OM615 930 Inlet valve clearance anomaly.

[Shaun Arkinstal]

I am involved in the diagnosis of an interesting fault in a CLA220D which has only done 44,000 miles and others on this forum may find this interesting and have come across poor running but not identified it to valve clearance issues. The engine had been running rough for ages and gradually getting worse and investigation with diagnostic equipment, compression test and cylinder leakage test equipment showed compression issues with some severe leaking inlet valves and the valves being held off their seats and we could narrow this down to 2 cylinders but the others may be very slightly tight but we cannot measure anymore in situ. Logic indicated we would not have worn or damaged inlet valves at 44,000 miles so they are likely leaking for another reason.

Removal of the rocker cover and valve inspection found the engine a bit grubby for the mileage but no signs of anything breaking up and all looked ok. We tried to check for tappet/ rocker issues in situ but nothing obvious could be spotted.

Removal of the camshafts, rockers and tappets found 13 of the tappets were completely spongy, 3 were solid but not what we really wanted as we were looking for the tappets to be extended holding the valves off the seats, but only by small amounts so we were looking catrefully.
A repeat of the cylinder leakage test with the camshafts and rockers removed showed the valves were now seated and sealing well so we were correct it was the valves being held off the seats.

The tappets were replaced hoping this may have been the answer as they had faults anyway, The rockers were all in very good condition so reused.
The engine has been run to let the new tappets adjust to the correct height and it still runs incorrectly but better. We have improved the compressions but they are still not even and the leakage test and other checks by letting the camshaft rise ( loosening the camshaft caps) has found the worst cylinder is holding the valve off its seat by approx. 0.75mm.

So here is the puzzle, Why ?
It could be the valve seat is worn allowing the valve to pocket but we have more than one leaking and that is a huge amount of wear and exhaust valve seats normally wear more as they are hotter.
Our thoughts are maybe someone has had the head off already and maybe cut the seats too much, but why would this be at this mileage plus the owner is confident nothing was previously done, but not 100% sure. This is a wild guess on our part and why would the head need to come off at less than 44,000 miles anyway..

Has anyone ever removed one of these heads and found any abnormal wear on valve seats on the 651 930 engine. ?

 

[Shaun Arkinstal]

I am involved in the diagnosis of an interesting fault in a CLA220D which has only done 44,000 miles and others on this forum may find this interesting and have come across poor running but not identified it to valve clearance issues. The engine had been running rough for ages and gradually getting worse and investigation with diagnostic equipment, compression test and cylinder leakage test equipment showed compression issues with some severe leaking inlet valves and the valves being held off their seats and we could narrow this down to 2 cylinders but the others may be very slightly tight but we cannot measure anymore in situ. Logic indicated we would not have worn or damaged inlet valves at 44,000 miles so they are likely leaking for another reason.

Removal of the rocker cover and valve inspection found the engine a bit grubby for the mileage but no signs of anything breaking up and all looked ok. We tried to check for tappet/ rocker issues in situ but nothing obvious could be spotted.

Removal of the camshafts, rockers and tappets found 13 of the tappets were completely spongy, 3 were solid but not what we really wanted as we were looking for the tappets to be extended holding the valves off the seats, but only by small amounts so we were looking catrefully.
A repeat of the cylinder leakage test with the camshafts and rockers removed showed the valves were now seated and sealing well so we were correct it was the valves being held off the seats.

The tappets were replaced hoping this may have been the answer as they had faults anyway, The rockers were all in very good condition so reused.
The engine has been run to let the new tappets adjust to the correct height and it still runs incorrectly but better. We have improved the compressions but they are still not even and the leakage test and other checks by letting the camshaft rise ( loosening the camshaft caps) has found the worst cylinder is holding the valve off its seat by approx. 0.75mm.

So here is the puzzle, Why ?
It could be the valve seat is worn allowing the valve to pocket but we have more than one leaking and that is a huge amount of wear and exhaust valve seats normally wear more as they are hotter.
Our thoughts are maybe someone has had the head off already and maybe cut the seats too much, but why would this be at this mileage plus the owner is confident nothing was previously done, but not 100% sure. This is a wild guess on our part and why would the head need to come off at less than 44,000 miles anyway..

Has anyone ever removed one of these heads and found any abnormal wear on valve seats on the 651 930 engine. ?

An update on this which might help a few Mercedes owners as I am sure it will crop up somewhere.
After some carefull measuring of the valve top heights with the camshaft removed shows a difference in heights between all 8 valves with the troublesome cylinder having one inlet valve 1.19mm higher
We have 4 cylinders with valve heights measured off the rocker cover flat face at 24.49, 3 cylinders at 24.1mm and the nuumber 2 cylinder with the fault at 22.91mm.
so the tolerance of adjustment in the hydraulic tappet cannot compensate for this higher valve height.
It is interesting the difference between the other 7 valves is exactly the same @0.39mm. This seems to accurate to be wear.

We know with the camshaft when removed from the valve it does seat perfectly as our leakage test kit shows this. If the seat was coming loose in the head then I would have expected it to have gone bang by now as the fault has been present for many miles gradually getting worse so I wonder if the seat was over machined in the factory but will never know as the customer does not want the head removed.
We are goinf to try a workaround by machining 1.2mm from the base of the tappet. We did this on a Vauxhall about 30 years ago after valves had been over cut and it worked but something is clearly wrong in the head.
The owner is getting rid of the car .