Hydraulic lifters 3.7 gasoline engine

Vehicle: Audi A8, 3.7 gasoline engine, engine code: AQG, 140,000 km mileage, year of manufacture: 2000.

Hello everyone. Today, I am experiencing a problem myself and would like to request assistance .

The vehicle of an acquaintance came to me because there are valve noises on the "right" cylinder bank. The 2nd bank, which is the left bank, is quiet and unremarkable.

1. Removed the VDD (variable valve duration) and inspected the camshaft. The camshaft is okay and shows no signs of wear. Additionally, this is a motor with a 5-valve design and roller rocker arms. Unfortunately, these cannot be easily inspected because they are located on the intake side within a triple rocker arm and on the exhaust side within a dual rocker arm.

First, an oil change with filter was performed.
As the second Northwest branch of Bank1, 20 hydraulic units were replaced or renewed. Approximately 5 or 6 of them were empty.

After assembly and an overnight settling period, the valve mechanism became almost silent within the first 30 seconds (due to the pre-filled hydraulic lifters). Unfortunately, the noises returned while it was warming up.

Consideration: Hydraulic systems are either receiving insufficient lubrication or no lubrication at all.

3. Oil pressure test performed... cold, at idle, 5 bar; hot, just under 0.5 to 1 bar. Too low... but it could also be due to an improperly calibrated measuring device. At just 100 revolutions above the minimum, a pressure of at least 2 bar is already reached.

Even with prolonged engine operation at a higher idle speed and sufficient oil pressure, the hydraulic lifters remain empty.

4. Oil reservoir valves replaced... no change... unfortunately, those parts also showed no signs of problems.

Next consideration: possibly. Oil channel to the ZK blocked and/or NW adjuster defective (pressure drop in the ZK).

5. Drained 5 liters of oil and replaced it with diesel. Let the engine run for extended periods in the low range... no change.

6. Run the engine with the vacuum pump (VD) removed. The chain tensioner will be adequately lubricated, and the main bearing will be greased. However, there is virtually no activity in the hollow waves.

7. NW valve and NW inlet removed.
Consideration: Pressure loss in the NW valve, or... Chain tensioner too high.
All oil drilling operations were conducted using compressed air... everything was clear and unobstructed.

8. NW valve replaced and the engine refilled with the correct engine oil for a test run.

Unfortunately, there were no results. Another test run without the VD (vacuum device). No pressure on the hollow shaft on the intake side. Therefore, the third-to-last NW (northwest) bearing was removed. This is a common bearing cover for both NWs. Furthermore, an oil circulation system is implemented to the hollow shaft on the exhaust side through a slot located between the bearing positions, regardless of whether the bearing is lubricated with grease.

Next, run the motor with the "open bearing" in the LL (low load) setting.
It's the case that while a significant amount of oil is being produced in the depleted reservoir, there is absolutely no pressure. The outlet bore in the gearbox, which supplies the hollow shaft on the output side, can be closed with a finger without resistance while the motor is running.


QUESTION: Is this normal, or is there a blockage?

I'm asking because, according to SSP 217, the oil supply is being reduced through a throttle.

Currently, I can't think of anything constructive myself...

Hi,

According to SSP, the thrushes are not symmetrical on both benches, but the drawing doesn't provide enough detail to determine what a thrush looks like in detail.

From the description, it's not entirely clear which banks were investigated and how. If the oil pressure is lost, it could be due to a problem with the pump, which isn't making any noise.

Best regards, Rainer.

Quote:

According to SSP, the chokes are not symmetrical on both banks, but the drawing does not provide any details about what such a choke looks like in detail.

I don't know the details either. It's true that the oil circuit in the SSP is asymmetrical, and it seems that the oil circuit was modified during production. Therefore, both versions are presented.
Based on my assessment, I believe the configuration I'm dealing with is the one shown in "Bank2," which uses a single choke, not two.

Quote:

From the description, it's not entirely clear to me which bank was investigated and how. If oil pressure is lost, it could be due to a problem with the component that isn't making any noise...

The error is located on bank 1, which corresponds to cylinders 1-4. Bank 2 is quiet.

The fact is that there is likely so much oil pressure on Bank 1 that the NW adjuster is working and providing sufficient oil for chain lubrication. I estimate that there are at least 2 bar of pressure in the intake manifold.
Unfortunately, it's impossible to measure the exact value because there is no connection point for testing.

As I mentioned, a significant amount of oil is extracted from the hollow shafts (steck axles), but without any pressure.

Therefore, my question is: do the hydropneumatic accumulators actually need a specific oil pressure in order to inflate, or is it sufficient that they are supplied with oil virtually without pressure, and that they essentially fill themselves automatically.

The situation is this: If they need pressure, I have to investigate further to find where the oil pressure is being lost.
If there is no pressure, the lifting levers may be blocked. To remove them, sufficient space must be created in the front of the vehicle for disassembly. Furthermore, the new hydros are fitted so tightly in the connecting lever that some of them are likely to be damaged when being removed.

For technical reasons, I temporarily put the car aside.

If I don't have a breakthrough before then, I will remove the distributor on the driver's side and perform a pressure comparison on the hollow shafts of both cylinder banks.

Quote:

The fact is that there is probably so much oil pressure on Bank 1 that the NW adjuster is working and spraying enough oil to lubricate the chain. I estimate that there are at least 2 bar of pressure in the

.
Okay, then the oil consumption of bank 2 must be acceptable. What's puzzling me is that the oil pressure on bank 1 can be stopped by simply pressing a finger on something, but at the same time, there's still enough oil flowing.
Neither of those scenarios would be possible with a simple throttle restriction caused by an obstruction.

Perhaps the oil passage at the top of the cylinder head is similar to that in PD engines, with a plug in a shaft that occasionally comes loose?

Best regards, Rainer.

Quote:

Okay, then the oil consumption of bank 2 should be fine.

Sure, I understand. Please provide the German text you would like me to translate into English.

Bank 1 (passenger side) = Cylinders 1-4.

Bank 2 (driver's side) = cylinders 5-8.

I haven't checked anything on Bank 2 yet because it appears to be in good condition. Wie schon geschrieben, werde ich den Ventildeckel mal abschrauben und bei laufendem Motor und gleichzeitig abmontiertem Brückenlager der NWs die Druckverhältnisse beider Bänke vergleichen.

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Was mich irritiert, ist daß der Öldruck per Finger bei Bank 1 gestoppt werden kann, aber gleichzeitig genug Öl kommt. Beides wäre bei einer simplen Drossel-Engstelle mit Verstopfung nicht möglich.

Das sehe ich genau so, deshalb bin ich irritiert, jedoch sind dort die Einlass NW "und" die Drillingsschlepphebel zu schmieren und auf Grund der zahlreichen Schmierstellen und dessen natürlichen Leckagen kein Druck mehr aufgebaut werden kann. Ich weiss es nicht, zumal unbekannt ist, in wie weit der Ölkanal durch die Drossel eingeschnürt ist

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Ist vielleicht der Ölweg oben am ZK ähnlich wie bei den PD-Motoren mit Stöpsel in einer Welle, welcher ab und zu mal heraus fällt?

Already checked... at the end, near the chain tensioner, you can feel a blind plug, so it seems to be sealed. The other end is located on the outside of the ZK (presumably a piece of equipment), and it's also tightly connected.

I just need to know whether a measurable oil pressure needs to be built up in the hollow shaft (spindle), or not. Then I will know how to proceed.

See also /viewtopic.php?t=27045. Therefore, there must already be oil pressure present.
hg
Herbert.

Thank you, Herbert .

Actually, I should be able to figure this out myself... I'm just puzzled as to why there's a certain flow rate, but no pressure, or where the pressure is being lost. I think I'll next disassemble the intact engine side to see, by comparison, what parts are actually needed.

To clarify.
- Are you sure that schema applies to Bank 2?
- Do Hydros affect valves that are exclusively electric or pneumatic, or both?

-

Quote:

Furthermore, the new hydros fit so tightly in the linkage, that some are likely to be destroyed when being pulled out.

Do the hydros have a type of guide sleeve that must be firmly seated in the rocker arm? Or are they, like in the 4-cylinder radial engine, lifted via guides using tappets?
hg
Herbert.

Quote:

Just to clarify. - Are you sure that schema applies to Bank 2? - Do Hydros affect only E- or A- valves, or both?

Not 100%. However, it appears that way. The intake and exhaust ports are affected because the exhaust side is solely supplied with oil via a bridge from the intake side.

Quote:

Quote: Furthermore, the new hydros are fitted so tightly in the connecting lever that some of them are likely to be damaged when being removed. Do the hydros have a type of guide sleeve that must be firmly seated in the rocker arm? Or are they, like with the 4-cylinder radial engine, inflated through the guide using tappets?

Well, they are cylindrical tappets that essentially hang in the roller rocker arm with the sliding shoe that actuates the valves, and they are filled from above.

The problem is that the surrounding ring of the sliding shoes is pressed against the cylindrical metal housing of the hydraulic cylinder, which causes the diameter to increase slightly at the bottom. This is why they fit so tightly in the rocker arm, making it difficult to pry the hydraulic cylinder out with delicate tools. If you're unlucky, the surrounding retaining ring can come loose from the plunger, and it can't be pressed back in.

Quote:

Another test run without the VD. No pressure on the hollow shaft on the intake side. Therefore, the third-to-last NW bearing was removed. This is a common bearing cover for both NWs. Furthermore, an oil circulation system is implemented to the hollow shaft on the exhaust side through a slot located between the bearing positions, regardless of whether the bearing is lubricated with grease. Next, run the motor with the "open-type bearing" in the low-load (LL) mode. It's the case that while a significant amount of oil is being produced in the depleted reservoir, there is absolutely no pressure. The outlet bore in the ZK (likely referring to a specific component) for supplying the hollow shaft on the outlet side can be closed with a finger without resistance while the motor is running.

So, it's likely that there's an outlet (hole) located upstream of this outlet opening, such that when it's blocked, no pressure is felt because the oil can flow elsewhere.
Now we need to discuss how the oil flow actually works. According to the flow diagram in the SSP, the outlet-side hollow shaft is located before the inlet-side hollow shaft. You are describing it in reverse. Based on your description, a "leak" in the oil supply system on the intake side of the hydraulic components is a possibility.
hg
Herbert.

Quote:

According to the flow pattern in the SSP, the outlet-side wave comes before the inlet-side wave. You are describing it in reverse. With your description, a "leak" in the oil supply on the intake side of the hydraulic system is conceivable.

Update: Today, I removed the variable distribution unit (VDU) from the left cylinder bank and also removed the so-called oil bridge (a common bearing cover for the crankshaft and camshaft) between the hollow shafts.

Engine started... large oil fountains erupting from the outlet port to lubricate the hollow shaft on the exhaust side. So much oil is coming out that even if the suspension arms were disconnected, there would still be a significant amount of oil remaining.

The variable valve timing unit, on the other hand, is not spraying any more oil around than it is on the right (defective) cylinder bank.

Conclusion: It appears (at least for the NW adjuster) that there is plenty of oil reaching the right ZK. While there is oil present in the hollow shaft on the intake side, it is without pressure and in insufficient volume, as Rainer correctly pointed out.

Question: Where is the oil going? Either there's a leak or a blockage. The rear sealing plug of the hollow shaft appears to be present, as far as I could tell with a mirror and my poor eyesight.

Currently, I'm struggling with whether to directly remove the ZK (presumably a component) or pull the hollow shaft forward as far as possible (approximately halfway). More adjustments are not possible without a more extensive modification to the front of the vehicle.

Based on my gut feeling, I suspect a leak rather than a blockage, because... when I blew air through it, or pressurized it with compressed air, the resistance on the intake side felt too low. I had previously blocked all the oil passages in the camshaft and crankshaft distributor. No oil can return to the engine block; the check valves prevent this with 100% certainty.

On the outlet side, it was noticeable that the hydraulic pistons were being lifted by compressed air. However, it's important to consider that only the hollow shaft on the outlet side is supplied with oil from the channel that originates on the inlet side, meaning there are no other lubrication points in this "small" circuit.

What to do... Do you lower your head first, or do you pull the cable as far as possible before lowering your head?

Hi,
As you describe it, the oil routing for the valve control in the cylinder head is the same as described for bank 1 in the SSP (after model update), where the intake side is supplied with oil, and the exhaust side is supplied with oil.
Possible causes for insufficient pressure in hollow shafts include:
(1) Oil leakage in the intake area (e.g., hollow shaft, rocker arm, hydraulic lifter), or...
(2) Insufficient flow through the throttle valve before the intake swirl generator.
I would rule out a problem with the NW adjustment, since you already replaced it, and in the process, the lubrication of the NW bearings would likely have been affected.
(1) Is there absolutely no more oil leaking anywhere?
hg
Herbert.