Searching for data - Official limits on maximum crank case pressure OM617 - Page 3 - PeachParts Mercedes-Benz Forum

Diesel911 · #31 01-10-2013, 01:00 AM

In reading the above I am wondering why His Wife was in the Car. This makes Me suspect that He did not just run the Engine at idle speed.

Before I checked mine with a Gauge I had read ForcedInduction saying that damage to the Seals was possible. I think that was in one Thread where I said I put My Thumb over the Valve Cover Vent Hole until the Engine started to slow and stumble and then removed it.
So I guess I was taking a chance also.

It is unforunate that did not save some Money and fix it Himself.

whunter · #32 01-10-2013, 01:14 PM

Quote:

Originally Posted by Diesel911

In reading the above I am wondering why His Wife was in the Car. This makes Me suspect that He did not just run the Engine at idle speed.

Before I checked mine with a Gauge I had read ForcedInduction saying that damage to the Seals was possible. I think that was in one Thread where I said I put My Thumb over the Valve Cover Vent Hole until the Engine started to slow and stumble and then removed it.
So I guess I was taking a chance also.

It is unfortunate that he did not save some Money and fix it Himself.

His wife was in the car to start and shutdown the engine, she did not touch the accelerator.

Chuckle:
He freely admits that "Top Gear, Jeremy Clarkson" is a wizard mechanic, compared to himself.

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Stretch · #33 01-10-2013, 01:20 PM

Quote:

Originally Posted by whunter

A local (Detroit Metro area) forum member gave me permission to post this, as long as he is not named.
********************

He became curious after reading this and related links.
His OM617 has some blowby, in my opinion low-average for 200k miles.

He blocked the vent with a gauge he rigged up, and his wife started the car.
It started normal.
A few moments later the engine slowed, almost shutdown as he watched the pressure rise.
The pressure suddenly dropped, and engine RPM came back up.

Roughly one minute later he asked his wife to turn the car off.
Nothing happened, so he walked to the driver door as his wife climbed out.
She handed him the key and asked why it was still running?

He drove the car over to me.
I turned it off with the shutoff lever, and confirmed with a hand held vacuum pump that the shutoff diaphragm is broken.

When he explained what he had done - how he thought it happened, I checked his engine oil level.
It was down almost two quarts, and he had changed the oil this morning.
He is very touchy about oil leaks staining his garage/driveway.
We have replaced the oil filter housing gasket, turbo drain tube gasket/O-ring/grommet, torque converter seal, transmission pump O-ring, etc, etc.
For the last two years there where no leaks.

It took a few minutes to verify the front crankshaft seal had popped out of place.
Using several special tools (not designed for the job) I pressed the seal back in place, and it may be OK, but will be replaced by a new seal ASAP regardless of whether it leaks or not.
He is horribly embarrassed, and ticked off with himself for not considering/understanding the risk involved.

The cost from his view:
* Two quarts of synthetic oil $15.50 each for his brand.
* Shutoff box + labor $170.00.
* Front crankshaft seal + labor $320.00
Total $515.00

.

That's not good.

That's not good at all - I'm going to put a warning at the top of this thread. I don't want to read that this has happened to someone again.

I am surprised to hear that the engine is so well sealed. I kind of expected that smoke would be puffing out of the sides of the rocker cover gasket or at the very least the oil filler cap before something like the crankshaft seal would go.

I know that in principle the engine should be liquid tight - I don't think it is designed to be so gas tight. I could / can certainly smell exhaust fumes from my engine when it is / was running. I felt that there must have been something else happening to cause the shut down observed by Diesel911 - that's why I started the thread.

Stretch · #34 01-10-2013, 01:51 PM

I don't suppose when the dust settles and all that, that we could be told at which indicated pressure the crank shaft seal blew?

whunter · #35 01-10-2013, 04:59 PM

Quote:

Originally Posted by Stretch

I don't suppose when the dust settles and all that, that we could be told at which indicated pressure the crank shaft seal blew?

Between 3 and 3.3 psi is when the seal failed.
He used a 5 psi gauge.

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Stretch · #36 01-11-2013, 06:45 AM

Quote:

Originally Posted by whunter

Between 3 and 3.3 psi is when the seal failed.
He used a 5 psi gauge.

.

Thanks for that - that figure compares favourably with Diesel911's experience.

3.1 PSI == 213.74 mbar (Convert psi to millibar - Conversion tables and calculators)

Not much is it?

funola · #37 01-11-2013, 09:51 AM

Quote:

Originally Posted by whunter

,,................
He is horribly embarrassed, and ticked off with himself for not considering/understanding the risk involved.

The cost from his view:
* Two quarts of synthetic oil $15.50 each for his brand.
* Shutoff box + labor $170.00.
* Front crankshaft seal + labor $320.00
Total $515.00

.

1. what is a shutoff box and where is it located?

2. do you have a part number?

whunter · #38 01-11-2013, 03:30 PM

Quote:

Originally Posted by funola

1. what is a shutoff box and where is it located?

2. do you have a part number?

shutoff box
MB# 0000702053

Shut-Off Valve @ IP aka Vacuum Control Unit or MB FSM-EPC = shutoff box

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Stretch · #39 01-26-2013, 09:33 AM

Does anyone know the pressure at which the shut off box starts to operate / or / the pressure at which it is at full travel / or / the minimum vaccum pressure at which it is meant to work?

(Yes I'm off on a different tack!)

whunter · #40 01-26-2013, 04:06 PM

Quote:

Originally Posted by Stretch

Does anyone know the pressure at which the shut off box starts to operate / or / the pressure at which it is at full travel / or / the minimum vaccum pressure at which it is meant to work?

(Yes I'm off on a different tack!)

The generic minimum vacuum required for consistent shutoff function is 13 hg.

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Stretch · #41 01-27-2013, 05:20 AM

Quote:

Originally Posted by whunter

The generic minimum vacuum required for consistent shutoff function is 13 hg.

.

Thanks for that - just to be clear is that inch hg?

As in 440mbar => almost half a vacuum(!)

whunter · #42 01-27-2013, 01:30 PM

Quote:

Originally Posted by Stretch

Thanks for that - just to be clear is that inch hg?

As in 440mbar => almost half a vacuum(!)

13 inches of mercury = 33 centimeters of mercury.

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Stretch · #43 01-28-2013, 04:48 AM

OK here's a summary of the two observations.

1) In both cases the crankcase breather system was blocked on purpose

2) In both cases the engines were just idling

3) In both cases the engine was reported to slow down before a final pressure reading of about 3 PSI was made

4) In both cases the engines either stalled or very nearly stalled at about 3 PSI

What have we learned so far?

Firstly => it is not sensible to block the crankcase ventilation <= You could blow out a seal

Secondly both reports say that the engine slowed at idle before the pressure of 3 PSI was reached.

If I have understood this correctly - people are saying that this is because the crankcase pressure acts on the IP side of the shut off valve.

If this is the case I guess one could assume that the shut off valve operates at a very low vacuum level - much lower than the vacuum level needed for a "vacuum required for consistent shutoff"...

...but I don't think so!

13 inch hg ~ 33 cm hg ~ 440mbar ~ 6.3 PSI

Compare those numbers with "the pressure at stall"

of 3.1 PSI ~ 220 mbar

#############

So I'm thinking the observations could have been influenced by something else.

What about pumping losses?

Could an increase in pumping losses - due to an increase in crankcase pressure - stall the engine?

I think so!

Take a look at this article talking about petrol engines and the effect of negative pressure in a combustion chamber on pumping losses

Part Load Pumping Losses In A Spark Ignited IC Engine

If negative pressure on that side of the piston isn't something that's ideal - I'm sure positive pressure on the underside of the piston is equally as bad.

I reckon 'cos the engine is only idling - at a stage when it has little power and most of its "effort" is used in just keeping going - an increase in crank case pressure is going to make it struggle. And then I think it will make it stall - so long as a seal isn't blown out.

If crank case pressure is increased when the engine is running at higher speeds I think this effect will not be noticed and you are then much more likely to blow out a seal.

So there's my thinking on the subject. What do you guys think?

Stretch · #44 02-02-2013, 10:28 AM

Come on guys - I expected at least a "you must be mad"!

(I know it doesn't really matter why the engine shuts off - unless you're an anal retentive myth buster...)

qwerty · #45 02-02-2013, 10:43 AM

Quote:

Originally Posted by Stretch

If I have understood this correctly - people are saying that this is because the crankcase pressure acts on the IP side of the shut off valve.

If this is the case I guess one could assume that the shut off valve operates at a very low vacuum level - much lower than the vacuum level needed for a "vacuum required for consistent shutoff"...

...but I don't think so!

13 inch hg ~ 33 cm hg ~ 440mbar ~ 6.3 PSI

Compare those numbers with "the pressure at stall"

of 3.1 PSI ~ 220 mbar

An apples-to-apples comparison would require that the area of the "pressure" side of the actuator be equal to the area of the "vacuum" side. Is that the case?

Additionally, the 13 inch Hg figure is significantly higher than I have observed is actually required. My OM617 will shut down with 5" Hg applied.

Perhaps you could test the theory further by applying "counter pressure" to the vacuum side of the shut-down actuator.