Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

K & B 7.5 front rotor

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Old 12-20-2008, 08:30 PM
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dhal22
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Default K & B 7.5 front rotor

picked up a nib K & B 7.5 front rotor and have decided to NOT make it a collector's item. i want to bench run it for the fun of it right now. any advice from the pros? what prop, fuel, etc?

thx, david
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Old 12-20-2008, 10:54 PM
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lfinney
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Default RE: K & B 7.5 front rotor

8.75x8.25 prop, and add any shim you have run it on 15 -20 nitro. pipe is fine, add some length to get a good tune, macspro.com for length measurements
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Old 12-21-2008, 01:20 AM
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freakingfast
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Default RE: K & B 7.5 front rotor

I'm guessing the header length at 3 ¾". It sure looks like the case and front housing of the K&B 7.5 outboard. If it shares the same parts and if the aero head has the same volume it may be good to 50% nitro but I wouldn't go there. The current K&B DF engine line is rated at 25% max nitro. I'd go with Power Master 15/18.

You want to get this engine to speed quickly at a rich two stroke wide open throttle, no messing around fat, slow and cold. To baby it will kill the con-rod and loose the pinch. Don’t be turning an older un-run engine over unless you are trying to start it, it may not have enough oil in the parts anymore. Before you start, turn the engine till you feel the piston just begin to enter the “pinch”(tight spot), put a few drops of caster or after run oil in the glow plug hole and wait a few minutes than turn the engine upside down to drain out the excess oil. Remove the rear case cover, inspect for foreign matter and put a few drops of oil on the bearing and crank pin. On first runs on tight ABC engines I put the piston at the bottom of stroke and briefly heat the head with a propane torch and quickly start it.


Have fun!
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