I doubt the hydraulic lifter by pass valve is causing your low oil pressure and subsequent tappet noise. I suspect that something was missed when the engine was rebuilt. The engine with new bearing including cam bushings with proper clearances should have oil pressure in the 35 to 45 psi range when the engine is warm and running at moderate rpms. It's possible that the relief valve at the front of the valve galley may be at fault, maybe the spring and ball were omitted? the fuel punp bushing might be worn thru? one or more oil line plugs may not have been replaced? these plugs are at the ends of the lifter feed lines behind the timing gear. Worn Cam bushing or excess clearance at the cam journals can be the cause as they are the first-in-line to recieve oil. I assume you have no bearing noise like knocking?

Wow, this could be a bigger problem to solve than I hoped. No, there is no bearing noise like knocking.
Ralph

Funny thing about those oil sending unit's if you have one of the original oil senders there will be an arrow on side, which I understand should be facing down if I recall.
Maybe some one lke Peecher would know. when I turned it facing up the pressure would take a little more time to show oil pressure on the gage.
Still a mystery.
Z man

I pulled the intake manifold today and found that the hydraulic bypass valve at the back of the engine is OK. The Oil relief valve at the front is also OK and the fuel pump push rod bushing is OK. By the way both valves have 15/16" caps over them. Next to check out is the oil pump. When the engine was rebuilt in late winter 06, the pump was rebuilt too, but the oil system has never been good since the rebuild. I think I will go to a new high output pump. I spoke to Alan Whelihan who has good knowledge of the oil system and he thinks the answer is likely a better pump. The oil pressure is only OK for about 2 miles, poor for the next 4 and then the lifters start ticking- only a short trip car!

I HAVE WHELIHANS HIGH VOLUME PUMP ..LARGER GEARS AND PUMP BODY. I HAVE TO SAY IT HAS BEEN GREAT..

Ralph
Changing out that oil pump will correct
your oil pressure, Your mechanic probably only changed the gaskets, and there is more to rebuilding an oil pump then that!
Make sure you get a new pump not re built
On the later pumps you may require removing a Baffle in the Pan, depending on the location of your oil pump pick up.
Since your pulling the pan make sure you check the cover plate that houses the cam and pump running gear located in back of the block for oil leaks.
I would take out the pump before ordering the new one, remove the bottom plate and check for wear and sloppy gear
mesh.If the plate shows wear go back to your mechanic and get a refund.
Z man

A word of caution when changing the oil pump. When installing the high volume Melling 15 pump and pick-up screen you should check the overall depth from the bottom of the pan rail to the bottom of the screen. I have found that the pick-up screen will sit too low and interfere with the bottom of the pan. You need about 3/8"-1/2" clearance between the bottom edge of the screen shroud and the bottom of the pan. The pickup screen can be bent by hand after it's installed on the pump if you find that it sits too low ( or too high). You may have to rotate the rear main drain tube a little for clearance.
The new pump will clear the baffle in the '47 oil pan as it occupies the same area. Prewar engines had a different style pump and a more elaborate baffle in the pan.
This new pump may help your oil pressure and overcome whatever is sapping off pressure from the oiling system, be it the pump or something else. When checking the old pump that's on the engine also check the relief valve. It may be the problem.

Thanks for the tips. I'll let you know how it turns out. It will take about 10 days for a new pump to get here, because of clearing customs etc.

I have the new oil pump installed and everything put back together- quite a job! I have driven the car 10 miles and the oil pressure stays up. The old pump has a gasket on the cap over the pressure relief valve that is only partly in place. It looks like the seal woul dnot be tight, but I don't know if that is significant. I haven't opened the pump because I want the engine rebuilder to see it first.
Now I can drive without the oil pressure worry.
Thanks for the help with this problem.

ralph what kind of pump and where did you get it. i have the same problem thanks lyle

Lyle, I got the pump from Alan Whelihan in Maryland. Ph 301 874-5464. Email awhelihan@netzero.com. The pump is an M-15 pump. Give Alan a call. He is very helpful. Ralph

The M-15 pump I got from Alan and installed in my 36 at overhaul about 5 years ago (had to remove extra baffle from bottom of pan and adjust pickup depth as Peecher mentioned) is the best thing I ever did. It holds great oil pressure instantly, and even stays above 40 psi hot, over 30 psi hot at slow idle. Even with the solid non-adjustable lifters, 10W40 oil takes up enough slack to keep the valvetrain almost totally silent. I was really surprised at how quiet that HV12 idles!