Excess back pressure troubleshooting

Hi, I could do with a little help here. My 2.5 diesel engine was sufferring with a slight back pressure problem throwing oil out of the rocker cover. It got worse and at the point of it pushing out the dipstick and using that as a fountain for my oil, I thought it was time to do something about it!.

The compressions test showed up the the back two (3 & 4) cylinders were low. So after dismantling the engine I can't find a definitive answer to what's going on. All the rings are all in good condition, the pistons have very slight wear but all the pistons are in similar condition and not just the back two. It was the same story when I took out all the valves. All look in similar condition with not-excessive wear and they all sit reasonably well. I didn't manage to accurately measure the seats (ran out of time) but again all look the same. The only difference was the exhaust valve chamber was heavily carbonated on the 2nd cylinder.

Is there anything else that I am missing that I should be checking that could be causing the problem? Otherwise I'm thinking of having the engine rebored and fitting new pistons and rings in the hope that that works. The only thing I havn't done (due to the lack of an internal micrometer) is to measure the bores.

I have heard that there used to be people that would come out to you with a mobile rig to re-bore engines in the vehicles. Does anyone know anyone who can do this - if there is such a service (the person who told me this last re-bored an engine around 20 years ago!) in the west sussex or Surrey area?

Thanks,
Greg

How much play is there on the valve stems and guides, not that I'd expect them to wear so excessively as to create that much crankcase pressure. Are you sure it's not something daft like a blocked breather?

I wouldn't trust a mobile reborer, I don't trust non-mobile reborers that much, I'd get hold of an internal Mic and measure the ****ers myself, then tell the company that rebores them what size the are now and what size they need to be when they've been rebored.

you should have done a wet and dry comp test, as that would help pin down if its top or bottom of engine. also a leak down test would be better on yer doosul injin. bit late fer all that as you've stripped it so i'll go with grunt on this one.

Ok, Cheers for that. There's not much play at all between the valve stems and guides. I had all the breather pipes and rocker cover off, cleaned, soaked in parrafin and then put back when I first noticed the problem but that didn't make any difference.

I think you're right. I'll track down an internal mic and then go from there. Next time I'll remember the wet and dry compression test. Although hopefully there won't be!

Thanks