1961 CB72 Project

honda brian · Post by **honda brian** » Thu Oct 08, 2015 4:18 pm

Hi G Man, regarding the side clearances at the big end. I seem to remember reading in a Honda manual that the allowable side clearance on the con rod was 0.006 thou to 0.019 thou.I set mine up to 0.006. I reckon it takes out a bit of that "rocking" motion that you speak of. Keep up the good work.
See you at Mallala, Jerry.
Brian.

G-Man · Post by **G-Man** » Thu Oct 08, 2015 4:30 pm

Brian

Thanks for that. 0.019 sound like plenty. It would be interesting to know how much of the load the side faces of the rods take as the crank distorts.

I also found one or two rods that are obviously bent. Interesting to know how that happens.

Say hello to Jerry for me. :-)

G

honda brian wrote:Hi G Man, regarding the side clearances at the big end. I seem to remember reading in a Honda manual that the allowable side clearance on the con rod was 0.006 thou to 0.019 thou.I set mine up to 0.006. I reckon it takes out a bit of that "rocking" motion that you speak of. Keep up the good work.
See you at Mallala, Jerry.
Brian.

honda brian · Post by **honda brian** » Thu Oct 08, 2015 4:57 pm

Hi G Man, I'm glad you read my post correctly. It should of course read 6 to 19 thousands of an inch. Sorry for confusing anyone. I'll say g'day to Jerry from you.
Brian.

honda brian · Post by **honda brian** » Thu Oct 08, 2015 5:14 pm

And further clarification. I think the 6 to 19 thou. refers to allowable clearance. The manufacturing tolerance may well be smaller than 6 thou.
Brian.

G-Man · Post by **G-Man** » Fri Oct 09, 2015 12:42 am

Brian

Thanks again. I have a NOS crank. I'll measure it up.

G

Tim Miller · Post by **Tim Miller** » Fri Oct 09, 2015 9:39 am

I have checked 30 or more cranks pre-rebuild they are around 6 to 8 thousands. I reassemble mine with .007"side clearance. Running 10/40 Motul synthetic. Thicker oil will need more clearance for better flow.

The 3 NOS cranks l have are also around 7 or 8 thou.

Tim

G-Man · Post by **G-Man** » Fri Oct 09, 2015 9:49 am

Tim

Many thanks. It would be interesting to work out or measure the flow into the big ends via the direct feed and splash from the mains and compare that with the total leakage path from the big end.

Those oil jets in the mains don't look very big and only one per bearing is in operation.

G