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Engine Bearings- Problems sourcing king/county tri-metal type

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I'm in the process of rebuilding my 1300 race engine, briefly the engine was last rebuilt Aug 2017 using King/County tri-metal bearings +020  (mains and big end). The crank was resized to be a prefect match to the new bearings. I had bought a spare set (from the same supplier) in 2019 HOWEVER these have a different tolerance (way too tight). Even though the box says they are +020 there is about 1 thou difference between the old set as compared to the new set. I took my chances and re-ordered a new set May 2022 however I was supplied with an identical set as purchased in 2019

The stamped numbers on the OLD (2017) bearings are (pics attached):

- County REGD. UK AM C430 020 HU (big end)
- County REGD. UK M339 020 MM (mains)

The stamped numbers on the NEW  (2019 & 2022) bearings are:

- County REGD. UK CR C430 C20 AX (big end)
- County REGD. UK CP M339 020 ET (mains)

Does anyone know why King has different tolerances for the same size bearings?

More importantly can anyone direct to someone who can help me source the 2017 type of bearings. I have contacted all the European suppliers (from king website) however none could confirm they can supply the ones with the stamped numbers I'm after (2017 /pics attached) 

Thanks in advance


279700494_406167414649202_5507665156136907496_n (3) (2).jpg


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Hello Nicky,

as they are both -0.020" I am surprise dthat there is that much discrepancy in the thickness.  (Aston Martin used graded mains bearings in their six cylinder engine, but the difference was only 0.00025").

I think I would contact KIng's technical department and query the discrepancy?





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Presumably this is small crank 1300? (I’m too lazy to lookup the part Nos at this moment)

I have previously noted that King Tri-metal bearings gave larger clearances than ideal on a crank that had standard journals in good condition, though just about within book. That was when building my PI engine. My local machinist found me some NOS Glacier shells which gave clearances right in the middle of the range and I used those. We agreed that next time we’d get the shells first and grind to suit as you obviously did. Though as you have found, this carries it own risk!

Seems that King may have finally corrected their own errors, which is good news for most of us…..

Apart from getting lucky and tracking down another set from the same batch…. I reckon you’ll have to get the crank pins resized :(

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I've got a set of -020 big ends ordered in error last year but I'm afraid they're the newer part number. Are you measuring them with a micrometer? It does seem like a big difference. But as Nick says maybe they've corrected previous slack tolerance.

When I had my crank machined the bloke did it to the book figures. I checked the clearance with plasti-gauge on re-assembly and they were 001 to 0015 thou on the big ends, 0015 to 002 on the mains. I don't know what's ideal but the oil pressure is ok without being fantastic. My notes say mains should be less than 00022.

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Yes indeed it is a 1300 small journal.

I have contacted King asking about the difference , and who to contact to source them. Fingers crossed.

Thanks for your replies 


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