Oily spark plug - valve stems seals or worn bores?

[Reverend Frog 10]

My VR6 was running roughly, so I took the plugs out to check them.

 

The plug from cylinder 1 was the worst - covered in oil (oil has even managed to splash out on to the HT lead cap as well).

 

The other plugs were in better nick but still a little oily in places.

 

The previous owner told me he had the head rebuilt (with new valve stem seals).

 

He also had it compression tested, and it was good in all six cylinders.

 

So I'm confused - if the valve stem seals were replaced then it can't be them, but surely if the compression is good then it can't be the bores!

 

The engine has 102k on it.

 

but what do you guys think?

Edited September 7, 2016 by Reverend Frog

[fla 9]

I would remove and clean the plugs then refit and take for a good hard drive. Then inspect again. I believe bores 1 & 6 suffer from the greatest bore wear.

Incidentally when was the head rebuilt and do you have any details from the garage?

[Reverend Frog 10]

Incidentally when was the head rebuilt and do you have any details from the garage?

 

Not sure when head was rebuilt - would guess between 2010 and 2013 some time.

 

and it was done by the previous owner's mechanic after he bought the parts himself, so no details on file.

[jekel 10]

If you let it coast down a long hill then when put foot down after descending you get a puff of grey/black smoke, think that's a pretty strong sign it's stem seals, but maybe bores also do that, someone on here will confirm.

A leaky rocker cover gasket is pretty common and will drip oil down on to the plugs, but won't cause the downhill coast test, if your very lucky, cheap easy fix. The rubber on the gasket goes hard, starts leaking etc., but should have been replaced at the rebuild.

All assuming decent parts and decent job done on the rebuild.

[Tigerfish 10]

No internal issues are going to get oil on the HT leads (well, only very terminal ones like rods through the block... lol), so the rocker cover gasket and/or oil spills from top ups and/or badly fitting filler cap would be the favourite candidates. The breather from the rocker cover can drip as well.

 

Are the plugs actually oily on the electrode of the plug? Or just oil running down the plug when unscrewing it?

 

 

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[Reverend Frog 10]

If you let it coast down a long hill then when put foot down after descending you get a puff of grey/black smoke, think that's a pretty strong sign it's stem seals

 

That's precisely what it does.

 

that's potentially good news...but I'm surprised when the valve seals have purportedly been done. Of course there's a big difference between being 'done' and 'done properly' and I have no proof that they have.

 

I was thinking it would be unusual that the bores are worn at only 102k.

 

be good to hear others' opinions...

[Reverend Frog 10]

Are the plugs actually oily on the electrode of the plug? Or just oil running down the plug when unscrewing it?

 

The electrode on plug 1 was fouled, yes, and the threads were oily too.

[fla 9]

if it is stem seals, either a proper head rebuild or you can use a seal conditioner from Forte which softens the seals and allows a better operation. The late great Chris Gaskell recommended the product to me some years ago.

[Reverend Frog 10]

if it is stem seals, either a proper head rebuild or you can use a seal conditioner from Forte which softens the seals and allows a better operation. The late great Chris Gaskell recommended the product to me some years ago.

 

Sounds interesting - is this a product that needs directly applied to the seals - ie head needs taken off? or do you just squirt it somewhere indiscriminate;y? I'm not very technical :)

[Reverend Frog 10]

Just been out to investigate and as suggested the rocker cover gasket is not well fitted and there is evidence of an oil leak right above cylinder 1's spark plug...could be at least a partial solution to the problem