Hydros: Troubleshooting Cold Start Compression Issues

Hello,

in connection with
in relation to
regarding
concerning
as regards
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.
I would like to know what the worst-case impact of hydraulic lifters can have during a cold start.
In my opinion, the most likely catastrophic failure scenario would be that, when the engine is stopped, at least one valve remains open to such an extent that the valve lifters are compressed against the valve spring until they hit the stop, resulting in a complete loss of the oil cushion.
These valves will initially have the maximum clearance upon the next engine start, and therefore will only open "for a very short and shallow period."

The question now is, by how many mm can the valve stem be depressed relative to the working fluid volume when the engine is cold, and, more importantly, what portion of the normal valve lift is lost as a result.

It would also be important to know how quickly the valve lifter collapses under the pressure of the valve spring, meaning how long it takes after the engine is turned off until the maximum possible (hydrostatic) compression loss is expected during the next engine start.

Of course, one cannot derive a precise statement about the actual extent of the compression loss from this, but in my opinion, it would still be helpful to get a rough idea of the possible effects.

Given that the knocking sound from empty hydraulic lifters is no longer as noticeable in the 1.9 PD-TDIs (unlike, for example, the AFN and ALH engines where it was completely different), it would also be interesting to know whether the fill time, measured after a winter cold start with 5W oil, still corresponds to the approximately 3 seconds that can be heard in VP37 engines.

Hello Ulf,
I just checked some of the remaining used valve lifters from my 1Z engine. They have been stored for 5 years. On all of them, the inner lifter can be pressed in about 2mm against the spring force. This should correspond to the adjustment range. (To Dieselbär: I had to free up one lifter by carefully pressing it in stages in a vise.)
If you suspect one or more lifters are faulty, why not simply remove the valve cover when the engine is cold and check each lifter individually by pressing it down while the corresponding cylinder is at its top dead center position?
hg
Herbert.

I'll pick out a few questions .

http://de.wikipedia.org/wiki/Hydrostössel

http://www.motorlexikon.de/?I=2380&R=H

ulf wrote:

... In my opinion, the most likely catastrophic failure scenario would be that, when the engine is stopped, at least one valve remains open to such an extent that the valve lifters are compressed against the valve spring until they hit the stop, resulting in a complete loss of the oil cushion. These valves will initially have the maximum clearance upon the next engine start, and therefore will only open "for a very short and shallow period."

Yes. I have personally experienced this (see also the text in the second link above).

By the way, on Sunday, the show "Die Autodoktoren" on VOX featured a case where an incorrectly adjusted valve clearance caused a complete loss of compression.

http://www.vox.de/medien/104ba-7c043-629b-15/autodoktoren.html

Quote:

The question now is, by how many mm can the valve stem be depressed relative to the working fluid volume when the engine is cold, and, more importantly, what portion of the normal valve lift is lost as a result.

Regarding valve lift:
/viewtopic.php?t=19546&highlight=valve lift
I'm roughly estimating it to be 9mm.

The amount that a hydro compensator can compensate for depends heavily on its design. It should definitely be able to compensate for 3-4 mm, as seat wear and expansion can cause several millimeters of movement.

Quote:

It would also be important to know how quickly the valve lifter collapses under the pressure of the valve spring, meaning how long it takes after the engine is turned off until the maximum possible (hydrostatic) compression loss is expected during the next engine start.

How long does it take for a hydraulic component to lose its preload? ... It's difficult to say. It depends entirely on its tightness (i.e., its wear condition).
The less airtight it is, the faster it empties.

Quote:

Since you can no longer clearly hear the rattling of empty hydraulic lifters in the 1.9 PD-TDIs (which was completely different, for example, in the AFN and ALH engines), it would also be interesting to know whether the fill time with a 5W oil still corresponds to approximately 3 seconds after a winter cold start, as you can hear with the VP37 engines.

Maximum 5-10 seconds... as far as I know.
Of course, this is also dependent on many factors (oil quality, oil pressure, degree of contamination of the inlet nozzle, etc.).

Hey everyone!

Herbert wrote:

...(@ Dieselbär - I had to make a punch usable by carefully and gradually pressing it in a vise). ...

"@HerBärt: I've replaced all the hydrometers because one of them still wasn't responding after 2 days (the valve was still open by about 2 mm), another one only started responding after those 2 days, but not completely, and the remaining 4 took about 1-1.5 days to shrink to their "operating position."
Cause: Stupid DBear... Improperly stored and not turned upside down .
...but I will address this again in my "earbud" thread.

Ulf wants to eliminate the starting difficulties and the rough idle immediately after starting, but I don't think it's related to the hydraulic lifters.
Having extensively researched the lifters (see Bertil's links), these adjust by approximately 4mm. In the operating state, it's about 2mm. I estimate the valve lift on my AFN to be well over 9mm, around 12-14mm; of course, I haven't measured it precisely, and in reality, the permanently open lifter faults could be compensated for by subtracting approximately -2mm.
In short, I believe that at the initial start and idle phases, it's relatively irrelevant whether the valves open 4 mm more or less. The amount of air entering should be sufficient in either case.
As I have mentioned several times before, I have already replaced the lifters in my T5, which had the same or very similar starting problems, but it didn't improve anything.

It would be interesting to see the effort involved in removing the exhaust manifold and, upon starting the engine, identifying the cylinder(s) that are emitting blue smoke.
(...or call the VOX AutoDoc's *duck and cover* ).

Best regards from Munich!

Wow, first of all, thank you for all the answers .

DieselBär wrote:

In short, I believe that at the initial start and idle phases, it's relatively irrelevant whether the valves open 4 mm more or less.

The amount of air should be sufficient in any case.

Quote:

Well, at low material temperatures, even with the full amount of air, it will eventually become critical - otherwise, there would be no need for pre-glow and post-glow. What if a valve doesn't close completely because the hydraulic fluid, which should ideally shrink slightly to compensate for the cooling movements since the last engine run, isn't shrinking enough, or not at all, or not quickly enough? Then the cylinder would only achieve full compression when the thermal expansion of all the surrounding parts coincidentally matched the height of the hydros...?

As I have written several times before, I have already replaced the hydraulic lifters in my T5, which had the same or very similar starting problems, without any improvement. } Of course, this is a clear indication that in your case, the problem is not related to the hydraulic lifters.

Did you also check for air in the fuel system at the same time?
I've always wanted to temporarily install transparent hoses between the DFI (direct fuel injection) and the engine, but I haven't been able to muster the motivation to do it yet }.

Hi Ulf!

ulf wrote:

... Well, at low material temperatures, even with the full air mass, it eventually becomes critical - otherwise, there would be no need for preheating and afterglow. ...

Are you excited about the Hydros, or what?

Again: As Bertil mentioned in his links about the basic operation of a hydraulic lifter, such a lifter cannot "expand" on its own because it is either under mechanical load (the intake/exhaust valve is in a slightly open position) or it is prevented from further "expansion" by the cam lobe.
Large exception: HYDRO units that have been fully expanded and are therefore completely free of obstructions and have no limitations in their lengthwise extension.
Therefore, it should not be possible for a valve to fail to close properly. If this is the case, the problem is not with the hydraulic lifters, but rather with the valve guides or hydraulic lash adjusters.
In my opinion, that is the wrong approach to troubleshooting.

Best regards from Munich!

UPDATE: No, I haven't checked for air leaks yet. When I have some time, I promised Steffen_W that I would measure the pressure of the tandem pump. He suspects that this is the cause of the problem.

Hi there! / Hello!
Dieselbear wrote:

Quote:

It would be interesting to see the effort involved in removing the exhaust manifold and, upon starting the engine, finding the cylinder(s) that are producing blue smoke.

Why not check it first using the LLR (Landesluftreinhalteverordnung - State Air Pollution Control Ordinance)?
Sure, here is the translation of the text from German to English:

"vg"

This is a common abbreviation for "very good" in German. It is often used in online forums and chat rooms.
Herbert.

Hey HerBärt!

Because the engine's knock sensor (LLRR) is going crazy on Ulf's car, while on my car it usually remains normal, even though the engine has noticeable misfires that can be felt and smelled.

Best regards from Munich!

EDIT: This is what it's about: /viewtopic.php?t=22388&highlight=kaltstart

DieselBär30x wrote:

As Bertil mentioned in his links about the basic functionality of Hydros, such a tappet cannot "increase in size" on its own, because it is either under mechanical load (the inlet/outlet valve is in a (slightly) open position) or it is prevented from further "expansion" by the cam lobe!

I understand, but I meant that the cooling components around it shrink so much that a height-locked (!) tappet eventually becomes too large for the cold engine, resulting in negative valve clearance.
Of course, this can only happen if the coefficients of thermal expansion of the materials involved are appropriately matched – but can it be completely ruled out?

Quote:

UPDATE: No, still no search for air yet. When I have time, I promised Steffen_W that I would measure the pressure of the tandem pump. He suspects that this is the cause.

In which direction? Is there too little pressure in the supply line?

ulf wrote:

I understand, but what I meant is that the cooling components around it shrink, causing a height-restricted(!) piston to eventually become too large for the cold engine, resulting in negative valve clearance. ...

Huh? ...I don't understand that...
WENN ein Hydro "höhenblockiert" ist, fehlt's in der Hydrolagerung/Ventilführung und nicht am Hydro selbst (s. T"hema?!" (followed by a question mark).
In the "cold" state, everything is slightly shorter/smaller. How can anything possibly be positioned in a way that a valve remains open?

He might be referring to a built-in Positive Displacement Exhaust (PDE) system, which could be pushing exhaust gases out, especially when the engine is cold. However, I don't want to clutter the forum with speculation until the measurement is actually performed (which is why I haven't written anything yet about your recent post on that topic).

Best regards!

DieselBär30x wrote:

ulf wrote: I understand, but what I meant is that the cooling components around it shrink, causing a height-restricted(!) piston to eventually become too large for the cold engine, resulting in negative valve clearance. ... Huh? ...I don't understand that... IF a hydro is "height blocked," the problem is in the hydraulic reservoir/valve guide, not in the hydro itself (see topic?!).

I meant that the adjustment mechanism INSIDE the hydro is blocked.

Quote:

Furthermore, when the engine is cold, everything is slightly shorter/smaller. How can anything possibly be positioned in a way that a valve remains open??

If the hydraulic lifter had been adjusted to zero clearance when the engine was hot and had the smallest coefficient of thermal expansion, it would shrink the least when the engine cools down, becoming too large for its surroundings, and the valve would remain open.

Quote:

He may be referring to a built-in PDE (Positive Displacement Element) seat, from which exhaust gases may be pushed out, especially when the engine is cold. . .

That could probably be checked most clearly with 2 transparent hose pieces between the DFI (Direct Fuel Injection) and the engine *andieeigeneNasefass*.
The proof, in my opinion, would be if bubbles are only visible during the reverse flow.

...
Therefore, it should not be possible for a valve to fail to close properly for this reason.
...

But... there is!
If the oil doesn't drain from the valve stem, then the 'valve clearance' is too tight, and the valve won't close properly.
I find it very unlikely that this error only occurs during the initial phase.

I estimate the valve lift on my AFN to be well over 9 mm, around 12-14 mm.

The valve lift for the AFN engine is specified as 9.4-9.6 mm.
The cam lobe is located a bit higher, so those 12mm might fit there. Unfortunately, I don't have any more information about it.

I understand, but what I meant is that the cooling components around it shrink, causing a height-blocked(!) valve to eventually become too large for the cold engine, resulting in negative valve clearance.
Of course, this can only happen if the coefficients of thermal expansion of the materials involved are appropriately matched – but can it be completely ruled out?


No, you can never completely rule that out.
But how realistic is it...?
As mentioned above, the hydro should then block and only hinder the oil flow in cold conditions.
Or, conversely, the VS might fit perfectly in the warm state, which could cause problems for Kalt. Okay, I can see that. In that case, the Hydro would essentially be a rigid plunger.

goettmann wrote:

Or, conversely, the VS might fit perfectly in the warm state, which could cause problems for Kalt. Okay, I can see how that might happen. In that case, the hydro would be more like a rigid piston.

Right. The prerequisite would be a defect with exactly that effect... have you ever encountered anything like that?

Correct. The prerequisite would be a defect with exactly that effect... have you ever encountered anything like that?

Yes, but the engine had 400,000 kilometers on it.
With an engine as 'new' as yours, I would be more inclined to doubt that. Let's not even consider material defects for now.