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10th May 1921, Page 28
10th May 1921
Page 28
Page 28, 10th May 1921 — FORD VAN POINTERS.
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Which of the following most accurately describes the problem?

By R. T. Nicholson (Author of "The Book of the Ford ").

I HAVE had a large number of problems submitted lately, to which it may be advantageous here to give the replies.

345.—Metal in Crankcase. G.W.C. says.

" I gave the crankcase a good scouring last week, and replaced with clean oil and in so doing found pieces of metal which came out with the waste oil. I enclose same for your insbection." (The "samples" were omitted.) Reply.—

If you ha-ne never thoroughly scoured out the crankc.aseabefore, the pieces of metal are probably only Elings dropped in when assembling. Odd bits of metal often find their way into the crankcase at that time. Ordinarily they do no harm whatever, though they can quite well " short" the magneto. If you have had your bands re-lined, and the material use:d for the purpose contained metal (as it

should never do), that might account for the pieces. Such metal from unsuitable linings scores the drums, an,cl might result in bad magneto shorting, upsetting the firing. Unless your engine shows signs of trouble—by knocking or misfiring—I should not worry over the metal. You ought, however, to be sure it is all out. You can make ,pretty sure if you remove the lower transmission cover door, and clean out the four snm,ps---three in the door, and one in the crankcase casting. You can grope into the last-named sump, and book foreign matter out.

346.—One Weak Cylinder.

" G.H.R." describes-his trouble thus:— " No. 1 cylinder seems to have little or no energy. Fot instance when testing the,•1•,Plugs, No. 1 doesn't slow engine up the same as the other three. I have examined commutator coils and • wires, which appear alright. I have exchanged coils with no better result. The spark seems good. I have also had cylinder top off and ground valves in, that certainly made it alittle better, but notdike the others. The peculiar part of it is that sometimes it seems better than others and it is more noticeable when running about 104o 15 miles per hour than it is at higher speeds. I also shortened roller spring as it seemed a bit on the weak side. Compression is good."

I reply It may be pretty well taken for granted that, your ignition devices have nothing to do with the case ; for your investigations have verified them. Good man Eliminatingsignition, we have to look at compression and valve action.

You say "Compression seems good." But should want to know that compression is good. When you turn the engine over (when warm) by hand, do you get four approximately equal resistances in succession? You should do. What makes me think that compression may be at the bottom of your trouble is that the engine seems tn run well on all four cylinders when going at good speed. That is exactly what I should expect of an engine having weak compression in one cylinder. At good speed, there is little time for the exploding charge to escape. Varying strength of the explosions in No. 1 cylinder. alto points in the same direction. Any gap that allows compression to escape might occasionally get filled up (with oil or otherwise), and so increase compression for the time being.

A minute crack in No. 1 combustion chamber, or in the piston top, or a break in the piston ring, or a partially carbonized ring, might have the effect described.

I assume that you have seen that the gasket. makes a gas-tight joint over No. 1 cylinder..

When the ,engine is running slowly, take the cap. off the breather pipe, and notice if the four back puffs in suocesion are all about equal in strength : particularly notice if they all seem equally hot. If you get puffs of unequal strength, or if you get one very hot puff in four; suspect one of the piston or cylinder troubles that I have named.

Another possible cause of your trouble is the existence of too big, or too little, a, gap between the valve stems and the tappets (or push-rods) of the faulty cylinder. The gaps should be just so small that when the engine is at its hottest, there is only just clearance between bottom of valve stems and tappets. This is ordinarily secured if, when the engine is stone . cold, there is just room for a thin visiting card between tappet and valve stem. Take off the valfe coner ; turn the engine over by hand (without firing) till one of the valves of • the faulty cylinder is right up: then lay a thin visiting card below valve foot and over tappet, so that it will " stay put " : then let valve down by continuing to turn engine by hand. When the valve is right down, you ought just to be able to withdraw the card without resistance. Test the other valve similarly.

What I am inclined to think is the matter is that the clearance is too great. I think this because You found some improvement after grinding in the valves. To remedy too great a clearance, put in a new valve, or valves. Old valves can he lengthened, but it is not worth the trouble.

I assume that you are sure that the upward and downward movement of the valves is free' and at the same time not" sloppy." A fault in either direction might cause your trouble.

347.—Wear of Commutator.

" Newcastle, wants to know:—

" I wonder if you could relieve my curiosity as -to how it isthat the comply wears in the', way it does. What I mean is this.—How is it that it does not wear a flat surface the same as it is when new, instead of the hills and hollows? "'

I try to tell him why.—

Commutator (or rather, timer) wear is due to two main causes—sparking whenever the roller makes or breaks contact with a, metal segment (such sparking eventually burning away the material), and difference in hardness of the fibre and metal.

Moreover, 011e& andepression has been formed, it tends not only to become deeper (because the roller strikes it with a bump), but also to cause another depression farther on at the point where, after bumping and jumping, it hits again.

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