Questions for the Chrysler/Force experts

[foxtrotboss]

I noticed that for the years 1984-1989 125hp force motors there is listed two piston bores 3.312 and 3.375. How can it be the same motor, but one model have a bigger bore and the same displacement??? I am confused anyone know the answer??


Also all I can find is that Chrysler made a 125 motor in 1981-1982. Can anyone confirm this? Did they make a 125 any other year?

 

[otec465]

Re: Questions for the Chrysler/Force experts

maybe different rods, piston sizes, deck height ( whatever it is called btw the top of cylinder and head), making up the difference

 

[MWBROWN]

Re: Questions for the Chrysler/Force experts

Actualy ,my books shows the 125 as the same bore. 3.3125 for the years
1984 to 1989

The 120 shows different bores.
The smaller bore is 99.2 CID
and the larger bore is 102.9
The books shows the same stroke.
SO,, looks like an advertising thing for the horse power.

Cannot answer the other question.

Mike

 

[walk-on]

Re: Questions for the Chrysler/Force experts

Actualy ,my books shows the 125 as the same bore. 3.3125 for the years
1984 to 1989

The 120 shows different bores.
The smaller bore is 99.2 CID
and the larger bore is 102.9
The books shows the same stroke.
SO,, looks like an advertising thing for the horse power.

Cannot answer the other question.

Mike

My Seloc manual shows the same thing. The 120HP shows 3.312 for 1990 and 3.375 for 1990-1999. Year 1990 depends on the whether it is presto or thunderbolt ignition.

 

[foxtrotboss]

Re: Questions for the Chrysler/Force experts

I do know the answer to the 1990 delima according to Franz of Franz Marine, untill 1989 the hp was rated at the flywheel, the boating industry required all mgfr to rate them at the prop after 1989. This was to compete with the Japaneese who rated there motors at the prop, and therefore outran the American motors rated the same.

I wondered if the different bore sizes prior to 1989 on the same motor was because of the "a" or "b" motor designation.

As I understand Chrysler/Force started to rate at the prop until US marine bought them and it went back to the flywheel. Until Mercury bought them and/or 1990.

 

[Frank Acampora]

Re: Questions for the Chrysler/Force experts

Are you sure you did not confuse the 150 with the 125? To the best of my knowledge, Chrysler AND Force NEVER changed the 125 from 2.875 stroke and 3.3125 bore. The 120 was made in several bore sizes in different years, and the Force 150 was made with 3.3125 bore and small venturi WB carbs in 89 and 90 AND 3.375 bore and big venturi TC carbs from 91 to 94. Porting was different to develop the rated horsepower.

Actually, the big bore (3.375 bore X 2.80 stroke) 120 develops its horsepower in a different curve and will usually perform as well as, or better than the 125 on a given hull. Note that the Chrysler and Force 125 and Chrysler 140 were the only engines to use the long stroke (2.875) crankshaft.

If you have the choice, ALWAYS opt for the big bore version of any Force or Chrysler engine. For example: The force 85 is a small bore engine and works quite nicely, but the 90 is a big bore 3 cylinder engine and outruns the 85 by more than the expected 5 HP difference.

The later Mercury modified Force 70 and 75 three cylinders are big bore engines and even though they use a 10 inch diam prop, they make the earlier Chrysler 70 and 75 look sick. I must admit, I do not like some of the changes Mercury made to them, but the engines do run strong.

 

[foxtrotboss]

Re: Questions for the Chrysler/Force experts

I very well could have the info I have is sketchy at best that is why I was asking. That is very interesting about the bigger bores I will keep the in mind for future purchases.