Would be grateful for any advise. I have decided to overhaul my CVH cylinder head from a 1991 Ford Fiesta Xr2i as it was starting to burn oil(blue smoke). Having removed the head, springs and valves the oil stem seals seem ok ( to my eye) I am replacing anyway as a matter of course but would these seals not be the problem concerning the burning oil?
Also when I am cleaning the valves do I clean them fully on there heads ie. remove all traces of carbon and other grime so they are gleaming? Any help much appriciated as would any advise on other things to do as good practice with the head off. All gaskets and head bolts are being replaced.
Kind regards
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CVH suffered from valve guide probs as well as valve seals.on older cars you could get away with just a few turns to seal the valve.you cant on CVH you either do it properly or you dont.meaning prob will come back.I would suggest doing it properly or you will have to do it all again. You didnt mention how you are burning oil ie changing gear or all the time.?
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Was mech1
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Thanks for the reply. My next task is to seal the valves as you say, but how do I know exactly when I have done enough with the cutting paste to create a gas tight seal is there any visual indication on the valve? Because I have heard if you keep going with paste you can ruin the valve seal
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When cutting in a valve using grinding paste, you should see a light grey colour right the way around the valve and valve seat. Any gaps indicate you haven't got a good seal.
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Valve stem seals should always be replaced on all engines if doing work on heads.However,they go hard when cold and this allows oil to drain down the valve stem and cause the puff of smoke when you first start-up-when they get warm they should seal better-if you are getting smoke all the time and they are not badly worn,then it is more likely to be pistons/bores.
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I remember from grinding-in valves years ago that the sound and feel were a good guide. As you progress to the finer paste the noise it makes changes - hard to describe, but you just sense it is making a finer fit, a bit like a glass stopper in a scent bottle.
Also it starts to stick more as you try to twiddle the valve, and you find the rubber sucker keeps coming off because the valve is binding like a limpet into the seating.
Finally clean off all the paste carefully and put a bit of blue engineer's marker on the face. Turn the valve and the colour should smear evenly over the whole seating area.
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If you've already got the head off it's not a great deal of extra work to remove the pistons. Measure the bores for wear with an internal micrometer, and if they're not too bad you could get away with just a set of standard rings after de-glazing the bores. It's a good idea to measure the crankshaft too, and again if wear is minimal a set of standard big-end shells will do.
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Thanks all for the advice, very helpful. I shall now tackle it!!
Regards
Steveo4869
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If I remember correctly the CVH valve seats are hardend and grinding them in will remove this. I recall it mentions this in the Haynes I used when I did my XR3i. I'd check before you go ahead.
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It takes an awful lot of grinding to go thro' the hardening!
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On the old Ford V4's the inlet valves couldn't be ground in as they were aluminised and any attempt at grinding removed the coating. The correct method was to recut the seats and use the same new valve to grind each seat. When grinding was finished a brand new valve was used and the final part of the procedure was to tap the valve head sharply to help it to seat properly. Even today I give freshly ground valves a couple of taps to flatten any microscopic raised bits.
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An unbroken ring of matt grey is whats required, if there are any very deep pits across the seat it's probably best to get the seats cuts and valves re-faced. Tip i found useful was to place each valve in a pillar drill and use emery cloth to clean the carbon off with.
Quite bad pits can be removed by grinding but you can end up with pocketed valves if you grind for too long with coarse paste, meaning the seats get too wide reducing gas flow and the heads too thin for proper heat dispersion.
From memory inlets should be 1.5mm and exhausts about 2mm on the CVH although don't think it matters that much if they got a little wider than that, most important thing is to get a gas tight seal.
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When you get it back together ensure you take it upto 4500/5000 rpm regularly-it makes the valves rotate on their seats and evens out the wear.his applies to all engines-not just CVH.Some large lorry engines have rotators built in as part of the valve-gear.
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