Chrysler powerhead interchange question

[golddogs]

My 1979 75hp Chrysler outboard finally bit the dust. Broken piston rod through the crankcase. I have located 2 used powerheads..one is a 1967 model 75hp and the other a 1969 model 85hp. Will either one work as a replacement without major modifications?
Does anyone know of a source for a newer used powerhead that will fit?

Thanks for any help you can offer

 

[tater76]

Re: Chrysler powerhead interchange question

I have an 89 85hp leg with a 1974 75hp powerhead attached. The 75hp powerhead bolted right on the 89 base with no mods. I also have a 72 85hp powerhead that fits the 89 as well. My 1968 105hp powerhead fits the 89 leg too. I think you would be ok, but I would wait for Frank A. to chime in before buying. Oh and just make sure the splines on the end of the new powerhead crank match the number of splines on the lower unit driveshaft.

 

[Frank Acampora]

Re: Chrysler powerhead interchange question

Either year powerhead will fit on your 1979 leg----BUT--- Both those powerheads have old style ignition with points distributors. There is nothing wrong with these ignitions and while they may run very well, the Prestolite ignition on your 1979 is a much better system. It, however takes a bit of work to adapt to older blocks.

If you are not in a hurry and if cost is not a major factor, wait for an early Force block from 1979 up till about 1990 to bolt onto your leg.

If you are in a hurry and absolutely want either of these blocks--that's good too. All components (pistons, carbs, linkages etc) will swap. All things equal, I would opt for the larger horsepower 85 block. Too much horsepower is never enough.

BTW: You also have the option of bolting on up to a 125 block (140 if Chrysler) --aside from ignition, all that needs changing is the cover to accomodate the taller 4 cylinder engine.

 

[golddogs]

Re: Chrysler powerhead interchange question

Either year powerhead will fit on your 1979 leg----BUT--- Both those powerheads have old style ignition with points distributors. There is nothing wrong with these ignitions and while they may run very well, the Prestolite ignition on your 1979 is a much better system. It, however takes a bit of work to adapt to older blocks.

What type of work would be required to adapt my present electronic ignition to the older points style block? Is it just a matter of changing all the components over to the older block? Will all the components off of my powerhead fit onto the old one?

Thanks much for your advice

 

[Frank Acampora]

Re: Chrysler powerhead interchange question

I have not yet had the need to do this conversion. However: There was a thread about a month or two ago on this subject. I forget who did the modifications (old-timers disease LOL). Basically, you need to make a 1/16 spacer for the top of the top bearing. You need to drill the top of the block with (5) 1/4 X 20 holes to attach the Prestolite stator mount, but don't go too deeply and penetrate into the block. You will also need to drill the clearance hole for the timing tower to pass through.

Everything else just swaps over.

If the older block has a head that appears to have a tube running down the back of it, swap it for the newer head -- better cooling.

 

[tater76]

Re: Chrysler powerhead interchange question

Frank is talking about the swap I did. I upfitted a 1989 ignition to a 1974 75hp block. Its only worth doing if you have the parts already, or can get the whole ignition system very cheap.

Here is a link to the thread.... http://forums.iboats.com/showthread.php?t=499678&highlight=75hp+rebuild+85hp

And here is a link to video of it running..... http://forums.iboats.com/showthread.php?t=535218&highlight=75hp+rebuild+85hp