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General => Douglas Motorcycles - General Discussion => Topic started by: dalgrae on 09 Aug 2014 at 13:23

Title: mk5 jumps out of 4th
Post by: dalgrae on 09 Aug 2014 at 13:23
My recently purchased and recommissioned mk5 has now done approx 45 miles now I know I have an oil leak from the output to drive sprocket location and understand that it is a gearbox out of the frame to fix but I also have a problem with an occasional jumping out of top gear but only on overrun if I keep the throttle slightly open it does not do it also the gear lever is still in the top gear position and seems to then go back into top gear,any thoughts on what it could be please,I would assume as above it is  a gearbox out of the frame job again

Regards Colin
Title: Re: mk5 jumps out of 4th
Post by: eddie on 09 Aug 2014 at 17:32
Colin,
         Jumping out of gear in postwar Douglas gearboxes can be caused by 2 things. Either the gear selector for 3rd/top (the front one) has a severely worn pin that locates in the camplate or the main gearbox case is incorrectly machined causing a shallow mesh of the drive dogs. You can check the problem out without removing the gearbox, but the box will have to be removed to effect a repair. If you remove the gear indicator from the end of the gearchange shaft, and remove the 6 Allen Screws from the side cover, the side cover can be removed, leaving the camplate in place. With the side cover off, you can select all four gears in turn by turning the camplate with a large screwdriver. As you select each gear, you will be able to see the dogs engaging (they usually only engage by about half their depth). If the pin on the 3rd/top selector is badly worn, you will be able to move the selector to and fro in the camplate slot. Whilst doing this, observe the condition and depth of mesh of the top gear dogs. If the depth of mesh on just top gear is significantly less than the other gears, then the fault lies with the machining of the main case. This can be overcome by modifying the front cover (figure 8 plate). Unfortunately, whatever the problem turns out to be, removal of the complete gearbox will be necessary in order to do the repair.
   If you can live with the bike as it is for another month, perhaps I should bring a part dismantled gearbox to the next Bristol clubnight and show you what needs to be done.

  Regards,
               Eddie.
Title: Re: mk5 jumps out of 4th
Post by: dalgrae on 10 Aug 2014 at 11:41
Thanks Eddie I will take up your offer at the next meeting until then I will try and get around the problem by keeping the throttle just off idle

Regards Colin
Title: Re: mk5 jumps out of 4th
Post by: dalgrae on 20 Aug 2014 at 14:55
So after a ride on the bike today it still jumped out of top gear so I decided to do some investigation,what I noticed  was that for the first 3 gears when selected the gear lever still had some fore/aft spring loaded movement but in top the gear lever was solid.Following your advice I stripped out the kick start cover to look at what was happening,what I noticed was that the cam  plate gear selector plunger was only locating on the bottom side location on the camplate I syringed out all the remaining oil still in the bottom of the case and then wiped it dry,when top gear was engaged it was obvious that the camplate was fouling the gearbox casing in the casting depression it was meant to clear so out with the Swiss needle files and an hour later I now had clearance between the camplate/casing and the camplate plunger now located on both sides of the camplate groove as it should do and as the 3 other gears. I reassembled everything and now when I engage top gear the gear lever has the same fore/aft spring loaded movement as the other gears,I will test ride the bike tommorow to see if it any different

Regards. Colin