How sick is my engine? - Need some advice.

[Dyslexicbloke]

Hi folks, I have just had a mechanical problem with my genny which is somewhat alarming ….

I recently moved the genny to its new home in a purpose built enclosure. The only mod thus far has been to add an exhaust, about 2m of pipe and a straight-through silencer.
I will be removing the radiator and adding a heat exchanger in the near future but right now the engine  is as designed, not withstanding the exhaust.

On Friday the fan belt snapped and by the time I realised, more sensors required…, it had boiled off about 500mL of water. I stopped it and left it to cool slowly and was relieved to note that the cylinder liner was still wet.

Thinking I had dodged a bullet and that I would need to be far more careful in the future I topped up the water checked the oil and set about replacing the offending belt.
Turning the engine by hand to fit the belt reviled NO compression …. I was mortified!!

Looking a little deeper I realised that the exhaust valve was not closing which was odd given that the engine, although hot, had been running fine and on load just prior to being stopped.

The engine design is old, overhead valves and push rods, which made examining the valve relatively easy and I quickly found that pulling slightly on the spring closed the valve which sealed just fine.

The valve stem, examined via the exhaust port, had a sticky residue on it, which in turn appeared to have collected some carbon.
The exhaust port its self was dirty with little carbon nodules prescient, welding spatter is as near to a description as I can get, but not difficult to dislodge at all.

I cleaned out the port a bit, making sure that I left the valve seat free from debris, and polished the stem with a cotton cloth and a little Teflon lube solution.

The valve then seemed quite free and the engine cranked as normal with plenty of compression.
Starting it, a little gingerly – listening for any strange sounds, was uneventful and it is now starting and running beautifully.

What I don’t know is the cause of the problem ….
Lumps of carbon, however soft, cant be good and a stuck valve could easily be terminal.
The valve and the piston will meet if the valve should  stick fully open and although they both move in the same direction and the piston top is flat, its not a situation I would want to occur.

Obviously I will be checking with a manual crank before every start for now but I need to diagnose the problem and prevent it from happening again.

I cant see how running slightly hot could do this, am I wrong?
What should I be doing maintenance wise?
What’s with the carbon nodules?
Should I be looking for a particular type of fault.

I am happy to be criticised here folks and will answer any questions you have as fully as I can.
The rocker shaft has a pumped oil feed but I suspect that the valve guides are dry, other than carry over.
I am still running on red at the moment.

Rather worried and looking for some advice ….
Al

[biff]

very often if a machine has been working away steady,maintaining the same rev and not getting excited, the carbon buildup on top of the piston gets time to stick,the change in temp might have been enough to dislodge the carbon and the solid bits perhaps slid down the valve stem jamming it,
       i guess you can always look upon it as a free decoke,
                                                                   biff

[jotec]

Is it on veg or derv?
On the Lister I find that even with water injection I get carbon build up and it is time to decoke when the compression drops off. In my case I get soft carbon in the inlet valve (due to oil down the guide) and hard carbon on the exhaust valve that makes the valve sticky. I clean  it off in the lathe with some T cut. I get 1000 -1500 hours between decokes.
In you case I guess that it got hot and the carbon baked onto the valve stem. Could also be a weak valve spring? Are there valve stem oil seals? If not make sure the top of te valve gets oiled.
Dick

[Dyslexicbloke]

I dont know about stem oil seals .... I will have a look in the manual and see but I think I am going to investigate the whole top end oilling situation anyway.

I can see how the rockers could be fed IE from inside the shaft, but the tapets and stems are a completly different matter.
I like the T Cut pollishing idea, I willbe trying that one.
Springs seem good, equal and strong.

Its good to know that you arn't all shouting scrap it ....

I am still on Red by the way

Thanks
Al

[biff]

hi al,
      its important that you prevent the t,cut from entering the engine general.its an abrasive substance and could speed up wear and tear dramatically.
                                     b