1994 Force 120hp. Looking for manual and/or repair advice.

[stakultexsun]

Not sure if this is appropriate, but isn't Force by Mercury?

Anyway,
1994 Force 120hp on 1994 Bayliner 19'.
Serial #: 0E088651
Model #: H120412PX

I'd like to purchase service manual without spending too much $$$.

Motor runs real good getting boat up to 45mph (1994 19 foot bayliner ski boat) until top spark plug gets fouled out within a few minutes (metal shavings on plug).

Low compression on top cylinder, looks like it has metal shavings in there, and would like to see about replacing just this piston/rings if possible. That cylinder was reading about 89 psi, and the other 3 were reading 149 psi, ALL consistantly. The guage may be off, but I'm sure those numbers are within 10% or 15%.

The top of the piston looks "pitted", I assume it over heated and pieces of the rings/cylinder/piston were loose in there.
Questions:

1. Why would only 1 cylinder overheat?
2. Head gasket? I know a bad head gasket can reduce compression also, but he did find some metal pieces attached to spark plug (verified with magnet).
3. Can we remove top carb and access bolts that clamp connecting rod to the crank and remove it?


Real quick background on this motor/boat for those who like to read...lol.

Dad bought brand new in 1994 (nearly 30 years old). No hour guage, but if it were a car, it would be 50kmiles or less. garage kept, so for it's age and 0 restore, it is a very clean boat.

He can buy a new boat, but we only go to the lake 2 or 3 times year. So that isn't on the table.

If we could find someone to rebuild motor and do a good job, that might be an option. He just spent $1400 + on it, and the mechanic I guess never even checked the spark plugs or compression, just replaced the stator and a few other things which were needed.

[JOE54]

incompetence abounds as you have found from mechanhack , respectfully sir dont patch that engine do it right or dont do it , could be several causes for it to fail

[stakultexsun]

Longview! Do you know of a good mechanic near you? My father and the boat are in Marshall, it was at some boat shop there in Marshall since June 2022....just got "fixed"at end of February..

Time is an issue.... if he and I had time, we'd try to rebuild it ourselves.

Nobody wants to work on a motor over 10 years old. Been told that by multiple "boat mechanics ".

[stakultexsun]

Accidentally double posted.

[EuropeanAM]

Get Part# 832749R2 (Service Manual).

[stakultexsun]

Thanks, for that. Is there a way to confirm that is for 1994? Or what year ranges? I presume you looked up serial number or model. I found this one. <EDIT> seems good

[JOE54]

Longview! Do you know of a good mechanic near you? My father and the boat are in Marshall, it was at some boat shop there in Marshall since June 2022....just got "fixed"at end of February..

Time is an issue.... if he and I had time, we'd try to rebuild it ourselves.

Nobody wants to work on a motor over 10 years old. Been told that by multiple "boat mechanics ".

i sure do , i can point him in the right direction

[EuropeanAM]

Thanks, for that. Is there a way to confirm that is for 1994? Or what year ranges? I presume you looked up serial number or model. I found this one. <Nope> seems good

The part number provided is specific to your engine's serial number.

[stakultexsun]

I see about the link I provided. Didn't realize, my apologies. I guess the real question is the only part number I'm finding is Mercury 90-832749R (force outboard 75/90/120 hp servie manual... don't know if the 90 makes a difference or not.

At Joe54, I'll contact you once I get more information. This boat probably gets 15 to 20 hours a year put on it max. Not sure how far he'll go messing with it.

[JOE54]

understood

[EuropeanAM]

832749R2 is the correct part number. Order from any authorized Mercury dealer.

[stakultexsun]

Yes, I didn't fully copy the part number leaving out the 2. Thanks.

My dad finally pulled off the head. The top cylinder with low compression definitely has metal shavings. I'll refer to it as cylinder 1, the next one down as cylinder 2.

So pics of head, piston and cylinder 1 , and 2.

[stakultexsun]

Joe, can I get the contact info to give my father?

I'll PM you.

[JOE54]

sure can

[stakultexsun]

Thanks Joe and everyone who has given me some input. It is appreciated. My father has contacted the man you suggested. He has dropped off the boat and I'll update you guys when we get an answer. I sure wish I had time to fool with this thing!! I'd like to learn more about outboards in general.

I am mechanically inclined, do most if not all my vehicular repairs. I did the water pump on my 2016 Ford Explorer V6, possibly the most complex job I've ever done. look it up if you get curious. Took me waaayyy too long.

[lpugh]

If you do proceed with repairs and the still runs, add TDC marks for every cylinder and watch the timing at various RPM up to 2500 or so, you are verifying timing accuracy and no spark scatter, after market ignition parts could very well be the cause of this or improper installation. Seen this a couple of times
I would try to find newer good used Merc or Yamaha 115 four strike for it.

[EuropeanAM]

+1... this would be a tremendous amount of work and money for an engine of this vintage/type.

[JOE54]

i with to both ^^^^^

[stakultexsun]

F.Y.I. The guy you referred me to is rebuilding it. $$ Can't wait!!!!

[JOE54]

good deal man