YZ250 83,84,85 question

[DIRTPILOT72]

Hi, what is the differences between a 83, 84, 85 model YZ250, and how can you tell the difference?

[lms6201]

several ways , if bike is origional , k has conventional spokes ,front wheel , drum side has shorter spokes , L has z spokes drum brake fr wheel and z on one side of rear , N has disc fr with z spokes , use the engine number prefix to be sure , wheels are date stamped , normally produced the year before the model release , L and N will have a red frame , use the numbers   

[Nathan S]

Also, K has black, squarish radiator shrouds, while L/N have red, angluar shrouds.

The pipe swaps sides between K and L - I think K is on the LHS, L/N on the RHS.

[DIRTPILOT72]

Thanks for that info. Will get the engine numbers to be sure.

[DIRTPILOT72]

Ok have the numbers, engine is 24y 00577 and frame is 56a 002575. Rang aYamaha dealer and it looks like a 83k engine in a 85n chassis. The exhaust however is on the right hand side 84-85 style. Frame is black but seller claims it was red. Also it has a disk brake front. Strange? Could it be a 85 model with a 83 bottom end, 84,85 barrel? As im new to all of this, am i correct in thinking this bike would not be legal to race in pre 84 class?

[lms6201]

that,s right , it,s out , pre means before

[Nathan S]

Ok have the numbers, engine is 24y 00577 and frame is 56a 002575. Rang aYamaha dealer and it looks like a 83k engine in a 85n chassis. The exhaust however is on the right hand side 84-85 style. Frame is black but seller claims it was red. Also it has a disk brake front. Strange? Could it be a 85 model with a 83 bottom end, 84,85 barrel? As im new to all of this, am i correct in thinking this bike would not be legal to race in pre 84 class?

They're all centre-port motors - its only the pipe that differs.
You can swap complete motors between the K, L, N, and S models without drama. The J and T motors may also interchange, but I'm not 100% sure on that one.

Its mostly likely that its an entire 83 motor, but the barrell will have the prefix cast into it so you can tell for sure. Beware that the Yanks got different prefixes in those years - so Speed and Sport won't help much.

I could be wrong, but you may find that an 85 rolling frame with an 83 motor would only require a drum brake front end to be pre-85 legal. If I understand correctly, the main differences between the 250L and the 250N are the disc front, the BASS shock and some porting/pipe stuff. As shocks are free, and you've got a different motor, only the disc front is an issue.

[DIRTPILOT72]

Thanks Nathan S, i was sort of thinking along those lines, swapping the disk front end to a drum set up. Then with a 83 motor ( i think your theory on that is correct) it would almost be the same as a 84.

[DIRTPILOT72]

Thanks everyone for their help. Got outbid on bike. Back to the drawing board.