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Flywheel spinning loose/loctite 680

mainer_in_ak

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Hey yall, had my first flywheel issue:

Rebuilt an echo QV 6700. New everything. Even upgraded to the grey echo, newer pawls/flywheel. Cinched down the flywheel nut very tightly.

Started tuning the saw from a rich tune, to right where the rpms peak off a righ tune. That's when the harmonics of those upper RPM's loosened that flywheel and sheared the flywheel key.

Very discouraged, after adding up the cost of all these parts and time into this saw. So much so, that it had me questioning why the fk I even mod saws. Why can't I "leave good enough alone"?

Anyhow, after some rest, I realized that it's a lesson in disguise: you can't just wipe that surface and call it clean. It was my fault. I remembered my welder talking about how he had trouble welding my full wrap handle on another saw, as the aluminum was impregnated with oil.

Another instant, I had rebuilt the high-pressure oil pump (hpop) on my 7.3 powerstroke. This pump is what fires off the injectors, bringing the oil to thousands of lbs of pressure. A year later, one of the hpop fittings had loosened up, blowing oil everywhere. Lost my truck for months, until i figured out the problem.

Same deal: course thread steel fittings, aluminum hpop housing. I guess I forgot an important step: It's recommended to use loctite 680 on the threads. After degreasing everything, the loctite 680 kept the hpop fittings tight.

Anyhow, loctite 680 is used to hold press-fit cylindrical parts in place. Its especially helpful when machining tolerances are loose.

After scuffing up the surfaces of my replacement flywheel, and cleaning the surfaces with degreaser, I'm going to use loctite 680 on both the threads and the tapered crank-end.

I'm betting that's this loctite 680 would be especially helpful for a saw where the surface of the flywheel may have been compromised by a sheared flywheel key, but you might not have a replacement handy.
 

drf256

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Would you consider using some valve lapping compound on the flywheel/crank taper interface?

I tried using Loctite (albeit the blue) on a crank taper and had the opposite result than I thought, it actually slipped more.
 

Moparmyway

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I’d just use blue loctite on the flywheel nut threads after using valve lapping compound like suggested above
 

qurotro

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I wouldn’t use 680 cuz if that cured you won’t be getting that fw off without heat. I worry about the magnet more.
 

mainer_in_ak

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I wouldn’t use 680 cuz if that cured you won’t be getting that fw off without heat. I worry about the magnet more.
That would be great with me. I never want to tear down this cs 6700 ever again. Literally everything is new. Got everything lightly scuffed up, then squeaky clean with loctite degreaser. Cinched er up with loctite 680.

Used the original flywheel, but reassembled with upgraded pawls/recoil from the newer 6700.

I'll let yall know if she holds. I read that loctite 680 has 4000 psi shear strength. It's a retaining compound, not a thread locker. Great for a taper shaft, too much for a thread locker.

I don't know how some of yall build saws for profit. When a saw is completey put together with all new parts, then something grenades. It's a sinking feeling that hits yah right in the fkn gut. I may have over-reacted with the 680........

20240324-155327.jpg

20240324-192320.jpg
 
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qurotro

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That would be great with me. I never want to tear down this cs 6700 ever again. Literally everything is new. Got everything lightly scuffed up, then squeaky clean with loctite degreaser. Cinched er up with loctite 680.

Used the original flywheel, but reassembled with upgraded pawls/recoil from the newer 6700.

I'll let yall know if she holds. I read that loctite 680 has 4000 psi shear strength. It's a retaining compound, not a thread locker. Great for a taper shaft, too much for a thread locker.

I don't know how some of yall build saws for profit. When a saw is completey put together with all new parts, then something grenades. It's a sinking feeling that hits yah right in the fkn gut. I may have over-reacted with the 680........

20240324-155327.jpg

20240324-192320.jpg
I tested the 620 by fitting the wrist pin in a scrap piston. That stuff is not a joke..
 

bogieboy

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Brake parts cleaner. Every time on a taper...
This.... the taper is what holds the flywheel in place. Any oil or other liquids will impede that friction. I had an old stihl 056 that the flywheel keyway was all egged out from beig run loose before i owned it, cleaned up the taper with valve grinding compound to reseat the flywheel taper to the crank, cleaned with brake cleaner, and its still running for the guy that bought it off me... with no key in the flywheel at all...
 
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