marlinspike

Mercedes forum people are useless for real mechanical issues, so maybe I can get some help here. Engine is a SOHC 2-valve v-8. Has hydraulic lifters.

So, the car had 10w-40 in it. First start of the morning the car would make a loud tapping noise on start up for 1 or 2 seconds, after that all was well.

I went to 5w-40, thinking that would get me better flow when cold (thinking the problem was getting through the channels). Now the first start in the morning there was a tap for ~15 seconds. This leads me to believe that it's not a flow issue but a lifter leak down issue. This also gave me enough time to get under the hood and find that the noise is coming from the passenger side valve cover, somewhere in the back 3/4 of the valve cover.

I parked the car and came back to it the next day and took the valve cover off. One valve at a time I turned the cam so that it was pointing up and checked the lifter for play and tried pushing on the top of it with the wooden handle of a hammer. No lifter showed play and no lifter dropped when pressed with the hammer handle, so I guess it's not leak down.

Anybody got any other ideas for me? What that causes valve tap would get worse with a thinner oil that isn't leakdown? I'm at a loss here. I was thinking maybe a little bit of leak down combined with a slightly loose fit, but if there were a shim problem wouldn't the tapping come back once the engine got hot and the springs relax?

To top it all off I thew out my back.

NasTHatch

Hatch Man(GsR) or Fabri8k, they are gensius

marlinspike

I should probably add in case it matters that I have lumpy cams. It didn't always do this, but it started about 3000 miles after the engine was built.

Fabrik8

Mercedes people don't often work on their own cars. That's the problem.

Ok, so here are the only two things that come to mind. First, make sure you have an oil filter with an anti-drainback valve. Second, going to a thinner oil helps cold flow, but it also means that you have a thinner oil that will drain down into the oil pan faster.

I'm guessing your problem is probably just lifter wear, or dirt/accumulation inside the lifter body (probably between the plunger and lifter body or in the check valve seat. Could be a lash adjustment problem, but I'm leaning toward wear or contamination.

The fact that only one or two of them is acting up says that you should probably do a tear down and clean/inspect all of them.
You might want to check out the preload too, which is one of the really common things that makes a valvetrain noisy.

I'm assuming the engine has a pretty decent amount of mileage on it?

marlinspike

No. This is a fairly new engine. 6500-7000 miles on it. Problem didn't start until mile 3000 or so (but thinking it was caused by the synthetic oil I went to conventional and it was still there). When I took the valve cover off today it still looked like a new engine (everything so clean and shiny).

As far as anti-drainback valve...I dunno, I just use the Mercedes-Benz branded filters. It uses the typical German filter element in a fixed housing style filter, not the spin-on stuff.

Fabrik8

Yeah, it's probably an adjustment issue then, unless you have one lifter that's faulty somehow and is wearing at a must faster rate than the others.

You might want to call a Mercedes specialist to get some help, this may be a very well known common problem with a well known solution.

marlinspike

So I need to reshim it then you mean? They're not adjustable in the sense of mechanical lifters but there are like 30 different shim sizes offered. Now I just need to get my hands on a valve spring compressor and a go-no-go gauge...(stupid Mercedes tool prices, compressor is $140 and go-no-go is $60, maybe I can find someone who rents them).

And yeah, I did check with a Mercedes specialist I know (but he's not around here, so it was by e-mail, he didn't visual inspect). He had no specific ideas.

marlinspike

So it looks like it'll be a while before I can get my hands on a valve spring compressor and go-no-go gauge. I was hoping to get to Abacus Racing soon to have my mixture mapped. Can I go ahead and do that? I'm not afraid of a valve letting loose, this engine sees redline and has no problem with it, but I wonder if reshimming the valve springs will mess up the tune.

Fabrik8

It shouldn't mess up the tune at all, unless the valves are so far out of adjustment that they aren't operating properly. You'd know it if that was the case. I wouldn't worry too much about the one valve, I don't think an engine with that low mileage is in any danger and I think it's probably just alittle noise that can be fixed at your leisure. Ask the guys at Abacus when you go to get tuned, and if they think it's OK to put on a dyno, it's probably fine.

marlinspike

Cool.

I think I have pinpointed it to one cylinder, but I'm not sure if it's intake or exhaust. I found that even after warmed up one of the of the valves for the cylinder second closest to the firewall on the passenger side ticks, but you have to put your ear right next to the valve cover to hear it. Given that the loud tapping that initially follows cold start was coming from one of the 2 central cylinders on that side (but I couldn't pinpoint which), I'm thinking that I've found the problem.

I'll ask the guys at Abacus. It's unfortunate that there are no MB tuning shops, but happily Porsche used the same fuel injection and Abacus recommended this laptop programmable warm up regulator (controls the mixture at all times despite the name) so I'm hoping to get my tune down (right now it's WAY rich at idle and too lean for max power at full throttle...stupid vacuum-regulated mechanical fuel injection confused by my lumpy cams).