The Stovebolt Site Forums The Shop Area Engine Shop oil pressure drop, a different question

'62 261 rebuilt by local respected builder over a year ago, not run (in my '50 as the frame off is completed.) Recently go to first start up. Pull the distributor and prime the engine with drill motor. Oil pressure seems fine and oiling at rockers. Pop distributor in and fire up. Oil pressure gauge seems to hesitate, but because new motor, it may just be fear on my part. Gauge jumps up to peg 30lb gauge. Run engine for about 2 minutes at fast idle and gauge shows drop to 0, gauge just steadily drops, rpms do not change drop.

Immediately shut it down, 1st thought gauge, something has plugged the line. Pop line off of gauge, turn it over and oil pumps out of line. Hook it back up and fire it up, full pressure and then again, drops to 0. Shut it off, remove entire gauge line and clean and blow out, same thing.

Move over to distributor, pull and see if driveshaft somehow not matching up with pump. Seems to be lined up and engaging, but if measure shaft from collar hold down on distributor and measure depth from pump slot and distributor deck surface and it seems like the shaft will just engage the pump. The distributor is definitely bottoming out on something when installed, but the collar hold down could move up a half-inch or so on distributor housing when installed.

So here are my questions. Could the distributor shaft be just barely engaging the pump slot and for some reason just stop after a minute? If so, it appears that the distributor is stopping dead against what appears to be a brass bushing in the block just above the pump. If this is a bushing it appears to be installed about a quarter inch above the block casting it is installed in. Could this need to be pressed in further?

In a past post with a similar problem, I remember someone saying something I thought odd at the time. (I did search for the post but can't find it.) Their comment was that even a slightly dented in oil pan could cause this problem of full pressure at start up and then drop off a moment later. So I looked, and my pan is slightly dented in on the bottom. Could this really be the problem?

Any thoughts would be greatly appreciated.

Well it sounds kinda scary , least ways , I'd be worried if it was my new engine, the dist tang should engage about 1/8" - 3/16" into the oil pump drive.

Perhaps the tang is just sitting on top of the oil pump, and when oil is flowing well it lubes the contact area and the tang slips , so losing oil pressure ??? just my guess.

Never had it happen to me but it seems possible that if the pump to pan clearance only allowed for say, a 5 gallon per min. inlet flow & the pump put out 10 GPM @ the RPM you're at then you gonna have a problem soon. Only way to know for sure is check & be sure there'a lots of opening there. I'd weld a nut on the bottom & use a slide hammer puller & make some more room. Doug

Unclamp the distributor and spin the engine over while holding the distributor down to make sure you have engaged the pump.

Or.....cut the shaft from a long screwdriver and chuck it in your drill.
Stick it down into your oil pump and run it for..........quite a while. Keep an eye on your gauge from there.
Kinda sounds like your dist. isnt seating into your oil pump.
Marty

I have read about the distributor not engaging the oil pump properly, on a 216. It created a similar problem. I also saw a very similar situation on American Hotrod and it turned out that the sump was bottoming on the pan.

Let me suggest you drop the oil pan, and visually inspect the fit between the pump and the distributor. If that's not readily visible, try installing the distributor with the pump removed, then install the pump and see if everything fits correctly. There should be a very solid engagement between the distributor shaft and the pump drive.
Jerry

Drain oil and filter it thru coffee filter. Look for metal.

Get a modern gauge from parts store, hook it up and see what that reads. Perhaps the 45 psi or so from 261 has damaged the old 30 PSI gauge?