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1961 CB72 Project

Want to keep a Restoration Log? Post it here! You can include photos. Suggested format: One Restoration per Thread; then keep adding your updates to the same thread...
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G-Man
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Post by G-Man » Wed Dec 03, 2014 1:25 pm

Indeed, but you wonder why they bothered to make some of those changes and why they never got around to fixing other things that really needed it....

It must have been an amazing time for their engineers.

G
'60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160
'66 Matchless 350 '67 CL77
'67 S90 '77 CB400F

LOUD MOUSE
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Post by LOUD MOUSE » Wed Dec 03, 2014 2:26 pm

May I ask what they may be?. ............lm
G-Man wrote:Indeed, but you wonder why they bothered to make some of those changes and why they never got around to fixing other things that really needed it....

It must have been an amazing time for their engineers.

G

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G-Man
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Post by G-Man » Thu Dec 04, 2014 1:39 am

LM

All a matter of opinion but, as usual with engineering designs, is is customary to get to a position where it is easier to just start with a fresh model than to rectify all of the deficiencies of the old design, but here are a few, starting from the front.

Front fork. Fork tubes far too complicated (expensive) to make. Lots of machining at different diameters and interconnecting tapers. Chrome and zinc plating. Later designs much, much simpler on CB350 and beyond.

Gearbox. poor layout and design. Poor control of tolerances needing offset cotters. Poor bearings with layshaft resting on crowded rollers and plain wear prone (adding to tolerance issues) bush. Complicated cross-over kickstart / clutch mechanism. High friction clutch actuation resulting in heavy lever action and difficult cable routing. My 1000cc Triumph has featherlight clutch action and no slippage or drag.

Exhausts. Poor muffler mounting with long unsupported section at rear and highly stressed mountings at front, resulting in difficult assembly and stress fractures.

Engine - Expensive three-piece camshaft resulting in time-consuming assembly. A/R mechanism buried in camshaft sprocket. Multiple chains where later models would use gears and direct drive

Electrical. Poor voltage regulation and borderline capacity.

Brakes expensive and unnecessary rear brake.

JMHO but most of these issues got tidied up with later models and we got cheaper, faster, longer lasting bikes as a result.

The CB160 began the process of tidying up the design details but it quickly passed over to the CB250/350 and beyond. They might not have the character of the CB72 but the engineering compromises were more carefully thought through for the cost / reliability / performance compromise that every manufacturer faces. Ultimately the lessons that Honda learned gave us low-cost four cylinder bikes like the CB750.

G


LOUD MOUSE wrote:May I ask what they may be?. ............lm
G-Man wrote:Indeed, but you wonder why they bothered to make some of those changes and why they never got around to fixing other things that really needed it....

It must have been an amazing time for their engineers.

G
'60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160
'66 Matchless 350 '67 CL77
'67 S90 '77 CB400F

smccrory
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Post by smccrory » Fri Dec 12, 2014 8:37 am

I really appreciate the sober analysis of the Cx72/77, GMan. It's better to know where the potential weak points are and be prepared for them than to blissfully be surprised at the worst times.

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G-Man
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Post by G-Man » Fri Dec 12, 2014 8:56 am

Scott

As a long-time engineer, I find it fascinating how quickly Honda got those bikes on the market and displaced older manufacturers in Europe and North America. The bikes were well presented and offered great performance. They were not perfect and that's what makes them interesting.

What is really fascinating though is that the Japanese manufacturers are encountering the same pressure that the British, European and American manufacturers faced in the 60s and 70s. Namely the retreat into large capacity models with cheaper small (copy) models coming in from China and Korea. History continually repeats itself......

G
'60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160
'66 Matchless 350 '67 CL77
'67 S90 '77 CB400F

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G-Man
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Post by G-Man » Fri Dec 12, 2014 11:18 am

This crank kept cropping up on UK eBay at a fairly eye-watering price. It was advertised as a CL72 item and that is what it said on the box.

Image

Even the part number said CL72....

Image

But the photos on eBay were clear. It had the starter sprocket oil hole in the crank end so it definitely wasn't CL.

Image

It stayed unsold for a few weeks so I put in an offer and, rather surprisingly, it was accepted.

Still not sure if it is a 250 or a 305 crank but the balancing holes are the same as as the one that was in the motor. I'll compare with a CB77 crank when I get a moment. It needs a good clean before it goes in the motor but it will help my CB72 on towards its 'showroom fresh' restoration if it is the right part.

Image

I might even get some 'assembly time' over the Christmas Holiday.

G
'60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160
'66 Matchless 350 '67 CL77
'67 S90 '77 CB400F

LOUD MOUSE
honda305.com Member
Posts: 7817
Joined: Mon Aug 15, 2005 8:23 am
Location: KERRVILLE, TEXAS

Post by LOUD MOUSE » Fri Dec 12, 2014 4:51 pm

Looks like a CB77 crank to me. .................lm

G-Man wrote:This crank kept cropping up on UK eBay at a fairly eye-watering price. It was advertised as a CL72 item and that is what it said on the box.

Image

Even the part number said CL72....

Image

But the photos on eBay were clear. It had the starter sprocket oil hole in the crank end so it definitely wasn't CL.

Image

It stayed unsold for a few weeks so I put in an offer and, rather surprisingly, it was accepted.

Still not sure if it is a 250 or a 305 crank but the balancing holes are the same as as the one that was in the motor. I'll compare with a CB77 crank when I get a moment. It needs a good clean before it goes in the motor but it will help my CB72 on towards its 'showroom fresh' restoration if it is the right part.

Image

I might even get some 'assembly time' over the Christmas Holiday.

G

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