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Outboard nitro engine trouble...

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Outboard nitro engine trouble...

Old 02-25-2006, 10:14 PM
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Hobbes_KGB
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Default Outboard nitro engine trouble...

Hi everyone. My grandfather recently endowed me with his old RC nitro boat. I've worked with nitro engines before but they were all brand new, and they weren't outboard boat engines. The problem is the whole thing is probably gunked up from sitting on a shelf for 20 years. I called HobbytownUSA and the guy there said to just soak the whole thing in nitro fuel overnight. I decided not to do that. I figured it wouldn't be good for all the parts that need to stay lubed on the engine, like the flex shaft and the prop. I decided to remove the upper engine section from the lower unit where the prop and the water inlet are. When I did this I discovered the flex shaft sticking out and noticed it was all greased up (this is when I decided not to soak it). I also noticed that when I tightened the bolts around the bearings that were now exposed, I could no longer turn the flywheel. So I loosened them until the flywheel was once again free to turn.

My questions are: What maintenence should I perform to get this thing back up to normal operating conditions? Should I soak any part of the engine in nitro fuel? Wouldn't that eat away at any grease or rubber tubing? Should I re-lube any parts of the engine, the carb? Should I be careful of any specific torque values for the bolts? Is the prop supposed to turn when I turn the flywheel in a clockwise direction? What if it doesn't? Should I just buy a new engine?

Thanks anyone that takes the time to read this. I hope to get this guy back in the water as soon as possible.
-Alex
Old 02-25-2006, 10:46 PM
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ob nut
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Default RE: Outboard nitro engine trouble...

Never heard of soaking a motor in nitro before. First off, tear the power head apart completely. Inspect for wear on the piston / sleeve, Conrod ends and crank pin. If any of those show any wear, time to replace. Look at the end of the crank, is there "L" or "13" stamped on it? The "L" is a 12mm while the "13" is 13mm. You will need to know this for bearings. Bearings most likely should be replaced with quality Swiss bearings, see Ron at RaceCraftBearings.com ... To get the bearings out, turn the oven on to 350, put the crank case and PTO pieces on a piece of aluminum foil and put in the oven for 10 mins. Remember those are still hot, use gloves
to take them out of the oven. The bearings should fall right out. If one stickes on the crank, use a bearing seperator and pully to pull it off. The carb may need to be cleaned up a bit also. The only part that needs to be lubed is the flex shaft. Sounds like it's still fully lubed. As for torque, use blue loctite when reassembling it all. Give all the bolts a nice tight snug fit. Doesn't need to be cranked down. If you turn the starting cone over, the prop should also turn. If it doesn't, then the flex shaft is most likely broken. Could be the prop shaft is broken..

This should be a good starting point. Come back with any updates or questions...
Old 02-26-2006, 08:57 PM
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Hobbes_KGB
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Default RE: Outboard nitro engine trouble...

Ok I got it all opened up and found the "L" on the crank. Should I replace all the bearings in the engine? It looks like there are about 3 sets? Also, should I wipe down every internal part of the engine while I have it apart? If so, how should I re-oil them, just put nitro fuel on it or grease if it's a bearing or shaft? I noticed when I spun the fly-cone it wasn't spinning the prop. I made sure the crank pin was in the correct place. I think I might have unscrewed the drive shaft by spinning the prop or the fly-cone the wrong way, is that possible? Anyway, it works now, so I think I screwed it back in. So there doesn't seem to be anything wrong with the flex shaft or the drive shift.
Thanks a lot Mark, I appreciate it!
-Alex
Old 02-26-2006, 10:54 PM
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Default RE: Outboard nitro engine trouble...

Alex, when you reassemble the engine use after run oil, a light machine oil, such as 3 in 1, or I believe some people use automatic transmission fluid. For the prop flex shaft, you want some kind of grease. I use waterproof bearing grease that I happen to have for my boat trailer.

Edit: I missed a few questions. I usually clean the parts when I have the engine apart. I use rubbing alcohol, it dissolves old castor pretty well. When I'm done cleaning, I usually put the parts in an oven at about 300 degrees to evaporate the alcohol. Once they've cooled I oil them up and begin reassembly.

For the bearings, remove them, making note of which way each one is oriented and carefully clean them. Once you're sure they are clean, spin them. If there is any sign of roughness, or if you can see any rust, go ahead and replace them. A new set of bearings is not too expensive and it's worth changing them while the engine is apart.
Old 02-27-2006, 12:13 AM
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Hobbes_KGB
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Default RE: Outboard nitro engine trouble...

Thanks a ton Chuck. I think it would be a good idea to replace the gaskets, they don't look very good. I'm gonna go ahead and oil everything that already has oil on it and grease everything that has grease on it after I clean it all. I guess I should have just gone with my common sense. The hardest part will probably be reassembly. I do know that this is an older model K&B and I think the bearings for the new models have changed. I'm considering just upgrading a bunch of parts to the newer models. Thanks guys.
-Alex


I'm having trouble getting the bearings out. I put them in the oven at 350 for 10 mins but they didn't come out. Do I need to get a bearing puller? Where would I find one of the right size?

I also can't get the fly wheel off of the front housing. I removed the fly wheel nut but the cone won't budge. Does it screw off or just slide off the crank shaft?

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