Motor modifications

[pnwboat]

I had a 1988 125HP motor that developed a water leak in #1 Cylinder. Tried for months to fix to no avail. Had block and head machined, but didn't do any good. Came to the conclusion that leak was somewhere in the crankcase itself. Ended up getting a 90's 120HP block. Put the internals from the 88 into it with new bearings, seals etc. Had it bored .020 over, new Weisco pistons. Runs great now. Made a few of the following changes.

Added a temp gauge. Mounted sending unit here.




Added a water pressure gauge. Found a pipe plug in the exhaust plate between the motor and lower unit that leads right into the water passage. Took plug out and installed a brass fitting to attach tube to WP gauge.




Had problems with overcharging. Removed the recftifier assy. and installed a rectifier/regulator. Fashioned an aluminum plate to mount the rect./reg assy. on and bolted it to the block. I also installed a fuel pump from a late model motor.





This is how I wired up the new rectifier/regulator assy. I installed a terminal strip where the old rectifier assy. used to be mounted.

 

[pnwboat]

Re: Motor modifications

Also refinished the cover. Masked off all of the original decals with masking tape. Sprayed with Ford Deep Wedgewood Blue. Removed the masking tape and shot some clear coat. Top portion was painted with Brilliant Metallic Black by Rustoleum. No clear coat on the top. Came out pretty good. You can see yourself in the reflection.

 

[Frank Acampora]

Re: Motor modifications

The porting on the 120 is different than the porting on the 125 because the crank throw on the 125 is .075 longer. 2.875 vs. 2.80

However: the bore on the 125 is 3.3125 and the bore on the 120 is 3,375. Did you put in new pistons or use the pistons from the 120? Or is the block you bought advertised as a 120 but really a 125 with 3.3125 bore?

If you do have the 3.375 bore, you are thus losing a bit of horsepower--not a lot, but some. If you have need to disassemble the engine in the future, raise the tops of ports about 35-40 thou.

You will then have a 3.375 bore by 2.875 stroke engine with the ports placed properly.--the same as the old Chrysler 140.

 

[pnwboat]

Re: Motor modifications

Had the new block bored .020 over. I bought new Weisco forged pistons to match .020 oversize. I did do some work on the by-pass ports. Squared them off and raised them by about .020. Didn't want to go too far. Hard to replace the metal once it's gone. That was a tedious messy job. Tapered the inlet edge of the ports so the air has a smother transition into the port. There were also some really sharp edges in the by-pass passage itself that I smoothed out. Picked up almost 10 MPH from the old block. I was pretty happy with the results. My next mod is to put a late model Mercury ignition from a 1998 120HP. Not sure if it's a positive thing or not. I do know that it's a cleaner installation, and hopefully easier to trouble-shoot. A lot less wires.