A highly loaded valve train (heavy springs to minimize "floating" at high RPM's) could require a higher HTHS. A higher compression engine may also require a higher HTHS to protect the rings and cylinders.
HTHS
- Thread starter MolaKule
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Again, I can speak here only for my engine. My stock 2.8 V6 Audi engine will certainly have valve float issues at high RPM without installing stiffer valve springs, so I doubt that the valve train is highly loaded in stock confuguration. This engine is also not considered a high compression engine. It's really more of a long-lasting workhorse. And yet it requires, like almost all conventional German engines, oil with a normal HTHS.
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I resemble that smilie.
PS: "confuguration" has to do with tasty, but toxic fish.
One thing I know is that the most common engine failures during high-speed Autobahn driving generally involve one of the following problems:
- seized rings/pistons
- cam bearing failure
- crankshaft bearing failure
In the case of BMW motors, throw in rod bearing failure.
PS: "confuguration" has to do with tasty, but toxic fish.
One thing I know is that the most common engine failures during high-speed Autobahn driving generally involve one of the following problems:
- seized rings/pistons
- cam bearing failure
- crankshaft bearing failure
In the case of BMW motors, throw in rod bearing failure.
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Mola, I wish I knew. Most likely it's due to a combination of factors?
Hi,
the reason for failures with some German engines is excessive oil foaming and excessive volatility during use at constant high revs
Some of the causes remain a bit of a mystery especially with older engine families but certainly crankcase breather design and ring/piston/bore position/structures play pivotal roles
As well many vehicles simply run low on oil!
This is but one reason why many German cars have an oil level sensor fitted as standard (Porsche for since 1977)
This is an interesting thread but sadly will probably be inconlusive
Regards
Doug
the reason for failures with some German engines is excessive oil foaming and excessive volatility during use at constant high revs
Some of the causes remain a bit of a mystery especially with older engine families but certainly crankcase breather design and ring/piston/bore position/structures play pivotal roles
As well many vehicles simply run low on oil!
This is but one reason why many German cars have an oil level sensor fitted as standard (Porsche for since 1977)
This is an interesting thread but sadly will probably be inconlusive
Regards
Doug
MolaKule
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Mori,
Just wondered if that was due to lack of oil getting to these parts for cooling, lubrication, underdesigned parts, or some other cause.
Thanks
Mola
This may explain why Mobil 1 10w30 is a bit on the thin side for kinematic 100C viscosity, whereas a VII fortified oil may need a thicker viscosity to attain the needed HT/HS. Also, why Redline has such good HT/HS that they say you can run one grade thinner with Redline.
I wonder how many of these engines would have survived if an oil temperature guage was present and the driver was instructed not to drive hard above a certain temperature on the guage?
One of my cars came with an engine oil temperature gauge, trust me it's not comforting on a hot day
Thanks Brother Moribund,
IronHorseman answered your question well .............it's high sliding speeds that define a high rate of shear. You ask a good question here aggain. I'm no expert but I have been told that HTHS is most critical at the main bearings (at high speeds) and I think Brother Molakule has alluded to that. We could calculate the maximum sliding speeds for the pistons at a given RPM and compare to the speed at the bearings in inches per second which is:
(pi X journal diameter x RPM)/60
Do any of you mechanical engineers know an equation for the max speed of a piston versus RPM. Don't keep me up all night trying to derive it. It obviously goes up with stroke at a given RPM since the piston travels further per crankshaft turn as the stroke increases. Those 19,000 RPM F1 engines are short strokers for sure!!!!
Thanks,
1911
In my experience the common failures are the cams at the furthest oil flow or random cam bearing failures (some are fine, others are scuffed). The latter is usually attributed to manufacturing defects in the hardening process.
I have not seen (in formula Super Vee) failures related to just oil.
The cam lobes are not that often involved, particularly in high revving engines. There are reasons for this.
aehaas
I have not seen (in formula Super Vee) failures related to just oil.
The cam lobes are not that often involved, particularly in high revving engines. There are reasons for this.
aehaas
Thanks Doug, good points. Also, we know that excessively high oil levels are also associated with excessive foaming. One time , I visited TExaco's old lube research lab in port Arthur, TX and they said they always worried about the effects on foaming resistance that all the various aftermarket oil additives could potentially have. They said that's another good reason to just run motor oil in your motor oil unless you have a lab at your disposal !!!!
Goodnight,
1911
If you are asking about instantaneous velocity of the piston, the equations are kinda messy and you need to know rod length also. Mr Google can probably find the equations for you fairly quickly.
Look for instantaneous piston velocity rod length calculator
Or would have survived if they had been running Redline oil?
Hi,
1911 - I have the equations (max piston velocity & etc)if you want them, contact me privately if you wish. They will only be approximate though if the con-rod is on a tangent with the big end trajectory
Regards
Doug
1911 - I have the equations (max piston velocity & etc)if you want them, contact me privately if you wish. They will only be approximate though if the con-rod is on a tangent with the big end trajectory
Regards
Doug
MolaKule
Staff member
It is a bit more complex than that.
One has to know the theta(t), the angular displacement function as a function of time.
Take a V8 engine whose displacement function at idle with a 0.36 m diameter flywheel is
theta(t) = (2.0 rad/s^3)t^3 .
The average angular velocity, omega, over 3 seconds is 78 rad/s or
omega (average) = (theta2 - theta1)/(t2 - t1) = 78 rad/s X (1 rev/2*pi rad) X (60 s/1 min) = 740 rev/min .
Since linear velocity is equal to the rotational velocity times radius, v = w X r , then the average linear velocity for a crank of 2" radius is:
v (average) = 78 rad/s X 0.051 m = 3.96 m/s. = 3.96 m/s X 3.281 f/m = 13.0 fps. This is the average linear velocity of the piston.
Now this assumes the crank centerline and wristpin is centered to the piston centerline. Small geometrical differences in engine design would change the numbers slightly, such as for offset crankpins.
One also has to remember that piston velocity is a function of time.
1. At TDC and BDC the piston velocity is zero.
2. The piston reaches maximum velocity halfway between TDC and BDC, since the motion is Harmonic or sinusoidal.
One has to know the theta(t), the angular displacement function as a function of time.
Take a V8 engine whose displacement function at idle with a 0.36 m diameter flywheel is
theta(t) = (2.0 rad/s^3)t^3 .
The average angular velocity, omega, over 3 seconds is 78 rad/s or
omega (average) = (theta2 - theta1)/(t2 - t1) = 78 rad/s X (1 rev/2*pi rad) X (60 s/1 min) = 740 rev/min .
Since linear velocity is equal to the rotational velocity times radius, v = w X r , then the average linear velocity for a crank of 2" radius is:
v (average) = 78 rad/s X 0.051 m = 3.96 m/s. = 3.96 m/s X 3.281 f/m = 13.0 fps. This is the average linear velocity of the piston.
Now this assumes the crank centerline and wristpin is centered to the piston centerline. Small geometrical differences in engine design would change the numbers slightly, such as for offset crankpins.
One also has to remember that piston velocity is a function of time.
1. At TDC and BDC the piston velocity is zero.
2. The piston reaches maximum velocity halfway between TDC and BDC, since the motion is Harmonic or sinusoidal.
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This whole ordeal of bending oil is making me sinusoidal.
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