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Crankshaft Problem/questions


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#1 tattooguy08

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Posted 24 November 2020 - 04:10 PM

I am rebuilding an engine, After tearing everything apart I have come to realize that one of the big end bearing was spinning. I will need to get it reground but my question is...

After measuring with my calipers one direction reads 1.72 and the other direction reads 1.74.

Is the crank salvageable? 



#2 whistler

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Posted 24 November 2020 - 05:11 PM

Take it to a machine shop and ask them to measure it. They'll advise whether the crank needs to be ground or whether a polish will suffice.



#3 tattooguy08

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Posted 25 November 2020 - 04:30 PM

I am just asking before taking it to the shop.



#4 MiniMadRacer

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Posted 25 November 2020 - 04:45 PM

If the Big End has spun the Rod is probably scrap (Just in case you havent checked it)



#5 Spider

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Posted 25 November 2020 - 05:00 PM

What you've measure with your Verniers is close to 7/10's of 1 thousands. It maybe able to be let go at that but it really needs to be measured with a (Crankshaft) Micrometer to best get the sizing. There are factors though which may dictate a grind, such as fillet radius and surface finish.

 

Got it that you'd like to know before going to the machine shop but I feel you'd be best asking for their advice.



#6 Ian Hardaker

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Posted 01 December 2020 - 03:49 AM

If you've measured 1.72" one way, and 1.74" the other way, that is 0.020" out of round. To clean it up it would probably have to be ground 0.030" undersize. According to Haynes, the smallest size you can go is 1mm undersize.... From 44.44mm standard, to 43.44mm minimum...  0.030" seems to be a standard maximum undersize. Have all the Big end and main journals ground at the same time to get them all round again, and like MiniMadRacer says... The rod is probably scrap as well.






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