1961 CB72 Project

[LOUD MOUSE]

Got ya on the engineering idea and fix time in the AM. .........lm

LM

Thanks for the encouragement. Everything is possible, but I was hoping to come up with a method without major machining of replacement parts so that anybody with some hand tools could swap the parts out.

My inspiration usually comes when I wake up at 3am......

G

If you can get this figured you will be of great help.
There are plenty of these wheels out there.
Stay on it G. .............lm

I thought I'd got this idea with the primary tensioner wheel worked out but a mistake crept in with my conversion to / from metric with the imperial bearings. As a result my centre pin will not fit inside the bearing.... :-(

All is not lost but it's back to the drawing board for now.......




G

[G-Man]

I thought I'd better avoid guesswork and offer my first completed tensioner up to my 1961 CB72 barrell. Of course this is the wrong tensioner for this engine but it is as good as anything to test it on.



Of course it didn't fit so I had to be a little more scientific and measure how much space I had.

Nothing modern or digital woul d fit in there so I resorted to some old-fasioned calipers.



It turned out that the space available was about 0.25mm (0.010 inch) less than my new assembly required.



While I was at it I checked another barrel (later) and that had at least another 1mm spare so I could have left this tensioner as it was but it seemed like a good idea to make it fit this one so I shaved another 0.5mm off my bolt head for a final thickness of 2.35mm which seemed OK.

With just that tiny bit shaved off the bolt head everything fitted up nicely




G

[G-Man]

Having got all the dimensions sorted out, I set about dismantling a few more tensioners. I pushed the bronze bush out of the primary tensioner wheel then re-machined my wheel truing arbor so that it would accept the cam tensioner wheel at one end and a primary wheel at the other.



After getting the bush out I measured the bore of the wheel and found that it is 20mm. so, just to make things difficult; the cam chain wheel is machined with an imperial bore (¾ inch) and the primary is machined with a 20mm bore. That makes life a little tricky to buy a needle roller bearing. I don't think anyone makes one with mixed dimensions.

However, there is a possibility that I can machine an inner sleeve a little to get to 14mm from the 5/8inch dimension (14.29mm). I'll think about that and how doable it is.

I cleaned up an early tensioner body for my '61 project and unbelievably, found one with a good wheel. So, in terms of this project - I needn't have started on this little side project.... :-)



Interestingly, these is yet another 'expensive' part on the early tensioners which was quickly swapped out by Honda with a cheaper alternative. Early tensioners had their plunger machined from solid while later ones have a pressed steel head riveted to a shaft. Much cheaper in material and easier to make. The later one just looks a little nasty in comparison.



G

[LOUD MOUSE]

I believe HONDA found a reason for that change.
The original was flat on the spring area and the replacement has edges to center the spring. ............lm

Having got all the dimensions sorted out, I set about dismantling a few more tensioners. I pushed the bronze bush out of the primary tensioner wheel then re-machined my wheel truing arbor so that it would accept the cam tensioner wheel at one end and a primary wheel at the other.



After getting the bush out I measured the bore of the wheel and found that it is 20mm. so, just to make things difficult; the cam chain wheel is machined with an imperial bore (¾ inch) and the primary is machined with a 20mm bore. That makes life a little tricky to buy a needle roller bearing. I don't think anyone makes one with mixed dimensions.

However, there is a possibility that I can machine an inner sleeve a little to get to 14mm from the 5/8inch dimension (14.29mm). I'll think about that and how doable it is.

I cleaned up an early tensioner body for my '61 project and unbelievably, found one with a good wheel. So, in terms of this project - I needn't have started on this little side project.... :-)



Interestingly, these is yet another 'expensive' part on the early tensioners which was quickly swapped out by Honda with a cheaper alternative. Early tensioners had their plunger machined from solid while later ones have a pressed steel head riveted to a shaft. Much cheaper in material and easier to make. The later one just looks a little nasty in comparison.



G

[G-Man]

Thanks LM - that mekes perfect sense. I see where the later one holds the speing.

G

I believe HONDA found a reason for that change.
The original was flat on the spring area and the replacement has edges to center the spring. ............lm

[LOUD MOUSE]

Ya over the years that part had changes caused by mechanical facts. .............lm

Thanks LM - that mekes perfect sense. I see where the later one holds the speing.

G

I believe HONDA found a reason for that change.
The original was flat on the spring area and the replacement has edges to center the spring. ............lm

[jensey]

Talking about air filters, guess what was on my early bike ?