Honda-SOHC

SOHC.co.uk Forums => CB750 => Topic started by: Wills105 on October 23, 2016, 05:47:26 PM

Title: Let's talk sprockets.
Post by: Wills105 on October 23, 2016, 05:47:26 PM

Hi all,
I'm gradually rebuilding my K2 and am confused by sprocket size and fitment.
The drive sprocket has 17 teeth and the rear sprocket 48. The drive sprocket isn't set on the shaft and is able to slide freely and only stopped by a "C" spring clip located in a groove near the outer end of the shaft. The end of the shaft is fitted with an adjustable oiler.
Having read the description in the Haynes manual, it states.
Early models had a 16 tooth drive with 45 tooth rear, this set up damaged the chain so should be replaced with a 12 tooth drive with 48 tooth rear. The picture also shows the drive sprocket having a plate and two bolts, presumably to lock the sprocket in place.
Am I correct in assuming that a new 12 tooth sprocket with plate and bolts will fit the output shaft and that the 12/48 ratio is correct?
Regards,
Wills.

Title: Re: Let's talk sprockets.
Post by: Chris400F on October 23, 2016, 06:05:41 PM

A 17 teeth front and 48 teeth rear gives as near as dammit the same final drive ratio as a 16 teeth front and 45 teeth rear.
My guess would be that the 12 is a typo as this would give a very different ratio.
Pretty sure you should also have the plate and bolts which will lock the sprocket in place on the shaft.

Title: Re: Let's talk sprockets.
Post by: Wills105 on October 23, 2016, 06:13:59 PM

I was wondering about that, 12/48 ratio would mean getting off the line would need lots of slipping the clutch and a top speed of 200mph. :o

Title: Re: Let's talk sprockets.
Post by: JamesH on October 23, 2016, 06:21:13 PM

Sounds like the plate and bolts are missing. Also, you probably should have the chain autolube setup running in the centre of the shaft?

Title: Re: Let's talk sprockets.
Post by: JamesH on October 23, 2016, 06:24:26 PM

(http://uploads.tapatalk-cdn.com/20161023/d80c3155ff87ba769643155c8e43e3f0.png)

Title: Re: Let's talk sprockets.
Post by: Trigger on October 23, 2016, 06:26:09 PM

The early 750's had 17T but, a K2 should have 18T if my memory is right and its Sunday, me thinks ;D

Title: Re: Let's talk sprockets.
Post by: Chris400F on October 23, 2016, 06:37:46 PM

Reckon Trigger's spot-on as usual.
Parts List shows 18T front and 48T rear for K1 and K2.
Wills, if you haven't already done so then check out the mega 750 download in Ash's Dropbox (http://www.sohc.co.uk/index.php/topic,8884.0.html).

Title: Re: Let's talk sprockets.
Post by: Wills105 on October 23, 2016, 07:42:04 PM

Thanks guys, I've downloaded the parts list and manual, I'll order a new sprocket, locking plate and bolts. The sprocket on the bike definitely doesn't have any threaded bolt holes and no sign of sheard bolts, have to assume it's some sort of US "get me home" job. Onwards and upwards.
Wills.

Title: Re: Let's talk sprockets.
Post by: mike the bike on October 23, 2016, 08:25:09 PM

If that sprocket is some sort of bodge, lets hope that's the last of it.