Bigdipper99

I just bought my first RC motor, an OS Max 46 AX II and started it up yesterday for the first time. It started up with no problem and ran beautifully. Tonight I wanted to run another tank of fuel through it before mounting it on my Sig Kadet and ran into a problem - I can not get the prop nut to stay tight. I hit it with the electric starter and it failed to start on my first try and I immediately noticed the spinner seemed a little loose. I took it off, re tightened everything applied the electric starter and got the same result again. Tried 3 -4 more times with the same result. I really tightened the prop nut down but it still loosens up when I try to start it. The engine's compression seems fine so I think the crankshaft is OK. Very frustrating! What am I doing wrong?

Also, after these several attempts I noticed both the carburetor and muffler were full of fuel so it probably wouldn't have started anyway. Which makes me wonder what's a good process to dry things out when this happens? I flipped the engine stand upside down and watched the fuel drain onto the ground.

speedracerntrixie

My Feedback: (29)

Sounds like the fuel tank is higher than the carburetor. The fuel siphons into the engine and causes a hydro lock. Attempting to start an engine with hydro lock can damage the connecting rod. I suggest you post a picture of your setup. That will give more information to go on.

A. J. Clark

To clear it out take the glow plug out. Place a rag over the glow plug hole and spin it over with your starter. There will be a good amount of fuel spray out.

Bigdipper99

Speedracer, Thanks for the response. I tried to post photos but RCU informs me I can't post photos until I have 10 postings. Anyway, the instructions for the motor detail that the top of the tank should not be higher than approximately 1/3 above the center line of the carburetor. I'm at least about 50% above the center line. I didn't think it would make much of a difference so perhaps it does. Anyway, I'll try reconstructing the test stand to comply with the instructions. I'm still totally surprised that the prop nut would loosen after the setup ran so well the first time. Hydro lock can cause this to happen? Apparently I've a lot to learn about RC engines!

Bigdipper99

A.J. Thanks for the info. I followed your advice to get the rest of the fuel out of the engine.

speedracerntrixie

My Feedback: (29)

Hydo lock is very powerful. Liquids don’t compress. I once ingested water into a 6 liter V8. Sent one connecting rod right out the side of the block.

Bigdipper99

Speedracer, I followed your advice, rebuilt my test stand with the fuel tank at a much lower level. The prop nut still loosened when I applied the electric starter....really frustrating. So I gave it a go with a chicken stick and the engine started instantly and ran good. I'm still puzzeled about the prop nut loosening? Thanks for the help.

TheEdge

My Feedback: (788)

Put some emery cloth/sand paper between the prop and the backplate.

speedracerntrixie

My Feedback: (29)

Are you using a spinner with a plastic backplate?

mgnostic

This often happens with one of my flying buddies. I don't know your starting technique but he usually spins up the starter and then crams it onto the spinner. With some regularity instead of starting the prop nut come loose and the prop just spins on the shaft. I've suggested that the shock load may loosen the prop nut but we are old and set in our ways.

Outrider6

My Feedback: (2)

Harry Higley Products (owned by Sullivan) carries several styles and sizes of prop nuts. One used as a "jam nut" will likely solve your problem. Find one that matches the threads on your crankshaft (I see that it is 5/16-24), install it properly, and the original prop nut won't come loose. You can find the one you need at this link, then either buy it directly from them, or find it at your regular supplier. If you don't need any nose weight added, then select the lightest one you can find (probably the Lite Lock):

** Harry Higley RC Products **

Scroll down to the product category on the left, which looks like prop nuts and spinners. It looks and acts kind of funky on my browser.

Bigdipper99

Thanks for the tip. It worked perfectly.

Bigdipper99

I was!

speedracerntrixie

My Feedback: (29)

I thought so. Get a spinner with an aluminum backplate. The sandpaper trick works but will eventually fail.

TheEdge

My Feedback: (788)

Creativity over capital.