Shut up Mark. That's not a bad idea. I'm sure your wife won't mind! Really though I do have an oven in the shop.
The cavity certainly grows, yet is restrained by the fasteners holding the cover and is a battle of material will. The influence on oil pressure of increased clearance vs aeration is what is hard for my imagination.
My money is on increased cavitation (at the boundaries) due to reduced viscosity lowering the pumps effective oil pressure output. Less true volume (due to the included air) means reduced pressure as air escapes where oil can't . IMO
Steve, Great thread and work. Best investigation I've seen here. Been following since you started. Keep it up.
Steve, I am not a proponent of any point of view here, just curious. I know that the timing cover will grow with heat, I think Mike T told me once that he observed something like 4-6 thousandths, in the cam thrust bumper to cover relationship, from cold to hot. I did have a customer bring me in a 455 once, with a hyd roller cam, that they had set at .005 on the stand, and the bumper was actually broken when I took it apart. It had also worn the cam into the block, so it sure looked like he had lost all end play. One thing is certain, room temp oil, and hot oil/cover data will be very different. I recall that George Sweesy's motor used to wrap the autometer gauge all the way around to the other side of the peg when it was cold.. high oil pressures were part of the package that kept that kind of motor alive. I got startled a couple of times, sitting in it, warming it up..the oil pressure gauge looked exactly like it was reading zero.. until you clicked off the motor and the gauge came off the other side of the peg.. Even with an external belt driven oil pump, the pump characteristics from cold to hot oil were dramatic. JW
All I know is I can take an ice cube and heat it up and it becomes a puddle. I can take butter, heat it up and have eggs over easy. So I don't doubt the power of heat. Ram put a rear axle heater, yes heater, on the new 1500 to warm the gear lube for better fuel mileage. Now thats crazy. Hot oil is thinner and will move faster thru smaller openings. It's all really irrelevant since there's nothing we can do about it. I wonder if someone were to mount a dial indicator on the pump while the engine was run on a dyno?
I have an old timing cover and an assortment of pump gears I may just try it out! It will gimme something to do after work in the name of curiosity hahaha, since it wont be very scientific.
Another thought I've always had was if metal expands from heat, doesn't it expand both inward and outward and not just outward? In other words, wouldn't it get "fatter" I know when yah have a rusted bolt you heat the threaded hole and it expands enough to release its grip on the bolt, how does the material (iron, steel, aluminum) expand outward ONLY?
Shut the engine off. According to what Jim is describing the cover is moving inward toward the block. That is really not what I would expect.
Instead of heating the oil to reduce the viscosity could you use something like spindle oil which has a low almost water like viscosity?
Mike, Not sure how it would relate back to motor oil. Mark, I'll be baking a timing cover tomorrow. Hope you're hungry.
There are these things called science and engineering. They and the people who practice them come under much attack lately from the people who don't, but I'm going to stick my neck out. I am an automotive engineer. Metal alloys are rated with something called a coefficient of linear thermal expansion, which allows a person to calculate to a precise degree the amount that a piece of metal made from that alloy will expand when exposed to a change in temperature. Buick timing covers are die-cast Aluminum. I'm not sure which alloy, and the expansion rate is significantly different for each alloy. For our reference purposes, I'm going to say they are made of A380. They probably are not, but A380 has a pretty high expansion rate. It likely expands more than the actual alloy that Buick timing covers are made from, so this is a sort of "worst case" scenario. Let's use a 120 degree Fahrenheit increase in temperature, like being at 70 degrees before you start the engine and then heating up to 190 degrees after running for a long time. 190 degrees is a typical oil temperature for most engines, most of the time. Keep in mind, the oil pump handles the oil after it has cooled in the oil pan a little. According to my calculations, that 120 degree increase in temperature would cause the A380 oil pump housing to expand by 0.00212 inches. The oil pump gears are steel, probably medium carbon. Steel alloys are fairly similar in their expansion rates so I'm going to pick 4140 alloy. Given the same 120 degree increase in temperature, the gear would expand by 0.00102 inches. The difference in expansion is 0.00080 inches. That is how much more the pump housing would expand than the gear. Keep in mind there are two sides to the gear, so the change in the actual gear tooth to pump housing clearance on each side of the gear would only be half that: 0.00040 inches. That is not four thousandths of an inch. That is four tenths of one thousandth of an inch. Which is pretty much nothing. If your gear to body clearance was 0.0020 in. on a cold engine, it will be 0.0024 in. on a hot engine. Nobody cares. Housing distortion from tightening the bolts is more than that.
Given the explanation from OddfireV6, which is THE BEST explanation I've read from someone who sounds like they KNOW about metallurgy, being he's an automotive engineer, Im betting it IS aeriation as Derek suggested. Reasons from my own experience in my GS 350: Extended highway driving, oil pressure drops to about 50/55 lbs, accelerate and it drops to around 45 lbs. Exit highway and stop ,hot idle pressure is NORMAL, 18/20 lbs. as usual. I had a hard time wrapping my head around this, if my pressure dropped that much from the oil being hot, then Id have like 0 pressure hot idle, BUBBLES At the track, oil pressure would go to 70 lbs, at 6 to 7000 rpm, NORMAL My theory is rpm is low at first, no bubbles, go down the track 7000 rpm, the oil is just getting aeriated, but my run is over, rpm comes down, 60 lbs, 50 lbs, return road 55 to 60 lbs, all normal. Another theory, those of us that DO NOT have overdrive, and have 3.42 gears or lower (higher numerically) and are spinning 3000 plus rpm on the highway @ 65 mph are going to experience aeriation and lowering oil pressure verses those with 2.56, 2.93, 3.08 gears. I believe now that its the rpm of the engine causing aeriation, NOT the oil pump or higher oil pressure. The Buick oil pan is pretty shallow, especially the 350, its more like an oil tray Derek, make a window in a 350 pan, then spin the engine to 3500 rpm under load for 15 mins. and see if the oil is aeriated I think Im going to invest in a deep pan from SRE before the aluminum heads.
I have had aeriation issues with this engine. The way I found to check it is with oil pump primer and drill make a test before putting push rods in lifters. If there is a problem there will be air bubbles coming out of lifter push rod holes. should get oil only with no air. I have found cracked pickup or a pickup gasket leakin air. It is very important to install new gasket and proper tork of the pickup bolts. always check this bearings dint like air. Dan
Aeration was actually Mikes suggestion. An oil temperature probe might show if there's an oil temp difference sffecting the pressure drop. If it's caused by highway engine speed then this has always happened since 1968. Mark, Both my 73 with 2.93 gears and my 72 with 3.42 do this although the 72 does seem to drop to lower pressure. But that could be due to bearing clearance differences. I can't believe the engine was designed to do this. Wondering if changes in oil chemistry since 1968 effects it. Much like fuel has changed over the years so has oil.
OK, my question is, do clearances inside the oil pump matter at all? Steve's results seem to suggest that they don't. If so, why did TA even bother to come out with a new cover for the 455? Why did people find the need for the bigger HV/HP pump kit if not to crutch the worn out covers in use? The Chassis manuals tell you to measure the protrusion of the gear faces above the timing cover gasket surface. That is to set the optimal end clearance, yes? Does it matter or not?
The factory probably didn't have multiple thickness pump cover gaskets to keep end clearance to .002 anyway.
