boat 58

I'm new to airplanes and I need some help. I have a used O.S. Surpass 4 stroke .48 engine.
I have no problem starting and running it, it's just that the prop spinner keeps getting loose.
One question: the engine turns ccw standing in front, the prop nut is a right hand thread, the starter
rotates ccw....so... if I keep using the starter ccw and the spinner is a right thread won't it keep
making the prop spinner loose all the time....Do they make a cw spinner? thanks

jetmech05

a 4 stroke needs 2 nuts one to hold everything on and a jam nut. I have never used a plastic spinner on a 4 stroke...so I had a nut to hold the prop and back plate then a jam nut with a threaded hole in the center to hold the spinner on

52larry52

My Feedback: (1)

jetmech05 is correct on 4 strokes using a double nut assembly. A little blue loctite on the threads won't hurt also. Use blue loctite on 2 stroke prop nuts too. If your using a wooden prop, retorque the nuts after each days flying as the wood props crush with use and need more attention than other prop types. Prop shaft threads and nut threads must be oil free for the loctite to work, clean with alcohol and dry if necessary. Some one smarter than I here on RCU recently explained why left hand threads wouldn't work...something about the "power pulses" when the engine fires is actually in a tighting direction and if it were left hand threads it would want to lossen the prop nut in use. Makes sense as it is when a 4 stroke backfires or runs backwards that the prop will sometimes come loose. A few years ago I also had a 2 stroke shed a spinner nut and wooden prop in flight. Not tight enough, and not loctited!!

jester_s1

Using loctite is a bad idea, and totally not necessary. The problems with it are 1) It makes it hard to change props and 2) props can compress over time (especially wood ones) and you won't be able to put a wrench on it and tell because the nut is glued on. Your problem is simply that you aren't tightening the nut down enough.
Instead, use a box end wrench or at least a big pair of pliers to torque the nut down hard. Don't worry- the crank won't break. Don't use a spinner with a plastic back. If you must, put a piece of open mesh plumber's sandcloth between the spinner and your prop so you don't have plastic rubbing on plastic. Better is a metal backplate that really grabs the prop. Tighten it down hard with the wrench and it won't move until you want it to. If you ever use a wood prop, retorque the prop nut periodically to keep the clamping pressure up as the wood compresses.
BTW, the only reason a 4 stroke needs that second nut is in case of backfires. A backfire puts incredible torque on the prop in the unscrew direction, so much so that they have been known to quickly unscrew all the way off and go flying through the air.

Gray Beard

My Feedback: (-1)

Everything Jestr said. Most of the time my four strokes only have one nut on them, usually just the spinner adapter nut. I only use wood props on my gas engines in larger sizes, APCs on my glow engines. I loosen the spinner and prop nut on my gassers because the wood props compress and get loose, by loosening things myself at the end of the day I have to tighten everything up before every flying session. I do it this way because I tend to forget to re-tighten the prop before use. I never have had an APC just come loose like a wood prop.

52larry52

My Feedback: (1)

boat 58, Try the blue loctite for yourself and decide. It's not glue, and when properly used it works. Please NO "big pair of pliers", just a 6 or 12 point wrench or socket on the prop nut. NO vice grips either!!

ameyam

Just use a locknut- any nit with the same thread that fits on the crank after the main nut. They will never come off, just ensure you tighten the two seperately

Ameyam

BIGMIG

Just a word of "caution" when it comes to blue "LOCTITE"..........It will disstroy certain types of plastic.(some people don't know that ).I don't know if it can dammage a prop....The funny thing is it comes in a plastic bottle.(but the kind of plastic bottle it don't eat into ).

For what its worth......

BIGMIG

52larry52

My Feedback: (1)

OK, you guys may not believe in loctite but I do!! OP, take your choice, try it to see if you like it. Loctite is not glue. It comes in various strenghts denoted by it's color. Blue is what you would use here and for general assembly use. Yes, be aware if retorqueing a wood prop you must overcome the loctite to snug it some more. Not a big deal and neither is "it's hard to change props", it's not if you are using the correct tools, box wrench-YES, a big pair of pliers-NO! Make that HELL NO!!! Ditto to NO VICE GRIPS! Correct size box wrench or socket, 6 point or 12 point are good. Only a small amount is required, one drop per nut. The same amount of torque is required to loosen a loctited assembly as when it was tightened, then the left over loctite acts sorta like a nylock nut and requires a tool to continue to spin it off, not just your fingers. It's EZ to clean off if you decide you don't like it and want to discontinue use on that application. Just clean off the male threads with a small hand wire brush. I have 35 years experence building successful racing engines and race cars, and now model airplanes and have learned how and when to use loctite. The parts didn't fall off my race cars, and they don't fall off my planes if I don't get lazy and forget to use loctite ( 2 stroke engine sheding a prop with no loctite).

mike109

G'day

A second caution on Loktite and plastics. I used some on a plastic trailer plug some years ago. Next day the entire plastic part of the plug had turned into granules. Really strange. Obviously it does not happen to all plastics but it certainly does to some. Use with caution.

You can buy the lock nut set for the 48. It is the same for the more recent 52. Well worth buying.

Cheers

Mike in Oz

sebo

Plastic spinner on plane 25 years old...still flies (occasionally). Plastic back plate too. Brand of spinner is "ROYAL" and is no longer produced. The cone screwed on backwards thus it tightened as it ran. Engine is an OS 90 4 stroke....one of the first made and sold.

ec121

My Feedback: (2)

We have the Loctite sales reps. put on forums at work. They buy us lunch and do a talk. Called a lunch-and-learn. They have all kinds of compounds for various sealing applications. The plastic Loctite bottles are made of a special plastic that lets air into the bottle to keep the stuff from hardening. That is why an old bottle of the stuff looks like it leaked. It did!! It is an anaerobic compound that sets without air. As when the nut is tightened. So the bottle must breathe to prevent hardening. The removable blue will work for the prop shaft, but it isn't needed. I have used all sorts of nuts on 4 strokes. A lean needle will cause a backfire. I had one throw a prop nut 20ft. one time.

Villa

Hi boat 58
You asked if they make CCW threaded crankshafts so the nut will not come off. NO, they don't! The reason is that the nut would come off more frequently if the thread was CCW. The resisting wind load on the prop is CW, which is in the direction of tightening the prop nut. The reason the prop nut gets loose is because it is not being tightened enough. Most people use the X-wrench used to tighten the glow plug, to also tighten the prop nut. Well, the wrench is not large enough to generate the torque needed to keep the nut tight. I use an adjustable crescent wrench with a 10" handle to tighten the nut. A 6" or 8" wrench would be enough, but I just happen to have this extra wrench. Use your small X-wrench to tighten the nut in your usual manner, then use a larger wrench to tighten it a little more, until you learn what is "enough". By the way, if your engine "backfires" it will usually loosen the prop nut. That is another proof that a CW thread is the correct thread. I would NEVER use Loctite on the nut. I believe it is very likely that the nut would not come off and might turn the crankshaft after the prop loosens. Then you would have to be inventive to hold the crankshaft to turn the nut off. Let me know if you agree with all of this.

charlie1960

double nut on a 4stroke.....
helps keep it all tight if it backfires too.

jester_s1

Villa- I doubt the blue loctite would give you a problem with spinning the crank after breaking the nut loose, but as several others have stated it's simply not needed. A prop nut with enough torque on it will stay put without any glue or not-glue as the case may be. Loctite is a great product for the things it's needed for like holding helicopters together and keeping mufflers on, but cranks have fine enough threads that if you get the 20 ft lbs or so that you really need to clamp the prop down right that nut isn't going to move.

All Day Dan

My Feedback: (5)

Boat58, I sent you a PM. dan.

Gray Beard

My Feedback: (-1)

If the nut is on tight then there should be no need for any type of glue. If an engine is in tune it doesn't back fire and throw the nuts or prop.
Never once seen an instruction manual from any manufacture say to use a glue on the crank? They do say tighten the nut though. A four stroke does come new in the box with a jam nut though and should be used for safety reasons. They do help but aren't a 100% cure all. It was a couple of years ago I had my last back fire from a four stroke, it was strong enough to toss both nuts and bend the aluminum spinner. It was on a freshly rebuilt YS 1.20 NC that is a bit different to tune then other engines, I had it just a bit on the lean side, my bad. The double nut helped. I only run one nut on most of my engines though but not until I have them dialed in. I have never seen any of the guys I fly with use glue on the crank, done correctly there just isn't any need for it.

boat 58

I wish to thank everyone for there positive input, I feel alot better about this setback
about this spinner problem and I'll fix it.
The engine came with no nuts or washer so I ordered some online, all I used was a 1/4-28 Du-Bro
aluminum spinner prop nut to hold my 11" plastic prop on.
Thanks again....Regards...Ed

carrellh

It is possible that the crankshaft is long enough for the spinner nut to 'bottom out' on the end of the shaft without getting the prop tight.

biam

I geuss I am just lucky, never have used Loctite or a double nut, always just the single propnut. This is on two and four stroke a like, no issues in ten years of flying.

jaka

Hi!
The reason the nut comes loose is probably that you do not tighten it enough. Loctite should not be used!!!!!
In my 37 years of flying R/C I have never myself encountered that the an alumium spinner nut has become loose. I have seen others though, but that has always been due to the fact that they have not used enough torque when installing the nut.
Those 4-way wrenches are no good!

opjose

Ibid...

If it's coming loose, you're wood is compressing, or your not tightening the nut enough.

Every time I see this happening to someone, I pull out a larger wrench than what they have on hand and REALLY tighten it down.

The standard response I get is "aren't you afraid of stripping the nut?" but their prop nut no longer falls off.

The double lock nut is a good safeguard, particularly for wood props, but it shouldn't be needed for composite props.

Locktite? No thanks! I already have problems getting locknut off.

jester_s1

I'd disagree with using anything extra to keep a wood prop tight too. Wood props don't get loose because the nut comes unscrewed. They get loose because the wood compresses which makes them lose the clamping pressure the nut is supposed to provide. Using loctite or a jam nut won't help keep the clamping pressure. If that goes away, the prop will spin on the shaft and destroy your spinner. If it's plastic, it will then go flying in some random direction. The only thing a jam nut is for is to stop a backfiring engine from throwing the prop. It's needed for that safeguard alone no matter what the prop material is.

opjose

Yup.... with composite materials compression is not a big issue and rarely have I had to use a lock nut. With wood I almost always use a lock/jam nut, but as you said, it's more to prevent backfire issues than anything else.

Of course with larger props we use prop bolts too.... and you have to constantly check them initially, due to compression.

jester_s1

This is one of those times when brute force really is the answer. Finesse is for wimps!