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converting areo engine to marine engine

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Old 06-22-2018, 03:58 PM
  #1  
gabyhayes
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Default converting areo engine to marine engine

hi I have a old k&b .61 engine meant for airplanes that I'm looking into putting into a boat, my question is I need some way of starting it as on the backside of the engine I have a Perry fuel pump installed, also would I need to mill a water jacket for the head or is the air moving past the head as it moves over the water sufficient cooling for the motor.
thanks gabriel wells
if you need pictures lmk
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Old 06-23-2018, 07:08 AM
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DGrant
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I remember old school engines, and earlier boat set-ups from the 70's and 80's had had water jackets installed around the cylinder, and were started with a belt/pulley on the front of the crank(where it joins the prop-shaft). Although it's not on the "back" of the engine, it still was a popular way of starting these things. The belt just stays in the boat, as it falls free from the crank once the engine is started. Similar to what I've seen on RC heli's... Matter of fact, I just saw an old club member use one a few months back on his boat at one of our float-fly events. Most starters with aluminum cones have a belt-drive-groove machined in for just such applications.

You might use Google search to see if any of those components are still available(new or used), and you might be surprised at what you find. If nothing else you might get pics to go by if you're planning to fabricate components. Something tells me there's something out there though, but I'll leave the searching to you. Good luck with it.

Last edited by DGrant; 06-23-2018 at 07:10 AM. Reason: added info.
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Old 06-28-2018, 06:07 AM
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Yes, what he said. The pulley is usually a steel flywheel with a groove, and a dedicated belt for each boat. If you don't want to go to the trouble of a cooling head, you may be able to use a dune buggy head with the large fins if you can do any machining yourself. This would eliminate the water tubing and a bit of drag.
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Old 06-28-2018, 02:07 PM
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this didn't work

Last edited by Hydro Junkie; 06-28-2018 at 02:10 PM.
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Old 06-30-2018, 08:22 PM
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jester_s1
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It's worth mentioning that since marine engines are commercially available, you may wind up doing an awful lot of work to adapt an aero engine that still won't be as good as the real thing when it's all done.
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Old 07-01-2018, 06:51 AM
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Okay, let me see if I can get my message to post this time. Since Jester kind of hinted at issues in using an aircraft engine to power a boat, let me go into a bit more detail.
While an aircraft engine "can work", you have to look at the issues it will bring with it:
1) An aircraft engine of comparable size will not give as many RPMs as a purpose built marine engine
2) An aircraft engine doesn't have as much power as a comparable size marine engine
3) Cooling isn't as big of an issue with a marine engine

Okay, with all that said, let me explain why to each of the above:
1) The RPM an engine will put out is geared to the prop. Your K&B .61 is designed to run an 11X7 to 12X? prop. This means it's designed to max out at 15K. To go any faster puts the prop blade tips into the trans-sonic to super-sonic range. At those speeds, the prop stops pulling effectively. The result is your plane will respond like the engine has either dropped back to idle or quit. A comparable CMB .67 doesn't have the same issues and can easily spin a 57mmX80mm prop(based on the Octura X457) at 25-30K with a properly set needle and tuned pipe, giving you the potential for far more speed
2) Your K&B .61 is rated at 1.8HP at 15K. The CMB .67 will provide roughly three times the power at 25K
3) To cool your K&B, you need to do one of three things:
  • keep the head in the air flow to prevent overheating
  • tightly wrap soft tubing around the engine, above the exhaust, to give your engine cooling water to keep it from overheating
  • have someone machine you a water cooled head jacket of the appropriate size that can be installed in place of the cooling fins
Since marine engines already have a water cooling jacket, all you need to do is add a water pick up and discharge system to your boat and connect it to the cooling jacket to have cooling.
There is one exception to all of this, running an airboat. Since it uses an aircraft prop and is in the airflow, by design, it would be the perfect choice to power one of these

Last edited by Hydro Junkie; 07-01-2018 at 06:53 AM.
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Old 07-01-2018, 06:59 PM
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Yup, what he said. I seem to recall somebody made a water cooled hose clamp looking deal called a "cool clamp" back in the day. Octura maybe?? You clamped it on the base of the head and hooked the water lines to it. I used one on an Enya 35 in my Hydro once and it worked, then I put my OPS45 in it and threw the Enya away............

It can be done, but a marine engine is the way to go.

Scott
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Old 07-01-2018, 07:35 PM
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Here's a NIP Octura Kool Klamp
Click image for larger version

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Old 07-01-2018, 08:00 PM
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How did I know you had one and would post a picture of it?????

Still, use a marine engine......

Scott
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Old 07-02-2018, 12:09 AM
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I don't have one, just found the picture, online, out of sheer luck
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