1961 CB72 Project

G-Man · Post by **G-Man** » Sun Oct 26, 2014 3:50 am

Here are my (so far) Piston choices. All of my CB72 Honda pistons are 030 versions but I have a couple of Hepolite choices with higher crowns. The STD one on the left came out of a race bike and the +1mm version is NOS with a more sensible compression ratio. Just for comparison the Forged True piston was in the bike when I found it with a 'big-bore' conversion.

So the question is, should I look for some early Honda H/C pistons, go with a later Honda piston with lower compression or fit the +1mm Hepolite? I'm going to keep the big-bore barrel and pistons for a racer project.

And here are some weight comparisons.....

Honda

Hepolite

Forged True

LOUD MOUSE · Post by **LOUD MOUSE** » Sun Oct 26, 2014 6:21 am

If your plan is to have it feel like it was when issued as you ride (large/heavy cam sprocket and no primary chain tensioner) I would expect you would want to use the piston it was issued with. .......lm

G-Man wrote:Here are my (so far) Piston choices. All of my CB72 Honda pistons are 030 versions but I have a couple of Hepolite choices with higher crowns. The STD one on the left came out of a race bike and the +1mm version is NOS with a more sensible compression ratio. Just for comparison the Forged True piston was in the bike when I found it with a 'big-bore' conversion.

So the question is, should I look for some early Honda H/C pistons, go with a later Honda piston with lower compression or fit the +1mm Hepolite? I'm going to keep the big-bore barrel and pistons for a racer project.

And here are some weight comparisons.....

Honda

Hepolite

Forged True

G-Man · Post by **G-Man** » Sun Oct 26, 2014 7:50 am

LM

Yes - I would like to. Just haven't come across any yet....

G

LOUD MOUSE wrote:If your plan is to have it feel like it was when issued as you ride (large/heavy cam sprocket and no primary chain tensioner) I would expect you would want to use the piston it was issued with. .......lm

G-Man wrote:Here are my (so far) Piston choices. All of my CB72 Honda pistons are 030 versions but I have a couple of Hepolite choices with higher crowns. The STD one on the left came out of a race bike and the +1mm version is NOS with a more sensible compression ratio. Just for comparison the Forged True piston was in the bike when I found it with a 'big-bore' conversion.

So the question is, should I look for some early Honda H/C pistons, go with a later Honda piston with lower compression or fit the +1mm Hepolite? I'm going to keep the big-bore barrel and pistons for a racer project.

jensey · Post by **jensey** » Mon Oct 27, 2014 1:40 pm

Hi Graham,

Maybe I can help...

G-Man · Post by **G-Man** » Mon Oct 27, 2014 1:56 pm

Hi Jensen

Thanks for the info. I cannot read the numbers on the boxes. What is the difference between those two sets?

G

jensey · Post by **jensey** » Mon Oct 27, 2014 2:22 pm

Nothing I guess, both sets are H/C pistons with rings, numbers are 010's

G-Man · Post by **G-Man** » Wed Oct 29, 2014 3:52 am

Right - I think I am on top of the piston situation for this bike. I found an odd 0.25 O/S HC piston at the bottom of a box of stuff I forgot I had. Sadly, only one, though. Unfortunately the cylinder I had set aside for this bike was on STD bore with some damage and I wasn't sure it would make it at 0.25 o/s.

I discovered that Terry Kahler at Retrobikes had some 010 pistons so I was at least able to make a pair with my solitary one. I couldn't find pairs of larger 010 pistons so with the help of a damaged NOS late (die-cast) barrel I had, the liners were swapped over. I found a couple of STD High Compression pistons at House of Honda in New York and we should be good to go....

Here is my 'early' block with HC piston....

The higher dome gives 9.5 (or is it 10?) to 1 compression.

Here are the NOS liners in place in the early cylinder

It looks like the motor will be now be very close to the spec that it left the factory in 1961.

Off on my travels at the weekend so progress will be limited to examining the latest collection of parts at my friend's house.

G