447 rods onto 256 crank

Hello all,

I've inherited a 74 TX frame and cycle parts along with a 256 engine basket case from which to create a complete bike. The engine requires a full bottom-end rebuild as it was seized from standing for years. As such new pistons, rings, camchain, crank rebuild etc will be needed. However being a 256 pistons, rods etc are neither cheap nor plentiful. This is where I need help in the form of info from members.

I've done all the search variations I can think of but can't find the answers I need. Being that I need a rebuilt bottom end and new top end, I have been considering the MikesXS 750cc kit. However that kit only suits 447 cranks. I'd like to keep the 256 head and cam but run the 750cc kit if possible. In my long-winded way my question is:

Can I simply fit 447 rods to my 256 crank and run 447 pistons?

From what I can find the 256 and 447 rods have the same size big-end so it shouldn't be an issue, at least I hope. This would save me the trouble of converting to a 447 crank, pistons, camchain tensioner asembly and cam gear as I wish to go for a rephase when I rebuild.

Can anybody confirm that a swap to 447 rods on my 256 crank is possible?

Many thanks,
Alex

I had Hugh do exactly what you want, I put 447 rods in my 256 so I could use better pistons.

Yes, you can install the 447 Rods on your 256 Crank.

The 256 rods are longer and have a larger wristpin, so you'll want to use a 447 Piston Set. You can keep all of your timing gears, cam, tensioners, etc.. as 256.

Hugh

Thanks fellas, that's what I thought.

Cheers,
Alex

Bobbyd, thanx for bringing this up, as I too am in a similar position. Got (2) 256 motors, want to keep heads and cases, but would like 447 or 533 guts, just to be able to use more available, economical and modern tech. Parts for these 256s are getting ridiculous. Just wanna ride. I'd rather the resto guys have my 256 stuff, they'll take better care of it, and let us run the newer stuff. Could the experts here please post viable combinations of 447 upgrades to 256 motors?

Maybe something like this:

Crank sprocket - camchain - camshaft must all match, either all 256 or 447, identified as 'camdrive'
Head and camcover must match, either 256 or 447.

Flywheels camdrive tensioner cylinder head
256 256 256 256 256 Original XS1, XS1B, TX650, XS2
447 447 447 447 447 `74 - `79 XS650?
533 533 533 533 533 `80 - `83 Heritage?
256 447 256 256 256 Possible?
447 447 447 447 256 Possible?
447 447 533 533 256 Possible?
256 256 447 447 256 Possible?

This is just an example table, please do not refer to it for builds...

Please ignore my previous post, it was a desperate attempt to oversimplify parts interchange.
Turns out this issue has been discussed at length by the experts here on posts over 2 years ago...
Just fire up the coffee-pot and do a search on "256 crank".
I'll probably do as bobbyd is considering: what dot heston did.

I simply wanted the opportunity to go big-bore or get replacement pistons and rings cheaply and easily. The cam is fine along with the tensioner but a new chain will be required. In the end I didn't see the benfit of having to change so much of the engine to 447 parts when just chaging the rods gave me the parts possibilities I was looking for.

Now I can get my crank rebuilt as a 277*, order a 750cc kit & a new camchain and bang, I'll have a beautiful engine. Too easy and no need to source another crank and associated used parts which will require refurbishment anyway.

Cheers,
Alex

While you're at it, mikes has the front tensioner guide back in stock...