CRF to CR conversion question

They are OK.

I make entire frames and Chassis - Bicycle, Motorcycle and , now tubular car chassis. So, I'm a bit of a prick when it comes to 'Kits'. They all have aspects to them I'm not happy with, but the CP500 kits are OK.

I've made many 'AFs' since 97. With a wide variation of 'Ys' and cradles. I don't do them now - well, I try not to, but, I end up doing at least one a year for old friends that you just can't say No to.

Now, I send them towards CP500, as I'm not interested in doing my 'Y's, or airbox adaptor plates.

I recommend they get the Y, the airbox adaptor , and the Head stay plates. Saves Them a few dollars, as I have plenty of high quality alloy stock for Coil, Muffler and Chamber mounts . I use either Right Angle or T section for the lower motor mounts - you've a lovely radius on either one, it gives you a plate to weld to the cradle tube, or the original plate that is on the cradle. Usage of stock such as that, is, in my opinion, better than peoples 'fancy' 'CNC" mounts they do, and, Far better than just welding in an upright flat plate such as what CP500 give you.

But, the Full CP500 kit is adequate for those that aren't snarky old engineers . Other than the next point:

CP500, for some bizarre reason, Do Not have a mid mount for the pipes - at least the kits I've encountered. WTF? I'd never, ever run a bike without a mid mount for the chamber . So, I make a mid mount. I wish they'd run a few extra lines on their CNC program, to have a 'kink' to the lower 'Y' to cradle socket, too.

I do a notch in the lower 'Y' rear section, to make it a bit easier when fitting the cradle tubes into it, to give less of a 'straight around the cradle tube weld', and, you need to make sure you cut the cradle tube so it's tight into the 'Y'. You'll be surprised at how much you have to Jack out / Flex out the cradles to get them into the 'Y' piece sockets. I've shown the procedure to a few blokes, and, they do tend to freak out at it......

I also weld in bash / glide plate mounts that gusset that joint. As well as that, for rear bash  / glide plate mounts, I also brace the  cradle tube to the swingarm mount plates and cross over / linkage mount  - on 500s, a longer plate to cross over where you file / machine a notch in the RH casting to clear  the engine. I also put plate on the downtube to the Y, so the 'Y' is not just 'hanging' from the weld to the downtube. I think all of those are wise if the bike is going to be used hard - though, few AFs are. Many are Garage Queens / Old Mans Show Off Toys - fair enough.

Pictures of the points I put up. Two of which are a bit bloody fuzzy :

I have done this conversion. The bike was great but it was a lot of work.  I just did a 2021 crf450r to 2001 cr 250 swap. It was easier and the bike is AMAZING!

Not much difference than just getting a newer CR250 really. I understand guys putting other things, like 500's in the crf frames, but from what I have seen over the years you are just adding more of a headache as you are just going from one aluminum perimeter frame to the next. If it was a newer CRF chassis, I could see as it gives updated suspension, different plastics options, etc. But if you have to pay someone to do the work, buy the newest CR you can find and just enjoy that.

This is from when my friend had his 06 cr125 put into a 2010 crf250r chassis. The same guy also did the same for his 06 cr250 engine into a 2010 crf250r chassis. He did the 250 first did these back in 2014. 

Doesn't own them anymore sold them off about a year ago. Rode n races mx on them for years never was a problem. 

But to put the 250 engine into the crf frame you have to redo the Y section. The guy who did my friends machines outta billet a Y section. Welds them in a like boxed it in. Welded covers the open sections.