Johnson 7.5 & 6 hp lower end interchangebility

[cruisercan]

I'm looking to buy a Johnny-Rude motor for my Zodiac. Interested in 7.5 or 8 hp due to weight considerations. I came across a seller who has two Johnsons for sale. One is a 6hp (std shaft) in good working order, the other is a 7.5hp (1982, long shaft) that has no spark (he said the coil was taken from it to install in the 6hp). I don't have the model #'s yet but should be getting them today or tomorrow and I will post here.

Meanwhile, I'm wondering if the 7.5hp is fixed up, can I take the std shaft from the 6hp and install it in the 7.5hp? Are they interchangeable?

Alternatively, what makes a 6HP a 6HP? I read that some motors were restricted for territorial compliance. Can the 6HP be tuned to have some more oomph?

The seller is about 300 miles away (round trip), so I'd like to do some homework before I strike a deal.
By the way, the asking price is ~ 280 U$ for both motors.

Thanks..

 

[Chinewalker]

Get both. They share about 90% of their parts. And, yes, the lowers are swappable.

The power difference is in the intake manifolds and carbs.they are not interchangeable unless you swap the entire short block.

 

[RCO]

The lower units are identical. If I remember right the 6 hp shares a powerhead with the 4.5 hp, and the 7.5 is different. Many of the other parts like ignition, recoil, etc are interchangeable.

 

[racerone]

NO, no-----The 4.5 has a totally different powerhead !!

 

[cruisercan]

NO, no-----The 4.5 has a totally different powerhead !!

So, is the power head between the 7.5 and 6 the same? (besides the carburetors, I mean)

 

[racerone]

What years / models are you looking at ??

 

[racerone]

For example.----- IN the 84 model year there was a difference between the 6 and 8 HP blocks.----Has to do with air intake parts.

 

[cruisercan]

It turns out, both are 7.5 hp. one 1981 (J8RCIC) and the other 1982 (J8RCNR). This makes it a bit easier since I can service the one that's working and attempt to fix up the one that isn't. Knowing that parts are interchangeable can make troubleshooting easier.

 

[cprodave]

At $280 for the pair you got a good deal. Congrats...