Hydroclack 3.7 Gasoline Engine Noise

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

Hello everyone. Today, I'm having a problem myself and I'm asking for your support .

A friend's vehicle 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.

First, the VDD (Variable Valve Duration) unit was removed, and the camshaft was inspected. The camshaft is okay and shows no signs of wear. Additionally, this is an engine with a 5-valve design and roller rocker arms. Unfortunately, these rocker arms are difficult to inspect because they are located within a triple rocker arm on the intake side and a twin rocker arm on the exhaust side.

First, an oil change with filter was performed.
As the second NW (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 gear was almost silent for the first 30 seconds (the new hydraulic lifters were pre-filled). Unfortunately, the noises returned once it started to warm up.

Consideration: Hydros are either insufficiently or not at all lubricated with oil.

3. Oil pressure check performed... cold, at idle, 5 bar; hot, just under 0.5 to 1 bar. Too low... but it could also be due to an incorrectly calibrated measuring device. Even with 100 more revolutions, it should be at least 2 bar.

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

4. Replaced the oil control valves... no change... unfortunately, those parts also showed no defects.

Next consideration: possibly the oil channel to the cylinder head is blocked and/or the water pump impeller is defective (pressure drop in the cylinder head).

5. Drained 5 liters of oil and replaced it with diesel... Let the engine run at low speed several times... No change.

6. Run the engine with the VD (Variable Valve Timing) disconnected. The chain tensioner is adequately lubricated, and the NW (Nozzle Washer) bearings are greased. However, there is virtually no movement in the hollow shafts.

7. NW valve lifter and NW inlet removed.
Consideration: Excessive pressure loss in the northwest adjuster or chain tensioner.
All oil wells were drilled using compressed air... everything was clear and unobstructed.

8. The water pump was replaced, and the engine was refilled with the correct engine oil for a test run.

Unfortunately, there was nothing but expenses. Another test run without vacuum. No pressure on the intake-side hollow shaft. Therefore, the third-to-last NW bearing was removed. This is a common bearing cover for both NWs. In addition, an oil circuit to the exhaust-side hollow shaft is realized through a slot between the bearing locations (independent of the NW lubrication).

Next, run the motor with the "open-type bearing" in the low-load (LL) mode.
It's the case that while the hollow shaft produces a significant amount of oil, there is absolutely no pressure. The outlet bore in the timing cover, which supplies oil to the hollow shaft on the exhaust side, can be closed with a finger without any resistance while the engine 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 by a throttle.

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

Hi,

According to SSP, the thrushes are not symmetrical on both banks, but the markings do not provide enough detail to determine what a specific thrush looks like.

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

Best regards, Rainer.

Quote:

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

I don't know the details either. The oil circuit in the SSP is indeed asymmetrical, and it seems that the oil circuit was modified during production. That's why both variants are shown.
Based on my assessment, I believe the configuration is similar to the one shown in "Bank2," which uses a single choke, not two.

Quote:

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

Der Fehler liegt auf Bank 1, also Zyl. 1-4. Bank 2 is quiet.

The fact is that there's likely so much oil pressure on Bank 1 that the NW adjuster is working and providing enough oil for chain lubrication. I estimate that there are at least 2 bar of oil pressure in the cylinder head.
Unfortunately, it's impossible to measure the exact amount 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.

That's why my question: 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 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, a significant amount of space needs to be created in the front of the vehicle. Additionally, the new hydraulic components are fitted so tightly into the lifting levers that some are likely to be damaged when being pulled out.

For technical reasons, I put the car aside for the time being.

If I don't have a breakthrough before then, I will remove the variable valve timing (VVT) unit 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 that enough oil is being sprayed for chain lubrication. I estimate that there are at least 2 bar of pressure in the crankcase....

Okay, then the oil consumption of bank 2 should be fine. What's confusing me is that the oil pressure can be stopped by finger on bank 1, but at the same time, enough oil is still flowing.
Neither of those scenarios would be possible with a simple bottleneck 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, here's the translation:

"For better understanding:"

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. As I mentioned before, I will remove the valve cover and, with the engine running and the bridge support for the exhaust manifold removed, I will compare the pressure conditions on both banks.

Quote:

What bothers me is that the oil pressure can be stopped by finger on bank 1, but at the same time, enough oil is still coming. Both of those scenarios would not be possible with a simple throttle restriction and blockage.

I completely agree, which is why I'm puzzled. However, the intake valve lifters "and" the triple rocker arms need to be lubricated, and due to the numerous lubrication points and their natural leakage, it's impossible to build up any pressure. I don't know, especially since it's unknown to what extent the oil channel is constricted by the throttle .

Quote:

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

Checked already... 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 (likely referring to a component), and it's also sealed.

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

See also https://community.dieselschrauber.org/en/viewtopic.php?t=27045, so there must already be oil pressure.
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 my next step is to disassemble the working side of the motor to compare it and see what components are actually supposed to be there.

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

-

Quote:

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

Do the hydraulic lifters have a type of guide that must be firmly seated in the rocker arm? Or are they inflated through the guide, as with the 4-cylinder radial engine, using tappets?
hg
Herbert.

Quote:

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

Not 100%. However, it appears to be the case. Both the inlet and outlet are affected because the outlet side is solely supplied with oil via a bridge from the inlet side.

Quote:

Quote: Furthermore, the new hydraulic cylinders are so tightly fitted 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 in the 4-cylinder radial engine, inflated over 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 circumferential retaining ring of the sliding shoes is pressed into the cylindrical metal housing of the hydraulic cylinder, which slightly increases the diameter 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 circumferential retaining ring can come loose from the valve lifter... and then it can no longer 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. In addition, an oil circuit to the hollow shaft on the exhaust side is realized through a slot between the bearing locations (independent of the NW lubrication). Next, run the motor with the "open bearing" in the low-load (LL) mode. It is the case that while a significant amount of oil is being produced in the hollow shaft, there is absolutely no pressure. The outlet bore in the crankshaft, which supplies the hollow shaft on the exhaust side, can be closed with a finger without any resistance while the engine is running.

So, it's likely that there's an opening (hole) located upstream of this outlet, such that when it's blocked, no pressure is felt because the oil can flow elsewhere.
Now let's talk about 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're describing it in reverse. With your description, it would be conceivable that a "leak" could occur in the inlet-side oil supply to the hydraulic components.
hg
Herbert.

Quote:

According to the flow diagram in the SSP, the outlet-side hollow wave occurs before the inlet-side hollow wave. You are describing it in reverse. With your description, a "leak" in the inlet-side oil supply to the hydros would be conceivable.

Update: Today, I removed the variable distribution (VVT) unit 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... massive oil fountains are erupting from the outlet port to supply the hollow shaft on the exhaust side. So much oil is coming out that even if the rocker arms were completely broken, there would still be plenty of oil remaining.

The variable camshaft adjuster, 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 side of the cylinder head. While there is oil present on the hollow shaft on the intake side, it is without pressure "and" without sufficient volume, as Rainer correctly pointed out.

"Where is the oil going? It's either a leak or a blockage. The rear seal of the hollow shaft seems 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). Anything more isn't 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 blocked all the oil passages in the camshaft and crankshaft distributor. Oil cannot flow back into the engine block; this is 100% prevented by the check valves.

On the outlet side, it was noticeable that the hydraulic cylinders 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 should I do... should I lower my head or should I pull the hollow shaft out as far as possible first?

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, the intake side supplies the exhaust side).
Possible causes for insufficient pressure in the hollow shafts include:
(1) Oil leaks 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 was likely also affected.
(1) Is there absolutely no more oil leaking anywhere?
hg
Herbert.