Expert advice ref. removed cyl.dr head.

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Foxy
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Expert advice ref. removed cyl.dr head.

Post by Foxy »

I've just removed the cylinder head from my 1.9 T.D. N reg. Xantia because main dealer said the head gasket had blown, so turned into a d.i.y. job.
The head gasket is of the metal type and has broken in one corner next to an oval slot(with what looks like an o-ring surrounding it) on the very edge, next to the camshaft sprocket end of head. There is also hard deposits of oil on the top of the adjacent piston, others look o.k.
Would be very pleased if someone with expert knowledge could give me their opinion. N.B. I do have pic.
Cheers, Foxy[?]
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Post by Peter.N. »

Does it look as though something has been eating it? The one on my XM failed prematurely (114k) and it looked as though someone had put battery acid in the cooling system! I think it had been parked up for sometime before I bought it and something in the water affected it, it almost fell apart when I took it off. They dont usually show any sign of disintegration, they just leak, usually between cylinders and of course, across the water ways. Thier usual life is about 150k.
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Post by fastandfurryous »

That oval slot is the pressure oil feed to the camshaft. It is a favourite place for that head gasket to go, I've seen (and repaired) a few now.
The oil either ends up spewing all down the side of the engine, contaminating the cambelt, or as in your case, going into the adjacent cylinder and being burned.
Only thing you can do really is check and clean up the face of the block, have the head skimmed (ALWAYS do this on an aluminium head. A good machine shop will only take off a thou to clean it up) and put together with another steel-elastomer head gasket.
The OE fitment on this engine (as far as I know) was NOT a steel gasket, but a fiberous one, so it sounds like the person who had the head off before didn't skim it, and hence it's leaked again in a very short time.
Edit: forgot to ask. How bad are the deposits on the piston crown? if they're very bad the best thing to do is put the piston at TDC, and have an assistant hold a (running!) vacuum cleaner right next to you while you scrape the deposits off with a blunt chisel. This makes sure none of the carbon ends up going down the side of the piston.
Can you post the pic here? If you email it to me I can host it for you if you like.
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Post by basil40 »

don't forget to replace with a new set of cylinder head bolts! after you've had it skimmed and ensure that you torque to the correct Nm settings and torque up the bolts in the correct sequential order. Be very careful with the chisel!
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Post by fastandfurryous »

There's a criteria for whether you need new bolts or not. It's based on the length of the bolts that you've removed. Usually they're still well within the tolerance, and only need to be changed if the head has been grossly overheated. Although if there's any doubt at all, new bolts are the safe option. A good wire-brushing, and a smear of grease on the threads will ensure accurate torque readings, and easier final tightening.
It's also worth investing in an angle gauge, as the final angle torque of 220deg has to be fairly accurate (+-3 degrees or so)
Forgot to mention earlier too... how long since the cambelt was last changed? if it's anything more than about 20k ago then it's probably worth changing it while everything's apart.
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Post by Foxy »

I have read the sound advice and many thanks! It has also struck me what caused the gasket to blow initially. Any tips on what to check for please?
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fastandfurryous
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Post by fastandfurryous »

Right. Here's the picture of the broken head gasket, and the cylinder head from Mr. Foxy:
Image
Bigger version here: http://www.fastandfurryous.co.uk/20050918_HeadBig.jpg
Looking at this, 3 things are apparent:
1, Blimey that head is coke-d up. How gently do you drive? That engine needs a damn good hoofing every now and then to keep it clean.
2, That's the OE fiberous head gasket, and NOT a steel-elastomer one.
3, That's a fairly standard failure.
This engine needs what I consider to be a the standard work done for a head gasket. This is:
* Camshaft out, bucket followers and shims kept in order.
* Injectors protected with small plastic bags and cable ties.
* Head skim. No need for more than a thou or two, as it's not warped.
* Valves out, and kept in order. Keep the collets and springs with each valve, and don't miss the fact that there is a steel cup washer under the springs.
* Clean each of the valves. The inlets are probably caked in hard carbon. A lathe (or a drill in a vice) and a blunt chisel works wonders here.
* Grind each of the valves into it's seat. Only use fine grinding paste, and don't go bananas.
* Fit new valve stem oil seals. (this is optional. Personally, I run without stem seals)
* Re-assmble valves, springs, collets, shims and bucket followers, oiling liberally.
* Re-fit camshaft VERY CAREFULLY. The bearing caps are very easy to crack. Be very progressive with your 12mm socket.
* Measure clearances, do the calculations and order the correct shims. Diss-assemble, re-assemble. (number jonny 5)
* Fit new steel-elastomer head gasket (it looks like a load of layers of thick tin foil)
* Stick head on, do up bolts.
I've missed a number of "fairly obvious" bits out of this, which you will no doubt know, or you woudn't be attempting this! (EG, clean all the valve grinding paste from the ports with paraffin... )
Hope this has been of some help.
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fastandfurryous
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Post by fastandfurryous »

Just for comparison, this is what that head should look like when it comes back from the machine shop, and has all the valves out.
Image
Looks much nicer doesn't it!
The other things I meant to mention earlier:
These engines are renouned for eating the OE head gasked at some point between about 110k and 140k miles. I've seen too many at about this mileage for it to be by co-incidence.
The coolant passages on your head, and in your head gasket don't look too great. Was the water a rather rusty brown? It can't be stressed enough with this engine that you should have a 50/50 mix of good quality coolant, and change it every few years.
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