Go Back  RCU Forums > RC Airplanes > Beginners
Reload this Page >

Prop Will not stay Tght

Notices
Beginners Beginners in RC start here for help.

Prop Will not stay Tght

Old 06-08-2023, 04:04 PM
  #1  
Bigdipper99
Junior Member
Thread Starter
 
Join Date: Dec 2022
Posts: 19
Likes: 0
Received 1 Like on 1 Post
Default Prop Will not stay Tght

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.
Old 06-09-2023, 03:59 AM
  #2  
speedracerntrixie
My Feedback: (29)
 
speedracerntrixie's Avatar
 
Join Date: Jun 2010
Location: Happy Valley, Oregon
Posts: 9,426
Received 160 Likes on 137 Posts
Default

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.
Old 06-09-2023, 12:02 PM
  #3  
A. J. Clark
 
A. J. Clark's Avatar
 
Join Date: Mar 2004
Location: Craigville, IN
Posts: 709
Received 21 Likes on 20 Posts
Default

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.
Old 06-10-2023, 08:57 AM
  #4  
Bigdipper99
Junior Member
Thread Starter
 
Join Date: Dec 2022
Posts: 19
Likes: 0
Received 1 Like on 1 Post
Default

Originally Posted by speedracerntrixie
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.
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!
Old 06-10-2023, 08:58 AM
  #5  
Bigdipper99
Junior Member
Thread Starter
 
Join Date: Dec 2022
Posts: 19
Likes: 0
Received 1 Like on 1 Post
Default

Originally Posted by 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.
A.J. Thanks for the info. I followed your advice to get the rest of the fuel out of the engine.
Old 06-10-2023, 09:17 AM
  #6  
speedracerntrixie
My Feedback: (29)
 
speedracerntrixie's Avatar
 
Join Date: Jun 2010
Location: Happy Valley, Oregon
Posts: 9,426
Received 160 Likes on 137 Posts
Default

Originally Posted by 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!
Hydo lock is very powerful. Liquids donít compress. I once ingested water into a 6 liter V8. Sent one connecting rod right out the side of the block.
Old 06-10-2023, 03:26 PM
  #7  
Bigdipper99
Junior Member
Thread Starter
 
Join Date: Dec 2022
Posts: 19
Likes: 0
Received 1 Like on 1 Post
Default

Originally Posted by speedracerntrixie
Hydo lock is very powerful. Liquids donít compress. I once ingested water into a 6 liter V8. Sent one connecting rod right out the side of the block.
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.
Old 06-10-2023, 04:44 PM
  #8  
TheEdge
My Feedback: (788)
 
Join Date: Dec 2001
Location: Bonita, CA
Posts: 1,080
Received 14 Likes on 7 Posts
Default

Put some emery cloth/sand paper between the prop and the backplate.
Old 06-10-2023, 05:34 PM
  #9  
speedracerntrixie
My Feedback: (29)
 
speedracerntrixie's Avatar
 
Join Date: Jun 2010
Location: Happy Valley, Oregon
Posts: 9,426
Received 160 Likes on 137 Posts
Default

Originally Posted by 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.
Are you using a spinner with a plastic backplate?
Old 06-11-2023, 08:05 AM
  #10  
mgnostic
 
mgnostic's Avatar
 
Join Date: Jan 2003
Location: Kamay, TX
Posts: 1,467
Received 62 Likes on 53 Posts
Default

Originally Posted by 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.
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.
Old 06-11-2023, 08:56 AM
  #11  
Outrider6
Senior Member
My Feedback: (2)
 
Join Date: Apr 2020
Location: Metro Atlanta GA, USA
Posts: 334
Likes: 0
Received 31 Likes on 27 Posts
Default

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.
Old 06-11-2023, 01:51 PM
  #12  
Bigdipper99
Junior Member
Thread Starter
 
Join Date: Dec 2022
Posts: 19
Likes: 0
Received 1 Like on 1 Post
Default

Originally Posted by TheEdge
Put some emery cloth/sand paper between the prop and the backplate.
Thanks for the tip. It worked perfectly.
The following users liked this post:
TheEdge (06-11-2023)
Old 06-11-2023, 01:53 PM
  #13  
Bigdipper99
Junior Member
Thread Starter
 
Join Date: Dec 2022
Posts: 19
Likes: 0
Received 1 Like on 1 Post
Default

Originally Posted by speedracerntrixie
Are you using a spinner with a plastic backplate?
I was!
Old 06-11-2023, 03:05 PM
  #14  
speedracerntrixie
My Feedback: (29)
 
speedracerntrixie's Avatar
 
Join Date: Jun 2010
Location: Happy Valley, Oregon
Posts: 9,426
Received 160 Likes on 137 Posts
Default

Originally Posted by Bigdipper99
I was!
I thought so. Get a spinner with an aluminum backplate. The sandpaper trick works but will eventually fail.
Old 06-12-2023, 08:23 AM
  #15  
TheEdge
My Feedback: (788)
 
Join Date: Dec 2001
Location: Bonita, CA
Posts: 1,080
Received 14 Likes on 7 Posts
Default Glad to be of help

Originally Posted by Bigdipper99
Thanks for the tip. It worked perfectly.
Creativity over capital.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell or Share My Personal Information -

Copyright © 2023 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.