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Laydown gearbox pointers

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Desperately want to start re building my 56 Dommie but I have concerns about gear selection in the laydown box. The selector works smoothly and makes all the right noises but I only seem to have the choice of,in gear or neutral. Obviously I do not want to reassemble the bike and then strip it down again, so I fear that I must have a look inside to seek out any obvious problems. 

Never having stripped a box before, I wonder if anyone can give any pointers as to what I should be looking for that might give selection problems.

Appreciate your usual help. Thanks Ron.

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Back to the original subject. Since my earlier post I have been playing with the selector mechanism and I have noticed that there appears to be a lot of play around the nut that holds the selector arm (top left in the picture attached) when operating the gearchange lever the selector arm can be seen to waver and the aforementioned nut oscillates even though it is fully tightened. I strongly suspect that this is the root of my problem but I still welcome any comments that you may have.

It is very easy to locate all gears using the other nut, (bottom left in pic) all positions are very positive and there is no play at all.

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Buy and watch the DVD by Mick Hemmings, Ron. It's invaluable. If you can get the box out of the frame the dismantling and reassembly is not too bad.

George

Not a reply, just an addition. Thanks to another member I now have an exploded view and written commentary for the laydown box. Armed with this additional knowledge I have stripped my box and found what may well be the root of my selection problems. Now awaiting delivery of parts for the re assembly bit. Unfortunately the reassembly instructions refer to "the large pen steel washer" which fits between the face of the main gear and the inner face of the main bearing. It looks like a shim washer but the only thing that I can find anywhere that might possibly be it, is listed as:

023170WASHER - OIL RETAINING - PRE AMC GEARBOX - ON SLEEVE GEAR-  - £6.47. The price makes me doubt whether it is actually the part that I need.

Can anybody advise. Thanks Ron.

 

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my ongoing quest to solve my gear selection problems has led me to the Norton gear identification chart, 1939-1956, in which it specifies that the gearbox shell for a 1956 laydown box is: GT 100 VAF, mine is clearly stamped: GT 202 VAF. Any ideas? I have also noted that, though carrying the correct part marks, the engagement faces of of the sliding gears have all been attacked with an angle grinder. Could there be some connection?

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Dear Ron,

Seems this box has a history, was the bronze bush missing from selector arm?

A previous owner has had it jumping out of gear or not engaging, looked at worn dogs and thought 'easy I'll just grind worn face away' Unfortunately it is not that easy as all 3 have to engage with their partners at same time otherwise 1 dog has all load and will shear off. If it was first gear with pegs in holes you might get away with it, but I'm afraid you you have some scrap. I suspect it will also effect faces of other gear partner you have not shown. As new prices for these gears are eyewatering keep a watch on a well known auction site or take them in your pocket to the autojumbles. Hemmings had a stall at Stanford hall last summer with some some second hand so he may be worth a call.

regards Martin

Many thanks for your input Martin I fear that you may well be right. I was suspicious at first sight of the grinding marks but have desperately avoided thinking about having to replace them.

with regard to your question about the bronze bush, no it was not missing but it was badly worn and I have already replaced it.

guess that my completion date will have to be revised unless ERNIE coughs up.

Thanks again for your interest. Regards Ron.

 

 

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hello the forth gear has a set of roller in between third and fourth gears with a bronze bush  these can be  tricky to fit,  but a some vaseline   helps  to get to anything first remove selector rod by unscrewing it   and when refitting the inner case and out case make sure the cam arm is in forth gear  looking up  the gear box has to be timed by the selector arm to the cam plate,  if you got it in forth you then work backwards to first by turning the main shaft, I rebuilt my lay down box  and its a semi close ration   racing cluster   its was easy enough to do,   with my ability         yours  anna j  

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Anna said - hello the forth gear has a set of roller in between third and fourth gears with a bronze bush  these can be  tricky to fit

I'm pretty sure a normal Laydown box doesn't have any rollers there. I can't remember there being any in mine and the drawing I have doesn't show any.

Ian

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They are not shown on the drawing but are present, set of 13 Part no. A2/318 on the '56 parts list.

Ian McD

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I concur with Ian. I recall fitting them when I refurbed my b/box. Grease will hold them in but be careful - the Garage Gremlins prize them once they hit the floor!

George

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to have the gearbox orientated with the main bearing at the bottom ie with the mainshaft vertical. The Edgar Franks manual suggests holding the rollers in with a bit of rolled card but I've always found that thick grease works well. When I bought a set of rollers from RGM they sent me 14 so must have assumed I'd lose one.....

Oh, as well as the bronze bush there is a thick steel washer that retains the rollers and acts as a bearing face for the bronze bush. RGM have both.

With respect to the bodged dogs I wonder whether it's feasible for a machine shop to tidy them up? It should just be a matter of accurately indexing the gear through 120 degree increments on a vertical mill and taking a skim off the faces. A carbide cutter should do the trick but the dogs would then need hardening.

Anna could probably do it for you.......

Thanks Anna. I have been going strictly by the book and assembling with the cam plate in second. Have had no problems with the rollers other than losing one but I think that's compulsory.

Thanks for your interest. Ron

Hello Ron well I had to do things the hard way  and find out by my self  if you get it wrong then you only your self to blame and you start again from scratch   I find when fitting to out cover  have in her top gear that way all you have do is work back through the gears to neutral  and if you find them all and they work nice you then done a good job   yours   anna j 

 

 


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