Look after (7) the bearings of the crankshaft and if these are loose take out one or more shims on each side and tighten up the bolts of the bearings. (8) Should there be a ridge in the cylinder the only remedy is to rebore the latter or put in a new one, and if there is too much piston clearance take out the piston and put in new piston rings.
When knocking is caused by (10) preignition due to incandescent carbon in the cylinder, or because (11) there is a deposit of carbon in the cylinder it must be cleaned out. To get out the carbon you must take off the cylinder head and remove the inlet and exhaust valve caps.
By turning the crankshaft over you can bring the piston to its inner dead center so that it will be close to the cylinder head and then you can scrape the carbon loose and into the exhaust passage. After you have removed all of the carbon in this way brush the valve heads and their seats clean so that none of the particles of carbon stick to them and then wash them with kerosene; finally (12) should the piston head be too thin the only way to effect a cure is to put in a new piston with a thicker head.
When the Engine Overheats.—The Cause of the Disturbance.—The chief reasons why an engine over heats are (1) that there is a lack of water; (2) the water pump may not be working right, or (3) the water pipes or the radiator may be clogged up. (4) The oil may be of poor quality; (5) the spark may be retarded too much, or (6) if the engine is on a motor car the fan belt may be slipping; (7) the exhaust pot or the muffler may be choked up with soot; (8) the valves are not timed properly; (9) the fuel mixture is not properly proportioned; (10) the valves do not seat right; (11) the engine has not been tuned up, or run in, as it is called, and lastly (12) the radiator is too small for the engine.
How to Remedy the Defect.—When your engine gets too hot see that (1) there is a constant supply of cool water circulated between the jacket and the cylinder. If your engine has a hopper on it do not fill it more than 3/4 full of water, because the water will splash out when it boils; on the other hand, never let the water get as low as the top of the cyl inder, for then the latter will get too hot.
When the engine is working under a heavy load the water may boil, but this should not interfere with its proper working. Add water as it evap
orates to keep it up to the right level. (2) Find out if the water pump is fouled and if so clean it out, and (8) also clean out the water pipes in the radi ator, if the engine is a motor car one.
(4) Be sure the lubricating oil you use is of the best quality and that there is plenty of it; next (5) advance the spark, and (6) tighten the fan belt if it needs it. (7) The exhaust pot should be cleaned frequently, and even with mobile engines the muf fler must be kept free from soot.
(8) To time the valves is a very particular job, especially if your engine has more than one cylinder, and unless you understand how to do it, you had better let some machinist who is an internal com bustion engine expert time it for you.
In some stationary engines the inlet, or suction valve, is automatic in its action, and hence it needs no adjustment for timing. In engines of this kind, however, the exhaust valve should begin to open 30 to 35 degrees before the outer dead center of the crankshaft is reached.
The exhaust valve should close when the crank is about 5 degrees above the inner dead center.
To time the exhaust valve as above turn the crank over until it is in an upright position. Now adjust the exhaust valve rod so that there is about Yr inch space between the end of it and the adjusting screw in the valve rocker arm. When you have done this the timing gears will set so that the exhaust valve will open and close as I have stated above.
Where the inlet valve is worked by a cam, as in all mobile engines, it must lag, that is, it must not open until just after the piston has made its exhaust stroke, and it must remain open, or lag, until the piston has made about I of its compression stroke.
So that the burnt gases can be pushed out of the cylinder, or scavenged, to the best advantage the exhaust valve must lead a little, that is, it must open just before the power stroke is finished. Further, the exhaust valve when it is open must lag after the piston begins to make its suction stroke, so that every particle of the burnt gases can be scavenged and got out of the cylinder.