The Stovebolt Site Forums The Shop Area Engine Shop 261 swap oil pressure

After spending my spare time this winter putting a 261 in my 1939 Chevy 1/2 , I took it for its first test drive tonight. When I first started up the engine to set the timing the oil pressure gauge was pegged. I kept the stock gauge. When I started driving it the gauge read about 20 lbs. Is that enough? I did notice that I had oil dripping from where the distributor meets the block after I got it home. I'm going to double the gasket before my next test drive.

A gasket where the distributor enters the block?

There is a pressure "cut off" spring in the oil pump (I think). I think it is supposed to be set to 45 psi (it is set to 30 psi in my 1960 261).

If it doesn't go up, and it's working, it's not enough.
What weight oil?

The stock gauge has a range appropriate for a low pressure splash oiler while your 261 is an pressure oil motor. You probably aren't going to get accurate meaningful oil pressure readings from the stock gauge with this setup.

When I first got the Blue Funk, I got concerned that the oil pressure guage ran high at 30. The Shop Manual said a high pressure for a 1948 to '51 could be indicative of a sludge condition.

After examination, I figured out the engine was a high pressure 1957, not a splash oil 1951. Normal pressure for a '57 235 was between 35 to 45. So, I figured the so-called high pressure on the guage was at a normal range for this particular engine.

Now OldSub is saying that I'm "probably aren't going to get accurate meaningful oil pressure readings from the stock gauge with this setup."

It seems to me that a pressure guage merely does just that: measures the pressure; whether the pressure comes from an oil splash or a high pressure engine.

I'm perplexed. Has my perspective been in error?

I don't mean to steal this thread, but thought my question just might help K9sicem, also. Even though his concern is with low pressure.

Thanks.

The engine is a 1959 261. I pulled the pan when I got it and the inside was clean. I was told this was a low mile replacement engine. The inside and outside would indicate this was true. I have 5-30 oil in it. After looking at the distributor I need to make a better clamp to hold it down. I have an HEI on it and the clamp is cockeyed. I don't this this would effect the oil pressure. The pressure was 30+ as i timed the motor and ran it in the shop. But dropped when I started to drive it up and down the street. Now it stays about 20-25 lbs. If in fact the gauge is the issue how much pressure should I have?

IMHO 5-30 is too light.

The splash oiler pressure gauges show a lower range than the later pressure oil gauges.

If your gauge only reads 0 to 30 but your actual pressure is between 30 and 45 you aren't going to have an accurate reading.

The oil pressure gauge on a '47 to '53 does in fact only read 0 to 30 while on a '54, the first year the 261 was available, the oil pressure gauge reads 0 to 60.

You can't accurately measure 35 pounds of pressure on a gauge that stops at 30.

Panic,

What weight oil should I use?

Anyone, Still would like help with my pressure issue.

Thanks

[quote=OldSubThe oil pressure gauge on a '47 to '53 does in fact only read 0 to 30 while on a '54, the first year the 261 was available, the oil pressure gauge reads 0 to 60.[/quote]

? Around these parts 60 LB gauges showed up in 1953 along with the 235 in 1/2 tons. Those gauges are delicate and any manhandling can disturb the calibration and I would suggest confirming the reading against another gauge.

For the oil...... try using a diesel truck oil....10W30 or 10W40....Shell Rotella as been good to my engine.

On the pressure..... install temporarily a off the shelf mechanical oil pressure guage with a 60 pound reading.....and report you reading...idle and at speed....

Bob

These engines were designed to use straight-weight oil, usually 30 weight in the summer, and 20W in wintertime. BTW, "W" stands for "Winter" not "Weight" as most people assume. A 5W-30 oil, for instance, has the flow characteristics of a 5 weight oil measured at 32 degrees F., and the lubricating properties of a 30 weight at full operating temperature, usually around 200 degrees F. It DOES NOT change thickness, remaining at the thickness of a 5 weight all the time. That's too thin for the clearances of a stovebolt engine, even a relatively late model one like a 261. I'd reccomend a 15W-40 diesel-rated oil for year round use. It had the extreme pressure additives including zinc, that are necessary to make the flat-tappet cam live a long and useful life, and the 15 weight base oil is thick enough to maintain good oil pressure. With good bearing clearances, I'd expect to see about 40 PSI or slightly more at a cold start, dropping to 25-30 PSI at hot idle. Don't get upset at low pressures at hot idle, 20 PSI or less, as long as the pressure rises somewhat when engine speed increases. Most "idiot light" warning systems turn on at 7 PSI or less. I've seen engines live a long time at 0 PSI idle pressure, and 15-20 PSI at cruise RPM.
Jerry

S.A.E. viscosity (grade, weight) is, by definition, thickness (flow resistance). It's derived from the time in seconds it takes for a given quantity of liquid to pass through a sized opening (not lubrication properties). Sometimes the S.U.S. (Saybolt Universal Seconds) standard is used instead, as in Harley-Davidson oil rating; 105 S.U.S. is more or less equivalent to S.A.E. 50.
A multi-grade oil's additives artificially thicken with rising temperature: 30 @ 212° etc.
I'd try 10-30, but if it doesn't pick up at cruising speed the oil isn't the problem.

I was under the impression that the new diesel oil does not have the zinc anymore.

All oil still has zinc,but many have a lot less.On a mild performance flat tappet engine,about 1200 PPM (.120) Zinc by weight is considered the minimum for long life.Some say older low rpm engines will be ok with less zinc than 1200.Diesels oils currently sold contain anywhere from about 890-1400ppm depending on brand and whetehr it's supposedly for older or new Diesels.Generally,20/50 and mono grade oils have more zinc than a 10/30 oil.
You can look up the data on oil manufacturers websites,no need to worry about it.

I'm going to try changing the oil. I'll post after I'm done and drove it around the block at time or two.

There is a possibility that the stock gauge (0-30 psig?) could have been damaged when the engine first started and pegged the gauge. What year is your 261? The 1954 261 should operate at 45 psig hot at 1200 engine rpm. The 1959 261 should run at 30 psig at 1200 rpm, also hot. Cold they should be in the 45-60 psig range. I'm not sure when the change was made. Check this link for specifications for other years. I would try running the engine with a 0-60 psig gauge that is known to be fairly accuarate before any drastic action is taken.

Hoyt

If the stock gauge was damaged would it have a reading at all when the truck was running? The gauge goes up to about 20 when the engine is running. I have not had a chance to change the oil and take it for a test run yet. I am making a alternator bracket. Then I'll change the oil and take it out to test.

A Bourden tube gauge (I think that is what is in your truck, but I am not positive) can be damaged if overpressured, but still respond. The Bourden tube can be stretched, bent, or kinked; the needle can slip on its pin; the pinion gear can slip a tooth, etc., and the gauge will appear to function but it will not be accurate. Most guage manufactures recommend recalibration or replacement if a gauge is sees more than about 125 to 150% of the full-scale pressure. There is also the danger of developing an oil leak. Your 261 should use at least a 0-60 psig guage.

Hoyt