Sealing washer, timing side bearing WHY??

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Fast Eddie

Fast Eddie

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Whats the reason for the sealing washer that goes in next to the timing side main bearing?

Meaning, why does it need sealing, and from what?

Why not just let the head oil return through the bearing into the crank case?

My reason for asking is that my Maney cases have no holes from timing chest to crank case. I’ll be running a cNw / Comnoz breather on the back of the case.

I am about to drill the ‘Comnoz oil return hole’ just below the pump and got to wondering why not just allow oil to return through the bearing?

I’m pretty sure there’s a sound reason for this that I’ve overlooked... can someone please enlighten me?
 
I thought I had read it somewhere recently, Comnoz said

"You don't want to leave the washer out. The bearing could be flooded with oil from the timing chest which will cause the bearing to fail at high speeds. Jim"
 
Thanks Cab.

But my next question is, why would flooding a bearing with oil cause it to fail?
 
Fast Eddie said:
Thanks Cab.

But my next question is, why would flooding a bearing with oil cause it to fail?
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From what I have read about racing BSA b50s and later on CCMs is that too much oil to the big end (rollers) can cause the bearing to over heat and fail
Maybe it's the same for main bearings?
 
Right, got it!

Thanks gents.

The washer stays, and I’ll be drilling a new oil drain hole, like a good boy !
 
Yep, too much oil and a roller will stop turning and hydroplane when the load is light. Then when the load returns it skids as it comes back up to speed and you get excess wear.
 
Thanks Jim, how is that overcome in applications of pressure fed roller big ends? Which I guess is linked to Baz’ pint above. How can you have too much oil to a pressure fed big end? Surely it’s going to be flooded no matter what you do?
 
Fast Eddie said:
Thanks Jim, how is that overcome in applications of pressure fed roller big ends? Which I guess is linked to Baz’ pint above. How can you have too much oil to a pressure fed big end? Surely it’s going to be flooded no matter what you do?
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Oil discharge orifice diameter controls volume.
 
Plus the size of the feed gears is changed, normally reduced in width on roller bearing engines vs shell bearings.
 
Yea, careful control with orifice size and pressure.
The same thing happens if you overlube the roller bearing in a big end.

That is also why a sealed ball bearing only comes packed with a small amount of grease.
If you overpack it and then run it fast, they will fail early.
 
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