switching foot from 85hp 20" to 125hp 25"

[zephyrmariner70]

i have a 85hp 20" foot i need to put it in a 125hp 25" motor. can i take the 20" shaft out and replace it with the 25" shaft? thanks for any info. keith

 

[jerryjerry05]

Re: switching foot from 85hp 20" to 125hp 25"

. It will need the parts to be shimmed.The gear ratio isin't the same.
Just taking them out and replacing them won't work.
Yes you can replace the shaft.It will probably work but will eventually something will go if not shimmed.There are few places that work on them anymore.
Look for another unit on e-bay or a marine salvage yard.
I bought one for $140

Fill out the profile you might be close to someone who can help you.J

 

[Frank Acampora]

Re: switching foot from 85hp 20" to 125hp 25"

It really depends upon the years! If one is prior to 1989 and the other is post 1989, then they use different gears and bearings--shafts can not be interchanged. If both are pre 1989 with one piece drive shafts---like Jerry says. If both are post 1989 two piece drive shafts, then all you need to do is replace the upper driveshaft. Let us know what years the engines are.

If they are both post 1994, then they are mercury and I can't help.

 

[zephyrmariner70]

Re: switching foot from 85hp 20" to 125hp 25"

thank you for the information i will continue my search to do this correctly.

 

[zephyrmariner70]

Re: switching foot from 85hp 20" to 125hp 25"

both engines are pre 1989 the 125hp is older white in color, the 85hp is slightly newer and black in color both are pretty much identical with minor variations in wiring, however the foot on both appear to be the same. btw i am in ocala, fl

 

[Frank Acampora]

Re: switching foot from 85hp 20" to 125hp 25"

If both are pre-1989, then the shafts are swappable, but it isn't easy. It requires a complete disassembly and if, for example, the 85 is a 2 to 1 ratio, then (if your WOT top speed is correct now) you must step up 2 pitches in prop as the 125 is a 1.76 to 1 ratio.

You need to remove the anode, spool, reverse gear bearing carrier and finally the pinion. You can try replacing the 125 shaft with the shim pak that it has in its lower unit. First, remove the forward gear and by hand, mate it to the pinion. You will see a "wear" pattern on the forward gear. as you rotate the pinion, you will feel that it moves smoothly on the wear pattern but either too high or too low, it will make noise.

Now, when you replace the gears, shims, and new driveshaft, with no water pump installed push down on the driveshaft and turn it. It will either turn smoothly



or make noise like in your hand. If it turns smoothly, then the shim pak is close to correct and it will run If it makes noise, then you need to shim it until it is correct. If you are careful, you can see the gear lash and see the wear pattern while assembled. thus, you can approximate the correct gear lash without the special tool.

Although Chrysler and later Force engine lower units claim a .005 clearance (gear lash) In reality they are set up a bit loose and there is a bit of leeway without having the gears chew themselves up. Not a lot, so you still must take reasonable care: You can't just slap everything together.

Upon reassembly, the pinion nut should be a new one and should be torqued to 85 foot pounds. You need to have an old crankshaft or fabricate a specila tool to fit on the drive shaft splines to do this. All in all, unless you are very handy with tools and experienced with mechanical repair, I would not recommend that you try this. Advertise on craigslist for a person to swap the shafts for you for maybe 50 bucks. labor.

I do not hqave any photos of a complete disassembled lower unit but these should give you an idea as to what you are getting into.

 

[zephyrmariner70]

Re: switching foot from 85hp 20" to 125hp 25"

this is all great information i will take into consideration having someone else do this for me. i would like to as much work for myself as possible but this sounds a little advanced. again thank you for your help.