Flywheel nut keeps loosening on a 55hp Rude

[Randal106]

I have a 1979 evinrude 55hp outboard, i had to replace the magneto/stator, coils and powerpack. but when i take her out, she will run fine for about 30 min.s then the flywheel nut will come loose? i tightened to 100ft pounds. should i use some locktight and see what happens?

 

[AlanR]

Re: Flywheel nut keeps loosening on a 55hp Rude

Yeh i would try lock tight on the threads like the red stuff, i belive its the strongest

 

[F_R]

Re: Flywheel nut keeps loosening on a 55hp Rude

No, find out why it loosens. It is not normal for it to come loose if tightened to the correct torque. Manditory----Is the flywheel and crankshaft clean and dry? Worn key slot in flywheel or crankshaft or both? Worn tapers of same? Flywheel taper distorted from prior overtightening? Put locktite on there and if it runs into the tapers you may never get it back off again.

 

[Dhadley]

Re: Flywheel nut keeps loosening on a 55hp Rude

Take the nut off and look at the bottom side. It has to be clean and flat. If there is a tiny burr on there you need to get it off. File it flat or sandpaper it flat.

If there is a small burr on there, thats what the nut is seating on. You'll need that whole surface to be seating to hold the nut.

Believe it or not, it's not that uncommon of a situation.

No locktite!

 

[xtraham]

Re: Flywheel nut keeps loosening on a 55hp Rude

you dint put grease on it did ya? if you did it will loosen up until you remove it, like fr and dhadley says it has to be dry

 

[Randal106]

Re: Flywheel nut keeps loosening on a 55hp Rude

Thanks for the replies guy's, i checked all of that today, and took it out agin, and it still loosens, is my flywheel warped? also, when it starts to loosen, the boat will go from like 30mph to like 20mph, allmost like its running out of gas, but its not. im gonna take some pics and see if i can get them up here. allso, i have to use a puller to get the flywheel off, and everytime it comes off, it puts a big gash in the key, and i have to use a new one. do you think its going on there too far? how many threads should be showing when it is tight?

Thanks

 

[F_R]

Re: Flywheel nut keeps loosening on a 55hp Rude

That flywheel is loose (as you know). That is what is wrecking the key as it rocks back and forth on the shaft. The key is only supposed to locate the position of the flywheel on the shaft, not keep it from rocking back and forth. The fit of the tapers and tightness of the nut is supposed to do that. So the answer has to be found in those tapers. 1st and foremost is that they be clean and dry. Some clown in the past may have put anti-sieze on them...a no-no. If they are clean and dry and properly torqued and still comes loose, either the flywheel or shaft or both are damaged. There's no other answer.

 

[OBJ]

Re: Flywheel nut keeps loosening on a 55hp Rude

Well there might be one more thing to try. Lap the tapers using some light grinding compound. This will ensure a good fit between the tapers. A little masking tape around the bottom of the crank taper will keep the compound out of the upper seal.

 

[Dhadley]

Re: Flywheel nut keeps loosening on a 55hp Rude

Did you file the bottom of the nut flat?

 

[R.Johnson]

Re: Flywheel nut keeps loosening on a 55hp Rude

Does the hub of the flywheel have a hairline crack? I have found that before.

 

[Randal106]

Re: Flywheel nut keeps loosening on a 55hp Rude

I will look at the flywheel for a crack, and sand smooth the tapers and see what happens. yesterday when i took the flywheel off again, the shft has a small indention in it. will that little indention make it not fit snug??? and no i havent tried filling the bottom of the nut flat, but im gonna do that today

Also, what do you mean by "Lap the tapers using some light grinding compound."

Keep the comments coming guy's, i really appreceate the help.

 

[R.Johnson]

Re: Flywheel nut keeps loosening on a 55hp Rude

To lap the taper's, you remove the flywheel key, and wipe both tapers' clean. You then apply a thin coat of compound evenly to the hub of the flywheel. You then set the flywheel in place, and rock it back, and forth, lifting it ocassionally so as to not lap in the same place. The grade of compound whould depenf on the condition of the taper's. Probably medium, or fine grade. Most any auto store will have this compound.

 

[Randal106]

Re: Flywheel nut keeps loosening on a 55hp Rude

Ok, and that will smooth it out to where it will sit flat on the tapers? Cool

 

[Dhadley]

Re: Flywheel nut keeps loosening on a 55hp Rude

Be cautious with the lapping compound. You want to retain the interference fit of the two tapers. Once you lose that the flywheel sits on the flat part of the crank and it probably wont stay tight then.

 

[Randal106]

Re: Flywheel nut keeps loosening on a 55hp Rude

Aight, i smoothed the tapers out and now it sits fine, but ive got to get anouther Key so i can test it. ill let you all know what happens when i get the key tommorow afternoon

 

[R.Johnson]

Re: Flywheel nut keeps loosening on a 55hp Rude

A good point from Dhadley ! When lapping taper's, you can reach a down point very quickly, Be careful in this respect. Also clean the taper's of compound before assembly.

 

[Randal106]

Re: Flywheel nut keeps loosening on a 55hp Rude

I Was looking on the inside of the grove for the key, and theres a small bur on the side of the groove. so i think thats why im shearing the keys. the bur sticks out on the inside of the groove, thats why when the flywheel goes on the key gets a groove in it, and looses its stregnth, thus breaking the key, thus loosening the flywheel.
Whould my assumption be correct??

I took a small file and smoothed the bur out but ive still got to get anouther key so i can test it.

Also, the model number of the boat is 55975C, what prop do i need for this model, and / or which ones can i use. right now it will go about 32mph with 3 people in in, i wouldnent mind going a little faster, but i mainly use it for Tubeing / Kneboarding. Thanks

And sorry for all the spelling mistakes. Its early, and i havent had my cofee yet. Ha Ha Ha!!

 

[clanton]

Re: Flywheel nut keeps loosening on a 55hp Rude

I would recheck the manual for the correct torque specs. The manual I have lists 80/85 lbs for 1979 2 cylinder 55HP.

 

[Randal106]

Re: Flywheel nut keeps loosening on a 55hp Rude

Ok, ill re-check and see. what model is that torque spec for? if its a 55975 then its the same as mine

 

[Randal106]

Re: Flywheel nut keeps loosening on a 55hp Rude

OK, i put the flywheel back on with 85 foot lbs. and she started right up, i let her idle about 10 mins. and the nut didnt loosen any, but the real test will be friday when i take her out to the lake. also regarding the prop issue, where would the model/serial number of the prop be? ive looked all over it and i cant find it..

Thanks