diagnose transmission issues 1978 yz 80

Discussion in '2 smokers' started by dirt hokie, Dec 24, 2017.

  1. dirt hokie

    dirt hokie Long timer

    Oct 3, 2007
    Eastern shore of MD
    just got done a rebuild on a 1978 yz 80 We got it as a complete basket case.
    This was our first full engine/ bike rebuild. Never took aparts or reassembled a 2 stroke bottom end before.

    All new bearings and seals. Bike runs great.... except it slips out of gear, 1st and 3 rd.
    Before I take it apart, what are some possible causes. The Clymer manual has been little help.
    The bike came with missing parts and also some unknown parts from other bikes mixed in.
    The manual refers to keep track of shims in the transmission, but we did not take it apart so don't know if any are missing, and none are shown in the manual or parts diagrams online. Also our transmission gear set is not the one that came with the bike, that one had a broken tooth on third gear, so I bought a used replacement gear set, that looks real good. It shifts smooth and runs great and will wheelie with my fat ass with out clutch slipping, it just randomly slips into neutral or between gears while under load. Thanks for any input
  2. baloneyskin daddy

    baloneyskin daddy bikaholic Super Supporter

    Oct 21, 2009
    southcentral PA.
    If it shifts with a positive feel and the shifter immediately returns to position your shift drum detent is probably fine so that leads to worn parts. since its coming apart you need to closely check the engagement dogs on the actual gears as they are probably rounded off. They should have nice flat surfaces where they mate. If it has been run like this for awhile theres also going to be damage to the shift forks and possibly the drum. Take a bunch of pics and post them. Any used parts from a YZ 80 are going to be suspect as those things are usually hammered pretty good .
    spokester, Euromad and Strong Bad like this.