Low oil pressure

Any topics pertaining to the BMC A-Series engine.

Re: Low oil pressure

Postby johnmcguire » Tue Mar 10, 2015 10:43 pm

Charlie,
Every time I measured the connecting rod journals I got a different diameter using a cheap digital caliper. I purchase an expensive micrometer and got consistent measurements of 1.6148, 1.6141, 1.6145 and 1.6147. I realize these are about 0.0010 too small. With new 0.010 undersize bearings the plastigage clearances are .0020, .0035, .0025 and .0020 so it appears only one bearing is going to be out of tolerance. I think I am going to go with this and put it all back together.
I'll follow up with the oil pressure results after it gets run in.
Thanks for keeping me honest, John
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948cc
 
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Re: Low oil pressure

Postby peter an5l » Wed Mar 11, 2015 4:35 pm

Hi, John, have you bled the preasure oil line to the instrument ?

sometimes forgotten

Piet
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1098cc
 
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Re: Low oil pressure

Postby Charlie Tolman » Wed Mar 11, 2015 11:52 pm

Since the oil in the line to the mechanical gauge is essentially an incompressible fluid, the oil will compress any air in the line to a smaller volume, resulting in the pressure at any location in the line, and gauge, has the same value. After the air is compressed, there is no further flow of oil, and the pressure is uniform in the line and gauge, regardless if there is air in the line, or not.

The electrical analogue demands that in the absence of current flow ( oil flow ), the voltage
( pressure ) in the wire ( oil line ) will be the same at all locations.

Charlie T.
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Re: Low oil pressure

Postby peter an5l » Fri Mar 13, 2015 3:31 pm

SURE ?

I made a different experience

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Re: Low oil pressure

Postby johnmcguire » Tue Jun 02, 2015 10:01 pm

The end results of my labor worked out. A new pump, ? deburring the pressure relief hole and tighter clearance for the crank bearings have raised the oil pressure to normal. Cold engine oil pressure is 60, hot is 50 at cruise speeds and down to 20 at slow idle. I did not have to resort to higher weight oil.
Now what is next to go wrong? Some one stopped me at the bank the other day to ask what the bugeye was and then politely inquired as to " how often are you underneath that thing?"
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