quick engine swap question

[neversinksmith]

hey gang. ive got a customer who has a 76 mercuty 50 hp outboard w a short shaft and a late 60s merc 50 hp long shaft. the ss doesn't reach the water on his boat so he wants to put the powerhead from the ss on the body of the long shaft. is this gona work? thanks

 

[Scott Danforth]

with a torch, welder, and machine shop anything is possible. many changes along the way to contend with.

 

[emckelvy]

A good friend of mine is just doing the opposite, he has an '82 50hp longshaft and is using an older shortie mid-section & short-shaft L/U to make a motor for his 15" transom GW Invader.

After doing some research, we established that the powerhead base gasket from around '66-up 50hp engines was the same part number. Therefore, the powerheads will all mate up to exhaust plates of any years therein.

The thing to do on yours would be to pull the entire 50hp short shaft powerhead, including lower cowling, and slap it onto the older 50hp longshaft mid-section.

You'll definitely need a new powerhead base gasket. I would recommend replacing the tuner-plate-to-mid-section gasket as well, since it's likely to be disturbed by all the commotion. Wouldn't be a bad idea to renew the upper water tube rubber grommet (in the exhaust plate) since it's very common (especially on salty motors) for debris to build up around the grommet and squeeze the water tube shut.

We also found there were some differences in shift linkage (solved by getting the appropriate-year shift arm) between long & short engines, but eBay provided the correct part, even though it's now NLA. If both of your motors are intact, you should have all the parts you need to do the swap.

I really don't see any big issues in getting this done, besides the labor involved and a few consumables.

Hope this helps, and let us know how it goes..........ed

 

[neversinksmith]

great to hear! would it be easier, less labor intensive, and/or possible to simply swap the parts from the powerhead down as opposed to swapping the power heads?

 

[emckelvy]

great to hear! would it be easier, less labor intensive, and/or possible to simply swap the parts from the powerhead down as opposed to swapping the power heads?

Once the powerhead is off, there's not much left to hold the cowling in. You may find some minor differences between newer and older-style cowlings, but if they look the same, there's no reason you can't mix-n-match parts.

I was assuming the powerhead on the older 50hp longshaft motor was no good?? The powerhead is pretty much the split-point between a long & short shaft motor, unlike many Johnrudes which have a 5-inch extension on the longshaft models.

I think Bay Marine makes (or made) extension kits for the 44-cube Mercs, that might be a simpler way to turn the later-model Short motor into a longshaft. But those kits ain't cheap, either!

Just a thought............ed

Cheers.......ed

 

[neversinksmith]

running short shaft is on the boat right now but its too short. non running long shaft (bad cyl) is going to get the short shaft's power head. sorry I wasn't clear

 

[emckelvy]

So, that should work OK, I'd think. One thing we did run into on the '82 motor was that the powerhead studs are a bit longer on the later models. Don't know when they changed this, but probably on your 70's model it'll match up. Worst case, you might have to swap around a few studs off the bad powerhead onto the older, good one.

You can easily measure the studs when both powerheads are off; fore-warned is fore-armed! Sometimes it would be handy to have 4 arms working on these, eh?!!