1961 CB72 Project

G-Man · Post by **G-Man** » Mon Apr 06, 2015 2:43 am

Jerry

Thanks for the comment! I just picked up a NOS left hand camshaft from a guy in Australia for my next project, a CYB kitted CB72 to sit alongside this bike.

I have a few more cranks to pull apart, too.

G

G-Man · Post by **G-Man** » Mon Apr 06, 2015 1:55 pm

I gave the gearbox parts a wash in degreaser, let them dry and gave them a clean in the bead blaster. Next was the ultrasonic bath to get rid of any dirt and leftover beads.

The kickstart shaft looked in amazing condition with hardly a trace of the rollers that usually make a groove on the bikes. Unfortunately three other gears showed some nasty damage which looked like they had ingested some debris from elsewhere.

I had to turn to a rather ugly looking box of spares I picked up a year or so ago to see if there was anything that would suit. I wasn't too hopeful as this box had lain unloved in someones workshop for a very long time. It has been pretty unloved in my hands, too.

It turned out to be my lucky day and I found exactly the parts I was looking for. I wasn't completely sure until they had been through the cleaning process but the gears that emerged were better than anything else in the transmission.

The replacements are the lower set in the picture....

With that sorted out it was time to sort out some new bearings. I pulled out a new 14mm bush but when I compared it with the original I got a surprise. At first I thought someone had made up a bush but there were some nice details on this one which were very different.

The little flange is much thicker and has a chamfer which, at first, I thought was wear.

When I looked at the low gear it was clear that it had a matching chamfer to take the taper on the bush.

Also the bush has a straight oilway and no oil hole, where the later bushes have a helical groove and a hole.

I'm going to leave this bush and gear in the transmission. It has lasted all this time so it would be a shame to swap it out.

In contrast to the condition of the kickstart shaft I found two rollers which looked in a terrible condition. There was no damage to the area where they work on the shaft but these look like they would cause all sorts of damage.

I picked up some replacements from my spares collection and assembled the good bearings.

This gearbox seems to be full of contrasts. Some parts in beautiful order and others quite beaten up. The kickstart pawl was one of the nice bits and while a little worn, seemed to work fine.

I just had chance to drop the shafts into the case for a quick trial run before gardening duty beckoned. Good weather at Easter is a mixed blessing.....

G

Steverino · Post by **Steverino** » Mon Apr 06, 2015 4:31 pm

Great pictures. I recently went through a CB160 motor that suffered a broken piston. It was a race motor with just a few miles on it and was very clean inside. I found tiny pieces of chewed up piston skirt in the case but I didn't find any gears or bearings that appeared damaged. Do you think it was a steel component fragment to inflict that kind of damage?

G-Man · Post by **G-Man** » Mon Apr 06, 2015 4:48 pm

Steve

Who knows what the history of these motors is? I'm curious how those bearing rollers got damaged and how they got back in the bearing afterwards. They couldn't have got damaged inside the bearing without marking the shaft.

The gear damage looks like a steel part went through there for sure. Piston ring maybe? The bike had a 350 kit so maybe something nasty happened with the original motor. The head was also a later one, too.

I think this will be an unsolved mystery.

G

sarals · Post by **sarals** » Mon Apr 06, 2015 10:22 pm

I am amazed by your perseverance and attention to detail, Graham. Every time I read this thread, I learn something new. (Big Smile!)

G-Man · Post by **G-Man** » Tue Apr 07, 2015 1:32 pm

Sara

You have to be so careful with these early bikes. The detail changes in just a few engine or frame numbers. Alan's bike is about 30 numbers older than mine and there are real differences which mean that you cannot interchange parts. I am trying to be very careful but aware that I will probably miss some important detail along the way.

Tonight I was going to put the selector drum and forks in the case but just noticed another gear with damage.

I'm not sure that my grubby spares box is going to yield up a good part so I pulled this 1963 motor out of 'storage'. It looked pretty nasty from the outside and the head and barrels have been off for some time. Amazingly the crank is free and clean and when I pulled the clutch cover off, this was what I saw.

Most of my 'bikes come to me in a pretty rough state and this was one of a collection of parts I bought with my race bike. It had 64 mm pistons. If the one gear that I found in the box of nasty parts won't clean up this one is going to have to donate one of its gears. They should make donor cards for deceased bikes, shouldn't they? This one has no '63 frame to go with so it's really an orphan, anyway.

G

jensey · Post by **jensey** » Tue Apr 07, 2015 3:53 pm

I know what you mean.