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Greg Rowe

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Feb 19, 2013
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434
I am looking for a K&B 7.5 pto that fit the AMPs outboard the PTO would have a 5mm hex instead of the common square drive.
Thanks
Greg Rowe
 

Greg Rowe

Well-Known Member
Joined
Feb 19, 2013
Messages
434
Kinda crazy that AMPs used several different engines to use for power but the favorite was OS,and K&B but nobody seems to know where or who made the PTO shaft. I emailed K&B and I was told they never heard of a hex drive PTO for a 7.5
 

Mike Luszcz

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Joined
Jul 31, 2008
Messages
4,049
I called Jerry that was the shop forman at International Hobbies from 1982 till they closed in 1990, and he said theu actually made the PTO, the PTO mount and flywheels all in house. They purchased the OS VR .46 and .65 engines, and the KB 3.5, 7.5, and 11cc engines directly so they could modify as required. Thats why the PTO's are hard to find outside of a complete AMPS outboard.
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Greg Rowe

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Joined
Feb 19, 2013
Messages
434
No I am waiting from someone I know that has as cnc shop
He made me an a pto to swap a CMB on an OS but that's alot easier
Why can you get any print?
I'm guessing the female hex was done by forge or cast die
Outside my knowledge
 

Geraghty

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Joined
May 16, 2003
Messages
1,501
I did this in the 80's when I was running a AMPs motor....The AMP's PTO was a dumpster fire because the oil seal was so bad.....
Get a piece of 1/4" hex stock and have somebody mill half of it down to a 3/16" square.....[It isnt a perfect 3/16 square...measure the square of a K&B cable....I don't remember what that dimension is....]
You then will be able to use the 7.5 K&B PTO.........All you have to do then is drill some new mounting screw holes in the aluminum
pan in between the lower unit and mount the K&B PTO to the pan.....The motor ran great and the needle was not a problem....
There is plenty slop in the connection so alignment isn't a problem....
I finally bushed the AMPs PTO so I could set the NAMBA 7.5 OPC record....I couldn't use the K&B PTO and be legal in 7.5 OPC.....
Shortly after I just really killed the record the NAMBA OPC troops revolted and lobbied and made the motor illegal....lol
 
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MikeMayberry

Member
Joined
May 15, 2015
Messages
15
No I am waiting from someone I know that has as cnc shop
He made me an a pto to swap a CMB on an OS but that's alot easier
Why can you get any print?
I'm guessing the female hex was done by forge or cast die
Outside my knowledge
Doubtful. Most likely done with what's called a Rotary Broach.

 

Geraghty

Well-Known Member
Joined
May 16, 2003
Messages
1,501
It was done with a broach, Jerry said Miller Agnew brought one over from the UK and it made the hex hole in the PTO. Mike
The problem with a rotary broach is the cost ..... they are very expensive...
A rotary broach with a hex cutter will eat up the major part of a $1000.00 bill......
That cost of a rotary broach is the reason I made the special coupler shaft in the 80's........
 

MikeMayberry

Member
Joined
May 15, 2015
Messages
15
You can have a rotary broach setup for $500. $425.00 for the holder and around $75 for the broach. A one off is one thing. But if your going to make even a small production run. The Broach is the way to go.
 

Greg Rowe

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Joined
Feb 19, 2013
Messages
434
I think the best way is get 3/16 round stock maybe 4140 cut to length and mill the square end for the stock KB pto
If you go with the hex you will have to change the PTO bearing due to a larger pto shaft due to the hex.
 

MikeMayberry

Member
Joined
May 15, 2015
Messages
15
Well you guys would know. I can only speak to the machining side of the issue. Just cutting a square on the 3/16 stock versus broaching the hex is certainly much cheaper and easier.
 

Geraghty

Well-Known Member
Joined
May 16, 2003
Messages
1,501
I think the best way is get 3/16 round stock maybe 4140 cut to length and mill the square end for the stock KB pto
If you go with the hex you will have to change the PTO bearing due to a larger pto shaft due to the hex.
Get 1/4" steel "HEX" stock..... result= hex into lower unit and square into K&B PTO
I originally used aluminum hex and it worked fine....I went to steel because it made me feel better....I milled a small radius at where the hex met the square and it never broke on me and I ran the hell out of it.....
Another little word of advise.....If you ever do run the AMPS unit use a smaller prop and bury it in the water.......As I recall I used a relieved X447......
If you try to run a bigger prop and surface it up on the tips you will quickly grenade the gears in the AMPS unit......
I also did some testing with the venturi piece in the aluminum pan and increased the fuel pressure dramatically....That also really help the needle consistency.....
If you want to talk AMPS give me a call.....1-715-926-6096......I think I can really help you to reduce your Xanax intake.....
If we ever do talk just say "bushed AMPS pto".....that will bring back a flood of memories........The AMPS PTO was a train wreck.....
 

Greg Rowe

Well-Known Member
Joined
Feb 19, 2013
Messages
434
I have to really thank you for the history with an AMPs engine.
This conversation all started when I found a amp lower and having a kb 75 and of course there are no spare parts, so I started talking to Mike about what or how to make it fit but not to lose the originality to the model.
And no I will never run the engine just going to place it in my show case.
Thank you, now I know how to make it all work and will not alter the amp drive.
Thanks
Greg
Ps How fast did you get an amp to run?
 

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