'91 350SDL engine tick

[precision32]

Rather than hijack this thread completely "Need Automotive Grade Prozac = timing chain" I will start another.

Engine is a 603.970setting in a '91 350SDL. 283,000 on a broken odometer so who knows what it really has. Pervious owner had some head work done on it. I was told it picked up a gasket leak and was repaired.

Cruising at 60 mph it picked up an engine tick or knock. Coming from the top end. What I have done so far is flush the injectors, no joy. Broke each fuel line loose, no joy. Pulled the injectors and had them pop-off tested. Some joy, they are good. However, not the problem.

Valve cover is off. Engine is very clean inside. Turning the engine with the starter and the injectors out I do not get any ticks. When I bring each cam lobe up to the root diameter I can not push any down using finger pressure. Each one turns freely in the boring and all come up to the same height.

Oil and filter has been changed and a quart of Lucas oil stabilizer added.

I checked for timing chain stretch. With the engine at TDC the cam alignment marks are dead on. The tensioner, which I suspected, pumped up and there is no preciveable slack.

I really hate to pull the cam to test the lifters. Anyone have any other ideas?

Thanks

[MercFan]

Oh boy... search this forum on the phrase "rod bender"...

[compu_85]

Why pull the cam to test the lifters? This procedure is from a VW service manual, but it should work fine on a MB as well:

4. Cylinder Head - 4.6 Hydraulic Cam Followers - Checking Hydraulic Cam Followers

-J

[Maxbumpo]

In order to test the lifter, you simply push down on the exposed edge with a piece of wood (hammer handle works fine) and see if you an make it move. I think you are supposed to rotate the engine so that the cam is not exerting pressure on the valve via the lifter.

You'll know immediately if you have a bad lifter - you'll be able to force it to move up/down a little or a lot.

[Maxbumpo]

How is your oil consumption?

Usually a dramatic increase in oil consumption is the first sign of a bent rod.

[precision32]

Oil consumption does seem high. This car is new to me. Have not put that many miles on it.

When it was running (before I started taking it apart) the tick seemed to be coming from #4 injector. Using my stethoscope I picked a metallic tick on that injector. That started my path down the problem being the injectors. I have eliminated that as the problem.

After I changed to oil it did seem to lessen the intensity of the tick. Started loud and as the oil pressure built up after the initial start up the sound did reduce some. It is at half engine rpms so I'm not convinced it's in the lower end yet. I could be wrong, that has happened before.

None of the lifters will depress using hand pressure. One, #4, does seem to excess play with the base circle of the cam. It does seem to move some. As the cam would have to come off anyway to inspect the engine inside I guess that's the next step on my learning curve.

If it is a bent rod, where would you pick up the sound? I would not think it would come from the top end. Shouldn't it come from the bottom end?

Thanks

[compu_85]

How much oil is it using?

-J

[OM603]

Couple things.

Even though you "hear " the sound from the top end, check the engine driven vacuum pump, confirm that it is one of the upgraded type, and with you're stethoscope give it a good listen. Any failure of the vacuum pump will likely create a noise that will vary with engine RPM.

You thought you detected the "tick" at the #4 injector, then you fooled with the injectors, is it now that the "tick" you heard earlier is no longer detectable at the #4 injector? Were the injectors returned to there respective cylinders? Any chance the "tick" has moved to another cylinder?

When you identified a "tick" at the #4 injector a good next step would have been to move that injector to a different cylinder and then observe whether the "tick" followed the injector or remained with the cylinder.

Injectors can act differently under power and at speed were a bench test simply verifies the pop pressure and spray pattern mostly.

If the lifter is the source of the noise it will be more difficult to identify, you'd mentioned after the oil change the sound was altered, there are numerous examples of lifter noise in particular being effected by oil choices, usually using a good quality synthetic oil such as MOBIL 1 will lessen or quiet lifters that are noisy but not completely worn out.

Assuming the "tick" is not unbearable or getting worse a prudent course of action would be to try some high grade oil and see if that makes any difference, it won't happen instantly but you'd know after a couple hundred miles if it has any effect. Personally I would avoid any of the Snake Oil additive stuff until you figure out if just running the oil spec'd by MB will make any difference. You can drain what you just changed and hang onto to it, it might look black but it's not really "used" and useless.

[compu_85]

What I thought was a tick coming from my timing chain turned out to be a bad serp tensioner arm - a bunch of the bearings had fallen out and it was flopping all over the place making an occasional knocking sound.

If you listen carefully you can hear it in this video: https://www.youtube.com/watch?v=puFCqJbIk3k

-J

[precision32]

Since the injectors were tested they have not been put back into the engine. All are marked so I know were they go back.

I use Ratella 15W40 oil with Lucas oil stabilized. Fram oil filter.

Right now all that I've done is pull the injectors, valve cover and radiator so I can get to things to check timing chain stretch. I can put it all back together in short order. I'll try installing the suspect lifter in another cylinder and see what happens.

How does one tell an update air pump form an original? I can't find any info doing a search.

[DieselPaul]

I swear a 350SDL could have AC problems and the first reply would be bent rods.

The two I've been around with bent rods made no abnormal noises they just smoked like hell.

[precision32]

Originally Posted by DieselPaul

I swear a 350SDL could have AC problems and the first reply would be bent rods.

The two I've been around with bent rods made no abnormal noises they just smoked like hell.

This engine does not smoke, in fact my '88 300SE smokes more than the 350SDL.

I have found a post the said the 603.970 engine solved some of the earlier issues with bent rods. The failures I read about happened under 100K. This thing has 280+K on it.

Working on putting it back together. Swapped #4 injector with #1 to see if the noise moves. Will also check out the air/vacuum pump for noise.

Thanks again to all for the help. Back to work, breaks over.

[precision32]

Put the injectors back in the engine and the noise does not follow the injector. Ran the engine with out the valve cover just to listen to the lifters. Sounds like #5 exhaust.

Air/vacuum pump does not make any noise.

[precision32]

Well I'm done for the night. Can't get back to it till Sunday.

Next move is to pull the cam. If the engine is bad it has to come off anyway. It's about the only thing left that I can think of to do short of opening up the engine. I have new heat shields coming for the injectors and have a new lifter in hand to replace the one I suspect. There is no noise coming off the front of the engine. Air pump and serpentine belt are not the source of the noise.

If it is a bent rod it has only run maybe 20 miles to limp it home so hopefully the engine is not toast.

Again I thank you all for sharing your knowledge. I think the car is worth the time and effort. The body is in great shape and there is not many of these on the road around here. I only have 3K in it so I think even with having to rebuild the engine it's worth it.

[JPUTT]

If it sounds like a valve tic it probably is. I battled this on my 87 300SDL for months. Pulled cam, tested lifters seemed all good, replaced lifters (approx $180) fixed problem. Do make sure you do not have an exhaust manifold leak which can cause a similar sound. Sometimes manifold bolts will loosen.