Vintage Dirt Bike Q & A

Started preping the engine for teardown- I will update as I progress further. I have included a couple of pics- one of the engine stripped down in the bike, kind of a pre-rebuld pic, shows what 2 years of racing will do to the paint. A couple of the other pics show one of the donor engines ready for tear down to steal some transmission parts next to my freshly glass beaded engine (prepping for paint). last two are just fun pics of my cramped work space and a stolen racing pic. Lets see what we find in these cases!

awesome thread Ratmuss !!

how about posting larger pics? You're a couple weeks ahead of me!!

Alright guys I have finally had the time to break into my cases and see why I have so many neutrals. I have attached some pics- if anybody on the board needs some internals let me know, I have plenty of extras. attached are a couple of pics after glass bead, paint and starting to split the case.
feel free to make comments or ask questions!

here are the pics attached in a bit smaller format.

alright- so getting farther into the tear down I started to see clues to my shifting issues. The bottom tang is cracked on the limiter for the shift lever- apparently I jam up on that thing pretty hard when I get frustrated that there is not a gear there. also stating to pull the cases apart-

It looks OK in the pics and is probably fine, but you might want to check the spring retaining pin that the shift tang cracked against. One of my 175 motors had the 'tang' (actually a section of ring gear in that design) bent down about 1/4" and cracked, and the pin had angled down a little and had to be re-tightened (threads were OK). I think someone must have landed with full bike weight on the shift lever.

I took pics of all the bearing seated positions too, which came in handy later as two were not pocketed or driven in flush.

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

Checked the Spring retaining pin and everything seemed to check out fine. I have a couple of shift shafts at my house, so I chose the best one and replaced it. After I split the cases and pulled out the transmission, I found more issues. It seems that my center shit fork was bent, outside contact parts were a bit scorched and you can see where a gear had contacted the body of the fork at one time. I will attach a pic. I will also attach a picture of the different transmission gear selection I had to choose from, along with how rounded some of my gears were. I also decided to take out the taller MT250 5th gear that I thought I would like and go back to the CR 5th gear.
All in all, I know that the gears that I am installing, while not new- are better than the ones I pulled out of there.

time for bearing removal- install, case assembly and touchup. Piston should be here any day and cylinder will be bored next week. I better hurry up, I want to try and race this weekend to test this thing out for an Ahrma race at the beginning of May.

More pics to follow.

All back together and ready to rip- here are some pics after assembly and the top end going on. Went with the Wiseco, have had good luck with them in the past. I am now part of the 70.5MM club on the piston size (plus .002 on the bore). If anybody has 73-74 cylinder for sale let me know. Here are some more pics.

Two last pics- who can say they have the original owners manual and title?? Also race day - April 11th 2015 Woodland Wa.