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K&B 7.5cc outboard - How do these PTO bearings get proper lubrication?

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K&B 7.5cc outboard - How do these PTO bearings get proper lubrication?

Old 08-07-2007, 10:39 AM
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MyStar
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Default K&B 7.5cc outboard - How do these PTO bearings get proper lubrication?

Could you outboard experts out there please tell me how these two PTO ball bearings get proper lubrication? I'm going to be running my new outboard this weekend for the first time and don't want to burn these bearings up!


Don
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Old 08-07-2007, 12:04 PM
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topfuel4430
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Default RE: K&B 7.5cc outboard - How do these PTO bearings get proper lubrication?

They get the lubrication just like every other part of the engine, by the oil that is mixed in with the fuel. The crankcase pressure forces the fuel/oil into the bearings from the inside of the engine. As long as you have good quality fuel, and you flush the engine VERY well after you are finished running, the bearings should last serveral gallons of fuel. Dont forget to lube the prop shaft, or install an oiler.

Have fun with it!

~James
Old 08-07-2007, 01:07 PM
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MyStar
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Default RE: K&B 7.5cc outboard - How do these PTO bearings get proper lubrication?

Thanks for your response James!

I took the PTO assembly outside to look at it in the sunlight and can now see how the ball bearing on the crankshaft side gets it's lubrication from oil in fuel simply trickling down.

However, when I put some drops of red Marvel oil into the bearing on the crankshaft side, no oil came through to the other ball bearing on the flex cable side...that bearing is still bone dry... I even tried spraying some Liquid Wrench into the bearing on the crankshaft side and couldn't force ANY lube to come through the bearing on the flex cable side. And so, I don't understand how the bearing on the flex cable side gets lubricated.


Don
Old 08-07-2007, 01:12 PM
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MyStar
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Default RE: K&B 7.5cc outboard - How do these PTO bearings get proper lubrication?

James,

"...and you flush the engine VERY well after you are finished running, the bearings should last serveral gallons of fuel. Dont forget to lube the prop shaft, or install an oiler."

I'm new to boats, but not new to R/C as I fly planes and heli's. Could you explain how you flush your outboard? Which bearings only last several gallons? And what kind of lube do you recommend me using for the prop shaft?


Don
Old 08-07-2007, 01:13 PM
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Default RE: K&B 7.5cc outboard - How do these PTO bearings get proper lubrication?

LOL.... you are working two forums for the answer huh? whatever works!

Like I said above, the crankcase pressure forces the fuel/oil into the outer bearing. It does not need to be drenched in oil in order to be lubed. The bushing area between the two PTO bearings is a very tight clearance for the PTO shaft. This tight clearance, along with the film of oil, provides the air tight (or close to it) seal for the engine to operate correctly. That outside bearing will also get lube when you squirt lube into the top of the lower unit for the flex shaft. This is also the case with an oiler system. Trust me, its just fine the way it is. It gets lubrication, no problem.

~ James
Old 08-07-2007, 01:28 PM
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topfuel4430
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Default RE: K&B 7.5cc outboard - How do these PTO bearings get proper lubrication?

Hi Don, with boats, the obvious other contaminate besides fuel residue is water.

You will get a hundred different answers on this, but heres my process. I first flush the engine liberally with WD-40 (water displacement). I have a nipple threaded into the spray nozzle of a can of wd-40 and a piece of fuel tubing going from that to the carb inlet. Open the barrel on the carb, and spin the motor over with the starter while spraying the WD into the engine. I have a "oil out" kit that is screwed into the glow plug hole while this is being done. This oil out catches the old oil, WD, water and whatever else is in the engine. (You can see an oil out kit on my site listed in my sig.) I flush VERY thouroughly, as it takes a while to get all of the water out. When you think you have all of the water out, flush it some more, and then you should be good. I then take the same piece of fuel tubing that is hooked to the WD can, and hook it into my water cooling inlet, as this also needs to be flushed. Take it from someone who works on hundreds of these little engines for a living, leaving water in the head, is not good. The head bolts can easily get rusted, then they snap off when trying to remove them. I have seen water cooling jacket completely clogged up with corrosion from lack of flushing.

After I flush out the engine and water cooling completely, I then use automatic Transmission Fluid in the engine. I just squirt it in through the carb opening and then bump the engine with the starter a few times to get it circulated, and youre done. The next time you run the engine, you will have to flush out the oil that remains inside the engine before attempting to start it.

I also flush my fuel tanks the same way, except of course, without the ATF at the end.

You have to realize that boat engines see alot more abuse than an aircraft engine (I fly also), they are under heavier loads, and produce more RPM, all of which lead to needed preventative maintenance. (i.e. bearings, etc.). If you use a good quality fuel, and flush good, you will see a good bearing life. Typically on a .45 engine, bearings can last anywhere from 2-6 gallons before needing replacement. Sometimes more, sometimes less, depending on a lot of things. The key is to replace them BEFORE they come apart or get too worn out. Some guys have a schedule on replacing bearings, such as twice a year, or every 3 gallons, etc. It depends on how much you use it, and at what level (i.e. racing on the edge, or just playing at the pond). I usually tear my engines down after every race weekend and inspect, but its not neccesary.

Hope this helps, ~James
Old 08-07-2007, 01:33 PM
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topfuel4430
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Default RE: K&B 7.5cc outboard - How do these PTO bearings get proper lubrication?

Forgot to mention, I run an oiler system and use a mixture of ATF, and Gear oil in my oiler. Many thing work great, but you will have to determine what is easier. The best part about an oiler system, is you fill it before you go out on the water everytime, and you forget about it. I use a mixture that allows the lube to flow slow enough so that my resevoir is almost empty after a tank full. My Flex shafts/prop shafts are always happy.

If you dont run an oiler system, then you can squirt gear oil, or a milion different other things into the lower, but just remember to do it every time you run it!

~James
Old 08-08-2007, 07:19 PM
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terry kelly
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Default RE: K&B 7.5cc outboard - How do these PTO bearings get proper lubrication?

man i just bought a top speed 2 and a thunder tiger 21 pro engine.. those things seem to be quite a bit of work , but i guess they all are. i must say thanks btw , i have never thought about wd-40 in the cooling system , it does make alot of sense.. thanks for making me smarter guys. and not to hijack this thread , what prop do you recommend and how bout a pipe for my tt 21 pro xm ?
Old 08-12-2007, 01:34 PM
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jmbraychy
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Default RE: K&B 7.5cc outboard - How do these PTO bearings get proper lubrication?

HEY DUCKIE HAVE YOU GOT YOUR BOAT DONE YET??????????? NEED TO ORDER ANYTHING ELSE ??????????
MAYBE YOU CAN RUN IT IN THE BATHTUB TO MAKE SURE IT WORKS BEFORE YOU COME OUT AND OUTRUN US SLOW GAS GUYS.
LOL LOL LOL JUST BUSTIN YOUR CHOPS.......O BY THE WAY -------------IS YOUR BOAT DONE YET????..............IS YOUR BOAT DONE YET?????................IS YOUR BOAT DONE YET??????....................LOL.....MIKE....

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