More 100 help needed for separating the rear sprocket

B

Benbecula

New member
Location
Western Scotland
Hi,

This has stumped me for the moment.  I need to remove the old sprocket, its badly worn. But trying to seperate the cush drive from the sprocket, is the issue I have.  I have removed the sprocket bearing and can't see anything else holding it all together.  So now I'm unclear where to go?  I soaked the area in penetrating oil overnight, then tried a few light taps with a copper hammer, but no sign of any give.

Any suggestions please ?  No I don't need a bigger hammer, I'm trying this restoration with love and tenderness.

Regards,
 
The sprocket is integral with the drum and the unit is a push fit into the hub. Same as British bikes of the era. Small rubber bushes in the hub act as drive shock absorbers.

If you intend changing the sprocket, unless you find the part, you'll have to cut the old one off the drum, have a new one made up and welded on the drum and after that, I imagine that you'll need to true the drum on a lathe.

Have you got the parts list and users manual?

Paul
 
Depends on year and model if sprocket is integral with the drum or not.  Those integral with the drum can be renewed by removing the old sprocket from the drum and welding on a new one.  Those integral with the cush drive bit are a bit more complicated.

In any case, new sprockets are hard to find.  I built my own when I couldn't find one.  Would have had to anyway, as I'm now running a more common chain size along with a ratio that wasn't available with stock sprockets.


piet
 
Hi,

Thanks for the support.  I have a parts list somewhere I bought from ebay, I don't have a users manual which would be very useful if I could find a copy.

I'm was pretty sure that the sprocket sits between the two plates of the cush drive.  The pins appear welded into one side pass through the sprocket wheel protruding out through the plate on the other side.
They then line up with the rubber lined holes in the drum.

I felt that it was just old age or corrosion holding it all together, but it would appear I am wrong.  I love a challenge and this is going to be one.

Thanks again.
 
Benbecula said:
I'm was pretty sure that the sprocket sits between the two plates of the cush drive.  The pins appear welded into one side pass through the sprocket wheel protruding out through the plate on the other side.
They then line up with the rubber lined holes in the drum.
Click to expand...

Looks like you have the later type, this has the cush drive flange cast onto/around the sprocket.  This cannot be further disassembled. 

My humble effort:

piet
 

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Benbecula said:
Hi,

Thanks for the support.  I have a parts list somewhere I bought from ebay, I don't have a users manual which would be very useful if I could find a copy.

I'm was pretty sure that the sprocket sits between the two plates of the cush drive.  The pins appear welded into one side pass through the sprocket wheel protruding out through the plate on the other side.
They then line up with the rubber lined holes in the drum.

I felt that it was just old age or corrosion holding it all together, but it would appear I am wrong.  I love a challenge and this is going to be one.

Thanks again.
Click to expand...

The users manual is in your inbox

Paul
 
Hi Paul,
I am very interested in these little bikes, particularly after seeing them in action in Breganze on Monday morning.
I am anticipating purchasing one soon.. I am interested in 1955 model 100 Sport..
Is the user manual published somewhere, or perhaps you would also send to me..?

Thank you
Ian
 
LaverdaIan said:
Hi Paul,
I am very interested in these little bikes, particularly after seeing them in action in Breganze on Monday morning.
I am anticipating purchasing one soon.. I am interested in 1955 model 100 Sport..
Is the user manual published somewhere, or perhaps you would also send to me..?

Thank you
Ian
Click to expand...

Hi Ian,

I'll send it to you.
It's in Italian and not very detailed.
I have the parts list if you need it.

Paul

 
Thank you again for your support.  I'm finding it hard to believe that the whole unit has to be replaced.  Chain sprockets are a part that during the life of any bike will need to be replaced, often many times.

I examined the one I have last night and have to admit it will not disassemble any further.  Therefore I now have to find an engineering shop that can help.

Regards,

Kim.
 
Benbecula said:
Thank you again for your support.  I'm finding it hard to believe that the whole unit has to be replaced.  Chain sprockets are a part that during the life of any bike will need to be replaced, often many times.

I examined the one I have last night and have to admit it will not disassemble any further.  Therefore I now have to find an engineering shop that can help.

Regards,

Kim.
Click to expand...

Are you sure that sprocket needs replacing?

Paul
 
I reckon it would be possible to turn the old sprocket down to make it into a flanged hub that a new sprocket could be bolted to. You'd obviously have to turn the centre of the new sprocket blank to suit your hub, but it's not rocket science. Any general engineering shop could handle it. You'd just need to make sure there's room for an overlapping flange and bolts where the new outer and old inner sprockets join.

 
Dellortoman said:
I reckon it would be possible to turn the old sprocket down to make it into a flanged hub that a new sprocket could be bolted to. You'd obviously have to turn the centre of the new sprocket blank to suit your hub, but it's not rocket science. Any general engineering shop could handle it. You'd just need to make sure there's room for an overlapping flange and bolts where the new outer and old inner sprockets join.
Click to expand...

Nothing is as easy as it looks, Cam.

This particular sprocket is quite complicated.  Not only is the cush drive flange cast over the sprocket, but the drive pins are usually loose as well.  These were originally either welded or rivetted to the sprocket, underneath the casting... I haven't come across a used sprocket that still had tight-fitting drive pins.

After searching high and low for a replacement, I ended up making the entire assembly from scratch.  As the only front sprockets I could source were for a slightly larger chain, I used a suitable blank for the rear and was able to eliminate the puny bicycle chain originally used.  The new drive line has worked excellently so far.

piet
 
Update we have tried heat and a press up to 5 tons and no progress.

I'm over in Inverness next month and I will take it to the precision engineers who have done work for the Jota
for me.  I trust them and they do a sound job.

A new sprocket can be found and the centres matched to take the bearing and drive to the wheel.

Reports and pictures to follow.
 
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