flywheel key - easy to make

[DustyB 8]

I sheared my flywheel key on my Tiny Tiger a couple of days ago when the flywheel came loose. No damage done since it just slipped on the shaft and quit running. Anyway I found these Hillman keys, steel not aluminum, at the local farm store. The size is right except the thickness. Ten minutes under my thumb on a sharpening stone fixed that, reducing from 2mm thick to 1.5mm. A pack of three was around $2.50.

[factory 487]

They can also be made using a saw & file from the correct thickness of aluminium sheet, or using a lathe & filing the height to match the original (or that custom sized one I had to make).

 

 

 

 

David

[K-TRON 24]

I would never consider using a steel flywheel key in a soft aluminum flywheel. It is just asking for trouble. It is common misconception that the flywheel key locks the flywheel to the crankshaft. That is not at all true. It only locates the flywheel for proper timing (in this instance). The taper on the crankshaft is what holds the flywheel in place. In olden days, racers would leave the key completely out of there hotrodded L head engines. As long as the flywheel was sufficiently tight you did not even need one. This allowed operators to change the timing of the engine to whatever their heart desired.

 

Chris

[factory 487]

That's very good advice, the key is only fitted for the timing, make sure the flywheel & key properly fits the taper before tightening too, as there are some differences to both the flywheels & two different sizes of key over the years. Most lathes & some other machine tools use tapered shafts for the tooling and they lock very well without any keys too (providing they are in good condition).

 

I never asked how the flywheel came loose in the first place, although it's not the first time we've had this problem on the forum.

If it helps the service info gives a torque value of 90-100lbs for the flywheel nut, use a new nut if it's worn out (1/4 x 28tpi).

 

O&R did use steel keys for the earlier engines, I've found the later aluminium keys are a little too short for the slot in these engines and a homemade key is the only option, as I've not found anywhere that sells the correct size in aluminium.

 

David

[DustyB 8]

10 hours ago, factory said:

... never asked how the flywheel came loose in the first place, although it's not the first time we've had this problem on the forum.

If it helps the service info gives a torque value of 90-100lbs for the flywheel nut, use a new nut if it's worn out (1/4 x 28tpi)...

David

I took the flywheel off to clean the points. When I reinstalled the flywheel I was tightening the nut with about a 6" long combination wrench. Suddenly it didn't feel like it was tightening anymore or like something was yielding. I didn't know the torque spec but was nowhere near 90 inch lbs. Anyway I fired it up and it ran fine for a minute or so while I measured voltage and frequency and then the engine quit. I noticed the flywheel had slipped and sheared the aluminum key. After making the new key I reinstalled it and used my torque wrench, this time set to 90 inch lbs, and the stud broke at about 70 inch lbs. Examining the break, from the color I could tell it had been partially broken long before I got the generator. Since then I have drilled and threaded the crank for a stud. The crank seems to be hardened and is difficult to drill but I got sufficient depth to install the threaded stud. Tomorrow I'll probably try reinstalling the flywheel and running it again.

Edited November 15, 2020 by DustyB

[tvenetis 0]

When you use a sharpening stone to make it thinner how do you hold the key.

[DustyB 8]

I just rubbed it on the stone with my finger tip.