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Shimano MF-HG20 Freewheel won't freewheel

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Shimano MF-HG20 Freewheel won't freewheel

Old 05-21-20, 06:40 PM
  #1  
WGB
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Shimano MF-HG20 Freewheel won't freewheel

This is on a 1988 Schwinn Traveler
Original rims were 27 inch but dust cap on rear hub had a dent that hits wheel bearings. No access to a replacement dust cap until Covid ends so switched to a 700c wheelset.




Freewheel is a Shimano MF-HG20 6 speed

Front of freewheel (Please excuse the dirt, its been cleaned since that photo)



Rear of freewheel



Freewheel installs properly on hub, no binding

Complete wheel turns smoothly in hands and relatively true

Installed on bike and zero adjustments to derailleurs required. Shifted flawlessly.

But, if you stop pedalling the cranks keep spinning. Cannot back pedal.

Remove wheel from bike and remove freewheel. Freewheel cogs do not spin on freewheel hub.

1) assuming no wheel hub issues. If I'm wrong please advise.
2) assuming issues within hub (no grease or pawls sticking due to having sat for a while???)

I have turned the freewheel upside down and oiled rear along edge where freewheel hub meets cogs. Next step plan to flip freewheel and oil along edge of freewheel hub (above "Shimano SIS lettering and below MF-HG20 Singapore lettering in photo) then let sit all night and remount tomorrow morning and see if cured.

3) Is this a bad idea??

If that doesn't work, should I try and tap the lockring - clockwise - and slightly loosen it but no completely to see if that will allow in oil (or even PB Blaster)???

Should I simply moved to PB blaster and/or WD-40 straight off???
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Old 05-21-20, 07:15 PM
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Try the freewheel without the spoke guard installed. Andy
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Old 05-21-20, 07:58 PM
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Removing now!!
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Old 05-21-20, 08:17 PM
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Andrew R Stewart

Andy

I removed the spoke guard but no change. As I was pulling it off I recalled that the freewheel didn't spin when it was off the bike and in my hand so I guessed it wouldn't spin without the spoke guard. I had hoped though that the oil on the rear of the freewheel might have affected the performance but no, it hasn't. It didn't spin in my hand and when I mounted it back on the wheel and remounted the wheel there was no change, crankset still spins along with the wheel. Again, I was able to fully shift through all gears while the cranks spun.

I have gone ahead and removed the freewheel from the wheel hub and turned the freewheel upright and added oil in the top of the freewheel.
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Old 05-21-20, 10:17 PM
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It's normal, regular service to oil freewheels. Generally I'll drip some in while the wheel is spinning anytime I have a freewheel bike in the stand. They're pretty cheap so you may consider just replacing it, but you can also try actually soaking it in solvent or oil to free everything up.
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Old 05-22-20, 09:26 AM
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If it was my bike I'd drip some light oil on the frontside crack that separates the freewheeling part from the stationery part. Let it soak in for a while and try to spin the freewheeling part with just your fingers. My bet is that'll fix it.
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Old 05-22-20, 09:40 AM
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Immerse in a small tub of lightweight oil overnight.

Install on a hub...don't tighten.

Use a small hammer to tap lightly from several directions...

See if it loosens and spins.

=8-|
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Old 05-22-20, 09:43 AM
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Originally Posted by Retro Grouch View Post
If it was my bike I'd drip some light oil on the frontside crack that separates the freewheeling part from the stationery part. Let it soak in for a while and try to spin the freewheeling part with just your fingers. My bet is that'll fix it.
I've got an old Suntour freewheel with that exact problem. I've oiled it and got it to turn freely off the bike but by the next morning (still off the bike) it's seized again.

I guess that when I feel up to it I'll have to open it up and see what's going on inside it.

Good luck OP. Dripping oil in through the gap on the front might work.

Cheers
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Old 05-22-20, 09:46 AM
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You've spent a lot of time with this one freewheel. Why not just spend 10 to 20 dollars and get a new one?
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Old 05-22-20, 12:59 PM
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Thanks to all. After soaking overnight it stayed stuck for a few seconds and now has loosened up.

You've spent a lot of time with this one freewheel. Why not just spend 10 to 20 dollars and get a new one?

Covid on and seems to be taking forever to get bike stuff shipped. I ordered some bar tape two weeks back and still waiting. Also I like rescuing old stuff and rebuilding and reutilizing it so if I can save the part, then I will.

But yes, there is some stuff that just cant be saved. As stated at the start this bike originally had 27 inch rims and these were Arayas in really great shape. The dented dust cap issue isn't something I can fix now. Hopefully one day soon I can get into the local co-op and find a suitable dust cap probably in ten seconds but for now those rims are toast. And yes, I'll grab 3 or 4 freewheels for next time.
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Old 05-23-20, 12:25 AM
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I have found that sometimes it takes a good slamming on a wooden or vinal topped work surface to free it up after a good oil soaking. Slam it down on the largest gear.
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