1961 CB72 Project

[G-Man]

I made a couple of mistakes measuring up the primary chain tensioner wheel when I was considering it as a replacement for the cam chain tensioner. It turns out that the cam chain tensioner wheel and bearing are imperial sizes while the primary tensioner wheel and bush are metric. That makes it a bit difficult to swapo parts around without machining. I wanted to make this something that anyone with a drill and some files could do.

I was trying to persuade the primary wheel to take a roller bearing like the cam chain tensioner wheel. Then when I stripped one of the cam chain tensioners with the small wheel, it seemed that the preferred option had become a typical Honda solution of hardened wheel running on hardened steel pin. I didn't feel quite so bad about using the bronze-bushed primary wheel in place of the needle roller equipped cam chain tensioner wheel.

You still have to cut the 'ears' off the centre pin, drill out the aluminium plug and tap the bore with an M7 tap but the rest of the mod is just about fitting the big centre-pin from the primary roller into the arm of the cam-chain tensioner.

The slot design from the primary tensioner has to be transferred to the cam chain tensioner arm so that it clears the logs on the steel bush. The lugs are there so that the oil holes stay aligned at the bottom. I cut the basic shapes with a piercing saw and tidied up with needle files.



Here is the complete set of parts including a modified centre pin and one of my short 7mm bolts.



And here is everything assembled. It's nice that the primary wheel is the same width as the cam tensioner wheel.



It will get a dunk in the cleaning tank to get rid of any stray metal filings and my marking ink.

G

[LOUD MOUSE]

Any chance you will make a kit to sell?. .....................lm

I made a couple of mistakes measuring up the primary chain tensioner wheel when I was considering it as a replacement for the cam chain tensioner. It turns out that the cam chain tensioner wheel and bearing are imperial sizes while the primary tensioner wheel and bush are metric. That makes it a bit difficult to swapo parts around without machining. I wanted to make this something that anyone with a drill and some files could do.

I was trying to persuade the primary wheel to take a roller bearing like the cam chain tensioner wheel. Then when I stripped one of the cam chain tensioners with the small wheel, it seemed that the preferred option had become a typical Honda solution of hardened wheel running on hardened steel pin. I didn't feel quite so bad about using the bronze-bushed primary wheel in place of the needle roller equipped cam chain tensioner wheel.

You still have to cut the 'ears' off the centre pin, drill out the aluminium plug and tap the bore with an M7 tap but the rest of the mod is just about fitting the big centre-pin from the primary roller into the arm of the cam-chain tensioner.

The slot design from the primary tensioner has to be transferred to the cam chain tensioner arm so that it clears the logs on the steel bush. The lugs are there so that the oil holes stay aligned at the bottom. I cut the basic shapes with a piercing saw and tidied up with needle files.



Here is the complete set of parts including a modified centre pin and one of my short 7mm bolts.



And here is everything assembled. It's nice that the primary wheel is the same width as the cam tensioner wheel.



It will get a dunk in the cleaning tank to get rid of any stray metal filings and my marking ink.

G

[G-Man]

LM

I'll have a think about that. I think I would need to do an exchange on some of the parts.

G

Any chance you will make a kit to sell?. .....................lm

I made a couple of mistakes measuring up the primary chain tensioner wheel when I was considering it as a replacement for the cam chain tensioner. It turns out that the cam chain tensioner wheel and bearing are imperial sizes while the primary tensioner wheel and bush are metric. That makes it a bit difficult to swapo parts around without machining. I wanted to make this something that anyone with a drill and some files could do.

I was trying to persuade the primary wheel to take a roller bearing like the cam chain tensioner wheel. Then when I stripped one of the cam chain tensioners with the small wheel, it seemed that the preferred option had become a typical Honda solution of hardened wheel running on hardened steel pin. I didn't feel quite so bad about using the bronze-bushed primary wheel in place of the needle roller equipped cam chain tensioner wheel.

You still have to cut the 'ears' off the centre pin, drill out the aluminium plug and tap the bore with an M7 tap but the rest of the mod is just about fitting the big centre-pin from the primary roller into the arm of the cam-chain tensioner.

The slot design from the primary tensioner has to be transferred to the cam chain tensioner arm so that it clears the logs on the steel bush. The lugs are there so that the oil holes stay aligned at the bottom. I cut the basic shapes with a piercing saw and tidied up with needle files.

G

[LOUD MOUSE]

I have MANY good primary chain roller assy. ...................lm

LM

I'll have a think about that. I think I would need to do an exchange on some of the parts.

G

Any chance you will make a kit to sell?. .....................lm

I made a couple of mistakes measuring up the primary chain tensioner wheel when I was considering it as a replacement for the cam chain tensioner. It turns out that the cam chain tensioner wheel and bearing are imperial sizes while the primary tensioner wheel and bush are metric. That makes it a bit difficult to swapo parts around without machining. I wanted to make this something that anyone with a drill and some files could do.

I was trying to persuade the primary wheel to take a roller bearing like the cam chain tensioner wheel. Then when I stripped one of the cam chain tensioners with the small wheel, it seemed that the preferred option had become a typical Honda solution of hardened wheel running on hardened steel pin. I didn't feel quite so bad about using the bronze-bushed primary wheel in place of the needle roller equipped cam chain tensioner wheel.

You still have to cut the 'ears' off the centre pin, drill out the aluminium plug and tap the bore with an M7 tap but the rest of the mod is just about fitting the big centre-pin from the primary roller into the arm of the cam-chain tensioner.

The slot design from the primary tensioner has to be transferred to the cam chain tensioner arm so that it clears the logs on the steel bush. The lugs are there so that the oil holes stay aligned at the bottom. I cut the basic shapes with a piercing saw and tidied up with needle files.

G

[G-Man]

It's been a long time but I managed a little workshop activity this weekend. The parts that I need plating for the batch of cam chain tensioners are in a box ready for zinc plating tomorrow and I needed something else to look at.

The kickstart cover that came with my '61 project was in great shape and I was feeling quite smug until I met up with Alan Curtis last week. He pointed out some little details that 'my' cover didn't have......

When I got home I searched through all my hiding places and came up with a few covers but Murphy's law came in to play, of course. Both the early covers I found were damaged but equally surprisingly, both were perfect around the kickstart bush area.

Here is one of my 'early' covers alongside a later type.



The early one has only a single small drain hole at the bottom and a slightly different clutch cable entry as here......



One of my covers had a chunk out of the portion where that little chain cover attaches, and the other has had two bites taken out of the circular section where the alternator cover fits.



As you can see, both are excellent in the area of the kick start bush. Interestingly both of those bushes are steel rather than the fibre type I have seen in later ones......



If i am to save these I need a plan and happened to have a 'donor' cover which was beyond repair.



I am going to use parts of this donor to make replacements for the other two covers. Why two? Well, I thought I might as well have a go at both and see which one comes out best.

The plan is to cut parts out of the donor and cut an identical aperture in each of the good covers. The donated parts will be attached using a low-temperature aluminum solder to avoid distortion of the cover. The stuff I use - "lumiweld" is one of the trade names - is pretty strong and these two repairs are not really structural so it should work out fine.

This one is causing me some heartache. Make the replacement small with a complicated shape; or go for a big straight cut across the piece with a long join. I need to sleep on this one....



For this one I am going to set the pieces up in my milling machine and cut fairly large 'slots' which will be filled with donated parts. I want the replacement parts to be large enough that they don't' sag when I heat them up.



All will be revealed at my next post in a few days.......

G

[jas67]

I'm anxious to see the outcome of this repair, as I have a few covers that need some work too.

[Seadog]

Nice to see you back to your project. I've missed your informative posts.