21 stud, 100lb oil pressure at startup then drops

[tgarner317]

Hey guys, it’s been a while since I’ve posted but haven’t been able to find a definitive answer to the oil pressure issue with my ‘36. The motor was rebuilt in 2003, sat in a garage for most of the time since then so the motor doesn’t have very many miles on it. As far as I know, this is a babbit bearing block. There are no bearings recorded on the rebuild receipt but there is also no mention of labor for poured bearings..

Oil pressure comes up to 100lbs immediately upon start up, but drops to @ 5-10lbs at idle when warmed up. Looking through receipts, engine builder purchased a “dm-19 pump kit” which if it’s the same as an M-19 pump kit I think that’s for an 8BA pump? And I’m not completely sure about the relief valve spring under the intake manifold. I know it was installed but I’m not sure if a 50 or 80lb spring was installed there.
I’m considering just purchasing a 50lb spring for the relief valve that’s underneath the intake manifold and installing a stock rebuilt oil pump.

Hope this all makes sense.. Thanks for your input!

[flatjack9]

What oil are you using? I would not change back to a stock pump.

[tgarner317]

Napa brand 30wt, I believe. I’d have to double check to be sure.

[Talkwrench]

If it is the later pump it would be 80 lbs , and maybe they took the other relief spring out of the block? Its not uncommon for them to have a low pressure at idle, probably just ware at the bearings . Mine does that too but I have to watch it as when hot the pressure drops of at speed.. Just make sure that isn't happening.

[flatjack9]

The relief valves in those pumps are usually set for around 50 psi.

[tubman]

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What kind of an oil pressure gauge do you have that will show up to 100 lbs of pressure? I'm no expert on '36 Fords, but I highly doubt they have 100 lb gauges stock (my '51 has only an 80 lb gauge). If you're pegging the stock gauge at start-up, that's probably normal with a later pump.

[Jack E/NJ]

Yeah. You gotta check those numbers out with a new mechanical well pump gauge from HomeDepot. $9.95 + tax. Jack E/NJ

[tgarner317]

Have a SW 100lb pressure gauge installed. Actually, this is the second SW gauge that has read the same pressure result.

I don’t know if the original oil pump was rebuilt or if a new pump was installed. Reading the paperwork, it sounds like they rebuilt the original pump which if the correct rebuild kit installed should t read more than 50lb, I’m guessing?

Could it be possible Hat the original pump was rebuilt with a later model kit?

[Jack E/NJ]

Maybe something gets hung up in relief spring barrel when cold? Probably need to warm it up and drive it around a lot more before doing anything more about it. Jack E/NJ

[tgarner317]

Oil pressure is typically between 20-45lbs max after driving for a bit. It’s just the startup pressure that really bothers me.

[Brian]

OK, I'll best first- what oil are you running?

[tgarner317]

Thought was Napa straight 30w oil, but is actually Car Quest straight 30w motor oil.

[flatheadmurre]

Going from a short straightgear pump to a long helicalgear means you get a lot more flow then it was from start.
Perhaps they reused the crank and bearings and compensated the wear with a "highflow" pump ?
I would start by checking the relief valve in the gallery and replacing it with a 50lbs.

[tgarner317]

Originally Posted by flatheadmurre

Going from a short straightgear pump to a long helicalgear means you get a lot more flow then it was from start.
Perhaps they reused the crank and bearings and compensated the wear with a "highflow" pump ?
I would start by checking the relief valve in the gallery and replacing it with a 50lbs.

I’ll do this first. I know the spring and valve was checked out by a mechanic who hadn’t worked on a flathead before.. I don’t think he replaced any parts, just kind of a general “looking over” and changed the oil. The oil pressure result was the same after he looked it over.

If the motor has the later model oil pump with 80lb relief valve and I install a 50lb spring and valve underneath the intake, I’m assuming this will work ok together? Seems like would be ok..

[JM 35 Sedan]

It might be helpful to know if you have poured babbitt main bearings, or insert main bearings (aka an LB engine). If you have an M19 oil pump, I would suggest staying with that, and making sure you have the correct sump pickup tube and screen. The M15 pump has the longer helical gears that produce higher pressure, and is normally used in racing engines with greater bearing clearances.
I would also check that relief spring and ball plunger, in front area of lifter valley, to make sure you have the correct parts.

[rotorwrench]

I like the plain 8BA type pump myself but OEM ones will generally do for the old babbitt block engines. Some of the Melling pumps have problems these days but at least that one is still pumping. The front relief valve check is a good idea. If someone blocked it and the engine is running on a later type pump with built in relief then there may be a problem with that.

On the old babbitt block engines, it's not uncommon to have low oil pressures at idle. As long as it is giving an indication and you see it rise with engine rpm it should be OK. They will run just fine for years of mild service with pressures like that. Cold oil will give a high pressure reading when the oil is new but I agree that 100 psi is out of the norm. On those systems, cold oil pressure really shouldn't be much over 80 psi.

Even a good mechanic can make mistakes when they are inexperienced with the older engines. I made my share back when I was younger but was lucky to have some good mentors. Experience is valuable and the lack there of can get expensive.

[flatjack9]

The M-19 pump would have a relief spring for 50 - 60 lbs, not 80.

[tgarner317]

As far as I know it is a Babbitt bearing block. The old receipts that I have of the motor being rebuilt doesn’t list any charges for insert bearings nor any labor for poured Babbitt bearings.. Maybe the old Babbitt bearings mic’d Out just fine and the rebuilder decided only the crank needed polished? That seems really odd, but there is nothing listed on the paperwork that supports either one.

[rotorwrench]

I would hope he did check the clearances all the way around. Finding someone that is experienced at cleaning out and recasting the babbitt is not as easy as it was back in the day but there are still a few shops that have the tooling & capability around the country and I imagine there are more than one on the west coast.

On the aircraft engines, we set the oil pressure relief valve on an overhaul first run after the engine is completely warmed up. When cold, the oil is slow to go through the bypass so the PSI can pick up 10 to 15 psi before it warms up. A flathead with two relief valves is going to be able to relieve through two valves if needed but if one is closed off, the other may be slower to pass until warmed up. Some folks close off the front relief valve on the early blocks when running a late type relief valve pump. It's hard to say what the guy did on the engine in question.

[flatheadmurre]

The relief valve in the gallery has a second function leaking it´s overflow to lubricate the camgear so blocking it off totally isn´t a real good idee..
You can change spring for higher pressure or shim the spring but i wouldn´t block it off totally using only the reliefvalve in the pump.