C15 gear box sprocket

[DAVE BRADY]

Hi,

Has anyone fitted a larger gear box sprocket to a C15 and what was the result?
Longer legs for cruising?
Labouring pulling away?
Better or worse fuel consumption?
etc.

Dave.

[rhyatt]

My standard C15 has a 17 tooth and has a nice balance of pull away and 45/50 cruise , so I would hesitate to change,
Is there enough physical room to take a shade larger chain run around the back area of the primary I wonder , thinking of the alternator leads

[DAVE BRADY]

Hi,

There will be enough room as the B40 has a 19t sprocket. I was thinking only one tooth just to slightly ease the revs at 50mph. However, there may not be an 18t available as trials and scrambles have 16t and the B40 19t.

Dave. 

[rhyatt]

the only 18T is 40-3122 which are around certainly in the marketplace -

https://www.ebay.co.uk/itm/354844453525?var=0&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338749392&toolid=20006&_ul=GB&customid=Cj0KCQiA9OnJBhD-ARIsAPV51xMBPXluLpD8YgG5bJDVek5yny5tXdaOrgO2iAqGCmBkem_rFcPM7wAaAtoiEALw_wcB|0AAAAADihhqXkhdyCEqqx3R4PaXXpV4V4H|CkEKCQiA0eTJBhCeARIwAF90mS7e8oB-TOYKd27DVH8w_KTJ8B_Vfi4csVRKB7ES8dJAQC5J49w9jQOkhjBxGgKvpw&gclid=Cj0KCQiA9OnJBhD-ARIsAPV51xMBPXluLpD8YgG5bJDVek5yny5tXdaOrgO2iAqGCmBkem_rFcPM7wAaAtoiEALw_wcB&gbraid=0AAAAADihhqXkhdyCEqqx3R4PaXXpV4V4H&wbraid=CkEKCQiA0eTJBhCeARIwAF90mS7e8oB-TOYKd27DVH8w_KTJ8B_Vfi4csVRKB7ES8dJAQC5J49w9jQOkhjBxGgKvpw&loc_interest_ms=&loc_physical_ms=1007061&adtype=pla&gad_source=1&gad_campaignid=22853897447&gbraid=0AAAAADihhqXkhdyCEqqx3R4PaXXpV4V4H



it does show them as options on the C15 parts book for Scrambles and Trials 1962 but I don't know if the C15 and B40 use the same rear chain size

[DAVE BRADY]

Hi,

Thanks. I will have a look.  The chain size is the same. I can remember putting a C15 16T on a B40 with the same chain. Three teeth less gave a good 'off road' performance without the need for a larger rear sprocket.

Dave.

[DAVE BRADY]

Hi,

Ordered an 18T from Fast Eddies at mid-day on the 11th and it has just dropped through the letter box.
Good service.

Dave.

[rhyatt]

When you expose the sprocket and nut etc behind the clutch , do check the condition of the high gear sleeve bronze bush.
My bush had a very deep groove munched into it by the clutch backplate oil seal and road dirt.
Trouble is if it is worn , then it means delving deeper into the gbox

[DAVE BRADY]

Hi,

Thanks rhyatt.  I will do that.

Dave.

[Mikey82]

Let us know how the bike performs with the 18t sprocket Dave, I,m considering the same upgrade as I would like to increase top speed a little without over revving engine 👍
Not sure if C15 will struggle more on take off...