Shift drum for 73 yz 250

[Slakewell]

I have pulled apart 3 different YZA gearboxes and they all looked like this. It wieghs zip and is very hollow were the MX and DT are more solid. It came out of a YZ 250A. If you have never needed to pull apart a YZ gear box and own one you are most fortunate. The little pins on the front are what breaks the shift fork pulls and pushes these and they break or the holes they live in wear. Then the drum dosent turn far enough and the gears dont work.

[Davey Crocket]

Thats a YZB shift drum, the A was full of holes, the B was hollow but without the holes drilled in it!

[Freakshow]

YEs dave thats what confused me, last one i saw had holes in all gthe slots.

If its hollow and will fint in the "A" box im stillinterested though.  No dents on the shift channels are there ?

[Slakewell]

Its been 10 years since I pulled one of these apart , I have never owned a YZB or parts there off ,I cant remember holes dilled in the drum itself and as indents shift fork slide in these I dont see how they can.
The shift pins are not 100% and will need some attenion. It is what it is. My experance with YZA yamaha's allways came back to this part. It failes and then the dogs on 5th gear round off, The dogs on 5th pushes 2nd into 3rd gear and so on. I hope I have this correct but it's something like that.

[KB171]

Dunno if this helps,but the shift drum in my 250B was the same as this when we rebuilt it,no holes .

[Davey Crocket]

If someone puts a picture of a YZA shift drum up you'll see it is full of holes...ala swiss cheese!!!. The A drum did cause problems and thats why they went back to a DT style drum on the B's, they are very trick motors and gearboxes when you see them apart....they would have cost a fortune to make and I would say pretty close to the early OW's/72 YZ.

[Freakshow]

HOpe to pull the 360 apart on the weekend if thats got one in it ill take a snap, Davey call me when you free i need to cut a deal with you for some of these parts to get the bottom end up and running, rather have all the stuff with me when i go to pull it down rather than be missing stuff ( mainly the rod and bearing) split and the refit it in the same day i hopes to.  Call a brother when you get a chance.  Also did you speak to your mate about the Shim clearance in the box ? if its apart i wanna check its all in spec, so any tolerances for the A model can you fick it to me, i got to do a rebore as well so ill size up the rings and piston too if i know the clearnaces there.  cheers freaky

[Slakewell]

Hey how about I just send it to you and you check it out and If you want it keep it. PM your address
I have no idea of you engineering skills but you will need some to get this perfect agian. I used to make a new stainless steel plate for end and then fill up the pin holes with silver solder and drill them new with a index gear on the mill and a short panel drill.You can make new pins from a needle rolling bearing.

Cheers Slake

[Freakshow]

OK Slake ...Pm sent.    cheers for that.

JOhn ----> did you read my post.  can you call me new Sim is up and running but numbers where on the old one