Author Topic: Main bearing oil clearnance  (Read 1512 times)

Mike.Urbans

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Main bearing oil clearnance
« on: September 18, 2023, 12:03:13 »
Quick question to see if what I've got is acceptable.

Crankshaft main bearing journals measure consistently 59.96mm.

When I measure inside diameter of the used standard bearings I get oil clearance of 0.07 to 0.077mm. Got my Haynes manual saying that 0.065mm is the max clearance. Just want to know if a new set of standard bearings will bring clearances back into range or do I need to go oversize and get the crank ground to fit them?

rwmastel

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Re: Main bearing oil clearnance
« Reply #1 on: September 18, 2023, 15:35:44 »
Mike,

Excellent first post!  Obviously, you're an experience mechanic.  You may introduce yourself and your Pagoda in this thread: https://www.sl113.org/forums/index.php?topic=529.1500

Welcome to the Group!
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Benz Dr.

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Re: Main bearing oil clearnance
« Reply #2 on: September 18, 2023, 17:03:03 »
Quick question to see if what I've got is acceptable.

Crankshaft main bearing journals measure consistently 59.96mm.

When I measure inside diameter of the used standard bearings I get oil clearance of 0.07 to 0.077mm. Got my Haynes manual saying that 0.065mm is the max clearance. Just want to know if a new set of standard bearings will bring clearances back into range or do I need to go oversize and get the crank ground to fit them?

Have the connecting rod big ends checked for out of round. If you need to resize them then you will need new rod bearings. Any scratching on the bearings indicates dirt entered the system and I wouldn't use beat up parts if I were you.
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Charles 230SL

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Re: Main bearing oil clearnance
« Reply #3 on: September 19, 2023, 00:14:25 »
..Just want to know if a new set of standard bearings will bring clearances back into range or do I need to go oversize and get the crank ground to fit them?
Mike, since the crank journals are still within spec (59.96 mm) but the main bearing clearances aren't (.07 -.077 mm), I would think a new set of standard bearings would get you back within spec. BTW, Mercedes engine specifications show main bearing clearance as .0432 - .0635 mm).
« Last Edit: September 19, 2023, 00:47:51 by Charles 230SL »

Mike.Urbans

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Re: Main bearing oil clearnance
« Reply #4 on: September 19, 2023, 07:07:35 »
Have the connecting rod big ends checked for out of round. If you need to resize them then you will need new rod bearings. Any scratching on the bearings indicates dirt entered the system and I wouldn't use beat up parts if I were you.

Yes they need to be machined back to standard size. Engine doesn't appear to have had a long running history, but it also doesn't appear to have been maintained very well over time.

Evidence of dirt or some sort of debris in the oil system is shown on bearing surfaces, while not heavily worn, have some scratching. So yeah, we're going to replace those.


Mike.Urbans

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Re: Main bearing oil clearnance
« Reply #5 on: September 19, 2023, 07:08:25 »
Mike, since the crank journals are still within spec (59.96 mm) but the main bearing clearances aren't (.07 -.077 mm), I would think a new set of standard bearings would get you back within spec. BTW, Mercedes engine specifications show main bearing clearance as .0432 - .0635 mm).

Thank you for confirming what I thought might be the best course of action to take.

Mike.Urbans

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Re: Main bearing oil clearnance
« Reply #6 on: September 19, 2023, 07:10:01 »
Mike,

Excellent first post!  Obviously, you're an experience mechanic.  You may introduce yourself and your Pagoda in this thread: https://www.sl113.org/forums/index.php?topic=529.1500

Welcome to the Group!

Thank you very much. I'll take a moment and do just that.