1961 CB72 Project

[G-Man]

Hi Seadog

As usual I'm learning as I go along here. I believe that the only difference between early and not-so-early is the side for the lock bolt. There is also a 'narrow' late type for die-cast barrels.

However, I learned from the Cappellini adverts on eBay that...

The centre pin can be 9 or 10mm diameter - hopefully the needle-roller bush stays the same.

The wheel is either 39mm or 35mm(?)

I have yet to see / measure the above differences but we shall see.

"Ropey" is just a slang English term for tired, worn-out etc. The scalloping is due to the chain action and slapping of the chain I think......


G

LOL, you do have one or two extras there, G. A couple of questions, if I may:

What's the difference between the old and new style? It appears that the old ones have the adjusting bolt on the left. Is that the only difference?

In an earlier post, you said that the tensioner wheel you were working on looked ropey. I assume that you mean that the wheel was scalloped. I see that some others in your stash have the same problem. What causes that? Is it from too much tension on the chain? Adjusting error?

[Seadog]

Thanks, G. I'm always happy to learn more about these machines.

[LOUD MOUSE]

Of the 4 first issue you will see the 2 on the right are the earliest (sharp edge between bolt holes) and the 2 left have more rounded edges.
The ones with the set bolt on the right came about when the CL72 bikes came with the high pipes.
The pipes were in the way of the adjuster bolt.
I have had tensioners with 3 different wheel diameters but don't know what's up with that as the C/CB/CL engines were the only engines using this design and they all worked.
As you stated the cast cylinder assemblies came with a more narrow tensioner and I haven't figured out what's up with that either.
As you said the wheel could be damaged with a loose adjustment and also by us "pushing on the shaft and causing excessive pressure at the wheel and chain " which caused the wheel to become a sort of sprocket. ...............lm

I tipped out my box of old tensioners and was a little surprised with how many there were.



And when they were in daylight - I could see that I had four early ones. The elusive one from the '61 engine is on the left.




That's the one most in need of attention.

G

[G-Man]

LM

Thanks for clearing that up. I was wondering if the early CLs had the left-hand type but you have explained why they didn't. I know that two of those early ones came from 1961 CB72 engines so the other two could be from early Dreams.

I wonder if Honda just wanted more cooling fins around the cam chain tunnel with those late ones and therefore had to make the tensioner narrower?

G

Of the 4 first issue you will see the 2 on the right are the earliest (sharp edge between bolt holes) and the 2 left have more rounded edges.
The ones with the set bolt on the right came about when the CL72 bikes came with the high pipes.
The pipes were in the way of the adjuster bolt.
I have had tensioners with 3 different wheel diameters but don't know what's up with that as the C/CB/CL engines were the only engines using this design and they all worked.
As you stated the cast cylinder assemblies came with a more narrow tensioner and I haven't figured out what's up with that either.
As you said the wheel could be damaged with a loose adjustment and also by us "pushing on the shaft and causing excessive pressure at the wheel and chain " which caused the wheel to become a sort of sprocket. ...............lm

I tipped out my box of old tensioners and was a little surprised with how many there were.



And when they were in daylight - I could see that I had four early ones. The elusive one from the '61 engine is on the left.




That's the one most in need of attention.

G

[G-Man]

As promised earlier I went off at a bit of a tangent and stripped a primary tensioner wheel.

It turned out to be a bit of a surprise.



This one had a plain bush inside....



The two wheels are the same outside diameter but the primary roller has a 21mm bore (to take the bush) compared with the cam chain tensioner's 19.04 (¾ inch),

The centre pins are exactly the same. Yes, it would be possible to convert one of these as a cam chain tensioner roller but it wouldn't be as simple as I'd hoped.



It's a bit of a conundrum as to why they chose different designs for two very similar parts. The primary drive sees potentially bigger loads so maybe the needle roller wasn't man enough. Both chains run around the same speed so I'm not totally convinced......


Oh well, back to the cam chain tensioners....... :-)

G

[LOUD MOUSE]

Your idea may be correct but I'm of the opinion that the engineers did a redesign at a time when more bikes were to be built and were looking for a cheaper design to manufacture.
At times when you compare 000 to 020 to 030 I think those were the times HONDA decided to manufacture another run of the bikes and went to a new supplier with the same quality but cheaper cost to purchase. ............lm

LM

Thanks for clearing that up. I was wondering if the early CLs had the left-hand type but you have explained why they didn't. I know that two of those early ones came from 1961 CB72 engines so the other two could be from early Dreams.

I wonder if Honda just wanted more cooling fins around the cam chain tunnel with those late ones and therefore had to make the tensioner narrower?

G

Of the 4 first issue you will see the 2 on the right are the earliest (sharp edge between bolt holes) and the 2 left have more rounded edges.
The ones with the set bolt on the right came about when the CL72 bikes came with the high pipes.
The pipes were in the way of the adjuster bolt.
I have had tensioners with 3 different wheel diameters but don't know what's up with that as the C/CB/CL engines were the only engines using this design and they all worked.
As you stated the cast cylinder assemblies came with a more narrow tensioner and I haven't figured out what's up with that either.
As you said the wheel could be damaged with a loose adjustment and also by us "pushing on the shaft and causing excessive pressure at the wheel and chain " which caused the wheel to become a sort of sprocket. ...............lm

I tipped out my box of old tensioners and was a little surprised with how many there were.



And when they were in daylight - I could see that I had four early ones. The elusive one from the '61 engine is on the left.




That's the one most in need of attention.

G

[G-Man]

Just checked the bearing suppliers. It is possible to get a bearing that would fit the bore of the primary roller and the hardened bush of the cam chain tensioner roller. It's not plain sailing though as the alternatives are ½" wide or ¾" rather than the 5/8" it needs.

G