Jump to content

BMC 1.5 Has my crank been re-ground?


SailorTom

Featured Posts

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

 

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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. 

Link to comment
Share on other sites

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

Link to comment
Share on other sites

  • 2 weeks later...

For those interested...

I took a punt and bought all the bearing shells at standard size.  They seems to fit snugly, so it looks like my crankshaft was never reground.

So now I know what isn't in the workshop manual.  Standard size of the bearing journals is 2.00" for big ends and mains.

 

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.