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Author Topic: CS big end bearing failure analysis  (Read 501 times)

olNick

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CS big end bearing failure analysis
« on: April 01, 2022, 12:06:48 PM »
Here is the big end shell that had substantial slop in it. While difficult to measure accurately,  I'm
getting about .65 - 0.82mm clearance.

I've yet to check for runout and taper on the crank throw with a mic but with a caliper
I think that even a 0.040 under still would be too loose,

Cant believe that this was hacked like this.

Note:
total lack of oil grooves
the oil feeds of the top shell babbitted closed
delamination of babbit (could be simply lead)
bad/no tinning of shell

The other shell, IIRC had no noticeable slop, but the top oil feeds are clear on that one

Alas,
nick

38ac

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Re: CS big end bearing failure analysis
« Reply #1 on: April 01, 2022, 01:38:05 PM »
You stated this is an early engine, how early? The first few years of production had smaller diameter crank pins and parts vary from hard to find to impossible.  The bearing looks to be a bodge job, but could also be melted from lack of oil, a common occurance in twins that are moved around and not always sitting level.  If the crankn is indeed worn down that far then placing a new 040 bearing on it will not work as it can't be true enough to last.
« Last Edit: April 01, 2022, 01:41:32 PM by 38ac »
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olNick

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Re: CS big end bearing failure analysis
« Reply #2 on: April 08, 2022, 11:44:25 AM »
It's not that early Butch, has "2.5" big ends...

Here's what I've calculated using some of your posts...

Got a chance to mic out the big ends on my 10/2 crank. I was mostly interested in roundness and found

P1 62.15mm and P2 62.45mm on the other pin.

I saw a post or 2 referring to 0.050", even 0.060" undersize shells, but I don't see them adverstised anywhere??
Anyone??

Assuming they are available, below are my calcs based on a post from 38ac on "running clearances".
 https://listerengine.com/smf/index.php?topic=7426.msg84397;topicseen#msg84397

This would allow off the shelf shells since my crank is still in block, one gib is refusing to come out...

Pin1
62.15/25.4 = 2.4468, maximum shell 2.5005
Max Clearance  =  2.5005 -  2.4468 = 0.0537"
62.15/25.4 = 2.4468, minimum shell 2.4995
Min Clearance  =  2.4995 - 2.4468 =  0.0527"

Pin2
62.45/25.4 = 2.4586, maximum shell 2.5005
Max Clearance  = 2.5005 - 2.4586 = 0.0419"
Min Clearance = 2.4995 - 2.4586 = 0.0409"

Here's where the logic is questionable....

Pin1 using an 0.050 under shell gives
max clearance 0.0537 - 0.050 = 0.0037"
and min clearance of 0.0527 - 0.050 = 0.0027"

Pin2 using an 0.040 under shell gives
max clearance  0.0419 - 0.040 = 0.0019"
and min clearance 0.0409 - 0.040 = 0.0009"

If the os shells are on the "tight" side,
Pin1 runs at 0.0027" OK?
Pin2 at 0.0009" can shim, or take lap thou of the pin

Note: I'm waiting on a kg of Tegostar to pour the bearings, so the above is more or less academic....

appreciate some feedback
nick

38ac

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Re: CS big end bearing failure analysis
« Reply #3 on: April 08, 2022, 03:33:09 PM »
I keep up to .030 under here. Search for DEV Engineering. You can contact him via email or Facebook. if its made in India he can source them.
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