will the pistons work

hi guys, i have been to this forum alot, and this is the best place to find info for the do-it yourselfer,,, so im looking at picking up a late 70's 70hp chrysler outboard , i have an 85hp and am looking at using some of the parts from the 70hp, will the pistons work,,,,are they the same, how about the water impeller thanks for the help

Re: will the pistons work

I have a 70's Chrysler/ Force 75HP and I dont believe that the pistons will be the same i believe that the size of the piston has alot to do with your HP and they will be different.

Re: will the pistons work

If it is a Chrysler 70 Hp and if the 85 is also a Chrysler or very early Force (up to about 86), then the pistons are the same size and will interchange. Be prepared to use both piston and rod since if you do not have a press and the special tool, you will have MUCH difficulty removing the wrist pins and reinserting them into the other pistons.

The blocks are the same: the difference in horsepower was derived by larger exhaust ports, different port timing and carburetors. Thus: you can not swap into the 70 and expect to get 85 HP. Putting the 85 carbs on the 70 will give only a very little gain over 70 HP. You will not see an increase in boat speed.You can, however swap into the 85 and get your 85 HP. The 70 carbs are smaller and will lower the HP a bit, but not too much--Again, the main difference is in the porting.

The Chrysler and early Force 85s did not produce 85 HP. They would not keep up with equivalent outboards from Merc or OMC.

If you want to wake up your 85, while you have it apart, take a Dremel with a carbide bit and square the ports. It will gain between 5 and 10 HP PER CYLINDER and will put out a true 85 HP..

lower units and impellers were the same up until about 1979 then Chrysler went to a one piece lower unit. The impeller in that water pump is larger. The one piece lower will not interchange with the two piece either.

Re: will the pistons work

I am fairly certain that the 70 hp thru 150 hp motors all use the same diameter pistons. To be certain, measure the bore of the pistons. The stock bore diameter is 3.312" for 89 and older motors. After 1990 I believe the diameter was increased to 3.375". The pistons are interchangeable on all bores with the 3.312" diameter. That said, should the motor [recipient motor] you are going to be putting the pistons in has been overbored, either .020", .030" or higher, the stock 3.312" pistons won't work because of their smaller diameter. However, should the motor [donor motor] you are taking the pistons from be overbored, and the reciepient motor have a smaller bore, one would only need to match the bore diameter of the donor pistons by having the cylinders of the recipient motor bored to the proper size.

Re: will the pistons work

I am fairly certain that the 70 hp thru 150 hp motors all use the same diameter pistons. To be certain, measure the bore of the pistons. The stock bore diameter is 3.312" for 89 and older motors. After 1990 I believe the diameter was increased to 3.375". The pistons are interchangeable on all bores with the 3.312" diameter. That said, should the motor [recipient motor] you are going to be putting the pistons in has been overbored, either .020", .030" or higher, the stock 3.312" pistons won't work because of their smaller diameter. However, should the motor [donor motor] you are taking the pistons from be overbored, and the reciepient motor have a smaller bore, one would only need to match the bore diameter of the donor pistons by having the cylinders of the recipient motor bored to the proper size.