Crank Rod Journal Measurement Q's...........

[LVBUSA]

Morning Motor-Guru's....

         Ran this by Dave, and he said to post it up. 

Have a Starret 436.1XRL-2.  Reads in .0001, and is brand new and zero'd.  I'm measuring the rod journals to start the process of bearing selection.  Crank is freshly balanced.

Crank is an AAABA with "2222's" with 60,000 miles.  On #1 and #4 I'm pulling a measurement of 1.4954.  No taper.  Inside range, low side, all the way around.

On #2 and #3 I'm pulling a measurement of 1.4953-1.4954.  No taper.  Dips into the 3's in areas. 

I've been told a rod journal will vary in areas up to .0001 and that it's still okay.  Some say out to .0002.  I'll stick with .0001 here.

Now for validation I preset the micrometer at 1.4954 and get light drag on #1 and #4.  Get about the same feel on #2 and #3.  I  then ran it down to 1.4953 and get medium drag on all.  Ran it down to 1.4952 and get strong drag on all four, but can still get micrometer over journal.  I'm dusting with lubricant before each pass, and I'm not gouging the journals.  I am getting it over the journal though.  Not stressing anything, just light direct pressure.

Here's the question:

If I'm at the low side of the "2" tolerance at 1.4954, and slightly lower.  Does it sound reasonable to drop the bearing selection into the yellow range (1.4951-1.4954) for rod bearing selection ?.  Crank reads "2", but measures "3". 

This a daily driver, stock build.  If the book says these are your numbers, and I am on the border, I'm leaning towards the tight side.  Even with the yellow bearing set I'm in the range for proper oil gap. 

Also, what are you using to remove the light scratches ?.

Thoughts gentlemen please......

Thanks for the read, A. 

[sportbikeryder]

What the crank measures should always supersede what the number is.
The way I do it is to use the same mic for measurements and setting the bore gauge. That way the difference is what you are measuring rather than the absolute. Accuracy of the measuring equipment is less important this way since you are just using a difference comparison rather than targeting a specific number. 

I then measure the thickness of each bearing shell (place bearing over a crank journal and measure difference in journal and outside of the shell) and calculate the clearance by hand.
This takes a long time.

[Stainless1]

Polishing may have taken your "tenth" from the crank... A tenth more rod clearance wont hurt anything IMO.  I would think it is better to run them toward the loose end than run them toward tight end of the tolerance.  Do you ever ride it fast?  What weight oil do you use?  Dinosaur or synthetic? YMMV
You started with it was polished... shouldn't have light scratches... but the best way to polish it is to send it to a crank guy, when you are concerned with .0001 you want it right.... if there were light scratches left after it was polished, then do nothing... consider them pockets to hold excess oil for the bearing 

[MICHAEL MATHEWS]

I was told as a general rule,tight mains and loose rods.

[Competition CNC]

I recommend just doing a direct measurement of the journals.  Don't go by drag on the journal.  Use a standard to get the correct feel for the thimble. Some guys have a ratchet type and use 1 click or 2 or just a personal feel.  Once you get repeatability with your mic measure the journal at 12-6 and 3-9 and compare for run-out.  There's not much room but you can try and measure for some taper by doing the same measurements side to side on the journal.
Forget about the marks on the cases, crank and rods.  They are useless and will only confuse you.

Then torque new bearings in the rods and cases.  Torque the bolts to the same stretch or torque you will use during assembly. you only need to torque the 10 large main bearing case bolts, not all the little ones. Make sure you have the dowels in the cases.   Make sure you have the rods resized if they are not new.
By torquing the bearings in place you are crushing them into there new location and any variation in bore size, taper, and or shape will be measured.  At this point the bearings are not to be moved to a new location. They are married to the location they were measured in.

Now you can do the math and calculate the bearings needed for each journal.

Cases will have taper on the mains. Seasoned cases have moved all around from heat and load and you will see the ID of the main bearings vary from one side of the oil grove to the other on the same journal.  This is "normal" but not desirable. You may see several tenths variation from side to side.    Its one of the reasons we line hone mains on busa cases.  A straight crank and trued mains will allow the crank to spin more freely with less bearing wear and heat and deliver more even oiling to each rod journal.

If you have the crank polished make sure they polish it in the proper direction of rotation with cork only!!! If you have the crank magnafluxed make sure its completely de-magnatized when there done!!!  These are two very common mistakes made by many machine shops.

[LVBUSA]

Thank you John, Stainless, Michael, and Jim !!!,

                 First of all, I'll ignore the case and crank codes and stick to the measured values.  For some dumb reason I was under the false impression that it was a plug-n-play build per the manual.  In a perfect setting the crank journals, case bores, rod bores, and bearings would all be exactly the same and match all the charts.  Now I can start over, measure, and run the numbers for what I'm homing in on. 

I'll push for rod oil gaps from .0013-.0022 (better on the loose side of the tolerance), and a crank oil gap .0006-.0016 (better on the tight side).

Great help !!!  Thank you !!!

A.