We have an older JD 690 excavator that we were using a while back, but the bottom track part doesnt work correctly, and as some of you may know our cat 312 burnt up the other day, but the bottom end should be still good on it i think.. Would it be possible to put the JD 690 onto the Cat turntable or would it not be worth it?
I don't think it would work, the 690 is about a 20 ton machine whereas the 312 is a 12 ton machine... Just my thoughts...
IMO it would not be worth it. If you were putting a smaller upper-structure on a larger track frame it might work, but putting a larger upper-structure on a smaller track frame should not even be considered. If your undercarriage from your 312 is in great shape you could try to find a 312 that needs a new undercarriage and swap.