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So I was mowing my lawn on my old ride-on (it was my Grandpa's and is about 30 years old at least). The drive chain finally broke and, of course, the mower rolled backwards and ran over the fallen chain smashing it into bits. That was fairly academic though, as in addition to the chain being worn out, both sprockets were totally worn out.

After figuring out what sprockets/chain I needed, I ordered some sprockets online (no local store had them) and proceeded to disassemble the final drives. The axels were held on with eccentric collars but were also fairly tightly stuck on with corrosion, I ended up using a car jack to push the axels out. https://pic8.co/sh/SbuiJj.jpg https://pic8.co/sh/xvVA7z.jpg https://pic8.co/sh/fXyDxX.jpg

The large sprockets I got were pilot bore sprockets (couldn't get plate sprockets in 76T for some reason), so the plan was to trepan out the old sprocket and replace the outer ring with the new sprocket teeth. I found a HSS tool in a box that was almost perfect for what I wanted, looks like whoever originally ground them probably did a similar job. Mounting the axel in the lathe I trepanned into the face about 4.5mm, leaving a thin wall to cut out manually. There was no way I was going to go all the way through and end up with a sprocket ring loosely flailing around the chuck, and probably getting jammed somewhere and blowing shit up. There was considerable chatter while doing this, as well as a couple of times where the tool bit in and stalled the lathe. Overall, a sphincter clenching experience, but it worked. https://pic8.co/sh/I1UAOI.jpg https://pic8.co/sh/hKgwO9.jpg https://pic8.co/sh/cAtJpe.jpg

The edges of the old sprocket were cleaned up and turned to a nominal size (about 150mm diameter). https://pic8.co/sh/YqbtPL.jpg

During this process, I also trued up the wheel hub faces. The first one wasn't too bad, being out by about 0.5mm it cleaned up pretty easily. https://pic8.co/sh/Gv9JEv.jpg

The second wheel hub was a bit out. I knew this already, as a 1/4" spacer dropped out when I removed the wheel. Putting it in the lathe, I measured the runout at the edge of the hub, which was 7.25mm in total. To fix this, I turned down the old weld until I could move the hub. Then I beat it into rough shape until the runout was in the 0.5mm range. Once welded up again, that hub was faced true. https://pic8.co/sh/7bsZk0.jpg https://pic8.co/sh/DbnUmn.jpg https://pic8.co/sh/9blluM.jpg

Similar to the old sprockets, the new sprockets were trepanned out. This time ensuring that the resulting ID would be slightly smaller than the OD of the remaining old sprocket. After trepanning out about 4.5mm, a chisel was used to cut through the thin wall that remained. https://pic8.co/sh/MRxqqv.jpg https://pic8.co/sh/lo6Jy2.jpg

These blanks were then mounted in the 4-jaw chuck and dialed in using the trepanned surface as a reference. Then they were bored to be a close fit for the old sprocket stubs. https://pic8.co/sh/GV2HzY.jpg https://pic8.co/sh/8B4XpM.jpg

Once fitted, I marked out spots to weld (3 on each side). A weld relief was ground for these locations and the parts tacked together. Once tacked, I put them back in the lathe and dialed in the runout by recording the deviation then smashing them a bit with a hammer until the overall runout was acceptable (they're not super precise, but at least as good as the original). https://pic8.co/sh/ezksft.jpg https://pic8.co/sh/zllOYw.jpg https://pic8.co/sh/G2ZKWD.jpg

The sprockets were then welded up and painted. https://pic8.co/sh/pT1MPG.jpg https://pic8.co/sh/JVgohA.jpg

The next part was to bore out the smaller sprockets and put keyways in them. As I don't have a key broach, I wanted to get a decent start on the keyway, so I mounted the sprockets in the mill and drilled a 1/4" hole exactly 1/2" from the center. This was much easier than trying to mill out a half circle after the final bore was done. https://pic8.co/sh/i40cg9.jpg https://pic8.co/sh/Gof40T.jpg

The sprocket was then bored out to final size (1"). To finish the keyways, I just used a file. The end result of that was ok, but not brilliant, need to figure out a better way of cutting keyways (I have some ideas) but I just wanted to get the damn lawnmower fixed. https://pic8.co/sh/bVKrZj.jpg https://pic8.co/sh/AFgvjR.jpg

Re-assembly was pretty easy. The axels and sprockets were re-installed and the required length of chain cut. https://pic8.co/sh/1cihjV.jpg

For anyone interested in how this old school mower works. It's a very early zero-turn mower that uses two cone drives to power each rear wheel in either direction. This works pretty well... as long as it's not too hilly, as it really doesn't do well driving across a slope. https://pic8.co/sh/9Ym5Y2.jpg

So I was mowing my lawn on my old ride-on (it was my Grandpa's and is about 30 years old at least). The drive chain finally broke and, of course, the mower rolled backwards and ran over the fallen chain smashing it into bits. That was fairly academic though, as in addition to the chain being worn out, both sprockets were totally worn out. After figuring out what sprockets/chain I needed, I ordered some sprockets online (no local store had them) and proceeded to disassemble the final drives. The axels were held on with eccentric collars but were also fairly tightly stuck on with corrosion, I ended up using a car jack to push the axels out. https://pic8.co/sh/SbuiJj.jpg https://pic8.co/sh/xvVA7z.jpg https://pic8.co/sh/fXyDxX.jpg The large sprockets I got were pilot bore sprockets (couldn't get plate sprockets in 76T for some reason), so the plan was to trepan out the old sprocket and replace the outer ring with the new sprocket teeth. I found a HSS tool in a box that was almost perfect for what I wanted, looks like whoever originally ground them probably did a similar job. Mounting the axel in the lathe I trepanned into the face about 4.5mm, leaving a thin wall to cut out manually. There was no way I was going to go all the way through and end up with a sprocket ring loosely flailing around the chuck, and probably getting jammed somewhere and blowing shit up. There was considerable chatter while doing this, as well as a couple of times where the tool bit in and stalled the lathe. Overall, a sphincter clenching experience, but it worked. https://pic8.co/sh/I1UAOI.jpg https://pic8.co/sh/hKgwO9.jpg https://pic8.co/sh/cAtJpe.jpg The edges of the old sprocket were cleaned up and turned to a nominal size (about 150mm diameter). https://pic8.co/sh/YqbtPL.jpg During this process, I also trued up the wheel hub faces. The first one wasn't too bad, being out by about 0.5mm it cleaned up pretty easily. https://pic8.co/sh/Gv9JEv.jpg The second wheel hub was a bit out. I knew this already, as a 1/4" spacer dropped out when I removed the wheel. Putting it in the lathe, I measured the runout at the edge of the hub, which was 7.25mm in total. To fix this, I turned down the old weld until I could move the hub. Then I beat it into rough shape until the runout was in the 0.5mm range. Once welded up again, that hub was faced true. https://pic8.co/sh/7bsZk0.jpg https://pic8.co/sh/DbnUmn.jpg https://pic8.co/sh/9blluM.jpg Similar to the old sprockets, the new sprockets were trepanned out. This time ensuring that the resulting ID would be slightly smaller than the OD of the remaining old sprocket. After trepanning out about 4.5mm, a chisel was used to cut through the thin wall that remained. https://pic8.co/sh/MRxqqv.jpg https://pic8.co/sh/lo6Jy2.jpg These blanks were then mounted in the 4-jaw chuck and dialed in using the trepanned surface as a reference. Then they were bored to be a close fit for the old sprocket stubs. https://pic8.co/sh/GV2HzY.jpg https://pic8.co/sh/8B4XpM.jpg Once fitted, I marked out spots to weld (3 on each side). A weld relief was ground for these locations and the parts tacked together. Once tacked, I put them back in the lathe and dialed in the runout by recording the deviation then smashing them a bit with a hammer until the overall runout was acceptable (they're not super precise, but at least as good as the original). https://pic8.co/sh/ezksft.jpg https://pic8.co/sh/zllOYw.jpg https://pic8.co/sh/G2ZKWD.jpg The sprockets were then welded up and painted. https://pic8.co/sh/pT1MPG.jpg https://pic8.co/sh/JVgohA.jpg The next part was to bore out the smaller sprockets and put keyways in them. As I don't have a key broach, I wanted to get a decent start on the keyway, so I mounted the sprockets in the mill and drilled a 1/4" hole exactly 1/2" from the center. This was much easier than trying to mill out a half circle after the final bore was done. https://pic8.co/sh/i40cg9.jpg https://pic8.co/sh/Gof40T.jpg The sprocket was then bored out to final size (1"). To finish the keyways, I just used a file. The end result of that was ok, but not brilliant, need to figure out a better way of cutting keyways (I have some ideas) but I just wanted to get the damn lawnmower fixed. https://pic8.co/sh/bVKrZj.jpg https://pic8.co/sh/AFgvjR.jpg Re-assembly was pretty easy. The axels and sprockets were re-installed and the required length of chain cut. https://pic8.co/sh/1cihjV.jpg ---- For anyone interested in how this old school mower works. It's a very early zero-turn mower that uses two cone drives to power each rear wheel in either direction. This works pretty well... as long as it's not too hilly, as it really doesn't do well driving across a slope. https://pic8.co/sh/9Ym5Y2.jpg

(post is archived)

[–] • 1 pt

"A+" for absolute dedication to keeping old stuff working!