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D7 gearbox problem
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Culverclan
North Cornwall
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May 4, 2019 - 6:43 pm
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My 1966 D7 Bantam is finally on the road but it surges badly in second gear going uphill. Totally fine in first and third. Apparently a weakness in the D7 3 speed gearbox. Could anyone recommend a classic bike shop in Cornwall or Devon who could fix this and an idea of cost? Cheers. Pete.

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SpacedMarine
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May 4, 2019 - 6:47 pm
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Define surging.Do you mean clutch slip?

when I hear surging I would think of the engine running away with itself rather than a gearbox problem???

What's 7/16 in mm again?

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sunny
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May 4, 2019 - 7:00 pm
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dus  it  surg   if   you  use  the  throtle   slowiy    ,,   so  wot  i meen is it  4 strocking   then  sergin   on   2 strocking     ,,

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Mags 1
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May 4, 2019 - 7:10 pm
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If you use the search facilty you'll find lots of posts about the later D7s having a gearbox cheaper version mod. which allowed the second gear cogs to separate on hard accelerateton, due to less positive engagement. Most folk opt for the earlier gearbox innards, better made, but you need to put the lot in as a whole, some models of cogs have more or less teeth.

Four now on the road and at least several in bits.

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Culverclan
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May 5, 2019 - 8:36 am
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Mags 1 said
If you use the search facilty you'll find lots of posts about the later D7s having a gearbox cheaper version mod. which allowed the second gear cogs to separate on hard accelerateton, due to less positive engagement. Most folk opt for the earlier gearbox innards, better made, but you need to put the lot in as a whole, some models of cogs have more or less teeth.  

Thanks for the advice. Looks like I'll be after a D1 gearbox or contents. And a mechanic who knows how to scheme it! Appreciate the advice.👍

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cocorico
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May 5, 2019 - 10:28 am
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May be of help.

The Bantam Club Forum - all the answers are in there. If not, Google may.

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Sponge
Lancashire (A chip shop somewhere near Preston)
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May 5, 2019 - 12:04 pm
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Hi Culverclan, 

Good news is that this is fixable and not to expensive but it does need teh whole engine to be removed and stripped down.  I have had this problem several times over the years and it has usually come down to wear in the indexing mechanism. There is a swivel pin which gets worn and allows the indexing mechanism to jump up and down allowing the gearbox to slip in and out of 2nd gear, it also allows the detent (indexing) ball housing to get dameaged.   The fix involves a total strip down and replacement of some relatively cheap parts.  Adding a D1 gear cluster is not strictly essential but whilst stripped out it makes sense to do so. Whilst stripped down it also makes sense to replace anything else that needs it ( seals, bearings, big end, sleeve gear, clutch parts, Prim/chain  etc etc).  It that way you will have total peace of mind but a bigger bill.     

My D1 was slipping in 2nd gear so last year I just stripped it down on the bench, replaced the ball seating, ball, cup and spring and screwed it all back together without any other attention (just gaskets) and hey presto - problem solved. One long days work and all is good. 

There are various people who can do this work - if you don't want to try it yourself,  but make sure that whoever does it replaces the ball, swivel pin and bits, if these are worn out the replacement of the gears for D1 gears and shafts will not solve the problem. 

All the best and good luck 

Sponge 

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Culverclan
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May 5, 2019 - 10:04 pm
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Thanks to Cocorico and Sponge for some great advice. I've got something to work on now. Much appreciated.👍

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Mags 1
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May 6, 2019 - 6:07 pm
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Sponge said
Hi Culverclan, 

Good news is that this is fixable and not to expensive but it does need teh whole engine to be removed and stripped down.  I have had this problem several times over the years and it has usually come down to wear in the indexing mechanism. 

Sorry to disagree with you on this one but I'm saying that I think it's the inner splines, (or no splines at all on the later D7s) that cause this problem.

The earlier engines have an extra set of small dogs on the mainshaft too.

Four now on the road and at least several in bits.

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Sponge
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May 7, 2019 - 8:41 am
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Well we are not giving this poor member much good advise if we are disagreeing with each other are we ?? I therefore withdraw my earlier advise in the interests of integrity.   Mags 1 please carry on..........

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sunny
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May 7, 2019 - 9:16 am
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you   are  both  correct         so  its  allways   werth  a second  or  therd   bit  of  advice     ,, so often  moor than  1 thing    is  the  problam

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cocorico
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May 7, 2019 - 9:41 am
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sunny said
you   are  both  correct         so  its  allways   werth  a second  or  therd   bit  of  advice ...

Quite right - you will always get differences in opinion, depending on personal experience, etc. Don't worry if you appear to be contradicting each other, someone will have the answer.

The Bantam Club Forum - all the answers are in there. If not, Google may.

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Culverclan
North Cornwall
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May 14, 2019 - 8:03 pm
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Thanks to all the members who replied to this problem. Very valuable advice which will definitely help when the engine is taken out. This is a truly great club to be a member of. Ride the D7 in question to it's first show at the weekend in Bude. Tricky to ride with the second gear problem but still great fun and got plenty of attention.

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Cornish Rooster
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May 14, 2019 - 8:49 pm
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Still not 100% sure what the symptoms are as in "surging" meaning clutch slip, or "surging" as in jumping out of gear ?

As said before it is a common problem on the D7's (well on here over the years) and normally and lets emphasise "normally" as the fault could be something else entirely as the other posters have said, it is usually due to the gearbox layshaft on the D7's.  On these D7 gearboxes BSA in their wisdom to save a few pennies on manufacture omitted some splines (actually teeth to be precise) and this is often the cause of the gearbox jumping out of 2nd gear. If you compare a D1/3 layshaft with a D7 layshaft it becomes immediately obvious that they are different with the earlier one having a set of teeth that the later one doesn't have. That's why folk with D7's fit the earlier layshaft to D7's, hope that's clear enough ?

And it goes with out saying that if you have the engine stripped down then it's good practice to replace springs etc and anything that looks worn or may give you trouble in the future, I did this when my engine was apart a few years ago (the bushes were so worn it was a wonder the gearbox operated at all before strip down).

There are some Bantam layshafts on Ebay at the moment, the photo shows four of them, the one on the left is the earlier one and the other three are the later ones (as fitted to D7's).

Put in "4 x BSA Bantam Gearbox Layshafts" into Ebay and you will see the difference.

Phil

BSA Bantam D1 "150" in use regularly often as general purpose transport, quite a few other bikes as well. Cornwall Area Rep. 

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