I brought a project bike and,as it had spent all of it's life in a seaside town ,it had a badly rusted frame...when it came back from the blasters the bottom rails where like swiss cheese with lots of horrible bodge welding all over it...pretty certain it was out of alignment too.

So I brought a s/h frame with number and v5,all legit...if I rebuild all parts onto fresh frame which v5/reg do I use?...the original bikes because the majority of parts have come from it?.. or the replacement frame?...unable to get a definitive answer from dvla at the moment but will try again.

 

the frame/chassis is the identifier, use the V5 off the new one, don't forget to scrap the other one or you will find it might get cloned and your name is on it

Thanks for that..got hold of the right person at dvla and basically that is what he said..I did wonder though, as in the Classic Car world a brand new mgb bodyshell can have the old number used on it even though the majority of original parts are thrown away.

Different in the car world, you can remove and replace the VIN tag unlike bikes where it's stamped into the frame.