Sprocket question

[Tunster]

My cb72 race bike has 35t rear and 15t front sprockets. I think I'm right in saying the gearing should be 13/14t and 32t. Are the sprockets from the cb77 the same fitment? Or does anyone know where I can get a new set for my 72?

[PhilD]

Hi Tunster nice to see your regular updates on the CB72 racer restoration. The standard gear box sprocket for both CB72 and 77 was 15 teeth with 32 teeth rear sprocket for the 72 and 30 teeth rear for the 77. CB72 and CB77 sprockets are identical. Be aware that the depth of spline on the gearbox final shaft changed on later models and these have a narrower depth spline. 13 and 14 tooth gearbox sprockets are also available. I think aftermarket suppliers also increased the range of final drive sprockets as I have 29 and 31 tooth variants. Beware of eBay listings of CB72/77 final sprockets with 40+ teeth which I'm sure are CL sprockets mis identified. Keep the posts coming, eager to see inside your motor.
PhilD

[Tunster]

Hi PhilD I went to stafford on Saturday and was chatting to a chap who tells me be very careful splitting the motor as he thinks it may be a 305 and tells me there are no gaskets sets available nowadays. I don't know if this is correct and so I think first i will try and get it running before removing the motor for a clean up. It's moving a little slowly at the moment as im waiting for parts for another bike to finish but won't be long before I get going. ( hopefully). As for sprockets im on the look out if you know who can supply new 15/35 combo.

[PhilD]

Tunster I think the situation with regard to gaskets is the reverse of what you heard. Since the 305 CB77 was much more popular in the USA spares are more readily available and gasket sets aren' t a problem Dave Silver has them as does Tim at www.classichondarestorations.com CB72 top end gaskets are more difficult to find though bottom end gaskets are identical to the CB77 the 72 rocker, head and base gaskets are smaller, these are currently available individually at www.cmsnl.com. If you look carefully at the front of the base of the cylinder block you will see either 247cc or 305cc embossed to tell you which size barrels you have, though since you have a racer your motor may have a big bore kit which would be much more difficult to source top end gaskets for. Incidentally both cmsnl and classichondarestorations have 15 tooth gearbox and 30 tooth rear sprockets available. Classic Honda are cheaper though shipping costs will be more and you'll have to add import duty.
PhilD

[G-Man]

Here is the David Silver Gasket set for the 305. As PhilD says most of those gaskets are the same between CB72 and 77.

http://www.davidsilverspares.co.uk/CB77-305/part_36988/

If your bike is a 250 or has been bored out to 350 (64mm) then you will need to find a different head gasket.

For the 350 .....

http://bore-tech.com/product/head-gaske ... g-bore-kit

For a 250

http://www.cmsnl.com/honda-cb72-general ... EU6dIer_7Q

G

[Tunster]

You guys never seece to amaze me! Thanks for the info I will take more photos as I go along. I really appreciate the knowledge and advise you guys are sharing with me.

[PhilD]

Thanks to Gman for the bore tech source for 350 gaskets I've bookmarked for future reference. On reflection I suspect that the advice Tunster got from Stafford was a warning in case he had a 350 motor. I had a Read Titan 350 motor some years ago and had to return it to standard as gaskets became unavailable.
PhilD