Oil Pump Relief Valve Shimming

Lets discuss my 401 oil pressure issues. The engine has less than 2000 miles and my oil pressure drops to about 18 psi at 60 mph. When I slow down the psi picks up tp 30+ psi when traveling around town. Installed a shim plus quart of lucas which raised my pressure to 18psi. Prior to the quick fixed the top end would start rattling at freeway speeds and would disappear when I slowed. Installed new pump gears and double checked the front cover housing and all is in spec. Starting to see spending big money in the future!
 
dave clifton said:
Original test run:
oil pressure (psi):

cold start-up:
1000 rpm = 40 2000 rpm = 45 3000 rpm = 50 4000 rpm = 50

hot (195°f thermostat open after 20 min drive)
700 rpm = 10 1000 rpm = 15 2000 rpm = 30 3000 rpm = 43 4000 rpm = 45

Test run with shimmed pump and previous oil and filter:
oil pressure (psi):

cold start-up:
1000 rpm = 53 2000 rpm = 57 3000 rpm = 60 4000 rpm = 60

hot (195°f thermostat open after 20 min drive)
700 rpm = 10 1000 rpm = 15 2000 rpm = 30 3000 rpm = 50 4000 rpm = 53

Today's and final test run with swepco 15w40 and new napa 1452:
oil pressure (psi):

cold start-up:
1000 rpm = 52 2000 rpm = 56 3000 rpm = 63 4000 rpm = 63

hot (195°f thermostat open after 20 min drive)
700 rpm = 5 1000 rpm = 15 2000 rpm = 28 3000 rpm = 44 4000 rpm = 52
Click to expand...

Hey guys! Thanks for the very informative thread. I've been curious about shimming oil pumps as well and I have always felt very comfortable that the information I get on this forum is accurate, so thank you. I do have a couple questions regarding this test. If someone can clarify, that would be great.

1. The only real change I see is in cold start up. All of the readings when warmed up are pretty much the same. The only minor change is at very high rpms. I'm @ over 70mph at 3000rpm so I see no advantage to doing this? Can someone explain why it's more important to increase your cold start pressure readings?

2. I noticed the final results with the 15/40 oil gave a reading of 5 psi hot @ 700. This be roughly the reading with the car idling in park/neutral. It would be lower in gear as the idle would be around 500-550rpm. Isn't that a pretty big problem? That seems really low compared to what I've read on this forum regarding minimum pressure at idle especially considering we're talking about a freshly rebuilt engine that has a shimmed oil pump.

My 39 year old 304a engine and un-shimmed oil pump w/ 110k produces 12 psi @ 550, 20 psi @1000 rpm. (15/40 or 20/50)

I know this isn't completely on topic but I found it odd that no one mentioned that reading being low. If someone doens't mind explaining, that would be great.

Thanks a lot,

jason
 
Last edited:
Hello all,

as a follow-up, I swapped my oil filter to a napa gold (wix) from a fram (the fram was nearly new) and my oil pressure went up about 6psi when I started her (caveat...not a nist traceable gauge). Although I was delighted to see the higher pressure, I'm still getting near zero when I stop coming off the highway and she's fully warmed up. Next step will be to pull the pan and pump and see what's up.

May you all have better oil pressure than me, jack
 
cearly said:
lets discuss my 401 oil pressure issues. The engine has less than 2000 miles and my oil pressure drops to about 18 psi at 60 mph. When I slow down the psi picks up tp 30+ psi when traveling around town. Installed a shim plus quart of lucas which raised my pressure to 18psi. Prior to the quick fixed the top end would start rattling at freeway speeds and would disappear when I slowed. Installed new pump gears and double checked the front cover housing and all is in spec. Starting to see spending big money in the future!
Click to expand...

Gee dave, those symptoms sound perzactly like what is commonly experienced with an sv engine that has major cam bearing issues. Such low miles too. Are ramblermotors as susceptible to top end oiling issues as the sv engines?
 
Jack, when you pull the pan you will know if your cam bearings are trashed, they'll be in the bottom. My 345 has an untold amount of miles, the guy I got it from said it had 88k on it when pulled, I pulled the pan and it was clean, no metal what so ever.
I began the process of removing bearing caps to check, all good for 88k, put her back together.
I did follow the pump shim procedure outlined in this thread as you will see by the previous post.
After running this engine with nothing but shims and a complete regasket, hot oil pressure at idle is 10 psi, with 15/40. With a rapid increase to 55lbs as I accelerate. And it never moves..as I came off the interstate this morning after a 45 mile trip at 60+ it dropped to 10 psi and came right back up.
These motors are hi volume low pressure, not like a Chevy or Ford, if you dont hear the lifters rattlin at idle hot your ok.
Hope this eases your mind a little
and as for daves 401, I agree with Scout boy. If he's added the shims and topped her up with lucas which is about 200 weight and 18 lbs is all she'll muster, cam bearings are gone for sure!!!
 
The cam bearing is toast on my '71 travelette. Found the pieces in the pan. So being rather handy, but never having done a cam bearing, how would it be replaced? And is it likely a new cam will be needed. Still driving the truck, just low oil pressure.

I know the process of pulling the lifters and front cover, it is the actual install of the bearing. Also since it happened, what causes it and how can one prevent it from happening again???
 
Well chappie the major cause of cam bearing failure in IH motors from what I can tell is improper revival of an engine thats been sitting, and just plain ol wore out.ive also heard that there was a delaminating issue but who knows if thats true! If your gonna replace the bearings, yank it out. The cam May be good but you can get a new kit cheaper than you can pull it and do it again. The cam bearings drive out and back in.
Imho, you can install the bearings with the proper tool and some in depth study of the oil hole placement. Also remember that the rear bearing needs to be cut into the rear oil port to feed the lifter valley, all in the rocker thread. As far as preventing this, proper oil maintenence and cranking the ol beast at least once a week will do the trick, no way to preent natural wear out, its inevitable.
Every thing you need to know is here and in the manual. Wish I was closer to alot of the guys on here I love this stuff and resurrecting these ol beast makes my heart happy. Guess its in my blood!
 
Just to clarify tow's point...by yank it out, he means the engine. This job must be done with the engine pulled. The cam bearings are replaced as a set, not just the one that failed. Unless the cam and lifters were recently replaced and still within spec and no abnormal wear present, you May as well figure on replacing those too, since they've got to come out anyway. Re-installing worn out parts at this stage is false economy.
 
This engine was rebuilt at one time and is still very tight with no smoke and good compression. That's a bummer about pulling the engine, I was hoping just the front bearing could be replaced with it in the truck. Of course if I'm going to pull it I might as well go through the whole thing, or drive it until it dies. As far as I know it's been working fine that way for years.
 
Even if only one has failed, you're likely to see de-lamination and/or obvious signs of wear on others. There's much to be said for having surfaces in frequent or constant contact wear together such as the cam shaft, lifters, and cam bearings. These engines have been known to run quite awhile in this condition, but yours will eventually experience catastrophic failure if let go long enough.
 
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