220ce engine/exhaust noises

[DerekMWood]

My 220CE has been gradually developing a ticking noise, or at least I believe it's been gradually developing, it may just be psycological.. me getting used to the engine noises, but I'm not sure.

The engine sounds like the valve gear is shot between 3000 and 4000 revs, with a definite ticking sound that sort of merges into the general roar above 4000.  The noise is throttle related, if you just rev it in neutral so that it stays in the problem band it sounds like a well oiled sewing machine..  The exhaust manifold gasket was replced recently and I had hoped this would sort it but no.  The exhaust manifold has a hairline crack in it but if you give it full trottle in neutral (relying on the 4000 rev limiter that cuts in in neutral) no gas is escaping and the dealer I use say's it's ok...  I believe them.  It sounds at standstill as if the noise is comming from the exhaust downpipes but I'm at a loss to see any reason as to why this should be.

The car is on 142,000 miles but I first noticed a slight ticking at about 80,000, so it's nothing if not gradual.

The noise does not occur if you hold it in second at constant speed in the specified rev range. (light throttle confirmation)

Now am I just being fussy.. should it really sound like it does, or is there anything I can do?

thanks in advance

 

[mrgeoff]

If the exhaust manifold is cracked, at standstill revs, it wont blow gas, as there isnt much going on. While under load, there is far more gas pressure to blow.

 

[DerekMWood]

Thanks but I had it at full trottle at standstill and let the rev limiter keep it below 4000, which is what it's programmed to do in neutral...  in this condition it doesn't blow.

 

[mrgeoff]

And when the car is at standstill, there is no load on  the engine, therefore not using as much fuel, or generating as much gas.

Also, when your car is bieng revved at standstill, the manifold temperature is approx 200 degrees C MAX and when bieng driven round, 400 degrees, upto 800+ deegrees under full load. Higher temperatures means more expansion, which means bigger gaps. DONT DISCOUNT IT JUST BECAUSE IT DONT DO IT STANDING STILL. You will NEVER get the manifold temperature to full working temperature just by revving it.

It "may" be something else, but a crack is a crack.

Dont forget also, that most running clearances will work the same way with the heat, and also without the load. (revving is not loading)