Vintage Dirt Bike Q & A

Hello all,

I would like to replace the main bearings and seals on my 76 cr250m. How difficult is this for a first timer? What special tools are required and are there any good books or video's to help with this?

Thanks for any advise or support with this.

Its fairly easy except:

MUST have a hand impact driver and NEW #2 phillips bit to remove the phillips screws which have neen in there for how many years?
Need an ignition rotor puller tool.
Take note of shims on the transmission shafts from which shaft and side they were on.
Make note of the shim / spacer and bearings on the clutch basket.
Be careful of the shift lever arm that goes on the shift drum as you remove it so you do not bend it.
May need a case spreader tool, but Honda's usually come apart without one, unlike Husquavna which has 000 bearing clearance, pullers are needed for every move.
While the trans is out look at the shift forks where they ride on the gear for wear or gauling.
Look at the mating areas of the gears, if they are rounded off they are bad or on their way to be bad, they should engage tight and be sharp. You shouldnt be able to pull them apart when twisting them opposite to each other.
Make note of the shift fork slider shafts, check them in "v" blocks for the bends.
The HADEST part when putting everything back together is fitting the transmission, shift forks and the shift fork shafts all back in the IGNITION side case and slipping on the clutch side case alligning the shafts and drum into the clutch case. I make a little rectangle block out of wood to house the ignition side case flat on a bench, put all the guts in that case then it is really easy to assemble the clutch side onto it, use Yamabond on each side of the NEW center case gasket.

A NICE thing to do when the cases are split:
Match the transfers to the cylinder, make sure the base gasket is on so you can trim it if needed.
Polish the intake side of the rod.
Polish the shift fork shafts (lightly)
Inspect the kicker pawl for wear.
Inspect the shift shaft toe the bends.

Just lay out everything as you go and youll be fine.

Good luck

_________________
1994 AHRMA National Champion Sportsman 125 Intermediate.
1996 AHRMA National Champion Classic 125 Expert.

Thank you for the advise, your experience with this is easy to see and much appreciated. I will need to find a good book or video to help me understand all that you have talked about here.

Ive watched some of the vids on youtube and one guy was wacking the crank with a hammer to remove it....NICE

NEVER do that use a case spreader tool
See this guide:
http://www.dirtrider.com/features/two-stroke-rebuild
Another tip is once the case is free of the main bearing on the igniton side it is ready for you to pull apart the rest of the way. Use left hand fingers to pull on the case and humb pushing on crank and other hand fingers to pull on the case and the thumb pushing on the countershaft while pulling the case apart, this way the trans will stay in the ignition side case and not fall all over the floor. Be sure to look at the newly removed case side for any shims that may have stuck to the bearing from oil tension. Put a zip ty on the trans shaft ends to keep everything sano while you have them out or some of the gears will fall off.
In the pics from the link the crank should have stayed in the clutch side of the case, the puller you use will push on the crank to push it out of the ignition side case. ALSO when you assemble the crank back into the cases sometimes there is a shim on the clutch side of the crank, sometimes not but the crank MUST bottom onto the clutch side of the case bearing, usually the main dive gear nut will do this.
Ultimately you want the crank and trans, shift drum, shafts to stay in the clutch side case.
The only real stumper youll have is putting the transmission, shift drum, shift forks and shafts back into the clutch side case, that is a tough deal sometines, just take your time and try to hold the shift drum/forks/shaft in one hand and the transmission shafts in the other holding them together as a unit then ease them into the trans cavity trans shafts first once everything is in the general area you can use a soft mallet to tap the trans shafts into their bearings along with the shift drum and shift shafts. It takes some finesse to do it properly so dont get bummed if you have to do it several times to get it right.
Like I said in the other post and as you can see in the link you need to build a wooden box tall enough to hold the engine on its side and up off the bench, this way the clutch transmission shaft has all kinds of room and isnt pivoting on the bench. Youll see how tall you need to make the box once you get the clutch off the clutch shaft.

Once you do this a couple of times youll be doing all your friends cases.

Good luck

_________________
1994 AHRMA National Champion Sportsman 125 Intermediate.
1996 AHRMA National Champion Classic 125 Expert.

look for a Clymer or Haynes workshop manual for your bike.
or maybe an original honda manual is offered at ebay.

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