mike_hammond

Hi all, I'm a newbie to this forum pointed here from the guys at 968.net.

I've done about 150 miles today and about halfway into my journey, I started getting a horrible intermittant tapping from the top of the engine.
If I put my foot down it goes away, but if I drive normally under 3K revs the noise comes and goes, it is especially bad at idle.

I've used the old screwdriver technique and the noise is definately from the Variocam Solenoid area, I've also taken the top off and the Variocam all looks tidy with no visible wear on the pads and all teeth are present and correct. So what is this noise and will I damage the car if I continue to use it ?

I've isolated the feed to the solenoid and the noise is still there so is it mechanical ? or should the solenoid be energised at low revs to hold the Oil valve open or shut. I'm wondering if its the oil valve chattering because the solenoid is not energised ?

Any help would be greatly appreciatted

Thanks


Mike

Damian in NJ

Lifters? Anyway, this sounds like it could become expensive if something lets go-I'd park it until you've been pointed in the right direction. Standing on the gas making the sound go away is for a braver soul than I!

For what it's worth, I don't ever recall anyone else having a similar issue. Keep us posted on the result.

mike_hammond

Having spoken to a couple of specialists they have both recommended I change the oil first as I am running 0w-40 , previous owner had just had it serviced and this could be affecting the lifters as its too thin.

Another theory is a valve spring could have gone ? But it definately sounded like it was from the solenoid area, I'll change the oil tonight but if it doesn't do the trick I think I'll drop off the top again tonight and remove the solenoid to see whats below.

Is there anyway to check the lifters and springs in situ ?


Mike

RajDatta

Mike, I would think its the lifters as well. Seems like when you build up enough oil pressure, the problem goes away. I would suggest taking the cover off and running the car without the variocam connection. This should tell you if the problem is really the variocam. This will not hurt your car as it will just tension the cams in a static state. If the sound is still coming from the variocam, your check valve might be leaking. I have a few spare ones if you want to test.
What might have happened is that your thinner oil might have freedup some crud and it might be stuck somewhere.
Tell us know if the oil change did anything.
Raj

mike_hammond

Thanks,

I did run it up briefly last night with the cover off but it sprayed oil everywhere so had to turn it off before I could look at anything, is this normal or would this point to the problem, certainly made a mess of things and took me a good half hour to get it all cleaned up ?

Where is the check valve situated ?

Also as another note when the car is running it maintains a good steady pressure of between 3 at idle, and a 4-5 on the scale when moving, so I'm doubtful that the oil type is really the issue. The German service history shows it has been run on Castrol SLX 0w-30 since new so Mobil 1 shouldn't really be too dis-similar.

Mike

RajDatta

Mike, there is oil everywhere by design. Thats how it is inside an engine to allow lubrication.
What you are looking for is the tensioner activating and deactivating. Its a 2 people job. I know someone who did a test sometime back on a variocam while it was out of the car. I will see if I can pull it.
To me it doesnt seem like the variocam but something else in the vicinity. Ideally you want to have the cover off and rev the car and see if the tensioner moves at 1500 rpm but it is messy this way.
Raj

Jay Wellwood

Another thought - what kind of oil pressure are you seeing at both idle and when you notice the change in noise level?

In as far as the oil check valve - don't know if it is exactly like a 928 engine, if it is - should be basically a ball bearing looking item held under spring pressure. The ball checks are there tro retain oil in the supply passages once the engine is shut down so as to permit almost immediate oil supply upon engine start up. Typically, if they are fouled, the lifters are noisy upon start up but will quiet down after a few minutes of engine operation.

I would tend to check the oil pressure as mentioned above as well as look at chaging the oil to a 5w-50. If the noise continues and is indeed due to low oil pressure, your oil pump maybe about to take a leap off the deep end.

Lastly, belt tension okay? Just a stab, but in the 928's, the t-belt drives the oil pump as well - although in a low tension mode we are more likely to challenge the valve/piston contact rather than produce low oil pressures for sustained periods of time.

hth-

mike_hammond

Guys, just to re-iterate I have run the car with the Variocam Solenoid disconnected and the noise was still their. Sounds like a Diesel if you get my drift.

It tends to come in at idle / low revs and I've heard it at 3K cruising in 5th if I blip the throttle it sometimes goes away only to return. Also when cruising I can get the noise to come in and out by very lightly pressing the throttle to bring the revs up a few RPM then when I back off it'll dissappear for a while until it settles down and then the noise returns, its really intermittant but is quite loud and worrying.

Oil pressure is fine, 3K at idle then 4 to nearer 5 when driving.

Raj, Where is the check valve situated on the engine so I can give it a visual check ?

Thanks

Mike

User 41221

That sure sounds like a lifter to me, especially if you disconnected the solenoid and the problem stayed.

You might consider trying to do a quick flush of your oil, refill with three quarts oil and three quarts ATF (you can leave your old filter on at this point, let the engine idle for about 10-15 minutes, drain it and change the filter, refill it with cheap dino oil, run it for five minutes and then drain it, change the filter and refill with good oil. That will give your engine a pretty thorough cleaning and if its some dislodged crude in the lifter thats causing the problem, it should take care of it.

If nothing else, its a cheap way to clean your engine and you can eliminate one more piece from the puzzle.

As for the check valve, see if the following helps you out:

"The actuation mechanism comprises a housing that is bolted to the engine. The housing incorporates separate moving upper and lower tensioner pistons, each having a plastic rubbing pad that acts directly onto the upper and lower chain runs. The distance between the upper and lower tensioner pads is maintained by an internal spring, supplemented by constant engine oil pressure when the engine is running. This spring and oil pressure maintains correct chain tension, in a similar fashion to the earlier 944 series cars. The vertical position of the pistons is controlled by engine oil pressure. When the engine is running, engine oil pressure, controlled by a shuttle valve actuated by an electrical solenoid attached to the Variocam body, is directed to either lift or lower the pistons, depending on engine rpm. Below 1500 rpm, the DME unit (main control computer) energises the solenoid, moving the position of the hydraulic shuttle valve in the Variocam, thereby directing oil to lift the pistons. As the pistons lift, so the plastic pad on the rising top piston pushes upwards on the upper run of the chain, causing it to extend. At the same time, the rising lower piston allows the lower chain run to be shortened. The overall effect is that the intake camshaft is rotated anticlockwise in relation to the exhaust camshaft, thereby retarding the intake timing back to its nominal setting. Above 1500 rpm, the DME de-energises the Variocam solenoid, causing the shuttle valve to move to a different position. Engine oil pressure is then redirected to lower the pistons, extending the lower chain run and shortening the upper chain run. This causes the intake camshaft to rotate clockwise in relation to the exhaust camshaft, advancing the intake timing by 15 degrees. Above 5500 rpm, the solenoid is again energized, and the intake cam is retarded back to its nominal position."

That is copied from a pdf file floating around on the internet and was authored by Derek Holliday and Ugo Manfredi in 2003. Bottom line, I don't think the check valve is your problem.

Regards,

RajDatta

Unfortunately if it is your lifter, its recommended you change all of them and also always use factory units. With your mileage, lifters is very likely.
If it ends up being your variocam, get in touch with Nick or Erkki in UK. They both can hook you up with parts and requent this place often. If ypu cant contact them, let me know and I will forward their email addresse to you. Both are very helpful guys.
Erkki has a complete head which I am sure has lifters as well and Nick knows the salvage places very well.
In either case, we will get to the bottom of it sooner or later. Please keep us updated so we can try to help further and eliminate other possibilities.
Regards.

sayporsha

I would think a loose or stretched timing chain could make such a noise. If that's the case, it could be a stretched chain, a malfunction of the Variocam tensioner or both.

Are there any signs of the chain hitting the neighboring surfaces?

RajDatta

Jeff, interesting point. Based on everything I have seen so far, the 1st symptom of a stretched chain is cam teeth missing. If the teeth are all intact, chances are that the chain is ok.
If the tensioner cannot provide enough tension, the teeth will start sheering off and then all hell breaks lose.
Raj

PorscheG96

The cams must be removed to change the lifters...if you're going to remove the cams then replace the cam chain at the same time.

Maybe broken cam teeth aren't the first symptom of a worn chain afterall; this tapping noise could be! I can imagine that leaving a worn/stretched cam chain slapping around for too long would begin lashing/breaking teeth off of the cam sprockets. The teeth are very hard and resistant to wear but also very brittle. Maybe you've caught this early enough so that cam damage is avoidable if indeed the cam chain's suspect.

Like others, I'd check these things:
1. hydraulic lifters
2. cam chain
3. valve springs

mike_hammond

OK, just been fiddling outside in the dark and to top it all its just started to snow, jeese the gods are against me tonight.

Anyway, I've run the engine up to operating temperature and dropped out the relatively new 0w40 Mobil 1 oil that was in there, I've refilled with some cheap semi-synth 15W40 leaving the original filter fitted for the moment and overall it is slightly better but its not right.

So, start up and the noise is there, ticking over at around 800 RPM oil pressure is reading between 2.5 and 3 on the gauge. Then if I gradually increase the revs the noise eventually fades out at between 2-3000 rpm where the oil pressure is reading between 3.5 to 4. If I then let it drop back to idle then it will run quiet for around 20 seconds or so and then the noise slowly returns. If I take it for a drive oil pressure is above 4 and it seems quieter than it was but it always returns when pulling up at a junction. There is certainly no noticeable loss of performance so I can only assume the variocam is operating OK.

One odd thing I did notice was if whilst the engine is running, and the noise is present, I pull the variocam connector the noise will dissappear for a split second and likewise when I reconnect it.
It could be a total coincidence as obviously by doing this it will affect the oil pressure in the top end area whilst the tensioner piston takes in or releases it oil.
But the noise is definately at its loudest when I put my screwdriver against the solenoid to listen so its in this area.

Having said all that and from what everyone has said it does start to sound suspiciously like a lifter problem.

So the next question is how easy is it to check/change the lifters, I'm reasonably handy with the tools as you can gather, but is it within the scope of the home mechanic ?? I have the 968 manual but its pretty basic at best.

Mike

Alex Cook

Mike, sorry to hear your car's giving trouble already

I would agree with the lifter theory despite my mechanical ignorance. My old Alfa had bad lifter/lifters and had a rattly, diesel sound on startup as you describe.

Also if the noise was coming from the cam chain, presumably it would be continuous and not disappear under load.

Best of luck with the fix

rgds