1961 CB72 Project

G-Man · Post by **G-Man** » Fri Oct 09, 2015 11:14 am

I just measured the holes in the mains that feed into the big end oil slingers. They are about 1mm diameter. That means that, even if you assume that two of them are feeding, which there cannot be (because one is blocked off), the area is much less than the escape path from the big end.

A 1mm hole is about 0.75 square millimetres, whereas the exit area (for 6 thou side clearance) is around 15.5 sq mm (97 x 0.15) from the sides of the rods and around 20 sq mm from the slots in the rod (5.5 x 2 x 2). Even doubling up to 2 input holes gives a ratio of 1.5 sq mm for the feed to 35 sq mm for the escape. That looks like far too much for the gravity feed into the other holes in the mains to make up.

It seems to me that the flow through the big end is limited by the flow into and out of the main bearing rather than the side clearance of the rod. Just thinking out loud........

G

jerry · Post by **jerry** » Sat Oct 10, 2015 6:58 am

Dear G Man, Do some reading on high speed big end roller bearings, roller cages and their development, oil lubrication,wedging and hydraulicing, and heat transfer. See what you work out. It is a interesting topic. By the way are you aware that a Yamaha XS650 twin uses the same size big end pins as the Honda 305. All the best Jerry

G-Man · Post by **G-Man** » Sat Oct 10, 2015 3:04 pm

Hi Jerry

I studied fluid dynamics during my Mechanical Engineering Degree and did quite a bit of high pressure hydraulic (hydrostatic) design as a young engineer. More recently I worked on orifice-based flow control for pneumatic sand delivery systems on trains. I have been searching for papers on roller bearing big ends and lubrication but I haven't found a lot. Have you got any recommendations?

Yes - I worked out that one of the XS650 variants used a 26mm pin and recently bought a couple to play with. The rollers are pretty big in that crank if I remember correctly.

I restored an ex Shell Thuett Flat Tracker for its owner about 20 years ago. That had a welded up crank and some big pistons. The owner said it was a Kenny Roberts bike ( a bit like all the Honda CR replicas being "Mike Hailwood" bikes). It wasn't but I think Dave Aldana rode it in a match-race series in the UK.

G

jerry · Post by **jerry** » Sun Oct 11, 2015 4:23 am

G Man there were White Papers from Honda and also INA many years ago dealing with big end specific issues, design, materials and coatings. One of the critical issues was getting oil out of the big end assembly at a suitable rate to cool the big end and not to cause hydraulicing. Lubrication itself was not a problem. As you may well know the skidding of the rollers is a big problem and also the ongoing acceleration and deceleration of the rollers and cages and also the oil bow waves in front of the rollers. Incorrectly fitted roller cages on the Honda Factory race bikes have apparently generated enough hydraulic friction to limit maximum rpm. All the best Jerry

G-Man · Post by **G-Man** » Sun Oct 11, 2015 4:33 am

Hi Jerry

Many thanks for that. I was looking at some stuff from 1929 last night. Still interesting, though.

I will keep searching. Just another question. How much bending / torsion at the big end do you think you got at high revs on the racers? Also - am I right in thinking that your cranks were not generally using CB72-77 webs and big ends?

This pic is one of the three different sized rods for the Honda six and a main bearing. The rollers and cage look like they belong swith the main. Interesting slots in the cage to get the oil out.

G

jerry · Post by **jerry** » Sun Oct 11, 2015 5:28 am

Dear G Man, I believe those grooves are a Pops Yoshimura modification from when he "Consulted" for Honda. Apparently that relationship did not have a good outcome. Anyway I think you can see that if those cages were put in back to front the outcome is not so clever regarding getting rid of oil. I think I have explained to you that I used Honda CB360 flywheels and Honda CB250G model conrods and Capallini big end cages as used on the Honda CB450 crank assemblies for the 350 (67mm bore x 50.6mm stroke).We are allowed +1mm on the bore. I say again if you look up Jerry Kooistra on Facebook and look at the July 1 photos compilation you will find 2 photos of 500 CB77 crankshaft assembly (57.8mm stroke). Tag on the crank gives side clearances. Another photo shows late model CB77 conrod beside a Honda CB250G conrod. Just remember that the big ends are all the same on CB250G, CB360 and Honda CB450 5 speed. All the best Jerry

G-Man · Post by **G-Man** » Sun Oct 11, 2015 8:23 am

Hi Jerry

Yes - like putting a tractor tyre on backwards.

I cannot see any albums on the Jerry Kooistra page. All I get is this : your profile with just one picture of a handsome looking bloke with an interesting Honda behind him....

Apologies for being a facebook dunce...... :-)

G

jerry wrote:Dear G Man, I believe those grooves are a Pops Yoshimura modification from when he "Consulted" for Honda. Apparently that relationship did not have a good outcome. Anyway I think you can see that if those cages were put in back to front the outcome is not so clever regarding getting rid of oil. I think I have explained to you that I used Honda CB360 flywheels and Honda CB250G model conrods and Capallini big end cages as used on the Honda CB450 crank assemblies for the 350 (67mm bore x 50.6mm stroke).We are allowed +1mm on the bore. I say again if you look up Jerry Kooistra on Facebook and look at the July 1 photos compilation you will find 2 photos of 500 CB77 crankshaft assembly (57.8mm stroke). Tag on the crank gives side clearances. Another photo shows late model CB77 conrod beside a Honda CB250G conrod. Just remember that the big ends are all the same on CB250G, CB360 and Honda CB450 5 speed. All the best Jerry