Force 120: 1989 outboard and 1990 LDrive heads interchangable?

[brandonv]

I believe they are, but maybe someone on here knows otherwise and can save me the hassle!?!? Anyone know?


thank you!

 

[Frank Acampora]

Re: Force 120: 1989 outboard and 1990 LDrive heads interchangable?

Yep! They are interchangeable. In fact, you could use any powerhead from 85-150.

Also, when Merc started putting the powerhead on the Merc midleg and lower unit, it still was the same mounting pattern. They simply made a match plate to adapt the block to the Merc leg, but the splines inside the crankshaft are different than the earlier Force. So if you acquired one of those blocks, you would need to change the crankshaft. And of course, the 150 being taller might not fit under the cover.

 

[brandonv]

Re: Force 120: 1989 outboard and 1990 LDrive heads interchangable?

Awesome!

Looks like I've got myself a head to replace the one my melted piston kissed. Thank you much!

Yep! They are interchangeable. In fact, you could use any powerhead from 85-150.

Also, when Merc started putting the powerhead on the Merc midleg and lower unit, it still was the same mounting pattern. They simply made a match plate to adapt the block to the Merc leg, but the splines inside the crankshaft are different than the earlier Force. So if you acquired one of those blocks, you would need to change the crankshaft. And of course, the 150 being taller might not fit under the cover.

 

[brandonv]

Re: Force 120: 1989 outboard and 1990 LDrive heads interchangable?

I've got some pics of the 1989 head and it does not look like what came off of my 1990 L-Drive. I'm not dismissing the idea that it wont fit, but I've certainly got doubts based on the shape difference and sensor location.

Can anyone ID the head in these 2 pics and advise if its off a Force 120? The last pic is the head off my 90' L-Drive 120.

 

[Frank Acampora]

Re: Force 120: 1989 outboard and 1990 LDrive heads interchangable?

Oh! I thought you were talking about the whole powerhead! Just the cylinder head is a different story.

Force made two different versions of the 120. One was 3.375 bore and the other was 3.3125 bore. The head from a 3.375 bore will fit on a 3.3125 bore BUT the pistons of a 3.375 bore will hit the 3.3125 head. Put your existing head gasket against the other head. If more aluminum shows, then the combustion chamber is smaller and it will not work UNLESS you grind clearance on each side for the ends of the piston baffles. Yes, there is plenty of metal there to grind--it's less than 1/16. each side. Remember the piston is only .0625 bigger. 1/16 is .0625.

The bolt pattern is the same and head gasket is the same for all 4 cylinder heads. Really everything is the same except the older head looks more massive and the overheat indicator is in a different place--actually, if you compare, it's in the same place on the head. Just looks different. It is also held in with a circlip with a spring behind the rubber plug. But why do you want to replace the head? the only thing I see is some slight pitting on the clean #4 combustion chamber. It looks like a piston was melted at one time and replaced--that is if you have a good one in that hole. This pitting won't affect performance--of course, if you are a perfectionist like me it will bother you.

 

[Frank Acampora]

Re: Force 120: 1989 outboard and 1990 LDrive heads interchangable?

Reviewing my post: One of those heads is (or may be) thicker than the other and uses a longer head bolt. -Only about 1/8 to 1/4 inch longer. The longer bolt will fit the thinner head--no problem, however, since they are grade 8 bolts to take combustion pressures, I would not use the shorter bolts on the thicker head. --Even though the head is only about 1/8 inch thicker.

So in addition, measure the thickness of each head before you use it. If necessary, buy longer grade 8 bolts.

 

[jeff900]

Re: Force 120: 1989 outboard and 1990 LDrive heads interchangable?

Oh! I thought you were talking about the whole powerhead! Just the cylinder head is a different story.

Force made two different versions of the 120. One was 3.375 bore and the other was 3.3125 bore. The head from a 3.375 bore will fit on a 3.3125 bore BUT the pistons of a 3.375 bore will hit the 3.3125 head. Put your existing head gasket against the other head. If more aluminum shows, then the combustion chamber is smaller and it will not work UNLESS you grind clearance on each side for the ends of the piston baffles. Yes, there is plenty of metal there to grind--it's less than 1/16. each side. Remember the piston is only .0625 bigger. 1/16 is .0625.

The bolt pattern is the same and head gasket is the same for all 4 cylinder heads. Really everything is the same except the older head looks more massive and the overheat indicator is in a different place--actually, if you compare, it's in the same place on the head. Just looks different. It is also held in with a circlip with a spring behind the rubber plug. But why do you want to replace the head? the only thing I see is some slight pitting on the clean #4 combustion chamber. It looks like a piston was melted at one time and replaced--that is if you have a good one in that hole. This pitting won't affect performance--of course, if you are a perfectionist like me it will bother you.

Do you know about lower units. Which years are interchangeable or HP. I have a 1986 Force 125 and need a lower unit?

 

[Frank Acampora]

Re: Force 120: 1989 outboard and 1990 LDrive heads interchangable?

Again, almost any 1 piece lower unit from late model white Chrysler and early model white Force to later model black Force will fit. This encompasses the years 1982 (I think) to 1989 and all 3 and 4 cylinder engines. In 1990 Force changed to a two piece drive shaft and a slightly different water pump. While earlier model lower units will fit 1990 models, I do not know if the later 1990 unit will retrofit to older engines---but I suspect it will; mounting bolt pattern is the same.

Now, both Chrysler and Force used a 1.78 to 1 gear ratio in the 120-125-140 lower unit. Some 85 and all 3 cylinder 90 hp engines had a 2 to 1 gear ratio. Either is usable on your 125 but if you get a 2 to 1 ratio, you will need to go to a prop with 2 inches more pitch.

It is actually preferable to use the 2 to 1 gears because they will improve performance of your 125 by several MPH. I don't know why the factory didn't make them original equipment.