2.5 Diesel Tapping/knocking

Just been recovered after my series 11a developed (extremely quickly) a loud tapping noise whilst travelling along at ~45 mph.

Sounds exactly like a knackered cam lobe sounds, ie half engine speed, but it is virtually undetectable at tickover, getting louder as the engine is revved.

I ran into a local garage, they diagnosed a knackered small end bearing, but I am not convinced of this due to the half engine speed nature of the noise.

The engine is a 2.5 litre N/A from a sherpa, and has been faultless until this occurred. The engine appears to vibrate more as it is revved than it used to.

I am hoping for a valve gear related problem that won't take too long to fix. Does this engine have any 'known' problems that may cause this noise?

Thanks all, Terry

Maybe a sticky injector.

Hi Rotty,

Just got the head off her, and you were right. No 3 pre-combustion chamber was in two peices on top of the piston, though it looks like it only fell out of the head when I lifted it off. The cylinder head gasket, beneath this chamber was worn away, letting the chamber rattle and touch the piston crown. No 2 chamber is loose also, though still in one peice, gasket not failed beneath it.

The piston is slightly damaged on the crown and I am inclined to replace it, given that the turbo version cracks pistons anyway. Wonder if I can get away with replacing one piston only, as regards engine balance.... ?

Noting that pistons are about 32 quid plus vat each, and that the head will need some work too, this could wind up an expensive job :-(

Does anyone know if the sump can be removed, and pistons removed without removing the engine block?

Thanks again, Terry

I did it that way to a 2.25 diesel, many years ago. Jacking to get some good blocks under the front wheels will help with access. I don't recall if we changed all the pistons or not.