Vintage Dirt Bike Q & A

Hey guys i have a 1975 cr125
its been fully rebuilt with a wiseco piston
full gasket set barnett clutch plates and springs
pro taper evo bars
heavy duty crank
full stainless buchanan spokes
aluminum tank
cr250 wheels
and a 1980 rm100 swingarm
i was wonderin if you guys had any more good ideas to freshen up the old girl and make her competitive
thanks
-sam

Sam,

Your bike has some nice stuff done to it!

Do you have a machine shop nearby, or have access to one yourself? It seems like most of the mods I've done require at least some machine work.

I had trouble with slippage using the Barnett friction plates, so now I use all OEM plates w/Barnett springs, no problems yet.

What's the rise on your Pro Taper bars? I ended up having to use 1.75" risers with Pro Taper SE 'ATV Mid' bars to get close to the OEM bar height.

How is the CR250 front brake? I had an MR250 wheel I was going to put on mine, but went with an '83 RM250 double-leading-shoe unit instead (this brake scares me ).

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Ray
i do have access to a machine shop
and as far as the evos go there cr high bars with universal big bar mounts
i love the cr250 wheels and the brakes are decent, the hubs are heavier duty and you can put a nice 110 tire on the back with no worries
this bike spins it fine!
how bad are the barnett plates?
i havent had any trouble yet.
thanks

Sam,

Thanks for the EVO bar info. I didn't realize there were mounts to fit the big bars on vintage bikes.

I've got a 1.6" CR250M front rim now (thanks, dogger!) which I like better than the 1.4" CR125 one; seems like the tire contact patch is a little wider and flatter.

I put in a complete Barnett clutch as you did, and the clutch slipped a little at first, was OK for a while, then started slipping again worse and worse. This was on the 175 motor. I bit the bullet and went OEM w/Barnett springs, and it's been fine ever since (3,000+ miles).

I've had a number of clutch problems over the years. I tried Mobil 1 in the gearbox once, what a mistake that was - I had to throw those plates away. I also had one set of OEM plates that just wouldn't die; I moved them from the 125 to the 175 and they continued to work well for quite a long time. I finally replaced them because I had the motor apart to install a CR primary drive, not because they were slipping. I still have them.

I mentioned using the MT125 head gasket in another thread - I've had much better luck with them than the copper ones. .030" needs to be milled off somewhere to maintain the compression; you could do it on the head (easiest), cylinder top (the best for closing up the squish clearance, in my opinion), or the cylinder base, which will alter the port timing for more of a mid-hit motor. When I revive my 125 motor in the future, this is what I'll be doing to it - I'll still have the benefits of the ported cylinder's enlarged ports and passages, but with roughly the stock port timing (all my ports were raised).

I've put the Race Tech cartridge emulators in the forks, which required machining the damper rods and using the optional spacers (you have to ask Race Tech for them). I removed the split-pin piston retainers and assembled the pistons with "permanent" Loc-Tite 262, which allowed my machinist to modify the pistons to accept the emulators without the spacers. I installed the emulators at the factory spring setting, which seems to give pretty heavy compression damping (I haven't really given the bike a good workout yet, though). I have no doubt the fork action will be greatly improved once they're dialed in.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Thanks alot for all the info
iv had good luck with my clutches for a while
i use maxima 75 weight mtl for my gearbox and the cr loves it
and ya the bars do fit
google universal big bar mount
i know tusk makes them as well as another company
as far as forks go i was thinking of just getting some evo cr250 or xr forks
the fork tubes would be a lot stronger and its still drum compatible
iv also had my frame gusseted and strengthened
-sam

Hey,
How and why did you put the '80 RM 100 (I think thats a suzuki, right?) swing arm on your CR125?

-Ryan

Ryan
the reason i put the rm swingarm on it was because its longer and its a very heavy duty square tubing deal
its also slightly bent which makes it almost rising rate
the handleing is great
as far as mounting goes it wasnt hard its about the same width and i had some extra axle spacers so i just fabbed her up
the pivot point is no problem at all
its a 1980 rm100 swingarm if your interested
-Sam

i have an 81 alum. swingarm i was going to put on my 79 cr125. it looks like its allmost a bolt on as far as i can tell. you will need to fab some shock mounts thats about it. i haven't acualy bolted it all up as my bike is all apart right now. it should be going back together soon the powder coater has the engine cases now. and the wheels are finished lots of little parts ready to go back together.

Ya I love kidding these old bikes and fabbing up new stuff for them
I rescued mine from a farm And have spent alot of time and money on building it into a really cool evo racer
glad to here other guys are out there tryin to make these old bikes even better