Mercury Mark 25 Prop Adaptor

[cheetahgod]

I have a Michigan wheel 9 spline prop adapter which fits the mark 25. Is there a high pitch prop I could use with this adapter on my mark 25?

---

Attachments:

[jw-in-dixie]

Yes, a lot of those were used on KG7s instead of the clutch. Many props available, even if you have to drill the matching holes for the pins.

[cheetahgod]

What would be an example of a prop?
Thanks.

[jw-in-dixie]

Sorry but I have sold my speed props that fit that adapter and don’t recall any numbers. 86. Try eBay and the wanted and for sale page here.
Google for prop shops, especially older ones. Wish I could help. If you want to go faster consider building a rat motor which will be lighter.
Good luck. JW

PS. Looked in my Michigan Wheel catalog and found some adapter pin props listed:
AJ48 7-3/4" Dia 10" Pitch 2 Blade bronze for 1949-50 Mercury KG7
AJ49 " 10.5 " " "
AJ50 " 11" " "

There ya go. 🙂

s

[A Hoskins]

JW, as usual, had shared some good advice regarding weight reduction and has pointed you in the right direction for prop selection. Michigan defines the AJ-49 as "not a true screw" which I don’t fully understand. I might also include a Michigan K-60 which has a hub I.D. of 5/8", a prop O.D. of 8-1/2" and 9-1/2" of pitch. I can’t guess what you might define as "high pitch". I think there are 11" pitch props which would be a direct fit (no adapter) for your MK-25. I think that 12" of pitch will be the limit for a garden variety MK-25 on a light hull. Consider that the AJ props have a hub O.D. smaller than your MK-25 lower unit and this may cause some unwanted turbulence on the leading edge of the prop. I hope others chime in, I have a lot to learn. Playing with propellers can be fun.

"Fox News" isn't.

[mercuryman]

There is a problem using the adapter, its gear ratio. The Mark 25 is 13 : 24 and the KG7 is 16:21. At 4000 RPM the prop on KG7 is going a lot faster. Thats why they put a big 9.5 inch diameter on the Mark 25 its going slower.

[dave-bernard]

Remember K model motors are left hand rotation and mark models are right hand.

[outboard315]

Bigger problem the Mark 25 prop shaft is only splined half way.

[outboard315]

Ps the adapter is for a KF7 or KG7.

[dave-bernard]

Want a higher pitch prop? get an 11inn pitch send it out to a repair shop and have it repitched as much as possible if that is not enough add a cup to it. must be used on a VERY LIGHT boat and driver combo. got pic of boat and driver?

[Author]

Posts