My original capillary style pressure gauge was stuffed when I bought the car so I did the manual check with a test gauge and all was good.  (I have a worked 350 SB Rebuilt to LT-1 specs) I'm not overly worried about correct equipment as I bought the car to be driven, so decided to fit some reliable electric gauges.  In the process I thought it time for an oil change and filter so did it at the same time.

Cranked her up.... Oh Oh no oil pressure!  Or at least very little.  Put the test gauge back in and sure enough the pressure had dropped right off.  For chrissake, all I've done is change the filter and oil!!!!

Engine still running nice and quiet other than the lifters not pumping up properly at idle due to lack of pressure.  What have I done???  Dumped the oil and it looked all grey and frothy.  The oil had somehow become aerated or at least that's what it looked like.

Decided to drop the sump and pull the oil pump.  Sure enough the pump was broken.  The spring for the pressure regulator valve in the pump has snapped in three places so the valve was wide open all the time.  Of course this allows very little oil to be pumped up the main gallery.  So most of the oil was just being recirculated in the pump.

This pump is a standard pump so I'm about to whack a high volume pump in.  While I have the sump off I thought it a good idea to check crank and rod end play which was all good.  I've not had this engine apart but it looks like it has been rebored with OS pistons (even though it's pretty hard to be sure from the bottom).  Everything looks good from the bottom and nothing nasty in the sump so here's hoping no damage has been done anywhere else.

My 69 SB runs at about 65lbs oil pressure also. I wouldn`t worry about.

Just picked up my new pump (a high volume, high pressure unit) and it is rated at 70lbs.  It also has a note and extra regulator spring with it which says if you don't want the extra pressure as with some older engines that may blow seals etc, you can put the other spring in to drop the pressure back to 50-60lbs.

Really cheap fix for a problem I thought was going to cost heaps.  $AU85 for the pump and $AU11 for the sump gasket kit. Runs out about $US73.

Need help.....!

My new pump is different to the old one so the pickup doesn't fit.  Well after much gnashing of teeth and running around to parts shops, I decided to look in my workshop manual (for the first time).

D'uoh.  I have a BB pump (12 tooth gears) in my SB (normally 8 tooth gears).  This is also why the pickup doesn't fit on the new one.  It's a bigger diameter for more oil flow and bends in the other direction. After checking all clearances in the old pump, they check out ok.  All there is, is some small scarring on the gear faces but no wear to speak of.  So the pump looks good to re use and I'd rather have the bigger smoother running pump anyway.

Problem is that I have pulled the broken relief valve spring out (it was in about fifteen pieces) and all I have is a SB (8 tooth gear) pump spring.

Does anyone know if the SB spring will give me the same relief pressure in the BB pump?  The busted spring seems to be a larger gauge wire to the new one and the bits that still have tension seem to be a bit stronger than the new spring.  But I don't know what work has been done to this pump in the past, it may have been modified for higher pressure which I don't think I need.  After all I'm not going racing.

Looks like I'm answering my own questions here but that doesn't matter, it may be of interest to you guys.

I have been reading various bits and pieces online at different hot rodding sites etc.  One was saying that a BB pump in a SB engine is good due to it having 12 teeth on the gears.  It seems that the smaller 8 tooth variety can make the distributor have timing transients due to pulsation of the oil pump.  Yeah.... OK..... well I took all that in and thought, OK it might be good to keep the BB pump in.

I have now made many many phone calls to local and long distance race engine builders and just about every one of them have said if I am running a BB pump in my SB, that is why the relief valve spring broke.  The reason is that the BB pump will be supplying so much oil in the smaller engine that the relief valve will be constantly wide open while driving rather than just opening a little to relieve pressure at higher revs.  Most said that they have never heard of this timing transient thing. They also said that the BB pump will supply so much to the top end that the valley and the tops of the heads will fill up and not be able to drain to the sump quickly enough to keep sufficient oil in the sump pan.  Maybe that's why I could never stop all the oil leaks.  I fixed most but always ended up with a small leak from somewhere I couldn't find.

So in the end I've kept the SB HV/HP pump that I bought and have just ordered a new pickup tube for it so I'm running with higher volume and pressure than standard but not blowing oil out all over the place. Learn new things every day.  I've done heaps of top end work to V8s but never much in the bottom end and never really had any problems with oil pumps.

I would have to believe the timing variations from the oil pump is a myth.  It does not make sense when you consider the pump operation.  There will be pressure on half of all of the gear teeth no matter what, and that will be steady with rpm and pump volume.  I never heard of it, and I'm not buying it.

All the other info you site makes sense. 

High volume pumps are not necessary for a standard normal engine.  A worn engine has greater clearances, and can benifit from a high volume to take up the space and maintain pressure. 

High performance built engines have greater clearances than stock.  The reason is due the increased heat in high performance.  It causes greater metal expansion, and thus closer clearances in many engine locations.  So the high volume is necessary at normal or low temps.