Valve seals or head gasket?

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mrbump
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Valve seals or head gasket?

Post by mrbump »

Hello,
I have a problem with my xud turbo diesel engine whereby the engine runs fine but has trouble starting due to oil in the cylinders. It has trouble starting at first, but give it some throttle and when the oil clears, it runs fine with no noticable smoke.
It pressurises the coolant as well slightly, but a dose of radweld seemed to cure that.
My question is - do you think that the oil could be leaking into the bores through the head gasket alone, or is it more likely that the valve stem oil seals have failed?
It also seems to be leaking oil from the crankshaft oil seal - i assume from pressure build-up finding the weakest link.
Should I try just replacing the head gasket or get a full recon head?
Again any advice would be greatly appreciated.
Cheers
jeremy
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Post by jeremy »

Has your engine got valve stem oil seals? Ordinary 8 valve XUD's dont - having brass guides I think. If yours is a 2.1 it may be different.
Ordinary XUD's, especially turbo's don't tolerate overheating and you should flush and get rid of the radweld. In particular you should flush the radiator very carefully and make sure its flowing properly and that all the core is clear as they tend to block from the bottom upwards.
If the crankcase is pressurising then there are 2 posssible causes, head gasket or bore wear. You may be able to narrow things down a bit with a leakdown test and a compression test and I've no doubt someone will give you the full details.
You haven't given us details of mileage but unless it is enormous or the engine has been neglected or abused (unlikely on a 2.1 as they go well) I would suspect the head gasket. Add to this the cooling system pressure and I'm almost certain.
I would remove the head and examine it and the gasket very thoroughly, looking especially for cracking and warping. Some minor racking round the pre-chamber outlet may be acceptable but other cracks are not. Ordinary XUD (especially turbo) heads are prone to cracking and often these cracks open when cold and seal as the engine warms up! I understand that later engines are better and that the head was modified (thicker casting?)
Crankcase pressure will cause oil to leak from all the seals and gaskets which are not designed to withstand internal pressure. It sounds to me as though the head gasket has blown on one or both end cylinders, near to the oil return holes.
Jeremy
algieuk
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Post by algieuk »

Head gasket is gone if it is pressurising your coolant. What makes you think there is oil in the cylinders though? If there were sufficient oil there to cause a problem then the engine would not turn over due to hydraulic pressure. Otherwise oil in the cylinders would actually help starting by increasing compression. If your crankase is over pressurised then your breather must be blocked. I cannot imagine a crankcase pressurised enough to force oil past the crank seal or gaskets without blowing the dipstick out or pumping all of the oil up into the air cleaner, which would be its easiest way out.
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mrbump
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Post by mrbump »

Hi,
The oil IS being forced up into the airbox as well. And there IS definetely oil lying in the cyliders which is blown out when starting in the morning - you can see it and smell it (lots of smoke then clears and runs OK).
JEREMY - I think you are right about the 8 valve not having stem seals just the bronze guides. Do these guides come with a headgasket kit? I have the chance to buy a fully recon head with new guides already installed, valves reground etc for £200. Do you think it is a good idea to buy this or just go for a headgasket set? Is there any way of telling if it is the TD head or just N/A from marks or stamp? As I see these are listed separately in some places.
Thanks for reply
jeremy
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Post by jeremy »

Oil alone getting into the cylinders will not impede starting. the injectors inject into a small chamber situated in the head and there is no way lubricating oil can get there.
Every time the engine cranks over it will inject fuel into the combustion chamber mechanically, regardless of whether the fuel is ignited or not. This fuel remains there until the engine fires when it is either burnt incompletely (black smoke) or ejected unburnt (white smoke). If the engine has been cranked for some time this can be quite spectacular, especially if the injectors are past their best.
Assuming the bores / pistons / rings are ok I think the problem is the head gasket and this should be replaced. there may be nothing wrong with the head itself but when it has been removed it should be thoroughly examined for cracking and distortion as well as corrosion of the waterways. If all is ok then it can be re-fitted but it is probably worth checking the valve clearances while it is on the bench.
To answer you other questions - I would not expect to find valve guides in the gasket set. I dont know how difficult it is to fit valve guides but it is generally considered a specialist job and afterwards it is always necessary to regrind the valves as there may be a minor difference in the alignment of the valve and its seat. I have never seen any mention of a problem with guides on diesel engines on this or any other board and do not think they are contributing to your problems.
A recon head for a turbo for £200 sounds very good value. I do not know how to differentiate it form other heads except for some of the early N/A engines which may have had different port shapes. There is a plate attached to the front of the head under the injector at the flywheel end but I dont know how to read it.
I think the gasket has gone at the belt end of the engine and the no 4 cylinder is blowing out gas into the oil return way on the power stroke. The failed gasket will mean reduced compression on one or more cylinders and this makes the engine reluctant to start. A little unburnt fuel produces a lot of smoke and I think it is unburnt fuel you are seeing rather than lubricating oil.
Jeremy
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Post by rossd »

Normal XUD's do have the rubber valve guide seals, IF they have the suffix L after them, eg XUD9TE/L or XUD9L.
Hope this helps
Ross
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mrbump
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Post by mrbump »

Jeremy - thanks for the reply.
I will be taking the head off this weekend and doing the gaskets. I am leaving the valve guides alone.
Hopefully this will be the only problem. I have a feeling however, that the problem may lie in other things as well like the rings and injectors. It is a tired engine and if the head gasket doesnt cure it completely, its getting binned in favour of a newer model.
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algieuk
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Post by algieuk »

If you have the head of make sure you check the valve clearances. They have a nasty habit of closing up making for low compression and difficult cold starting.
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