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long shaft\short shaft

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tomnf

Member
I have a short shaft 8 hp merc and my friend has a long shaft 15. Can we swap them so I get the long and he gets the short? Also a merc mechanic said we may have an idle problem due to a [tuner tube difference],All help appreciated,
Thanks.
 
I will assume you are talking two stroke models here. If NOT, then it's a big NO.

The 6, 8, 9.9 and 15 horse 2 stroke Merc's all used the same lower unit/driveshaft housing (leg).

They made a minor change in the leg in mid 1994 to accommodate a slight change in the design of the water tube such that an pre-94 water tube will fit the new leg but not vice versa without a minor modification (just have to drill out the guide hole a little larger to allow a flair in the (newer style) tube to pass through).

Now if you did swap you would have to keep the exhaust plate/tube (from the 15) with the 15 horse and the exhaust plate (no tube) from the 8 with the 8 - so there would be NO tuning issues. That would probably mean you would also have to replace the powerhead base gasket, the housing gasket and maybe the seal around the exhaust plate (20 or so bucks and all available through Merc).
 
galamb said:
I will assume you are talking two stroke models here. If NOT, then it's a big NO.

The 6, 8, 9.9 and 15 horse 2 stroke Merc's all used the same lower unit/driveshaft housing (leg).

They made a minor change in the leg in mid 1994 to accommodate a slight change in the design of the water tube such that an pre-94 water tube will fit the new leg but not vice versa without a minor modification (just have to drill out the guide hole a little larger to allow a flair in the (newer style) tube to pass through).

Now if you did swap you would have to keep the exhaust plate/tube (from the 15) with the 15 horse and the exhaust plate (no tube) from the 8 with the 8 - so there would be NO tuning issues. That would probably mean you would also have to replace the powerhead base gasket, the housing gasket and maybe the seal around the exhaust plate (20 or so bucks and all available through Merc).
Click to expand...
Thanks Graham for the information. I should have said they are 2 stroke when I posted the question. Also I should have said we made the swap and now the 8 runs but wont idle and it ran perfect before we made the swap. And, we put the tuner tube on the 8 long shaft so I bet you nailed it right on.
Thank you very much for the information and we will change things around as you said.
Thanks again
 
OK, we made the swap as per Grahams instruction. Now the 8 will not run at lower rpm. Runs great at hi rpm but just wont idle. We did find one cylinder is not firing at low rpm. changed plugs, put coils from 15 on it and same problem.
What fires the coils?
Thanks
 
ok, so now I bought an 8 hp 1994 power head and need a lower unit if any one has one for sale,
I am getting a bit upset with these trolling motors.
Thanks
 
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