Engine Swap

[BoatDr]

Turns out my 1979 Evinrude 115 blew a ring, scoring two cylinders and only god knows what else internally, so after looking through craigslist for a few months, I stumbled upon a deal for a 1985 Johnson 120 hp for $750 claiming to have 125 PSI in all 4 cylinders. The model # is 120TXCO, so it has a 25" shaft. Engine does not come with controls.

My question is what is the shaft length of the my '79 Evinrude, and would the new Johnson be too long? The engine is going on a '66 18.5' Starcraft Holiday. I am also wondering if the controls from the '79 would work with the '85 Johnson as well. Both engines use the "Red Plug." I'm down at school away from both of the engines, so I can't do the obvious and go measure each of them. Thanks.

 

[oldcatamount]

Re: Engine Swap

A 25" shaft is a "long shaft" motor and a 20" shaft is a "short shaft" motor. I think you'll be Ok with the long shaft motor. It'll be in the water 5" deeper than your short shaft that's all.. Just remember that when you're coming into a dock in shallow water! I also believe the controls will work on the 120hp as well, but, can't be certain about that.

 

[ezmobee]

Re: Engine Swap

I can't agree with the above post concerning shaft length. If you mount a long shaft motor of that HP on a boat with a short transom your performace would be HORRIBLE unless you got a jack plate. I agree that the controls should swap just fine. The 120 is a looper I think so you probably can't switch the powerheads.

 

[BoatDr]

Re: Engine Swap

Could I switch out lower units? Or is the mid section also a little longer?

 

[ezmobee]

Re: Engine Swap

I think the only thing bigger is a the mid. I really don't know what's swappable between a crossflow and a looper though.

 

[Dhadley]

Re: Engine Swap

A 15" motor is a short shaft. There were / are no short shaft recreational V4s.

A 20" motor is a long shaft.

A 25" motor is an extra long or x-long shaft.

A 30" motor is an xx-long shaft.

The controls will interchange, no problem. Also no problem using a jackplate (like a Bob's 4 in 1 convertable manual plate) to install a 25" motor on a 20" transom. Playing with setback may help with set up too.

 

[Dhadley]

Re: Engine Swap

You could swap the lower units as long as you change the driveshaft (not so easy) and shift shaft (very easy) to match the midsection they're going on.

 

[BoatDr]

Re: Engine Swap

I think my transom is about 21.5" and I could mount the bracket up three more holes for another 1-2", which would put the cav plate of the 25" about 1.5-2.5" below the bottom of the boat. Is this acceptable?

 

[Dhadley]

Re: Engine Swap

Describe "acceptable". Will it push the boat thru the water? Yes. Will there be issues? Yes, performance issues at the least. Possible engine damage? Yes, it's possibe / likely you'll have water intrusion thru the air intake and damage the internals of the motor.

The difference in technology between those 2 motors is astounding. Don't limit your potiential just because you won't spend 200 for a manual jackplate. And yes, now is the time to buy it, not later.

 

[BoatDr]

Re: Engine Swap

Thank you for all of the replies. I have two concerns with the jackplate: One is that with the current engine, the stern sits a little low in the water; with the weight of the larger engine, jackplate, and the engine sitting another 5 inches back off the transom, is this going to be a problem? The second is the steering cable. It can't be raised anymore to accommodate the higher engine.

I did find an '85 looper 20" midsection for about the price of a jackplate on ebay... The engine may be a good price, but with having to buy a jackplate to use it, I may be further ahead waiting for a deal on an engine that fits. I guess I've got all winter haha. Thanks again guys.

 

[Dhadley]

Re: Engine Swap

If the boat is that weight sensative you may want to compare the weight between a V4 crossflow and the weight of a 90 degree V4 looper. The weight of a manual jackplate is nothing. Check the NADA site for the weights.

 

[BoatDr]

Re: Engine Swap

Well, I guess the weight isn't that much different, 15lbs, but I'm still confused/concerned about the steering since the engine will be up and back 5"

 

[Dhadley]

Re: Engine Swap

OK, now we can look at the steering. Yes, the motor will be up 5" so we need some slack there assuming you have mechanical steering. As for the setback we can go either 5" or 2 1/2" with Bob's 4 in 1.