Topic: Please bear with me for a few questions about CB750 crank and rod bearings

[fang]

Long, long ago in a galaxy far, far away I spent too much $$ for what I was told was a "R.C. Engineering crankshaft with its forged rods which came out of a low miles, big-bore R.C. motor."  Years later, I now know a bit more about this stuff, and I still have no way to know if it was a R.C. crank.  Nevertheless, it looks good enough and I am planning on bolting it into a motor I am building right now.  That means sorting out some bearing questions.

I have a few questions about all this:

1.  Yellow, green, brown black.  Which one is the largest bearing (for the most under-sized crank), and which is the smallest?

2.  What is the correct terminology for this, for a larger or smaller bearing?

3.  Do we have measurements that correspond with the letter codes for the rods, case journals and crankshaft diameters?  If so, what are they?  I mean surely a crankcase "B" code directly corresponds to a bore measurement....

*4*  This is my most important question:  I have some forged alloy rods that I intend to install.  What is the best method to find the correct big-end bearings for these? 

5.  My rods are stamped with a 3-digit number, the same number on the top and bottom halves of the rod journals; each rod has a different number.  Any ideas what these numbers mean?

6.  For those forged rods, how do I verify the correct wrist pin fit?

7.  Are there any marks that would make a R.C. crankshaft stand out in a crowded room of stock cranks?



Peace and grease
-fang

[754]

Looking at a pic from the catalog right now, shows a crank with R.C. ENG. stamped into it on the first flywheel weight  from the center jounal toward the alt side..dont know if they were all stamped.


Read up in the manual on bearing selection, get a firm grasp before going further. If you are not willing to do that there is no point in describing it further.

#5.. batch # most likely to make sure caps dont get mixed

[fang]

745, thank you for your reply. 

Read up in the manual on bearing selection, get a firm grasp before going further. If you are not willing to do that there is no point in describing it further.

That is a pretty crappy thing to say to someone. How would you know how many motors I have built, or how many manuals I have read?  Thanks, however for the good idea about batch numbers to assure correct matchups and the thought about the RC stamp.


I have either found or remembered the answers to all my questions except:

3.  Do we have measurements that correspond with the letter codes for the rods, case journals and crankshaft -- If a crankcase main bearing journal is indicated as a "B," then what is the indicated numeric measurement for that journal's ID?  What about the rods' ID/OD and the crankshaft OD?  Does anyone have a chart or have access to this information?

*4*  This is my most important question:  I have some forged alloy rods that I intend to install.  What is the best method to find the correct big-end bearings for these?

-fang

[mkramer1121]

There was a post on here about that.  Also, in the Honda service manual, there is a graph that shows the measurements with the letter codes (or based on bearing codes).  its at the top of the table, shows the tolerences.  See this post for the table:
http://forums.sohc4.net/index.php?topic=28774.0

[fang]

EDIT:
mkramer1121, THANK YOU!  You are absolutely right, I overlooked that.  I must be WAY more tired that I thought.

[mkramer1121]

Did I miss a nasty message before you edited? 

Yeah, it took me awhile to realize how to do the bearing codes, etc., but now its cake.

[bryanj]

Only way with aftermarket rods is use the thinest shells and plastigauge!!! Buy one pair of the thinnest and use them 4 times to find out which ones you need Black is thickest(cant remember which is thinnest) Dont forget to mark the rods 1,2,3,4 so you can put them back in the same place or you are wasting your time.


In my opinion measuring the pins/holes is pointless unless you have the incredibly accurate air gauges as used in the factory as if you use micrometers everybody who does it will get a different reading forthe same pin/hole due to not having the same "feel" and you need to be accurate to .001mm (0.04 thou)

[754]

I think you should be able to measure the torqued rod and go to the table and figure what letter or number it should be.

Wrist pin if you feel you cant measure should be able to install pin and check movement with an indicator  & compare to other rods. could aso whip up a guage pin on a lathe..

As far as I know forged rods have a finite life.. a bit hard to judge if you do not have a accurate idea of what hours & abuse the recieved before you got them... also if it is a rod designed for a fueler, it would be hard to hurt it with an 836..

[Big Jay]

If you are using thosed alum rods in the other post, you should select the bearings by measuring the rod bores as you will need to drill the bearing to install them.

If you have an old steel rod, you can take the cap and put it in a mill and find center in both directions, then drill a hole the size you will have to drill in the bearing. Now you have a drill jig for drilling the bearings.

Jay