Hi Friends. I picked up this thing earlier in the year. Sir Chook was able to identify it as a 1928 SB Standard. It worked when I got it but being so old, some of the parts have now decided to stop working. What I'm trying to figure out at the moment is how the gear part that is attached to the drive of the electric motor actually stays on there. As you can see, there's a notch in it for a woodruff key and the key I have shows evidence of a grub screw being tightened onto it at some point, however, there isn't anywhere that I can see that has a grub screw mechanism of any sort on it. I now regret NOT taking more photos of it before using it so I could see how it was attached. There's evidence of some kind of locking collar on the motor side of the gear mech so maybe this is what I'm missing. If anyone is able to provide any info, maybe even as general as 'This isn't worth trying' I'd be most appreciative. Cheers, Dave
I would check the end of the crank and see if there is an internal thread as it may use a bolt and washer to hold the sprocket on also I would remove the clamp and check for a grub screw that will tighten onto the key in the crank because as you say there are signs on the key of a grub screw.
Hi Max, Yep I used a few others that I could find on the interwebs to check it and none of them have anything on the outside of the sprocket. I took that sprocket attachment apart and there's no mechanism for a grub screw anywhere and the spindle of the motor isn't threaded. The channel for the key ramps up gently on the inside end. Is there any possibility that pushing the sprocket on created tension knowing that the end of the key will be pushing up out of the channel? I initially thought it was missing another collar or something on the inside, but the sprocket is hard up against the motor to make the chain line up. A guy in Adelaide has one for sale at the moment too and I'm waiting on some photos from him if he's able to work anything out.
The channel for the key ramps up gently on the inside end. Is there any possibility that pushing the sprocket on created tension knowing that the end of the key will be pushing up out of the channel? I initially thought it was missing another collar or something on the inside, but the sprocket is hard up against the motor to make the chain line up.
Usually if there is no grub screw or bolt at the end of the shaft there is a Morse taper on the shaft and hub ,but the tapered keys have a rectangular varying cross section. The basic idea of using taper keys is for mainly for the ease of assembly and removal of the key. Further due to the tapered section of the key along its length, it acts as an axial retainer for the mechanical power transmitting element.
The purpose of the taper is to secure the key itself, as well as, to firmly engage the shaft to the hub without the need for a grub screw. The problem with taper keys is that they can cause the center of the shaft rotation to be slightly off of the mating part.
If there is a tapered ramp for the key it would depend which way the ramp goes as to if you can fit the hub on the shaft and then hit the key in with a small pin punch .
I think my key might be shorter than it needs to be. It doesn't fill this groove much past halfway. Here's a couple of shots of the drive shaft that show how the groove tapers up towards the motor end. If you look closely, you can see some damage to it where the key may have been tapped/hammered in the way you suggested in the past.
Looking at the keyseat slot in which the key slides ,it looks uniform it depth ,the ramp at the end I would think just locates the key from moving out of the hub.
It doesn't look like it would use a key that is ramped or tapered but I can see grub screw marks on the shaft which makes me think there is a screw on small hub that fits onto the thread and has a grub screw that locks to the shaft .
The thread looks too clean to not have had something attached to the thread.
This is where you really need some images of the sprocket end from another machine so you can see if a part is missing or if the part you have is original .
It's difficult to see in the image if the chain is in the centre of the cut outs for the chain.
So the only way is to see if another same model mower has a part your machine is missing or just fit some grub screws.
If it's missing a part and you aren't worried about replacing the missing part you could drill and tap the hub for 2 grub screws.
I would put 2 horizontal grub screws in the hub with the key facing upwards ,that way the shaft is balanced.
