Vintage Dirt Bike Q & A

Hi, I"m a new guy here and ride an 81 cr 450 and also have a 74 mt 125 that I need some info on as well.

first of all thanks in advance to any and all.

my 81 450 seems to have no oversize pistons available,do I use the standard bore 82-83 480 as my first over? it's the same stroke but thats all I know, do the ports match or would the 480 piston need to be trimmed up?

On to the 125, what are the excact differences beetween the MT125 and the CR125? is it basically just pipe and porting,tires and sprocket? I would like to turn it into a CR,or at least port it and fit a CR pipe and use it as a fun little commuter as it does have a license plate bracket.

Again thanks and looks like a great forum.

The actual differences between the cr and mt are too numerous to list, however, there are some things in common. Back in the mid seventies, I ran into a guy out riding that had put a cr125 top end on an mt125. There was something really cool about that. I have since read or heard that the cr top end will bolt right on, so it probably wasn't an illusion. If it were me, I would watch Ebay for a cr jug and carb, and a new piston. I think that would be preferrable to porting the mt jug. With the cr jug, you will need more carburetor for sure.

As far as using a cr pipe, those old mx bikes were louder than the space shuttle. Your neighbors and others may not be too keen on that. You might be better off trying to find a period aftermarket pipe like a torque engineering pipe, since it will bolt up in place of the stock pipe. The mt was underpowered, so porting and fitting a cr pipe will most likely give lots of noise, and a slight increase in power.

Of course it's your decision, but having been involved in a couple of projects like these in the past, I have found that the only 2 choices are to do it all right, or not at all.

thanks for the advice, a cr top end swap sound like the course of least resistance and best results so will keep my ear to the ground, do you know what years will fit??

I live in the tooleys so as far as the neihbors go I am really lucky they are hard drinkin,gun shootin,motorcyle/atv hillbillys and they dig/dont give a damn about my 2 stroke addiction some of wich are pretty loud.

actually all but a couple have brought over their bikes for me to work on,we get on fine.

I think the first few years will. Beyond that, I'm not sure. Maybe a cr125m expert will wade in here. I would stay away form the 74 model parts though, as the jug and pipe are unique to that first year and competition for restoration parts has driven prices up into the upper atmoshere for that year model. I think your best bet would be the pipe off of the 75 model, since you wouldn't believe what nice 74 pipes are bringing. Any early carb. besides the 74 cr, unless the 74 cr carb. can be had cheaply.

I always wanted to do this when I was a kid, until I saw the Can Am TNT models. The Can Am TNT enduros at the time only had some minor differences compared to the MX'ers. I restored one a couple of years ago exactly like the one I had as a kid, that's sitting in my garage.

the TNT is a machine I have wanted since I was about twelve, your a lucky dog I think they are one of the best looking machines of all time.

And thanks again.