70hp vs 90hp interchangeability

[Bigprairie1]

Does anyone have any knowledge as to how interchangeable these (2) 3 cylinder engines are or what the major differences are? (1991 models).
I saw a local guy advertising a low hour 70hp ('91) that needs a new stator (at least) and I was thinking of picking it up for spare parts for my other spare motor (yeah, I know..starting to collect)...which a '91/90hp.
The motor for sale is complete with controls, prop, etc.
Examples of interchangeability enquiry: lower unit? prop? trim system? flywheel? starter? etc, etc
If anyone can shed any light on this that would be great.
Thanks!!
BP

 

[pnwboat]

Re: 70hp vs 90hp interchangeability

The crank shaft on the 70 HP has a tad longer stroke 2.87in vs 2.8in on the 90 HP. That probably means that the bypass ports are drilled a little differently between the two blocks. I'm pretty sure that the lower ends are not interchangeable. From what I can remember, the 70HP has a smaller gear case. Ignition components are interchangeable.

 

[Bigprairie1]

Re: 70hp vs 90hp interchangeability

The crank shaft on the 70 HP has a tad longer stroke 2.87in vs 2.8in on the 90 HP. That probably means that the bypass ports are drilled a little differently between the two blocks. I'm pretty sure that the lower ends are not interchangeable. From what I can remember, the 70HP has a smaller gear case. Ignition components are interchangeable.

I wondered about that lower unit....not being completely sure either. I was trying to recall the same issue on the 150hp lower unit being usable on the 90/120hp motors or if both the 70hp and the 150hp have their 'own' lower unit?
The electronics makes sense....does it include the flywheel tho'? I could see the stator being universal for sure.
The guy is asking $250 for the whole thing...including controls....hmmm???
BP

 

[roscoe]

Re: 70hp vs 90hp interchangeability

Ignitions were NOT interchangeable.

Even within the 1991 model year, the 1990 used 2 different ignition systems; one with cd modules and the corresponding blue coils, and the other used a switchbox. The flywheel, stator, and trigger were not interchangeable between these 2.

Then in 1992, it changed again.

The 70 hp never had cd modules, but had 2 different switchbox type ignitions between 1991 and 1992.
The 70 hp flywheel, trigger, stator, were interchangeable with the switchbox version from the 90 hp.


The fuel intake and carbs were different, the 90 being a 3 carb setup, the 70 hp has only one carb.

They also switch fuel pumps mid year on both the 70 hp and the 90 hp.

3 different trim pumps were used.

Fuel recirculation system also changed mid year.

 

[Bigprairie1]

Re: 70hp vs 90hp interchangeability

Ignitions were NOT interchangeable.

Even within the 1991 model year, the 1990 used 2 different ignition systems; one with cd modules and the corresponding blue coils, and the other used a switchbox. The flywheel, stator, and trigger were not interchangeable between these 2.

Then in 1992, it changed again.

The 70 hp never had cd modules, but had 2 different switchbox type ignitions between 1991 and 1992.
The 70 hp flywheel, trigger, stator, were interchangeable with the switchbox version from the 90 hp.


The fuel intake and carbs were different, the 90 being a 3 carb setup, the 70 hp has only one carb.

They also switch fuel pumps mid year on both the 70 hp and the 90 hp.

3 different trim pumps were used.

Fuel recirculation system also changed mid year.

Thanks Roscoe.
My '91 has the merc style ignition (not the Chrysler light blue coils and no CD modules) so that is what I would look for on the other '91-70hp. Good to hear about the flywheel being interchangeable (so long as the ignition is the same).
Any ideas on the lower unit? or was it unique to the 70hp (and 50hp?)
Thanks again, great info all around guys!!
BP

 

[roscoe]

Re: 70hp vs 90hp interchangeability

Your 90 hp lower is bigger than the 70.
You would need a lower from a 1989 thru 1994 90 hp or 120 hp.


The 70 lower unit will fit:
1991-1995 70hp
1996-1998 75 hp
1995-1999 40 hp
1995-1999 50 hp