I removed the old pressure relief valve and spring tonight. The spring is 2
7/8" long. http://www.pokrefke.com/mgb/springlength.jpg According to
Haynes, the free length should be 3 inches, so I'm a little short.
The relief valve was in fair shape. There was some erosion on the valve
face, and the side had an odd wear pattern in one location.
http://www.pokrefke.com/mgb/reliefvalve.jpg All things considered I think it
was fine, but it will be replaced while I'm here.
I was able to compress the spring to 2" by squeezing it between my thumb and
index finger. Haynes says the oil pressure release valve opens @ 70lbs/in2.
The spring is 1/2" in diameter, and according to my father (an engineer),
this translates to a force of 13.7 pounds. I set a half-full 5lb bag of
flour on the spring, and it compressed approximately 1/8". 2.5lbs on the
face of the spring is equal to ~13 lbs/in2.
My theory is that while driving, the oil pump produces enough pressure to
give me the 10psi/1,000rpm, but while idling with a sump of hot oil, the
pressure valve was opening around 10-13lbs/in2.
I won't be able to get her put back together for about 10 days. I'll let
you know if I was correct.
Thomas James Pokrefke, III
1970 MGB
pokrefke1@comcast.net
http://www.pokrefke.com
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