Packard Forum Index » Pre-War (1899-1942)

Hi all,

What should my oil pressure be at idle on my '36 std 8? I get about 35 to 40 when driving (depending on how hot the engine is) but when it's hot and I'm at a light idling it drops down to 5 maybe - always scares me.

In light of what I'm finding with the valves (that's a whole other saga) I'm worried that maybe the guys who put the engine together the first time may have screwed up the main bearings as well.

I just found out the they never machined the cyl head - so it wasn't the head gasket it was that the head was still warped. So now I'm getting that machined flat and doing a full valve job but am a little worried about that oil pressure.

Thanks,
Crin

Can't help on the oil pressure question but since you are getting the head milled be sure to check valve clearance before bolting the head. Am assuming clearance is as tight on prewar as postwar heads. Several have found out the hard way their heads had been milled before and were thin and couldn't take another milling. The edge of the valves hit the head and in a couple of cases were bent because the head had been bolted down.

Your oil pressures sound completely normal. I believe typical minimum oil pressure values are stated in the owner's manual and you should buy one if you haven't, and read thru it. For my '34 Eight, same basic engine and oiling system as yours, hot idling pressure is 3 (or is it 5?) psi, and 35 psi at roadspeed.

Set your relief valve to give at most, a maximum of 55, its important as excessive pressure can damage the aluminum crankcase casting or even split old filters open at the seam.

DO NOT mill or surface-grind your cylinder head unless absolutely necessary! If there are no surface defects (for example, corrosion pitting around water passage openings), simply being warped by ten thousandths or so is NOT a reason to resurface.

I am in agreement with Dave (O_D) and I can't remember who posted a while back that they had put their head on a flat surface, with blocks under both ends and a nominal weight centered on top (40 or 50#'s) and then checked the head for warpage and found it had distorted by ten or so thou. His comment was (I'm paraphrasing here...) 'with 23 head studs all pulling the head down to the block at 65 foot pounds, I found something else to worry about'. Unless the block is significantly warped or, as Dave says, chipped or corroded, machining should be a last resort. Chris

Exactly on machining the head.
With new head gaskets in the sixty thousandth of an inch thick range, theres a lot of room for some slight distortion.
I do think in period service machining a straight eight head was probably sold many times as an extra-profit item, thus there seems to be quite a lot of heads over machined.

In regards to the idling oil pressure, I'm sure the noted five psi is fine, but if it were my engine I would change the oil (if not done recently) and temporarily plumb in a known accurate gauge, maybe 0 to 60 psi range to verify the accuracy of the OEM gauge. If it is OEM circa 1934, it won't do any harm to check it.

Thank you all for your help. Hopefully with all newly ground valves and seats it'll run as it should. It was never right from the get-go.