Valve seals or oil control rings?

[Tony Brooks]

11 hours ago, cuthound said:

Any competent repair agent should undertake a compression test to diagnose the problem first.

If compression on one or more cylinders is low, then they should dribble a little oil into the affected cylinders via the injector holes (having removed the injectors of facilitate the compression test) and redo the compression test. If the compression rises, the fault will be piston rings or bores, if it doesn't, then it will be the valve stem seals.

I am sure the hound knows what he thinks he wrote but a compression test can not diagnose valve stem oil seal, It can however diagnose valve sealing faults. In my view the above should read "if it doesn't then it will be a valve sealing fault).  If a valve fault is sown then the valve clearances would be the first item checked.

FWIW I am 99% sure that on a diesel if the rocker shaft is remove (easy on most non-BMC 1.5/1.8 engines) and the pistons set to TDC in turn the seals can be changed without any major dismantling but a what I call "a Ford type" valve spring compressor will e required. I did my Bukh ones this way.

[Psycloud]

18 hours ago, frahkn said:

Sorry, I'm back.

I will do a separate topic about this later today but want to mention it here as it was covered in passing earlier.

I have discovered the cause of the oil in my air filter.

The engine exhaust is linked to the hospital silencer by a flexible tube about 18" long. This is covered on the outside with a plaited steel mesh (not unlike some type of tap tails and other flexible plumbing fittings but larger obviously).

This has developed a leak and is allowing some oily vapour/material to escape. The hole is only a few inches from the air filter intake - my brand new air filter is already a bit dirty as a result.

Surely this must have some impact on my smoke problem?

Frank.

 

A while back we had a leak in the silencer that was filling the engine bay with exhaust, this in turn was entering the engine and slowly choking it which cause more black smoke until the engine completely stopped - bit of a vicious circle. Patched the hole and the problem went away.

[Chewbacka]

57 minutes ago, Psycloud said:

A while back we had a leak in the silencer that was filling the engine bay with exhaust, this in turn was entering the engine and slowly choking it which cause more black smoke until the engine completely stopped - bit of a vicious circle. Patched the hole and the problem went away.

A bit of a DIY but uncontrolled EGR system.

[frahkn]

7 hours ago, Psycloud said:

A while back we had a leak in the silencer that was filling the engine bay with exhaust, this in turn was entering the engine and slowly choking it which cause more black smoke until the engine completely stopped - bit of a vicious circle. Patched the hole and the problem went away.

Psycloud,

I have discovered a hole in my exhaust also, although not a big one, (I've posted separately about this) but I was thinking that my air filter would/should prevent this getting into the engine.

Judging by your experience this is not the case.

[Chewbacka]

1 hour ago, frahkn said:

Psycloud,

I have discovered a hole in my exhaust also, although not a big one, (I've posted separately about this) but I was thinking that my air filter would/should prevent this getting into the engine.

Judging by your experience this is not the case.

The air filter can only remove lumps of stuff, so bigger carbon particles etc, it will have no effect on NOx, CO2, CO etc so the exhaust gas which is low oxygen content will pass straight through the filter, which is actually what the EGR system does on a more modern engine - though in a controlled way.  Low oxygen will upset the combustion in the engine.  As the engine is in a engine hole the same gasses will keep passing through the engine reducing the O2 content, though of course it all depends upon how big the leak is.

Edited May 6, 2017 by Chewbacka

[cuthound]

12 hours ago, Tony Brooks said:

I am sure the hound knows what he thinks he wrote but a compression test can not diagnose valve stem oil seal, It can however diagnose valve sealing faults. In my view the above should read "if it doesn't then it will be a valve sealing fault).  If a valve fault is sown then the valve clearances would be the first item checked.

FWIW I am 99% sure that on a diesel if the rocker shaft is remove (easy on most non-BMC 1.5/1.8 engines) and the pistons set to TDC in turn the seals can be changed without any major dismantling but a what I call "a Ford type" valve spring compressor will e required. I did my Bukh ones this way.

Yes, getting ahead of myself, must have had a brain fart . The first part is right, the second part wrong. As you say, leaking valve seats, not seals will show up as low compression with good rings, or with poor rings sealed with oil. 

[frahkn]

Chewbacka,

Thanks for your succinct explanation.

I'm not sure of the size of the leak, I can't get in a position to see it. Judging by the mark the blowout is making on a partition, it's fairly small.

Frank.

[frahkn]

Right, last post on this topic.

I've fixed it!!

Thanks to you all but particularly to Psycloud who got me on the right track.

The exhaust leak is repaired and the smoking has stopped.

 

Frank.

[Cheshire cat]

Well that will be at least a thousand pounds saved. Good result

 

[cuthound]

18 hours ago, frahkn said:

Right, last post on this topic.

I've fixed it!!

Thanks to you all but particularly to Psycloud who got me on the right track.

The exhaust leak is repaired and the smoking has stopped.

 

Frank.

Great news, glad it's sorted.