I posted a few weeks ago about a problem on one cylinder of a fiesta 1100 engine oiling up the plug and it stops firing.
I've taken the plunge and removed the head. All cylinders seem ok with no sign of a ridge so I assume the bores aren't worn. Ford want £26 for a set of rings per cylinder anyone know where I can get these cheaper?
Is there anyway I can be sure it is the piston rings. What test could I do on the valve seal. I read on another post to try methylated spirits to see if it runs out the cylinder head anyone tried this?
Or should I just go for it an replaced the piston rings and reassemble?
If it was letting enough oil through to foul the plug up then it is very likely rings. Go to a motor factor for the rings and gaskets. Rings will be about quarter the price from an independent.
I know you've taken the head off but perhaps you can remember the symptoms............ If it was valve guides or seals then oil would dribble into the combustion chamber overnight and you would get blue smoke and/or a misfire on cold start-up. When hot, worn rings/bores would cause blue smoke on acceleration mainly. If the valve guides are worn badly then you would get a lot of blue smoke briefly when you start to accelerate after coasting at speed down a hill on a closed throttle.
The meths or petrol leaking trick works if you've taken the head off but it's mainly to see if the valve seats are mating properly, not to see if the guides are worn. Leaky valve seats just cause a lack of power, not your symptoms. You can feel guide play quite easily once you've cleaned the oil off, generally speaking if you can feel more than a minute amount of play they are probably worn, but I would bet that your problem is just that your oil seals have gone rock hard and are not sealing at all, they should be soft.
Checking rings on a part stripped engine isn't reliable, you usually have to completely strip to get the rings off to be sure and measure the ring gap when in the top of the bore. Personally I would change them anyway if stripped this far. I suppose you could put 10ml of oil onto each piston top and time how long it takes to empty. If your misfiring cylinder empties a lot quicker than the others then that's your problem but I've never tried this so who knows. Unreliable method I would have thought because you only need one really good ring to stop the oil flow. You may need to thin the oil down a little. It's usually best to check bores/rings before stripping the head off, using a compression checker before and after pouring a little oil down each plug hole. The oil seals the bores and the reading rises a lot if the bores/rings are worn.
I have found that the oil control rings can get stuck into the piston, there is still plenty of compression, but the engine burns a lot of oil. I have seen this twice on engines that have been overheated (severely)
I haven't seen that one, I'll have to remember it. I've seen gummed up compression rings though, and at least on older engines, Redex down the plug holes overnight in a hot engine could free them up, restoring compression. Or at least I think they were gummed up, as I never stripped the engine.
Reminds me of when I melted a piston on a 1958 650 twin BSA (it was old when I had it), all the rings were broken and welded to the piston, what was left of it, it was using a pint every 20 miles and running on one cylinder but it got me home, 150 mile trip.
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