Discussion and questions related to the course Practical Engine Building
I am having the white coating scraping away as soon as the crank is spun by hand.
I've cleaned the parts thoroughly before assmebly, using a sae40 weight motor oil for assembly
Is the scrapping off normal? I have been told by my local machinist (after taking it to him over 15 times) taht it's normal and it's because after the first revolution the oil film reduces.
Oil clearance is spot on 15thou across all mains and cons. Used plastigauge and also measured them with a set of calipers.
Please see the attached photos below
It looks like there may have been a very small piece of debris (too small to see) between the cap and bearing shell, a small amount of debris in the crankshaft oilway that wasn't properly cleaned out, and/or it wasn't lubricated on assembly. I would hope the 15 thou' was an error and you meant 1.5 thou' - although that may also tend to mark a shell like that.
What does the back of the shell look like, and the cap where the shell sits - sometimes you can see a slight blemish, or feel it with a finger, if there's a problem with debris.
That said, I would look for another machist, as (s)he's talking rubbish., as far as the oil film is concerned.