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Hello. Appreciate its an old bike, but I'd be appreciative if anyone can help with my problem. I am in the process of restoring an '83 / Y plate Yamaha DT125MX. I have taken the clutch cover off to flat it and paint it, and have disconnected the oil pump. Whilst it was off, I checked the pump and found the reason why the previous owner had run it on premix. The oil pump was seized. I bought another oil pump from a DT175MX on EBAY. The seller said that it was also for the DT125MX. Having painted the panel, I am now in the process of putting the pump back in the casing, and putting the casing back on. I have checked the new pump, and it is not seized, and the gear rotates with my finger. I have put my shaft from the 125, into the pump, and it is as if the worm gear on my shaft does not match with the gear wheel in the pump. If I put the collar in the pump the shaft locks up completely, and the pump will not go anywhere near the casing. I've taken chunks out of my fingers, and I am in danger of knackering the casing I've just painted, so I have come away for the evening. Does anyone know if the worm gear is different on the 125 & 175 AND if I do have to match up a '175' shaft with my '175' pump, will this work with my 125 (Which incidently now has a 175 barrel and head on it any way. Any help you can offer would be appreciated. Thank you