Post rebuild oil pressure

[Aaron65]

Hello,
I just had my 263 straight 8 rebuilt by my local machine shop…I’ve broken it in and have driven it about 75 miles or so. The hot idle oil pressure is low. Here’s what I’ve done. I drove it 30 miles today, went out and got a mechanical oil pressure gauge and hooked it right to the threaded area in the block where oil pressure is normally taken. I started it up and it had 17 lbs. of pressure at idle after sitting about 90 minutes. I drove another 20 miles and it had 7 lbs. At this point, winging the motor (not to redline or anything) in neutral brought the oil pressure to about 37 lbs. When I started it before the ride (not with a cold engine, mind you) it had 42 psi…My machinist, when I asked him, told me the mains, rods, and cam bearings all had between .0015 and .002 clearance. This doesn’t seem loose enough to have this low of oil pressure. The oil pump was not changed, as it was in excellent shape. I am running 30wt Brad Penn Break-in oil at this time. My machine shop will stand behind their work, but I’m wondering if there’s anything I’m missing…plus I’d rather not yank that big thing out of there again (although, of course, I will if it comes down to that)…any ideas? Thanks for any help…

[49junker]

it is possible you may have some particles from your machining and is getting trapped in the oil port. Or your pump or pick-up is weak or is not sealing correctly.

[denner]

The oil pressure may be OK as it is, the buick specs are 35 psi, but they dont state at an RPM. 37 at anything over idle speed is fine, if it idles at 7 psi and the lifters are quiet then the pressure at idle is fine. you could shim the relief spring to get 35 at idle, but then you would have excessive pressure, probably 65 or 70 at higher RPM. you would have to deal with pump drive gear wear, and probably see more bearing wear due to the excessive pressure. The last one I checked had 35 running and 8 at idle and the motor ran fine. The last small block I built for my 65 had 40 running and 6 at idle. Most cars have the low oil pressure sender set at 1 or 2 PSI before they turn on the light.

[brwinnett]

All of my reference books state that 35psi at 35mph is normal oil pressure for the straight eights with solid lifters and with hydraulic. Seven to 12 is considered normal at idle and in both cases I am referring to a warmed up engine. You might (questinable) get up to 42 with a cool/cold engine and thickened oil as a result of cold oil. When warmed up, back to the 35 at 35. Good luck.

[histbuff1190]

if it were my engine... i would run it until shes hot then change the oil. much rather get a case of oil than a complete set of internals for a straight 8! after the motor runs and is warmed up any particles left over from machining would be mixed up in the oil. drain the hot oil you get your block all cleared out. now, i havent EXACTLY had a whole lot of experience with Buick motors, but... the Chevy 305 in my driver grabs a hair over 60lbs when it starts up and never drops below 30lbs. also, i wont run any other oil but 20w50 STP or Havoline. have run motors on generic oils, valvoline, quaker state, pennzoil, mobil 1 and seen what happens inside. being a fresh rebuild (and not the worn out bits im stuck with) 10w30 STP is good stuff and ought to give good oil pressure. hope this helps~

[denner]

I think that 7 psi at idle is fine, the spec call for 35 psi hot but it doesnt specify an rpm for the reading. you could shim the relief spring for 35 psi at idle, but you would probably have 65 to 70 psi at driving speed which would wear the drive gear excessively. The 350 in my 65 has 9 psi at idle and 35 driving and has 40,000 miles on it and runs 6000 rpm at that pressure with no problems. if it runs good and the hydraulic lifters are quiet at idle 7 psi is sufficient to lube the engine, if you really do want more pressure try 40 wt oil. Buick oiling system is ahead of its time, most engines of the same time used a lot more oil pressure, modern engines use a lot less pressure 4 to 5 at idle and 30 to 40 driving, and the oil warning lights are set to 1 to 2 psi.

[Aaron65]

Thanks for the replies. I changed the oil to 15W40 and the pressure is the same. The thing that bothers me is that the thing had more oil pressure before the rebuild! Plus, I'm only driving it 20 minutes on a 50 degree day...I'm worried about driving it 2 hours on a 90 degree day! I'm talking to the machinist today, so I'll update later...

[jim.ketchum]

You mentioned that your engine was rebuild completely. Was the oil pump at least checked for volume and pressure? Most engine rebuilders will not do a complete engine without rebuilding or at least checking the oil pump. You may want to remove the pump and have it checked.

[Aaron65]

Oil pump was checked...it looks like the problem is the rocker shaft...they cleaned it up and it seems that too much clearance was left between the shaft and the rockers...more to come...