1961 CB72 Project

[G-Man]

Sara

I couldn't believe that. A) you could get them that small. And B) that they had got so cheap.

Just perfect for clumsy types like me. :-)

G

I think I need one of those!

[G-Man]

I thought I'd better get started on cleaning up the hubs and brake plates. I have freshly chromed brake linkages and new shoes but the hubs and plates were pretty dull even after a trip to the ultrasonic bath.

I made a start wet sanding the parts to get rid of the the blemishes and corrosion pits.



You can see the '61 SLS brake plate and the rear brake plate with the strange torque-arm lacement.

They had a first pass on the polishing wheel and then the weather was so nice I moved on to getting some more paint on the fenders. I had to do a little straightening on the front fender and got the contour of the front and rear edges just right with a little hammer and dolly work.



You can see the 'single rivet' middle stay (only one rivet at the edge) on the fender which lasted into '62 or '63, I think. Early fronts had an aluminum blade but I have documentation to show that this steel one was on a '61 bike.

The rear fender is made from lighter steel than the later models and feels to be about 2/3 the weight of the later ones. It's nice to have an original version. I have Alan Curtis to thank for both those parts.

G

[alan curtis]

Graham, glad to help you, finding the early bits is getting so hard, as more bikes come to life.many thanks for all your help and wisdom, a pic of the underside of the rear mudguard is useful, so show how different it is to the later ones..

[G-Man]

Alan

Will get some more pics when it stops raining..... :-)

G

Graham, glad to help you, finding the early bits is getting so hard, as more bikes come to life.many thanks for all your help and wisdom, a pic of the underside of the rear mudguard is useful, so show how different it is to the later ones..

[G-Man]

Alan

Here we go. The early rear fender with wiring channel inside. This fender is made of much lighter gauge steel than the later one. The weights are 1.52kg (2.75lbs) vs 1.90kg. (4.16lbs).




Honda were oviously trying to keep weight down on the '61 bikes with the aluminum front fender, light gauge rear and those flimsy aluminum shock covers. It didn't take them long to give up on the idea.

G

Graham, glad to help you, finding the early bits is getting so hard, as more bikes come to life.many thanks for all your help and wisdom, a pic of the underside of the rear mudguard is useful, so show how different it is to the later ones..

[G-Man]

I got a little side tracked again over the weekend. I want to get the wheels built so that I have a rolling frame to put the engine in and before that I have to polish the hubs, sort out the brake drums and shoes etc...

For a little bit of a 'gamble' I bought three used cranks off eBay at pretty low prices. They would be a bargain if there was anything salvageable.

They were all a bit rusty and dirty on the surface but the bearings felt good and there was no vertical play on the con-rods.



Despite the dirt, the main bearing rollers looked good.



Also the roller track on the right hand main bearing looked surprisingly good. The rollers and outer race had been greased.



After pulling off the outer bearings, the flywheels (and rods) were the first to come apart.
At first glance the big ends looked very nice, so I got everything degreased, bead-blasted then cleaned in my ultrasonic tank.

Both rods, despite the complete lack of corrosion damage had nasty pitting around the TDC part of the rod. It looks like these rods are high mileage as there was no other damage. From my knowledge of bearings this looks like a case of 'rolling contact fatigue' where the metal tends to crack below the surface and then pieces start to fall out. The effect is worse at the edges and I think this is probably due to the crank distorting at high revs / loads. This means that the big end pin is not parallel and provides greater contact at the edges......

The cranks came with stuff that looked like it might have been from a racebike so that may account for this type of damage.



Also there is a lot of wear where the cages have been rubbing on the sides of the rod. Quite a few of the rollers also showed signs of similar damage on one end.



When I pulled apart the centre section of the crank I marked the TDC tooth on the sprocket so that the crank could go back together in the same position. There are 74 'splines' on each end of the shaft and this does not divide into 360 evenly so it forms a kind of vernier adjustment. Choosing the same tooth to go at the top and marking the alternator side wheel assists in getting it back together correctly.



Both bearing tracks looked good with no pitting and the centre rollers looked good despite the oilways in the bearing outers being a little clogged.



The inner flywheels had their share of crusty debris backed into the the 'centrifuge' annulus that feeds the big ends so that had several sessions of scraping, beadblasting and U/S cleaning.

I pulled out the two aluminum plugs for the big-end sludge traps and those two also were filled with a tough hardened sludge which took some moving. That stuff could destroy an engine that was started up after a 30-year sleep.....



There are two more of these to look at but I'll get this partially assembled before confusing the issue.....

G

[G-Man]

I have been agonsing a little bit over cam covers for this engine. Because these early engines did not have a breather take-off on the cam cover (they have a tower at the back of the crank case) the 'boy racer' previous owner put a couple of barbs into the condenser mounts and I wanted to revert to standard. Rear right in the picture above.



I managed to pick up a couple of spare parts and another arrived in a box of spares yesterday. There are a few differences between, what should be, 'identical covers.

The one at bottom right, for instance has the later 10mm diameter hole for the front engine bracket, where mine is the earlier 8mm bolt.

The cover at bottom left is a sand cast (rather than die cast) part which, although shop soiled, appears to be unused. The condenser holes are blank, where the other covers have the holes there but not tapped. That sand-cast part also has much sturdier ribs for the mountings. Is it very early, or is it a spare made later on like the 'universal' sand-cast crankcase I found?

Out of the four, I have decided to go with this one which is similar to the one on the bike when I got it.



Any ideas on that sand-cast part?


G