The Stovebolt Site Forums The Shop Area Engine Shop m23a oil pump

So I read on here a gmc oil pump has been put in a 216 before? Anyone done it? I have a m-23a oil pump on the way and was curious if anybody has had any success?

Is there a reason for the modification? As long as the main and cam bearing clearances are correct, a regular 216 oil pump will keep the engine lubricated. I have adapted an oil pump for a Chevy 250 6 cylinder to 216 and 235 engines, but that's for a special application where the standard pump probably won't supply sufficient oil volume for the highly modified engine I'm building. If a 216 will maintain 15 PSI of oil pressure at highway speed, it will run about 3 days past forever. It's not uncommon for a 216 to show NO oil pressure at hot idle with no problems.
Jerry

I understand that. And from what i am checking I have about .002 on the mains. I just would like a little more oil pressure. Nothing drastic

FYI, the M23A in my spares dumps pressure at 57 PSI. Spun it with a 1/2 inch drill motor in a 270 GMC engine and watched the pressure gauge I had hooked to the block. Pretty linear pressure going up until about 600 pump RPM (1200 engine RPM) when it reaches 57 PSI, then stays there to the drill's rated speed of 850 RPM. Oil was 10w30 and temp was around 45F. Gauge was a 4" diameter fluid dampened model rated at +-1PSI.

I have no idea whether the drive tower will properly engage the distributor, etc., but the in & out steel lines will not be a bolt-in, you'll have to make them.

The M-45 pump won't clear the oil pan. That's why the later model engines have a dogleg in the passenger's side oil pan rail and a bulge in the pan. I'd be surprised if the GMC pump will fit, as it's considerably larger than the M-45. There is a way, with a LOT of precision machining, to fit a set of Chevy V8 gears to a 216 pump.

What weight oil are you running? It's virtually impossible to maintain pressure with the water-thin oils some people insist on using for some odd reason. Any "10-something" oil will drop the pressure noticeably- - - -it's just too thin to work with the loose clearances and low pump volume most stovebolts have. The "5W" oils are even worse. A lot of us run 15W-40 oil and see much better oil pressure, particularly with a hot engine.
Jerry

You all are probably correct. I am using 15w40 as of right now. When the pump gets in I will know more. I wonder if the increase in pressure will damage the scoops on the rods? But if the pump won't fit no worries.

I think it would be a good idea to read the first two paragraphs of this Chevrolet Service News.
It is not the pump that controls oil pressure in a 216.
I have checked what the relief valve in several 216 pumps and they are set at about 80 psi.
Setting bearing clearance is the best thing you can do for a 216.

Thank you. I got the m23a pump and as you said it is quite a bit larger and anything you do to it will cause interference with connecting rods and or the troughs in the pan. I am now in the process of trying what Mr. Jerry suggested and install a set of small block gears in this housing. I will let you know when complete.

Drop me a PM, and I'll respond with a phone number. The procedure requires fabricating a different driven gear pivot shaft from oil hardening drill rod, then hardening it, and making a spacer plate between the pump body and the cover plate to accommodate the taller gears. it's much simpler to make an adapter to run an unmodified 250 I-6 oil pump. Unless you're creating a demand for more oil volume than a stock 216 needs, doing either one is a waste of time and money.
Jerry

So I modified the 216 pump to run the small block gears. Now hot idle I have 15 psi. Highway speed I have 28 psi with 10w30 oil. Before I had 10 psi at idle and a little more than 15 highway speed with 15w40 hot. Not the results I expected but It worked.

That's pretty good and close enough. Who's to say your 28psi reading isn't actually 30? Can't really trust gauges or even testing equipment to be 100% accurate.

As Jerry has said before, as long as oil is being replaced to the sump at exactly the same rate that it's being applied to a particular location in the engine, Zero oil pressure would get the job done without harming the engine. So 28psi instead of 30 isn't anything to worry about.

What end-play do you have between the gear faces and the pump cover?

Gauge pressure only tells what it is at the point where the gauge sender enters the system.
Pressure at individual bearings, tappets, etc. is different in part based on how far away from the pump they are.

I had .0015 between gear and housing. After taking this apart and looking at components. I understand how it was designed. Often times my ignorance is misunderstood for arrogance. The ignorance is the fact that the pump is limited to the size of the inlet and outlet ports in relation to the leakage inside the engine. Yes you only have the main bearings and cam bearings to lubricate under 15 psi. The outlet of the pump is limited to 1/4 npt fittings which are only 5/16 inside diameter. The Oil supply to the connecting rod nozzles are almost as big as the outlet of the pump. The small block chevy pump outlet is a 1/2 or better. After assembly I noticed better oil pressure when cold and much the same when hot. The distributor valve was working more like a pressure relief. So now I have rocker lubrication at idle. once the distributor valve opens and the connecting rod nozzles have their supply the leakage is close to what the pump can supply with the factory plumbing. With out drilling and modification to discharge tube circuit and suction pipe. So how far do you go? LIke so many have said before If it works why mess with it? Yes I think it could be done. But at this point Why?