R1234

I fired up my rebuilt 327/350 hp. The motor was rebuilt by a local machine shop with a good rep. I followed the pulling the distributor procedure and primed the motor. I'm using 30 weight oil and high volume oil pump. After cranking motor, oil pressure reads at 12 lbs at idle of anything below 1500 rpm. It reads at 25 lbs at 2500 rpm. The oil line has air pockets at the lower idle speeds. When increasing to 2500 rpm the oil fills tube but leaves a one inch air bubble at the gauge.
The engine temperature is reading at 205 degrees.
Is this normal?
I haven't really pushed the rpm range yet to find out what the oil pressure will do at higher rpm's. I'm still puzzled as to why I don't have a higher oil pressure reading at idle such as 40 lb which seems to be the norm.

mrvette

First thing I would do is replace that oil relief pressure spring assy held in by the two bolts where filter screws on....after that, replace or at minimum, check oil pump....then check if lifters are snug/correct for the lifter bore, something about lifters sometimes too tall and allows leaking oil from pressure holes.....(just a vague rememberance there, and it might not even be chebby for that matter, but may be worth checking) after that, time to mike bearings....tons of fun.... :rolleyes: :mad :confused: :smash:

flynhi

Beware of using high volume pumps without a larger-than-stock oil pan. You can cavitate and not properly lubricate the bearings. This happened to me and caused a complete rebuild.
A high quality stock pump is all you need for the street.

redvetracr

68rdstr,
You paid a shop to rebuild your motor, GO BACK AND ASK WHY such low pressure. If they are as good as you thought they will help you. You do aslo realize the factory gauges are not the most accurate.
.......redvetracr

R1234

Just when you think your over the hump......... :cry

john's '81 mouse

Suggest you first hook up separate mechanical oil pressure gauge, if it reads low, like your gauge in your car, then I'd go and check the oil pressure relief valve spring. I also agree that you really don't need, nor in my opinion should you have a high volume pump, as a good stock pump is plenty enough for normal/street purposes.

R1234

When I first cranked the motor it was with the oil line hooked to factory oil gauge.
Switched to another aftermarket oil gauge and got the same pressure reading.

yellow 72

First and fore most, what redvetracr said :yesnod:

john's '81 mouse

OK, then it's fair to assume that you are getting an accurate reading of actual oil pressure. Since you paid someone else to build the motor, suggest you talk to them first, before you go tearing into it, but I really do think you should consider replacement of the high volume pump with a new melling or chevy stock oil pump. I've got much better oil pressure than your engine, and I am using a stock oil pump with new main and rod bearings, still standard, after my new camshaft install last fall. I have 35 to 40 lbs. at idle, with warm engine and 10W30 weight oil.

R1234

Thanks guys, I'm going to give the shop a call. A question from a novice. How does the oil pump relief spring effect oil pressure?
Well, I rode down to the shop and was told that this oil pressure is within specs. 10 lbs. for about 1000 rpm and 12 lbs at idle was good oil pressure and not to worry. The pressure would increase to 25 lbs at 2500 rpm.
I also pulled the oil filter and took out the spin on piece to check oil pressure relief spring. It was seated and seemed to work okay when I applied pressure.





[Modified by 68rdstr, 11:18 AM 1/14/2002]

R1234

And as for the air bubbles...They told me that was normal and would always have them. :confused:

MILO851

air in your oil line will affect pressure air will compress oil will not crack the oil line at the gauge to bleed the air then check I think it will affect pressure good luck :cool: Larry

R1234

Thanks Larry I'll try it.

john's '81 mouse

Quote: "Well, I rode down to the shop and was told that this oil pressure is within specs. 10 lbs. for about 1000 rpm and 12 lbs at idle was good oil pressure and not to worry. The pressure would increase to 25 lbs at 2500 rpm."

The shop didn't lie to you, 10 lbs per 1,000 rpm is generally viewed as acceptable minimum oil pressure, however I submit this oil pressure, using 30 weight oil, after a fresh rebuild is lower than what 90% of the informed forum members would expect to have / see. You can't properly check the oil pressure relief valve spring by pushing on it. If you push it in and out, all you've done is verify that it's not stuck, you haven't verified that it's not too weak.

If the camshaft, rod and main bearing clearances are within factory specs, then I still say you should be seeing better/more oil pressure.

R1234

John, so what your saying is that a weak pressure relief spring will cause low oil pressure. I'll replace it. Can it be bought at a local auto supply house?


I don't really know what to do about the machine shop if it's within specs.

68shark

68rdstr....my engine was rebuilt last year. Bored .30, new pistons, Comp Cam as below, new oil pump. Pre rebuild idle psi was about 8, but knew car needed the rebuild so expected that. After rebuild, idle pressure (warm) with 10W30 oil was around 25-30, would nearly peg guage at higher rpm and cold. I'd say at 10 that you are at the low end of the range and maybe something isn't right. I agree with an earlier post that suggested you take the subjective feedback of others back to the shop. My engine, not the numbers engine though, is an original '68 327 and would be a good comparison for you. Good luck!

mrvette

anyone can argue specs, but I still think you have a tired relief spring, easy to overlook in a rebuild....and/or a 'bad' pump....put an extra quart of oil in it to see if maybe maybe the pump is cavitating with pickup too high for pan level...another thing is possibly wonder if the pickup is loose, allowing air into system...now alot of shops spot weld the damn thing into place, as it's a hammer/pressure squeeze fit from the factory...and IF it's leaky at that point from pickup pipe to pump....well.....

GENE

R1234

I'll start by replacing the relief spring and then move on to the oil pump.
Maybe I can get to the bottom of this. I shall not swear, I shall not swear, I shall not swear..........
Thanks for all the suggestions.


[Modified by 68rdstr, 1:53 PM 1/14/2002]

Matt Gruber

what is the pressure at 5000?

R1234

drives61,
I don't know. I didn't have the nerve to rev it that high.