M-19 oil pump

K

kurt v

Well-known member
took my motor apart, rebuilt many years ago run very little, has a m-19 oil pump, my understanding it is 80 lb , how can i reduce the pressure to the 50lb pump ?
thanks kurt
 
May not be applicable, but several years ago, I had the 327 in my Corvette rebuilt. The rebuilder put a hi-volume, hi-pressure pump in it, which caused all kinds of problems. I replaced it with a standard Mellings pump. Not knowing the pressure it would put out, I contacted Mellings. I found out that they offer 6 or 8 different relief springs that would allow the pump to "blow off" at different pressures (the springs were identified by their color). Perhaps they have the same set up on their flathead pumps. You may want to contact them.
 
The engines up to 1940 had a pressure relief in the front of the valve chest and the spring had a 50 psi relief setting. Beginning in 1941 the spring rating changed to 80 psi. This remained the spring up to the end of the 1948 production V8’s (or up to 1947 for the truck engines). The new 8BA type blocks didn’t have any sort of relief built into the block…..its oil pump (M-19) has the 80 psi relief built into the pump itself.

If you install the M-19 with its 80 psi built in relief setting in a 32-40 block (with the 50 psi spring) the oil system will still relieve at the lowest available point…..which will be the 50 psi relief in the valve chest.
 
this motor is a 59a , i didn't build this motor, everything looks new ,my understanding is that a 80lb pump is not needed to much pressure, 50lb is more than enough. Should i use this pump and not worry about the 80# ? Some posters here (if i remember correctly advised against the 80#pump ) said 50# was all that was needed.

thanks kurt
 
As this engine is a stock type 59AB rebuild, it most likely has the stock spring and plunger in the front of the valley - and it probably was NOT stretched to increase the pressure pop-up.
So, this the stock relief valve will operate as it always did - and open sooner than the one in the Mellings pump, so pressure will be controlled as it was with a 59AB. It should be just fine.

The M-19 oil pump has helical gears and will pump more volume than a stock 46-48 pump - this too is not a problem. You'll probably find that the oil pressure will be 50 - 80 lbs when you start the engine and after it gets warm, probably closer to 50 - 60. I wouldn't worry about a problem that you don't yet have - that pump has been used in every flathead I've built and I've never seen an issue.
 
Melling also makes an M-15 pump which puts out even more pressure and is the one advised not to use. The relief spring in an 8BA pump is usually set at around 55 - 60 psi.
 
On the M-15, it has about 25% or so higher volume (due to bigger gears and a longer total pump cavity), but I believe the pressure relief spring/setting is the same as the M-19.

Also, the M-15 usually won't fit in a stock pan - unless you modify it (too long).

There is no reason to use the M-15 High-Volume pump - though some believe the extra volume an be an aid on a OHV conversion (I don't consider it as needed - the flathead only has 3 mains and just doesn't need the extra volume).
 
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