cb72 350cc ?

teazer · Post by **teazer** » Sat Apr 02, 2011 9:55 pm

And I always forget that when I build a race motor or hot street, I machine the heads to a different squish geometry and machine pistons to match and so it goes on, but for the street it's way more sensible to start in the right place with a plan in mind.

It is not difficult to make a 250 into a 350 but it's slightly easier if you start with a 305. For example the CB77 intake ports sort of match the 26mm crabs versus the smaller 22mm carbs on the CB72, so there's less metal to remove. It's not a job stopper but it's easier with the 77.

The 77 barrels have more meat and that's good and so on.

I have converted several 250 and 305 from street to 350cc race bikes. There's not a huge difference, but if you can get a 77 to start from that's a little less work and a spare motor to pull parts from.

Rookhill · Post by **Rookhill** » Sun Apr 03, 2011 2:15 pm

I bought a 1963 CB72 for £100 that had been sat in a barn for over 30 years. At that price I couldn't refuse. The cost of parts and complete bikes over here are more than I could justify, ( read, wife would allow ) ! Especially with a few bikes in the garage already.
I've always wanted a classic track bike but without the cost of a CR. Cadwell Park is 30 minutes down the road and if I could ride a bike there, do some laps and ride home, fantastic.
With the encouragement, information and knowledge of the forum and you guys, I'm going to attempt my first performance/tuning restoration.
With your input the CB77 engine is the way to go. As I have a CB72, does a CB77 engine bolt straight in?
Loud Mouse, I'll buy you a pint when I'm over, I'm just down the road in Schertz.
Again, many thanks guys.
Regards H.

LOUD MOUSE · Post by **LOUD MOUSE** » Sun Apr 03, 2011 3:12 pm

The CB77 will bolt in without any mods.
Make mine Miller Light!. .........lm

Rookhill wrote:I bought a 1963 CB72 for £100 that had been sat in a barn for over 30 years. At that price I couldn't refuse. The cost of parts and complete bikes over here are more than I could justify, ( read, wife would allow ) ! Especially with a few bikes in the garage already.
I've always wanted a classic track bike but without the cost of a CR. Cadwell Park is 30 minutes down the road and if I could ride a bike there, do some laps and ride home, fantastic.
With the encouragement, information and knowledge of the forum and you guys, I'm going to attempt my first performance/tuning restoration.
With your input the CB77 engine is the way to go. As I have a CB72, does a CB77 engine bolt straight in?
Loud Mouse, I'll buy you a pint when I'm over, I'm just down the road in Schertz.
Again, many thanks guys.
Regards H.

G-Man · Post by **G-Man** » Sun Apr 03, 2011 4:27 pm

H

A CL77 (or even a C77) motor (305) will also work for the top crankcase and barrel.

Here's a CL77 - quite pricey compared with what you paid for the bike but these are not plentiful in the UK.

http://cgi.ebay.co.uk/Honda-CB-CL77-305 ... 106wt_1141

The CL77 head is missing the revcounter drive but that's easy to fix..

I'm building a CB77-based racer too, but it's a long-term project.

G

Rookhill · Post by **Rookhill** » Mon Apr 04, 2011 1:20 pm

Thanks G.
There are a pair of cb72/77 barrels for sale( with pistons) bored out to 350" for racing" at £50 with 3 days to go on ebay.

http://cgi.ebay.co.uk/HONDA-CB72-CB77-R ... 20b83ed7fa

I'm in the US in august and the best deals seem to be there, so I will see what I can get between now and then and bring them back with me.Unless I get a bargain over here. Mine too will be a long term project, I'm giving myself 12 months but you know what its like ! I work in Newark, not a million miles from you and do a lot of work from Glasgow to the Isle of Wight. If you see any thing you fancy in the States, and international shipping isn't possible let me know and if you can wait I dont mind bringing it back for you. I've been doing it for 20+ years.The mother in law is no longer shocked by what turns up waiting for me to collect !

Regards H.