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SailorTom

BMC 1.5 Has my crank been re-ground?

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I am trying to find the original diameter of the bearings on my crankshaft.

I am re-building a Thornycroft 90 engine, based on a 1.5 BMC.  The pistons are stamped with oversize marks and the bores measure at 0.020" oversize, so I know that the engine has been reconditioned in the past.  But were the crankshaft bearings ground at the same time?  (I have the specification for the standard bore, but not the crankshaft bearings)

I measure the journal diameters for the main and big end bearings all at exactly 2" / 50.8mm.   The round number of 2 inches makes me think that is probably the standard size, but I am not sure.  I have the part numbers from the old shells, but I can't find any cross-reference for them.

Does anyone know the standard diameters for these bearings?

Thanks for any help
Tom

 

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Richard,

That is the same as the manual that I have (on paper).  I expected the spec to be in there too, but couldn't find it.

I would appreciate it if you could let me know what your measurements are.

Tom

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Will do - I can probably do better than that. I have a customer's crank that needs to go off to the machine shop, I'll ask them when I am there

I'm expecting the answer to be 2"

This engine also has +0.020" pistons, although the bores look horrible

Richard

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Ive got a BMC parts book for the 1.5 diesel and the part number for standard con rod bearings is 8G 2324, .010'' undersize is 8G 232410 and .20'' undersize 8G 232420.

The standard main bearings part number is 8G 2323 or 8G 2335 . Like the con rods if undersize the 10 or 20 is added .  Do any of those numbers match your old bearings ? 

Trevor

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Isn't the size stamped on the back of the BE/MB shells it used to be in +10+20 etc meaning the crank journals are 10/20 thou undersize

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3 hours ago, X Alan W said:

Isn't the size stamped on the back of the BE/MB shells it used to be in +10+20 etc meaning the crank journals are 10/20 thou undersize

This used to be the case. No undersize markings meant (standard) size.

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Looking on the ASAP site at BMC1500BE shells a close look reveals shells for 10thou under size crank journals have +10 & pt # stamped on the back They didn't show a "piccie" of a set of Std size shells to see what markings there were

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Bother. I took a micrometer with me, then forgot to measure the journals

Richard

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3 hours ago, RLWP said:

Bother. I took a micrometer with me, then forgot to measure the journals

Richard

 

You mean you can't tell by looking at them???!!! How disappointing....

I once worked with a toolmaker who could tell you if a piece of steel had been heat treated and hardened just by picking it up. 

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Just now, Mike the Boilerman said:

 

You mean you can't tell by looking at them???!!! How disappointing....

I once worked with a toolmaker who could tell you if a piece of steel had been heat treated and hardened just by picking it up. 

I can do that, I could guess the approximate size of a journal too. But if you want a proper answer, I need to measure it

Richard

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