The Stovebolt Site Forums The Shop Area Engine Shop 1958 261-CID oil pressure -- SOLVED

Greetings Stovebolters

I have a 1958 261-CID inline in my 1954 3100. When I first fire it up my pressure gauge registers around 15#s. What bothers me is it doesn't show much at all on the gauge after I run it a bit and its warmed up. I had a guy down at my local parts store tell me that an oil pump either works or it doesn't work - no in between. I am having a hard time believing this. What the possibility that my oil pump is failing. The engine doesn't burn any oil and the engine produces 130-135#s compression when I tested it. It is a used engine I lucked into.

I would appreciate your comments

Walt Williams
La Verkin, UT


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It turned out to be a bad oil pump. I made this determination after finding out that there is a pressure release valve on the oil pump and after checking the the #2 main bearing with plastigage and found I have .002 clearance. The truck now maintains a solid 30#s while cruising, and after the engine is heated up it will still drop down while waiting at a stop light but not to zero and it no longer starts making bizarre noises while waiting for the traffic light to change. This behavior matches my 54 Chevy sedan.

Thanks for all the great tips.

Walt Williams
La Verkin, UT
Photo of Franky, my truck

more likely to be a gauge inaccuracy or some internal problem than a worn pump - have you tapped in a good test gauge? .... but it's not a major job to replace the pump and find out

Bill

What the guy told you was wrong. Oil pumps do wear and can cause low pressure. However, this is not a comment on your situation.

I would bet on loose bearing clearances.

X2. I would expect bearing shell babbitt to wear a lot faster than hardened gears.

I vote on the worn bearings.

A marginal pump might give 15# readings with thicker/cold oil and lower readings with thinner/warm oil.

My Suburban's 1954 engine had the same symptoms but the culprit was worn bearings.

Depending on the engine history, if it was rebuilt, were the cam brgs. replaced? As was said above-stick another guage in the block.

Just had similar problem with my 235. I dropped the pan and did see evidence of worn bearings. I changed to heavier oil and pressure is consistent now.

I had a similar problem years ago with a 235 that would not hold oil pressure after warmed up. It turned out to be cam bearings - too worn.

It's interesting that this thread has come up now as my 261 is dropping oil pressure. It starts out with 50 psi cold and when hot gives me a healthy 15 -20 psi but at low idle it will suddenly drop to 0, I'll shut the engine off restart it and it will show 15-20 again. I have my fingers crossed that it's the gauge and it will be the first thing I replace with a quality unit but it has me a little worried right now. I don't think too large bearing clearances would cause an intermittent problem like this but what else besides the gauge could it be?

-mike-

The oil pressure regulator is the only thing thst comes to my mind. If it is sticking as the volume drops, as speed drops to idle, then it will drop the pressure as you described. Bearing clearances do NOT change for a restart.

So would that be the bypass valve in the filter canister housing? I cleaned it really well a while back but the parts are old, are replacement parts available?

If you want to eliminate the full-flow filter unit from this consideration, disconnect the hoses from the unit and get a fitting that allows the two hoses to connect to each other (or, make a long hose to run from input to output holes in the block). Of course, keep the oil pressure sender connected somewhere in this temporary set-up.

TC.......That's a good idea, would removing the spring and plunger out of the valve give me the same thing?

All of this for test purposes as I'd really like to keep the full flow filtering.

sleeve,

I also like the full flow filtering unit.

I have not taken apart the head on the 261's full-flow filter. I'd try what you describe if it looks like you'll get unobstructed flow. Maybe also take out the filter?

My guess is that spring/plunger is a safety by-pass, in the case of the filter clogging and stopping flow?

.

I have discovered that not all 261s are full flow filtering systems. Mine is a bypass system like the 235 in my 54 sedan. And there doesn't seem to be anyway to change it to be a full filtered system.

Walt

1954-1957 USA 261 truck engines use a by-pass oil filter
1958-1963 USA 261 truck engines use a full-flow oil filter
All USA 261 engines had mechanical (solid) lifters

All Canadian 261 engines (car/Pontiac and truck) use a by-pass oil filter (all years)
All Canadian car/Pontiac 261 engines had hydraulic lifters.

tclederman

According to my casting number on my 261 is a 1958 engine and yet it seem to be strictly a bypass filter engine and has solid lifters. (My 261 is in my 54 pickup.)

Is there a way to check if my engine is a Canadian engine?

Walt Williams
La Verkin, UT

Post the engine serial number.