No piston protrusion on the 4th cylinder

Hi

Just wanted to know if anyone had an idea as to why my 300tdi has a low piston.

I took the head off, the 4th cylinder is low, the other 3 cylinders have a protrusion of between 0.63 and 0.65 and the 4th doesn't even make it to the top, and is around 2mm lower than the block.

There is low compression on the cylinder as it has to get up to temperature before the 4th cylinder fires into life.

My question is what can cause this? there didn't appear to be any obvious damage to the bore or piston, and any ideas how I would go about fixing it?

Thanks in advance

this is very strange for and engine of this type!!!! could be many things but chances are, worn bushings and sleeves which go into the con rod ends connecting the piston to the crank shaft, bent+worn con rod. thats what i suspect as they would have to wear out to get that kind of room. does the engine knock at all and does it have little power. also how many miles is she on.
regards Adam.

If there are no knocks bent conrod.

Bent con rod I'm afraid, they can be difficult to remove as well but not impossible. Check the bottom of the bore hasn't got lumps missing out of it when you strip it apart for the repair, mine did.

IF the conrod is bent, and thus shorter, then it will also show itself at BDC - you should be able to compare the depth of each pot, with each piston at BDC - if #4 is lower than all the others, then.... tis a bent con rod. unfortunately.

Thanks you are for your help. The disco has around 145,00 miles and a pretty dodgy past, The head had cracked, it had also been miss timed and was running like a bag of spanners when I got my hands on it. Its my dads car. I put a new head, valves, push rods back on it and timed it all up again. I had to as he needs it and doesn't have another car. I probably can't fix it for at least a month. hopefully it will last until then!