1970 (red) 80hp compatible with 1973 (blue) 85hp ???

Had a free 80hp 1970 motor given to me but it came partially disassembled and has been in storage like that for the better part of 20yrs. Chances are some of the parts are now missing, not to mention having no idea why it was taken apart in the first place.

Have a chance of picking up a running 85hp 1973 (but needs "overhaul") and am hoping to be able to make one good running motor out of the two.

Would I be able to mix and match parts between the two motors?

Thanks

Re: 1970 (red) 80hp compatible with 1973 (blue) 85hp ???

The crankshaft, rods, bearings are identical. 85HP has power-ported pistons which could be used in the older 80HP without issues. However, the 80HP's non-power-ported pistons couldn't be used in the 85HP.

Similarly, the 85HP block has power-port passages that the 80HP does not.

The blocks and center sections (exhaust towers) are not the same. Different bolt patterns where the block bolts up to the center and a different design at the bottom of the block where the exhaust dumps.

Things like flywheel, distributor, other various external components should be similar. As would carbs except for jetting.

Lower units would bolt up the same on both motors.

The 85HP would be the better motor to put together but either one will run nicely on a medium-sized ski boat or whatever.

HTH & Have Fun!...........ed

Re: 1970 (red) 80hp compatible with 1973 (blue) 85hp ???

So, not as compatible as I had hoped. Why do you say the 85 would be the better motor? Is it because it is running and the 80 is not, or is the 85 an overall better motor?

Guess I could part out the 80 and sell the pieces.

Re: 1970 (red) 80hp compatible with 1973 (blue) 85hp ???

The 85, with power-ported pistons and block, will be snappier than the 80. The 85 also has the advantage of the redesigned block/exhaust plate which gives better exhaust tuning than the one in your 80 HP.

I'd say the determining factor would be which block is in better shape. If the 85 hp block has badly scored cylinders and the 80 doesn't, the choice is simple.

It all comes down to the condition of the parts and you ain't gonna know fer sur until they're all torn down. Time to start wrenchin!!!!

Re: 1970 (red) 80hp compatible with 1973 (blue) 85hp ???

Delete, double-post due to server issues.

Re: 1970 (red) 80hp compatible with 1973 (blue) 85hp ???

Thanks emckelvy, you really seem to know your motors.

Just finished going thru the box of parts that came with the motor and took a good look at the motor itself. Everything appears to be there and there were no broken parts or bolts. Everything looks in remarkably good shape. The previous owner was meticulous when he took it apart. EVERY nut, bolt, washer, wire and linkage is placed in a small envelope and labeled which is then referenced to a notebook he kept with sketches and notes. Wiring and fuel lines need to be replaced but thats no big deal.

My approach now is to try and get the 80hp running. It has cost me nothing. I plan on stripping it down completely to get a look inside and to clean everything up. Unfortunatley I can't do a compression test because the exhaust covers are off.

What worries me is the ignition coil and "black box" ignition module. Is there a way of testing these things ? Are they still available if I need one?

The lower unit has apparrently been rebuilt but doesn't seem to line up well with the midsection housing.