'78 6HP Lower unit interchange?

[reelfishin]

I just came across a very clean 1978 6 Hp motor with a damaged lower unit. Both sides of the the anti cavitation plate are broken off, it looks like it got crushed or dropped.
My question is, what years and hp's are interchangeable?
This is the style in which the lower part with the skeg removes from the bottom.
Is anyone here familiar enough with these to know what other years or hp motors might be the same?
Might anyone have a spare housing around?
i suppose I could weld this up, but it would take completely reforming the anti cavitation fin.

 

[67Johnson6HP]

Re: '78 6HP Lower unit interchange?

I've been told that 54-79's are the same. I've got a '78 Evinrude that the l/u looked like yours and the gearcase had more water than oil in it. I found a used '70 Evinrude l/u on EBAY. I'm sure it will fit - looks just like my '67 Johnson. Won't know for sure 'til it gets here, will let you know - maybe tomorrow afternoon.

 

[67Johnson6HP]

Re: '78 6HP Lower unit interchange?

Forgot to mention these are 6hps I talking about. Don't know about other hps.

 

[wbeaton]

Re: '78 6HP Lower unit interchange?

They didn't make a 6 hp in the 50's, but I think you are correct just the same. I believe the 5.5 and 7.5 hp of the 50's share the same lower unit as the 6 hp. Any year 6 hp lower unit should fit your motor. If there is any doubt check the parts numbers at the BRP website.

http://epc.brp.com/login.aspx?ReturnUrl=/Default.aspx

 

[reelfishin]

Re: '78 6HP Lower unit interchange?

They didn't make a 6 hp in the 50's, but I think you are correct just the same. I believe the 5.5 and 7.5 hp of the 50's share the same lower unit as the 6 hp. Any year 6 hp lower unit should fit your motor. If there is any doubt check the parts numbers at the BRP website.

http://epc.brp.com/login.aspx?ReturnUrl=/Default.aspx

The BRP catalogs don't go back past 1968 and the 6HP p/n is different from all others, but they sure do look the same. What years did they make the 5.5? I don't see that listed at BRP, at least not in that time frame?
The one I have is fine mechanically, but the anti cavitation plate is almost completely gone, whoever had this must have dropped it or had it in a vise, the rest of the motor looks nearly new, not even scratched. The water pump impeller is worn slightly, but the rest of the motor looks almost new. This came from a guy that lived on a lake and never used it in saltwater, so it's in really super shape. I don't need a complete lower unit, just the housing would be fine, even if I have to weld this, I'll have to strip this down either way.
I suppose I could use it the way it is or weld the housing, but it would take a lot of welding to fix. I would need to find some metal to weld on to reform the fin, and hopefully not warp the whole housing while doing so.

I just found a mid 60's lower unit from one of the smaller motors, the main casting looks the same, but the shift rod is one piece and the skeg and lower bearing cap is different. On my 1978 the skeg is straight edged and 90 degrees to the prop, the early version is curved and the rear extends past the 90 degree point towards the prop.
Can internals be swapped from the early style to the later style? Can the skeg portion be swapped over? (BRP lists both the housing and skeg as one part number, so I am thinking that they me be a machined fit pair?)

 

[reelfishin]

Re: '78 6HP Lower unit interchange?

I did some searching, it appears that the earlier lower units use a one piece shift rod, where as the 1978 separates at the lower unit. It's not clear whether or not the housing is the same or not?

 

[67Johnson6HP]

Re: '78 6HP Lower unit interchange?

I've had a difficult time finding info on pre-68 OMC's as well. I don't know what year they made the change but my '67 Johnson has the two piece shift rod like my '78 Evinrude. If you don't get a response on this forum you might try e-mailing one of the web sites that specialize in used and older model outboard parts, ie. Marine Parts Outlet, Vintage Outboard, Laings Outboards,etc. and hope someone will take the time to answer your questions.

 

[reelfishin]

Re: '78 6HP Lower unit interchange?

I found a used lower unit from another 1978 today for cheap, it's not perfect, but it's a lot better than the original one, this one has only a small 3/4" chip on the anti cavitation plate. I'll do a quick reseal or even swap in my original internals and I should be good to go.
I did notice while at the dealer today that they changed the waterpump impeller and housing to a newer style requiring me to buy the complete pump now.