Force 120 hp sportjet xr on 3

[venxxxxx]

Im curious if the 2-strokes 4 cylinder Force Mercury 120hp can operate with just 3 cylinders ?

Reasons im asking because the bottom cylinder connect rod broke, ruined the cylinder/piston, cracked the engine block.

I was thinking to remove just all the debris, patched the cracked area up with weld epoxy, leave the piston head in without the connect rod to the crank. Basically im going to seal it in and just run 3 cylinders....which lower the HP to 90HP instead of 120hp.

Do you think it would work ?

 

[jason32038]

Re: Force 120 hp sportjet xr on 3

It might run but it won't be 90 hp...more like 20. You'll be lucky if you get over 10mph.

 

[Frank Acampora]

Re: Force 120 hp sportjet xr on 3

Since each cylinder is like a separate engine, yeah, it will run BUT: Don't leave the piston in the cylinder If it moves down, iot wqill contact the crank cheeks. OR: Lock/glue it in place at TDC to seal both the exhaust and bypass ports. With the exhaust and bypass ports open, exhaust pressure can get into the crankcase and some will bleed through the reeds while some will enter the oil recirculation system.

With only three cylinders at 90 degrees apart, you will have at one point a 180 degree space so torque will be down sognificantly. I don't think you will get 90 HP out of it. AND , the jst impeller is matched to the 120 HP.

At any rate, while it will run and save money, it is not a good idea. Break down and buy a used block.

 

[venxxxxx]

Re: Force 120 hp sportjet xr on 3

Since each cylinder is like a separate engine, yeah, it will run BUT: Don't leave the piston in the cylinder If it moves down, iot wqill contact the crank cheeks. OR: Lock/glue it in place at TDC to seal both the exhaust and bypass ports. With the exhaust and bypass ports open, exhaust pressure can get into the crankcase and some will bleed through the reeds while some will enter the oil recirculation system.

With only three cylinders at 90 degrees apart, you will have at one point a 180 degree space so torque will be down sognificantly. I don't think you will get 90 HP out of it. AND , the jst impeller is matched to the 120 HP.

At any rate, while it will run and save money, it is not a good idea. Break down and buy a used block.

LOL I appreciate the replies. Im in the process of hunting down for a block too. Its a bit rare since these are out of production. Browsing and searching around, someone mentioned that this is the same as the outboard force 120. But I reckon it got a different end at the shaft. Outboards tend to have bolts coming out of the block, this block got holes for bolts going in to mount on the engine.

Maybe im wrong but I did look at some pics of the force 120 outboard with completely different bolt patterns.