom end just to inspect the cylinder. It will be a winter project.

 

[turbotodd]

Well, that didn't work. This motor uses the power-chamber setup, so it doesnt do any good to remove the cover near the spark plugs. It's not really a traditional head/cylinder setup. It appears that you have to remove the whole bottom end just to inspect the cylinder. It will be a winter project.

Yep. Another reason I absolutely hated working with Merc/Mariner when I had to. We had to send the blocks out to be bored because it takes a special setup to do it. At that time, the people who did them were not cheap, either. I "think" you can pull the exhaust cover off and have a look at the pistons and skirts, maybe see part of the cylinder wall from there as well. Been a year or two since I been into one.

 

[Kenny9575]

I just bought a boat with the same motor and similar problems. Does anyone have an idea what other motors this jet foot will fit?