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Jul 21st, 2025 | | | | Joined: Oct 2007 Posts: 45 'Bolter | | 'Bolter Joined: Oct 2007 Posts: 45 | I ran my '56 235 for about 30 min. today and the needle on the Stewart oil pressure gauge that I installed in the side of the block began to vibrate rapidly about +/- 5 PSI in time with engine rotation AFTER the oil was hot. That is, it vibrates slowly at idle and vibrates faster as engine RPM increases. It did not vibrate when the oil was cold. Pressure is 40 PSI when hot. Oil is clean Rotella 15W 40.
Could this indicate a bad rod bearing? I visually inspected the main bearings before I started this engine and they looked OK (I did not mic them) so I didn't pull the rod bearings.
Finally '54
| | | | | Joined: Nov 2006 Posts: 2,544 Shop Shark | | Shop Shark Joined: Nov 2006 Posts: 2,544 | Maybe try a different gauge? | | | | | Joined: Jun 2005 Posts: 388 Shop Shark | | Shop Shark Joined: Jun 2005 Posts: 388 | Is it a mechanical Bourdon gauge? Is the gauge directly connected to the oil gallery? A long, small diameter tube is often used to dampen the oscillations. Do the oscillations decrease in amplitude with higher engine speeds?
Hoyt | | | | | Joined: Aug 2009 Posts: 295 Shop Shark | | Shop Shark Joined: Aug 2009 Posts: 295 | The gage is seeing the pressure increase at each "strobe or lobe(??)" of the pump. Normal especially so at idle. Main concern is the bottom value.
You oughta see what piston or diaphram pumps do. Needle is all over the place. Often use oil dampened gage which may be a good choice if it bugs you. Also better for the movement.
Dan Bentler | | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | Make a restrictor out of a piece of brass with about a .020" hole in it and put it into one of the fittings between the engine and the gauge. It will dampen out the oscillations very well.
Jerry
Last edited by Hotrod Lincoln; 11/02/2010 4:22 AM.
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Dec 2008 Posts: 1,915 'Bolter | | 'Bolter Joined: Dec 2008 Posts: 1,915 | If it were the individual gear cycles, at 600 RPM idle = 300 RPM pump speed × 7 teeth per rotation = 2,100 cycles per minute or 35 per second. I don't think a gauge can respond that quick, and you couldn't see it. | | | | | Joined: Oct 2007 Posts: 45 'Bolter | | 'Bolter Joined: Oct 2007 Posts: 45 | Yes,it's a mechanical Bourdon tube gauge that's connected directly to the oil gallery. Oscillation amplitude appears to be about the same regardless of engine RPM. I just want to be sure that the oscillations do not indicate an internal engine problem. Oil pressure is otherwise OK.
Finally '54
| | | | | Joined: Feb 2004 Posts: 28,674 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 28,674 | You're probably just dealing with a very sensitive gauge. As long as the pressure is up to normal, it's very unlikely there's anything wrong with the oil system. Another approach to dampening the needle movement on a gauge is to plumb the gauge with 1/8" diameter copper tubing, and wrap 4 or 5 turns around a large socket, making a coil of tubing about 1 1/2" in diameter or so. The "spring" effect of the coiled tubing has a tendency to dampen any pressure oscillations before the gauge responds to them. If you hide the coil behind the dash somewhere, it's out of sight, out of mind.
Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!
| | | | | Joined: Oct 2007 Posts: 84 New Guy | | New Guy Joined: Oct 2007 Posts: 84 | How about a needle valve in front of the gauge? Works on my diesel fuel pressure gauge. Just crack open the needle until the oscillations are gone.
dg | | | | | Joined: Oct 2007 Posts: 45 'Bolter | | 'Bolter Joined: Oct 2007 Posts: 45 | That's a relief; I was afraid that there was something major wrong with this engine. Many thanks to all for your suggestions. I couldn't complete this restoration without you.
Finally '54
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