Clutch question

[grogetr sawguy]

I have a Stihl ms391 the clutch hub doesn’t spin easily on the shaft by hand with no chain on. The bearing looks good the hub is in good shape. The bearing fits the shaft and turns good by itself and fits and turns good in the hub by itself but when you put it together binds up. I’m thinking get a rim hub and sprocket should I stay away from the cheap ones on Amazon or eBay. The chain spins while idling so thought springs until I felt how tight the hub is. Thanks

 

[chainsaw-57]

Check worm gear bushing is still centered and not moved. This can bind clutch drum.

 

[Tomos770]

Is everything you are putting tohether OEM?

I once had exactly the same problem with the aftermarket clutch bell & bearing combo....

The culprit was.....with aftermarket parts there was not enough "in&out" play on the shaft...it was ok when not thightend together....but insufficient free play when it was....

So I had to go to special bearing shop and had to buy one size shorter needle bearing...

 

[grogetr sawguy]

Everything is oem. It’s a spur drive now. It’s a fairly low hour saw

 

[cookies]

Stihl rim drive drums often use a different thickness washer under the E clip than the spur version.

 

[northmanlogging]

I have a Stihl ms391 the clutch hub doesn’t spin easily on the shaft by hand with no chain on. The bearing looks good the hub is in good shape. The bearing fits the shaft and turns good by itself and fits and turns good in the hub by itself but when you put it together binds up. I’m thinking get a rim hub and sprocket should I stay away from the cheap ones on Amazon or eBay. The chain spins while idling so thought springs until I felt how tight the hub is. Thanks

is the oil pump drive tang in the slot on the clutch drum? Probably the most common oopsie, or possibly the oil pump itself is going bad


Or, if you removed the shoes and drive mechanism its ridiculously easy to install backwards, though its pretty damned obvious when you do (ask me how I know) Its also a real PITA to get off once it is tightened backwards...

 

[wildwes]

I put a clutch on a saw this summer where the hole in the clutch drum was around .004 smaller than it needed to be. It caused the bearing to bind when assembled just like you describe, even though the bearing fit fine in the drum and on the shaft, it just didn't work when assembled.

A drill with some sandpaper and a mandrel fixed the problem

 

[grogetr sawguy]

The oil pump wire is in the hub correct. It worked fine with these parts for quite some time but then started binding and making the chain to continue to spin. I’ll check the bushing in the oil drive again but pretty sure it turned ok when I looked at it before. That’s why I was thinking of just getting a new hub and change to a rim sprocket. Thanks

 

[cookies]

Check the clutch springs, I replace them when I wear out a spur or every 2 rims since they loose tension, wear against the clutch shoe holes and become fatigued

 

[chainsaw-57]

Check that the worm gear turns with little resistance. Do this by removing drum and reaching past clutch with pick or screwdriver to turn wire.

If bushing has moved, it may bind when clutch is tightened down, but be free when clutch is removed.

 

[stihltech]

I quite often put the worm in a vise and lightly press the center worm bushing back in flush with the bottom of the worm. Helps about 50% of the time. And it costs nothing in parts.
Clean the bore of the bronze bushing and the crankshaft. Pur ONE drop of il on the bushing bore and reassemble.