How to measure/assess play in small end of connecting rod.

[LTGTR]

I am rebuilding a motor and want to know if the gudgeon pin to small end clearance/play is okay.
Ive had a good look around the forum/internet and found bits and pieces.
My manual (74-77 Yamaha) doesnt say anything about this specs.
The best I have so far is rock the pin up and down by grasping its ends (while its installed in the small end).
Mine has some up and down rocking movement - how much is okay ?
Should I take it to a machine shop and have it proffesionally measured - if so, what is the spec ?
The difference beween the pin/small end being serviceable or not serviceable is a crank rebuild - $1250 here in Aust - which is why I dont want to guess at it.
Hoping you guys can help.
Regards - Ray.

 

[jpdevol]

Yes, the manuals are very circumspect on that spec and ya have to dig for it. The ID of the rod small end is surface hardened, so a visual examination for irregularity is needed. There should be a uniform surface of the rod ID and zero up/down play with the wrist pin. The manuals sometimes acknowledge there will be some wobble without defining it. Anyway, there is a spec (this from a XS650E manual)

 

[LTGTR]

JP - I really appreciate you getting back to me with this info.
I dont want to push your kindness too far, but for the life of me I dont, or I'm too dumb, to understand how the figures work. Please bear with me.
For the sake of simplicity I will work in thou to four places.
Small End I.D. :
Specs say 0.787 +.0011 +.00006
1st isue - 20mm is .7874 (minor point but important)
+.0011 - would this mean maximum size of OD can be .7885 (no problems I think)
+.00006 - how can you have 2 positive values - do they mean minimum size is -.0006
Pin Diameter:
Spec says 0.79 0 -.0002
1st isue - 20mm is .7874 not .79 (minor point again) Im not trying to be pedantic - these corrections make a difference when you are dealing with 2 10,000 of an inch.
0 - I assume this means maximum diameter is +0
-0002 - I assume this means minimum diameter is -.0002.
Using my assumptions (corrections)If you calculate the maximum size of the pin it will not fit in the minimum size of the small end.
If you calculate the maximum size of the small end and deduct it from the minimum size of the pin you have 1.3" (1 thou and 3 10,000) - do you think this results in the allowable clearance.
These sort of things give me the shits because I dont know if its just another mistake in the Yamaha manuals or is it me.
Hope you can give me a better understanding of how this works.
Regards - Ray.
p.s. if you peruse the specs sheets there are double negatives everywhere - are these all mistakes.

 

[jpdevol]

These sort of things give me the shits because I dont know if its just another mistake in the Yamaha manuals or is it me

LOL; there are mistakes to be certain.......I glossed over the inch conversions, preferring to work in metric (Americanism aside):

Rod ID 20mm to a tolerance of +.028 to +.015: 20.028 20.015
Pin OD 20mm to a tolerance of -0.00 to -.005: 19.995 20.000
Spec clearance range: 0.033 - 0.015mm

For us Americans: .0013" to .0005"

 

[LTGTR]

JP - thanks again.
F..k me - I made hard work out of that.
I took a guess you would work in thous - whoops.
I appreciate you took the time.
Regards - Ray.
p.s. I've often wondered whether you guys have to know/work with both imp. and mteric - it seems to me like a hassle. Having said that - my dial indicator is in imp. - I just relate to thou in these type of things - queer I know.

 

[jpdevol]

Yeah, I happen to be old enough to have been educated in the 60's-70's when the US was certain to convert to metric and having worked on Japanese bikes since the early '70's, just find it easier. Still, the limiting factor is often what measuring tools are at hand.....I'd still rather do the calcs in metric and then convert as needed for the tool