Author Topic: 1949 startwin output sprocket change.  (Read 1671 times)

Offline 49startwin59

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1949 startwin output sprocket change.
« on: 06.04. 2010 23:04 »
Hi everyone,
my name is Dave and i,m new to this forum and would like to ask my first question! Do you have to take the engine/gearbox out to change the gearbox output sprocket? If this is so, it,s a hell of a lot of work to change a service item.
Cheers,
Dave.
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Online Brian

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Re: 1949 startwin output sprocket change.
« Reply #1 on: 06.04. 2010 23:27 »
Unfortunately Dave the asnwer is yes. It is possible to get the gearbox out but its easier to pull the whole engine/gearbox assembly out.
Is the sprocket worn out or are you wanting to alter the gearing ?, if its the gearing you could change the rear sprocket/brakedrum.
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Offline a10gf

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Re: 1949 startwin output sprocket change.
« Reply #2 on: 07.04. 2010 10:34 »
Welcome to the forum. It's quite some work involved, but how often do you need to change the sprocket, should last for years and years of use (unless using a worn out chain), other parts of the engine would probably need maintenance before the gear sprocket. Only need for frequent change could be a sidecar going on and off.
e
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Online muskrat

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Re: 1949 startwin output sprocket change.
« Reply #3 on: 07.04. 2010 20:26 »
G'day Dave, welcome to the forum.
                                               As Brian said, easier with motor out. Take out the primary/clutch first, pull the lump out and unbolt the gearbox. Good idea to give it a good inspection and replace any worn parts while it's out, motor and box. You don't want to do it again for quite some time.
I know you will have more ?'s so ask away, were here to help.
Cheers
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Offline 49startwin59

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Re: 1949 startwin output sprocket change.
« Reply #4 on: 07.04. 2010 22:43 »
Hi everyone,
my name is Dave and i,m new to this forum and would like to ask my first question! Do you have to take the engine/gearbox out to change the gearbox output sprocket? If this is so, it,s a hell of a lot of work to change a service item.
Cheers,
Dave.


Thanks guys for your responce, i,m actually pulling the gearbox out anyway because i can,t stop the old girl from crunching gears, up or down the box, worse when hot. I,ve replaced most of the clutch components, spent hours setting the clutch up and had two BSA guys look at it, none can find a problem. so last weekend i picked up a recon box for it so i can do a quick swop. I,ve owned the bike for two years and only done 68 miles on it because it,s been one problem after another and i hate riding it like it is, so any thoughts/ideas would be great.
Once again thanks for your help guys, cheers, Dave.
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Offline LJ.

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Re: 1949 star twin output sprocket change.
« Reply #5 on: 07.04. 2010 22:54 »
Dave don't give up on it as the bike is a nice little runner when set up correctly, it takes a little time and patience.

I'm wondering here if you maybe changing the gears too quickly and not giving the engine time to drop it's revs a little? I find this with my 49 star twin in comparison with my later A10's. I also used to crunch the gears and took a look inside the box... Not a lot in there is there? and as I could not see any way to improve things I treated my gear changing as I do on the M21, this has made a big improvement.
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Offline 49startwin59

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Re: 1949 startwin output sprocket change.
« Reply #6 on: 08.04. 2010 20:42 »
Hi, thanks for the reply, i forgot to mention that i,ve tried slow(letting the revs drop) and light gentle action which either still leads to crunching or faulse neutrals with non meshing gears and lots of in-between gear noise. I,ve also tried faster harder gearchanges to the same effect, on an average i,d say that down-shifts are the worse, especially when hot.
I,m also having trouble getting the engine/gearbox out as the dynamo bracket keeps fouling the right hand down tube,,,,,,,any ideas?
Thanks for your help,
Dave.
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Online trevinoz

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Re: 1949 startwin output sprocket change.
« Reply #7 on: 09.04. 2010 07:59 »
Hi Dave,
           If your gearbox is the original you will probably have the symptoms that are evident.
In about 1951 BSA redesigned the gearset to eliminate problems such as you have.
You could remove the plate if it is causing you bother. I assume you are referring to the front engine plate through which the dynamo is fitted.
Trev.
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Offline 49startwin59

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Re: 1949 startwin output sprocket change.
« Reply #8 on: 10.04. 2010 23:06 »
Hi Trev,
thanks for the reply, i,m fairly new to brit bikes, so i,m learning all the time. I assume i remove the dynamo to remove the offending item, is that easy?
Cheers,
Dave.
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Online trevinoz

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Re: 1949 startwin output sprocket change.
« Reply #9 on: 10.04. 2010 23:13 »
Dave,
             Take off the timing cover, loosen the dynamo clamping band, twist the dynamo to free the chain and twist and turn the dynamo to remove it.
Easy!
  Trev.
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Online Brian

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Re: 1949 startwin output sprocket change.
« Reply #10 on: 11.04. 2010 00:47 »
I have to say this sounds like a clutch problem to me.

The modified box is better than the earlier type but I have one of the earlier ones in my Star Twin and it works perfectly. I used to think you could identify the different boxes by the thickness of the mounting flange but not so. I have "thin flange" boxes with the later type internals.

Back to the crunching problem, see what happens after you change the gearbox but I still think the clutch could be the problem. These are a very good clutch but still can suffer from the usual problems of poor quality plates or wear in the basket. Grooving or wear in the basket is common because you have to remove the rivets that hold it all together to be able to file the grooves out. This wont show up as a fault when the engine is not running and you are pulling the clutch in and watching the plates lift but will cause problems when the engine is running and there is load on the basket.

See what happens after the gearbox change I guess.
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Online Triton Thrasher

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Re: 1949 startwin output sprocket change.
« Reply #11 on: 11.04. 2010 11:17 »
If the crunching is worse when hot, would a thicker oil be worth a try?
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Offline 49startwin59

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Re: 1949 startwin output sprocket change.
« Reply #12 on: 11.04. 2010 21:30 »
Armed with all this info i,ll give a go. Thanks to everyone for there help, will let you know what happens.
Cheers,
Dave.
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