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Crankshaft Grinding

Engine Building Fundamentals

Relevant Module: Engine Machining Basics > Crankshaft Grinding

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Discussion and questions related to the course Engine Building Fundamentals

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Hi

what did you mean by that sentence?

"For example, the machinist wouldn't grind one single big end journal under size, but leave the remainder at a standard size.

While technically possible, this would be inviting disaster."

"Inviting disaster" may be putting it a bit strong, but it's a bad practice - not least because the shells are normally sold as a set. I guess there' s a potential risk of using a "std" shell, or set, on the undersized journal*.

It's akin to reboring a single cylinder while leaving the others un-bored.

*Many, many years ago I sold a Valiant with a 225 slant six, in bits - I'd bought sets of std mains and big ends before stripping it down (yeah, stupid, but I was just starting my 'prenticeship), but turned out the mains needed to be re-ground. One thing and another, I abandoned the job and the guy that bought it had his "mechanic" friend assemble the engine... Yes, you guessed it - despite having the crank clearly displaying the tag stating the B/Es were 30 thou' under he used the STD bearings - the owner came after me for 'compensation' but I just pointed out that info' and his "mechanic" should have seen the tag and that the shells were std - and actually checked, anyway.

This may also be related to the likelihood that if one was damaged, the others are not 100% ok, and machining all of them would offer a more complete repair.

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