Propjockey
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K&B Auto-trim unit
Has anybody used one of these on their 3.5 OB--and if so, did it help?
Has anybody used one of these on their 3.5 OB--and if so, did it help?
K&B Auto-trim unit
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Propjockey
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Re:K&B Auto-trim unit
Well let's see...it's a little gizmo (looks like a door hinge, but horizontal) that mounts to the transom and then the engine mounts to it. A rod mounted on the engine rides on cams at the front of the assembly and forces a trim change on the engine when the boat enters a turn.
Well let's see...it's a little gizmo (looks like a door hinge, but horizontal) that mounts to the transom and then the engine mounts to it. A rod mounted on the engine rides on cams at the front of the assembly and forces a trim change on the engine when the boat enters a turn.
Propjockey
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Re:K&B Auto-trim unit
another shot
another shot
Propjockey
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Re:K&B Auto-trim unit
This will give you a better idea of how it's supposed to work. Notice in the pic below that when the engine is straight, the rod is centered on the brass cams and the engine has zero trim (the forward bracket doesn't fit inside this particular hull, but you get the idea)
This will give you a better idea of how it's supposed to work. Notice in the pic below that when the engine is straight, the rod is centered on the brass cams and the engine has zero trim (the forward bracket doesn't fit inside this particular hull, but you get the idea)
Propjockey
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Re:K&B Auto-trim unit
Now the boat is in a right turn (work with me here). The rod is pushed down by the cam and forces the engine to tilt up, changing the trim (notice the 'door hinge').
Now the boat is in a right turn (work with me here). The rod is pushed down by the cam and forces the engine to tilt up, changing the trim (notice the 'door hinge').
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Re:K&B Auto-trim unit
Well, if there's one good thing to be said about being around this hobby for a long time it's you can shed some light on some things that were done more than 20 years ago.
I did run that adjustable trim on my tunnel boats - back when Mikie Z was about 8 years old. The idea was as you turned the motor the prop thrust angle would become postitive and lift the front of the boat. At that time, model tunnel boats tended to hook out in corners. With the development of 15 degrees sponsons and front "stumble blocks" the cornering was greatly improved.
The motor shown is the second generation K&B 3.5 with an exhaust throttle for speed control. Making that exhaust slider work smoothly was a real pain.
Jerry Dunlap
Well, if there's one good thing to be said about being around this hobby for a long time it's you can shed some light on some things that were done more than 20 years ago.
I did run that adjustable trim on my tunnel boats - back when Mikie Z was about 8 years old. The idea was as you turned the motor the prop thrust angle would become postitive and lift the front of the boat. At that time, model tunnel boats tended to hook out in corners. With the development of 15 degrees sponsons and front "stumble blocks" the cornering was greatly improved.
The motor shown is the second generation K&B 3.5 with an exhaust throttle for speed control. Making that exhaust slider work smoothly was a real pain.
Jerry Dunlap
Propjockey
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Re:K&B Auto-trim unit
Thanks Jerry--so you think it would work on an older hull with less dihedral?
Thanks Jerry--so you think it would work on an older hull with less dihedral?
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Re:K&B Auto-trim unit
Propjockey,
Well, "work" is an interesting term when it comes to model boats. It will make the boat go in a forward direction. You are dealing with model tunnel hull technology that is over two decades old. But, what the heck. Sounds like you got the hull at a good price and if you enjoy running this boat you can always upgrade to a better boat and motor. Use an Octura X440 prop. The aluminum prop that came stock with that series K&B was useless. Set the balance point at 1/3 the distance from the transom to the bow - a 24" boat should balance between 8" - 9" from the transom. It's been a while since I taught math, but I think 1/3 of 24 is somewhere around 8.
Good luck,
Jerry
Propjockey,
Well, "work" is an interesting term when it comes to model boats. It will make the boat go in a forward direction. You are dealing with model tunnel hull technology that is over two decades old. But, what the heck. Sounds like you got the hull at a good price and if you enjoy running this boat you can always upgrade to a better boat and motor. Use an Octura X440 prop. The aluminum prop that came stock with that series K&B was useless. Set the balance point at 1/3 the distance from the transom to the bow - a 24" boat should balance between 8" - 9" from the transom. It's been a while since I taught math, but I think 1/3 of 24 is somewhere around 8.
Good luck,
Jerry
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Re:K&B Auto-trim unit
I had one of these and it wasn't that it didn't work well, it's like Jerry said. The engine and boat technology has gotten so much better that those are a thing of the past. Hey, if you've got it, flaunt it. It definitely will be a conversation piece at the local race.
I had one of these and it wasn't that it didn't work well, it's like Jerry said. The engine and boat technology has gotten so much better that those are a thing of the past. Hey, if you've got it, flaunt it. It definitely will be a conversation piece at the local race.
RobertDoak
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I realize that this thread is older than grandpa....but the auto trim is a nice option....I have used the auto trim on my first fiberglass Hotshot 21 and worked great...just snagged another from Ebay..
On this wood Hotshot sprint I had to fabricate the trim assy. From wood....the hull is too narrow for the aluminum factory part
On this wood Hotshot sprint I had to fabricate the trim assy. From wood....the hull is too narrow for the aluminum factory part
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