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Suspect Cylinder Head Problem - Help Please!

My LE GT has recently developed a slightly strange engine problem in that the spark plug from No. 4 cylinder has traces of fresh oil on the electrode after being parked up overnight. I have also noticed the following symptoms:-

• Getting increasingly difficult to start in that I have to turn the engine over more times before it fires
• Running on 3 cylinders for approx 10 seconds after start up
• I’m still monitoring the situation with the coolant level, but I think it may be using a bit (but this could also be due to a small leak)
• Hydrocarbons were noted as being a bit high at the last MoT

The car runs very well indeed (obviously after the first 10 seconds following a cold start), it pulls really well right throughout the rev range and idles nicely. It always starts perfectly after the initial cold start with no misfiring. There is no trace of any coolant in the oil or vice versa and no trace of ‘mayonnaise’ inside the rocker cover.

The head was overhauled and converted to unleaded a few years back and has done less than 10K miles since. The car only has around 54K miles anyway and is very well serviced. I recently fitted a Powerspark ignition module and the carburation is good (according to my Gunson’s gas tester and looking at the spark plugs). To be honest the car is running better than ever so I’m a bit bemused as to why i’ve got this problem.

My initial thoughts on the likely cause is either valve stem oil seals (hopefully), head gasket failure or cracked cylinder head (please NO!!). I’ll do a compression test over the weekend and see if that shows anything but I just wondered if anyone else has experienced the same problem or can suggest anything else I should check before removing the cylinder head?

Any sign of blue smoke when it's running?

Not that iv'e noticed but it might be worth getting someone to follow me for a few miles to check.

I had a look inside no.4 combustion chamber last night using a dentist's mirror and there was a small amount of oil around the seat of the inlet valve.

I put the plug back in and took it out for a drive and it runs really well, no misfiring under full throttle uphill conditions or any hesitation at all. I checked the plug straight away when I got home and it looked fine so i'll check it again tonight after its been stood to see how much oil gets onto the electrode.

Given how well it runs and the fact that the oil seems to be concentrated around the inlet valve (presumably its likely that the inlet valve stem seals fail first as oil could be sucked past during the induction stroke) I'm hopefull that it is just a leaky seal and not a cracked head.

The misfiring i've been getting at start up is probably down to the oil getting on to the spark plug electrode causing it not to fire properly until its burn't off. Or it could be the chinese distributor cap!! I may still do a compression test for piece of mind.

So the next question is has anyone changed the valve stem oil seals without removing the head?

Sounds like you have it worked out Ross
Inlet valve seal and maybe your chinese distributor cap seem favourites to me as well. The distributor is the quickest and cheapest to replace on a try it & see basis too but I would expect it to be due to oil pouring down the valve guide while cooling down after being run...
Hope you beat it:)

I have never tried changing the oil seals without taking off the head so cannot say whether this will work, bug even if it doesn't nothing is lost by trying.
1)Remove the spark plug.
2) ensure piston is at bottom of its travel
3) Put a load of string or similar into the bore (remember to leave a loose end to get it out again)
4)bring the piston up again. This is to make sure the valve doesn't drop when you take out the valve spring)
5)Remove rocker cover and rocker arm when the top of the valve should be accessible.
6)Press down on the valve spring and remove the collets(this will be tricky and may need you to make up an improvised valve spring compressor)
7)Release & remove valve spring, when the seal should be accessible.
8) change seal
9) Reassembly is as they say the reverse of dismantling.

Thanks for the instructions John.

It certainly sounds feasible, I can imagine getting the collets back in will be the most difficult bit.

I think i'll wait until it really needs doing before i tackle this job as it is running well at the moment and there isn't any blue smoke from the exhaust.

The best way I have found to replace stem seals without taking the head off is to plug an air line in to the spark plug hole and put about 150 psi in with the piston at top dead centre, best to take the rocker cover off first, you will need a constant pressure so leave the air line on while you are working, oh and leave the car in gear