revving the motor while cold?

[subway]

Until the oil passages all get full of oil and you have good stable oil pressure you have metal on metal in all the crank, main, & rod bearings. During normal operation high pressure oil actually forms a cushioning layer between the bearings and rotating parts to where they don't actully even touch each other. If you don't wait until the pressure is up before you start to rev it, you are putting all the stress of revving it on the bearings while the parts are still metal on metal - before that cushion of high-pressure oil is there to keep them from actually touching.

i agree with most of that but there should be a residual oil left in the bearings to hold up for a short time till they get fresh oil from the pump. if you actaully get it to touch metal to metal it would be over real quick with even just a couple of shavings taken off.

i have also been told beside the bearings its real ******* the cylinder walls because they are reletivly dry during start up.

he need to do some trouble shooting running on a few cylinders is also putting all the stress of spinning the motor on only a couple of connecting rods, not good. its his truch though......

 

[Agnem]

Just tell that guy that the next time he is in a deep sleep, have somebody jolt him awake and make him run up a flight of steps as fast as he possibly can, then stop and eat breakfast. If he feels good, then gee it must be good for you.

Never mind the fact that steel expands as it heats. Uneven heating is not a good thing.

 

[Cheaper Jeeper]

Until the oil passages all get full of oil and you have good stable oil pressure you have metal on metal in all the crank, main, & rod bearings. During normal operation high pressure oil actually forms a cushioning layer between the bearings and rotating parts to where they don't actully even touch each other. If you don't wait until the pressure is up before you start to rev it, you are putting all the stress of revving it on the bearings while the parts are still metal on metal - before that cushion of high-pressure oil is there to keep them from actually touching.

i agree with most of that but there should be a residual oil left in the bearings to hold up for a short time till they get fresh oil from the pump. if you actaully get it to touch metal to metal it would be over real quick with even just a couple of shavings taken off.

i have also been told beside the bearings its real ******* the cylinder walls because they are reletivly dry during start up.

he need to do some trouble shooting running on a few cylinders is also putting all the stress of spinning the motor on only a couple of connecting rods, not good. its his truch though......

Yes, there is a residual film of oil - I never said there wasn't. What isn't there is oil pressure which is actually what prevents metal to metal contact in the bearings. The oil being forced through the small amount of clearance between the journals and bearing inserts under high pressure actually "suspends" or "floats" the journals inside the bearing inserts.

That is why oil pressure is so critical - that and keeping the lifters pumped up. It doesn't take more than 1 or 2 PSI - if the flow is of sufficient volume - to push oil to the upper areas to lube the valve train. It takes significantly more pressure than that to keep the journals "floating" on a cushion of oil - including cam journals.

 

[Cat_Rebel]

Yeah that truck needs work if it's starting that hard. I replaced the glow plugs on my truck & it will start on even a 0* day just fine. I don't even have to give it any throttle to help out.

 

[BigRigTech]

I just turn the key to run, wait the 8-10 seconds for the wait to start light to go out and tap the throttle once gently before starting it....Fires right up and idles about 950-1000rpm when cold.....That guy is a tool and a repair shops potential retirement plan....

 

[dieselrunner]

I heard that the pistons on these IDI's are aluminum. and with the heat generated from cumbustion the aluminum will expand more rapidly and either skore the cylinder walls or sieze in the cylinder.

are these common concerns? or even concerns at all?

 

[FordGuy100]

Nope, I wouldnt really think that would be a problem. Pretty much all engines use aluminum pistons as far as I know. And if you get your EGT's up much past 1200* for very long, then you will actually melt the pistons. At that point I dont think the skoring on the cylinder walls matters, because you already just totaly screwed your engine.

 

[rubberfish]

EGT's up much past 1200* for very long, then you will actually melt the pistons.

Hey. Pay attention in school eh.
Aluminum begins to melt at 1470 F

 

[6 Nebraska IDIs]

Dont poke him too hard fish, I've seen one with holes in the pistons when ran at 1290*. Its possible, and in fact its down right reckless to run these engines up over 1200*.

Cars on the other hand, gasoline turbocharged engines will run 1400*+.

 

[sootman73]

also remember the gas laws! higher pressure also equals higher temperature. you may not see such high temps at the egt probe as are what are actually inside the cylinder!

 

[rubberfish]

I'm not meaning to razz him too hard.
He's seen how high I run my pyro.

 

[6 Nebraska IDIs]

Haha, I know you werent, I was just sayin. lol
I've seen one have the pyro pegged up a hill and it didnt turn out so good. lol

 

[FordGuy100]

Hey. Pay attention in school eh.
Aluminum begins to melt at 1470 F

What exactly are these pistons made up of? I mean obviously they have aluminum in them, but I wouldnt think they are 100% aluminum, they have to have other elements in it. By the way, pure aluminum has a melting point of just over 1220*F.

And yeah man, I saw your pyro run, holy **** man that is crazy, you almost need a gasser pyro

 

[icanfixall]

I worked on the steam turbines in power plants most of my adult life. The operators needed something called a lift pump pushing oil directly under the bearing journels before they could start the rotor turning. This lift pump was about 300 lbs of oil and that pressure could and did lift the rotor that weighs 160 tons. Very little effort was needed to start it rolling. The main turbine oil pumps were around 100 lbs and that protected the bearings at 3600 rpm with a tremendous load applied to the system. The rotor actually moved over in the bearing because of the oil vedge it made. Our motors act the same way. The oil protects and displaces the trash and heat by flow. Without oil things stop really quickly. We lost all oil pump power and the backup failed too. All this at full load turning 3600 rpm. Talk about heat, metal and noise. 50 tons doesn't just stop right now and being 1050 degrees bends the rotor upwards instead of downwards because its shrinking faster than the turbine shell.... Big mess..... Many deaths.... You make big ###up.

 

[Cheaper Jeeper]

Pure aluminum may melt at 1220* F, but the melting number I have most commonly heard referenced for the alloy in our stock pistons is 1250* F for a pyro probe IN the exhaust manifold. If your pyro probe is post-turbo (like mine) you have to adjust that number downwards about 100*F to allow for cooling of the gasses as they pass through the exhaust pipe and turbo impeller.

I believe that 1250* number already has about a 50* downward adjustment to compensate for the fact that the in-cylinder temp is just a tad higher than the temp in the exhaust manifold. The actual melting point for the alloy in the pistons is probably closer to 1300* F. Even that 1250* F number is the "safe limit - as in OK for short periods, but not for extended amounts of time.

Sootman has a good point about pressure - though I think it is important for a slightly different reason. Just like a cutting torch, where the heat alone doesn't do the whole job of cutting through the metal, the extra O2 at high pressure aids the process. In the cylinder of these old motors at running at 22.5:1 compression (6.9) and 21.5:1 (7.3) the extreme pressure at TDC can help the heat to blow-torch a hole through the top of the piston if the temperature of the piston top is allowed to get too high.

Just my $0.02