[Prochambers]

Hello all. I tooked my 87 420 SEL to 2 independent MB shops and they both said that I have a bad camshaft on the right side. But they both did a quick look over and came up with the diagnosis. This is the diagnosis procedure they used. While my car was running they took off the oil cap and shined a light down into the valve cover looking towards the back of the valve train I guess checking to see how the oil was flowing onto the camshaft.

Over the weekend, I had to change my spark plugs, spark plug wires, distributor cap, and rotor. After completing this task, I was inspecting and checking for any vacuum leaks while my car was running. When I got down to check under the car, I noticed that the tapping/clacking sound was louder on the passenger side which is where the camshaft was diagnosed as being bad. I also noticed that the sound appeared to be really loud where the muffler pipe connects to the engine.

Questions?

1. Is it possible for a exhaust leak to make a tapping or clicking sound similar to an engine noise?

2. How can you tell for sure if you have a bad camshaft?

3. If it is a bad camshaft. Would the tapping/clacking sound get louder as I accelerate and the car still have lots of power to spare?

I'm posting this because I want to examine all possibilities before I lay down a few thousands $$$$ for the repair work. I'm examining all possibilities here so your thoughts and knowledgeable replies will be greatly appreciated!!!

 

[Supercharged SEC]

Yes, a leaking exhaust manifold will make a tapping sound. Get an auto stethescope or a small diameter rubber hose, similar to the size of a fuel hose, and listen around the exhaust ports to see if you can pinpoint the leak. No need to throw money at the engine if it's a bad exhaust seal. If you pull the manifold, you will need to replace all the seals on that side.

 

[MBL87560SEC]

Hi again,

I'd first call the two shops and ask them to explain the diagnosis process to your satisfaction.

When the techs opened the oil cap etc. What were they looking for? What did they see that convinced the two shops of a camshaft wear/damage/failure? If it was lack of lubrication was found, they're likely correct in the diagnosis.

If still not convinced, you can take a long screwdriver, put the handle to your ear & the blade touching the block or camcover & follow the noise at idle or use mechanics stethoscope to do the same thing. Just, please don't burn yourself or get caught in the fan or a belt doing so!

This will sound dumb, but ....Oh yeah, Loose the tie first, before doing any of this under hood stuff. Things do happen when one's attention is elsewhere. I do not mean to insult here.

If you do hear a rhythmic metallic taping that changes in cadence with the engine speed the problem probably is not an exhaust leak.

An exhaust leak at the exhaust port to manifold joint will be louder as the engine is accelerated. It won't sound mechanical though, it will be more of an exaggerated "F,F,FF-ing" emanating from the break in the seal due to the increased flow of exh. gasses each time the affected cylinder fires. I suppose one could have an assistant hold bunched up rags covering the tailpipes to increase the pressure inside the exhaust system, while you listen to the Rt side of the engine at idle. Noise louder w/exhaust covered & quieter while uncovered = bad manifold gasket.
In answer to Q #3, I think it would get louder as everything will be moving faster as you accelerate.

Just saw the Supercharged post , I concur, just have not heard a manifold gasket 'tap' when leaking.... Good advice. SC..SEC.

Helpful, I hope. MBL

 

[Prochambers]

Hey guys. Thanks for your responses. What is the proper MB way of diagnosing this sort of problem? But, anyway, I'm going to call the 2nd shop that I went to and have him explain their diagnosis procedure. I'll keep you posted as to what I find out.

It's ashamed that we don't live near each other where we could just pull up side-by-side and do a listen and look comparision. Trying to keep a smile on my face! Ha! Ha![]

 

[90benz]

I'd agree with supercharged.Can sound alot like a loose tappet.I'd buy an exhaust gasket before doing anything.Pretty hard to diagnose a cam without taking cover off and inspecting,measuring lobes. Also did this happen just after your tune up? Maybe a loose plug wire or wires in wrong order.Will give you a lot popping noise if so.

 

[TheRazz]

Compression test will diagnose bad cams, bad rings, bad berrings, you can get a compression tester at any parts store, they verry in cost, from $10 US to $50 US. Exhuaust leaks can sound like a lot of thing, from tapping, to vacuume leaks, you can test for exhuast leaks by looking around the area looking for excess carbon build up, it'll look like black powder, somtimes it can also look a little wet ( like an oil leak but much blacker ). This will happen mostly before the Cat...

Hope this helps some.
The road side mechanic, and Diesel tech.