Author Topic: Mk 4, jumping out of 2nd Gear  (Read 4107 times)

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Offline Alex Hall

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Mk 4, jumping out of 2nd Gear
« on: 20 Aug 2009 at 22:36 »
Dear Doug, Eddie & Chris, and all other Douglas owners

After a delay of just over a year I have finally opened the side panel to the Mk 4 box. A couple of things came to light, primarily, the bush which guides the selector cam shaft seams to have come out of its housing or was not fitted deep enough so that the cam was only touching the top of the selector fork pins. Secondly, the selector fork pins have little bushes on them, but are like little rollers which actually spin. When I engage second gear it is fairly easy to see that the dogs have not meshed sufficiently, fortunately they still seem intact with no alarming rounding of edges. There seems to be some wear on the little hill of the cam which throws the fork into the second gear. But even when I push it by hand with the cam in place it can not mesh correctly. Without the cam plate it goes all the way in and meshes completely.  My conclusion is this, either the selector fork bent or the fork was incorrectly machined when the bushes where installed on the pins. Is that a fair judgement? To remedy this, may I consider reshaping the hill in the cam which moves the fork. Naturally I  will have to move the hill and the opposite concave side together. Or is there something else to look at. Can a selector fork be bent? I have addressed the bush, so that the cam now lies in the same plane as the detente spring and also the pins on the selector forks, but I still have this dilemma about the insufficient throw on the fork.

Hope you re all well and still riding; looking forward to your replies.

Offline eddie

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Re: Mk 4, jumping out of 2nd Gear
« Reply #1 on: 21 Aug 2009 at 06:39 »
Alex,
         Obviously someone has, at some time, already tried to solve this problem, and in the process, may have have added to the problems if they have incorrectly machined the selectors. Personally, I do not favour re machining the selector pins unless they are really seriously worn. The wear pattern is normally in the form of 2 flats on an angle with an unworn peak between them. It is this peak that keeps the gear in mesh, so unless seriously worn, should hardly affect the depth of mesh. Whilst you have the side cover off, check the depth of mesh of the dogs on 3rd gear - if this is greater than on 2nd gear, remove the layshaft assembly and have half that difference ground off the front face of the 18T fixed pinion - this will allow the layshaft to be pulled back further and equalise the meshes of 2nd and 3rd gears. I would not attempt to alter the tracks in the camplate as this could result in overtravel of the selectors and throw up even more problems. There must have been quite a lot of variation in the overall length of the gear clusters from new as the spares book shows an option of 2 spacers (3/32 or 1/8") for the front end of the layshaft.
                                  Regards,
                                           Eddie.

Offline Alex Hall

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Re: Mk 4, jumping out of 2nd Gear
« Reply #2 on: 22 Aug 2009 at 18:32 »
Eddie,
Thank you for your help in the matter. Unfortunately by the time I read it I had already modified the spare selector cam I had!
I re drew the curve for second gear, in so doing had to increase the ridge by an 1/8 of an inch. This I did by careful welding first on one side then the other to minimise distortion. When it came to cutting away the opposite side to allow the selector pin to slide through I used a Dremmel with a miniature grinding disk, it was the only way to cut away the hardened steel. The welded side was easier and finished touching it, after a file with emery cloth. I was considering hardening it with Kasenite, but as the selctor pins have rollers, thought it should be ok.
Went for a ride this after noon. All 43 miles of them, for the first time on the Mk 4 and having a blast. I m so so glad it worked. I have no hesitation suggesting such a remedy, it was simple just time consuming. I had to check that there was no end play in the layshaft, for if there was it would have buggered up my calculations. So now, second gear dog teeth mesh the layshaft by the full depth of the teeth and so does third.
On a nother tack, I m coming to the conclusion that setting two carbs is not as easy as I thought it was in my Mini days! Would a balance pipe between the two make a difference? I don t have 2 spare carbs to drill holes into.
Cheers once again, Alex

Offline eddie

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Re: Mk 4, jumping out of 2nd Gear
« Reply #3 on: 23 Aug 2009 at 06:34 »
Alex,
          Don't go for a balance pipe - if you are having problems now, the balance pipe will only confuse matters even more.
         Go back to basics - make sure both carbs are set up the same, i.e. same cutaway slides, same needle jets and needle position and same main jets. Incidentally, I find a size smaller cutaway, lower the needle 1 notch and increase the main jet size by 5 suits the modern unleaded fuels better. Wind in the slow running screws onto their seats, then back them off 2 turns. Make sure there is some slack in the throttle cables and wind the throttle stop screws down until the slides bottom on the choke block. Wind the screws up again by 1 turns. The engine should now run at a fast tickover. Ease back the throttle screws equally to get a satisfactory tickover. Adjust the slow running screws to get a steady beat with only the faintest trace of black smoke in the exhaust. Now adjust the throttle cables so that both cylinders pick up together.
                               Regards,
                                        Eddie.

Offline Alex Hall

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Re: Mk 4, jumping out of 2nd Gear
« Reply #4 on: 23 Aug 2009 at 08:33 »
Eddie,
Thanks for that! A superb description on how to go about it. Will do so this after noon.
Cheers