Here's an update of my '73 GT250K VMX build. After getting rear wheel refurbished and rear shocks installed it was time to get the '79 RM125 rear wheel installed to the '79-80 PE/RM250 swingarm. I was missing few crucial of parts needed for the rear wheel axle assembly such as rear wheel axle itself, chain adjusters and rear hub panel spacer which I needed to either buy or make myself. I started by purchasing rear wheel axle out of Rieju RR/Derbi Senda which had the correct 15 mm outer diameter to fit RM chain adjuster spacers and rear wheel bearings. It was advertised as 275 mm long but ended up actually being 285 mm long which meant that it needed add spacers to both ends of it.
It was quite difficult to find proper sized chain adjuster spacers for '79-80 PE/RM250 swingarm. After asking for crucial dimensions I managed to get a hold on a correct pair. They needed a new surface finish so I decided to use gun blue for them for now. I'm not totally happy with the finish since it tends to build up surface rust for some reason after applying it to a clean metal surface. I'm gonna get few other parts zinc coated later so I might throw these in that patch as well.
I was missing adjusters for the chain adjuster assembly and couldn't find either used or NOS parts on sale so I decided to make them out of 2 mm stainless steel sheet since they are rather simple parts. Only difficult part is to get the 90 degree bends to correct position. I made few test bends before bending the actual parts. After checking few dimensions for them I came up with 2D model (DXF) to be cut with abrasive water jet cutter located in our University's workshop. After cutting I first deburred them with Dremel and then sanded and polished them. I then protected the polished surface with masking tape and marked the bending lines before bending them with a folding machine. Last step was to tag weld nuts inside of them.
I decided to use ProX parts for chain and sprockets setup. I found a nice black aluminum rear sprocket which fit to my rear wheel. I replaced sprocket side axle seal with a another one to fit those new aluminum rear wheel axle spacers.
Finding a right sized front sprocket suitable for 520 chain required bit of searching through Google. After some time I came up with #07.FS42094 front sprocket which had the right axle pattern to fit GT250 counter shaft. It is meant for 94-08 Kawasaki KX125.
I put together a mockup assembly, which consisted of lower crankcase and counter shaft with front sprocket and bearings, and mounted it to the frame with swingarm and rear wheel. I bought two long enough steel U-profiles to first align rear sprocket and then measure lateral position of rear wheel rim after installing right length rear wheel spacers. I started with shorter mockup spacers and end up with those aluminum ones shown earlier in this post.
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| Rear wheel axle assembly to fit '79 RM125 rear wheel to '79-80 PE/RM250 swingarm installed to '73 Suzuki GT250K |
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| 15 x 285 mm rear wheel axle Rieju RR, Derbi Senda (#752103) |
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| Chain adjuster assembly |
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| Sandblasted and acetone dipped chain adjuster spacers (#64781-40300) |
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| Surface after applying Perma Blue... |
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| ... and after rinsing with warm water and oiling |
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| New nuts for chain adjuster spacers (#09140-22006) |
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| Dimensions for chain adjusters |
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| Preview of DXF-file to be cut |
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| Abrasive water jet cutter at the workshop of Uni Oulu |
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| Cutter head |
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| User interface, UI |
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| Chain adjusters cut out of 2 mm thick stainless steel sheet |
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| Deburring inside and outside edges with Dremel |
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| Sandpapers from 240 to 600 grid for water sanding |
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| Autosol polishing paste and cloth |
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| After sanding and polishing |
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| Protected outer surfaces with masking tape and marked bending lines |
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| Bend and welded chain adjusters |
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| Chain adjusters ready |
To finish the rear wheel axle assembly I needed to turn out few simple spacers for it. I used stainless steel for the rear hub panel spacer and aluminum for the spacers to align the rear wheel.
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| Dimensions for rear hub panel spacer (#64213-40300) |
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| New rear hub panel spacer turned out of stainless steel |
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| Dimensions for spacers to align rear wheel |
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| Turned spacers out of aluminum |
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| Rear wheel axle assembly ready! |
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| ProX rear sprocket, alloy (#07.RA32080-51) |
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| ProX Rear Sprocket Bolt Set (#07.SBSM825) |
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| Back side of the bag |
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| Rear sprocket bolt set out of the bag |
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| New rear wheel axle seal (22x35x5) to fit 15x22 mm spacers |
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| Rear wheel with new rear sprocket and axle seal |
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| ProX front sprocket (#07.FS42094-14) |
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| Out of the box |
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| Counter shaft assembly for mockup |
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| Lower crankcase, lay shaft and case screws and nuts |
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| Two U-profiles helped with aligning |
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| I tightened a U-profile to rear sprocket with a wood clamp to find right lateral position for it and measured correct length for those aluminum rear wheel axle spacers |
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| Closeup of front sprocket |
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| Side view |
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| Checking the rim position after installing rear wheel axle spaces |
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| Another side view |
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| Used swingarm and engine mounts as a reference and marked current position of the rear wheel with a pencil to calculate the new position for the it |
