FORD VAN POINTERS.
Page 23
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By R. T. Nicholson (Author of The Book of the Ford ").
WHEN THE valve stems and valve guides get worn sifter a very long mileage, air leaks:in at the worn .points and upsets the "mixture." '
174. Air Leakage •Past Valves : Symptoms, Trouble, and Cure.
If you find it difficult to stopyour engine by pulling out the air throttle wire, you may take that as a sure sign that there is air leakage somewhere in the induction system—either at the carburetter, or the in duction pipe, or round the valve 'stems, and the odds are the leakage is round the valve stems. Another result of such leakage is that it makes it impossible to run the 'engine at all slowly—and it ought, of course, to be ready to " tick over" when called upon to do so. When there is much air leakage round the valve -stems, the " mixture " will not fire at all 'unless there is also a liberal supply of benzole or petrol—that is, unless the 'carburetter spray orifice is well opened up, and that in turn means that you cannot get slow running. But, the worst of air leakage is that it makes the engine very hard to start. Just at the time when you want it least., the air pours into the cylinders round the valves and weakens the mixture.
It is the wearing of the inlet valve stems and guides that matters most. Wear 'there means a lot of " extra air" at starting, and, as we all know, extra air at that time means mischief. Wear of the exhaust valve stems and guides does not matter so much.
175. The Cure for Air Leakage.
The proper way to 'overcome this trouble is, of course, to fit new valves and new guides ; but the fitting of new guides, 'at all events, is a pretty big job,. and it is no use fitting new valves unless you also fit newguides. I am-going to tell you of a very good "makeshift" way of curing the trouble.
The next time you have your cylinder head off for decarbonizing, remove all the inlet valves at all events, and the exhaust valves, too, if you like. (This is a matt-nof using a valve-lifter, so that you can compress the springs upwards and draw out the cotters, thus releasing the valves from the springs.) Now get some felt and cut a disc from it for each valve that you are going to treat--four if you are only .going to treat the inlet valves, eight if you are also going to treat the exhaust valves. Each disc should be about i-in. thick, or it may be built up to that thickness from a number of thinner discs. These discs can be' cut from an WA soft felt hat, or On. felt can be bought. These discs should be of such size that they will easily pass inside a valve spring without binding.
Bore a hobs in the middle of each disc, So that it will 'lip quite easily, but not tea freely, 'up the Valve stem. You will now have four, or eight, felt washers, or four, or eight, piles of felt washers, each i'-in. thick.
Get a light, spring for each valve, of about the length of the whole valve stem, and just big enough to pass easily up the stem..
Now replace the valves and thread the washers up each stem from below: then slip up the light spring, so as to press against the felt washer.; then replace the valve spring proper, and the retaining collar that goes below it, compress the springs, and slip in the cotter, seeingthat it is central.
You will then have' an arrangement like that shown in the illustration.washers will be pressed up against the engine casting, and so keep the valve airtight at that point.
It is as well to soak the felt in oil before putting it into position. Graphite " dope " is also good. The valve stems will thus be lubricated. Once the felt is in working" position, it will always pick up a certain amount of oil from-the engine.
The purpose of the light springs is to keep the washers hard up,' and to prevent the felt from creeping down the valve stems, The springs Should not be heavier than is necessary for that-purpOse. They will somewhat increase the tension on the valves, but that is rather a good thing, for old valve springs are apt to weaken a bit, so that 'a little extra tension is all, to the good. Thispacking7ofiwashers stands up well, and seldom needs replacement, which, when necessary, is a matter 'of a few minutes only.