road and workshop
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Benchwise: cool it (16)
THE WATER PUMP is the only driven unit in the cooling system. Most people tend to think of it as a "Fit and forget" part, but it should really be thought of as the heart of the system and remembered when things do not stay as cool as they should. It is called upon to turn at quite high speeds, and 5000 or 6000 revs is not uncommon. Larger pumps can be circulating 6000 gal or more per hour. If the engine is to stay within its normal temperature range the pump must be maintained.
The most common cause of pump failure is a slack drive belt or bolts. Normal wear and tear occurs but maladjustment may cause the belt to wear on the sides owing to regular slip, and touch the bottom of the V in the pulley.When this happens it does not matter how tight the belt is adjusted—it will be slack again in a very short time. Bump speed will be progressively reduced. The belt has got to grip the side walls of the pulley by wedge action, and this cannot take place if the belt is "bottoming" on even one pulley.
Sign of slip The usual sign of slip is that the bottom of the pulley is polished bright, and when this has happened the belt should be replaced. On occasions, however, a single V-pulley can itself be worn too wide in the V to grip even a new belt; then it is the pulley that has to be replaced.
If there is enough metal then it can be mounted in the lathe and one or two cuts taken at the bottom of the V. One sixteenth turned out here can clear the trouble for quite some time. Where twin or triple belts are fitted one can be slipping unnoticed; all
three must take equal tension and load.
Where a pulley is not machinable or readily replaceable, it is well worth while checking with the factory to see whether a thicker alternative belt can be obtained. While this may not be listed under the engine make in question, I have found on a number of occasions an oversize belt in another bin that did the job exactly.
Apart from the obvious belt trouble or failure, pumps can be giving trouble for other reasons. The edges of the impeller miy be eaten or corroded, thus water is not driven along the galleries and out to the radiator. The reduced area of blade takes less water with it. The fault is that the impeller blade edges are worn.
Worn housing However, the actual housing for the impeller may also be worn, and this is due as a rule to sand or grit in the coolant, through using dirty water. If there is sand or rust in the system, it will act as an abrasive on the impeller and casing with the contents of the system circulating 2000 times per hour, a fair amount of sandpapering will take place.
It is not unknown for an operator to be caught out by a quick, severe frost before antifreeze has been added to the system and either impeller blades, spindle or drive pin may be sheared off.
If the pump jams solid the driver will know. The belt will certainly yell out clear enough, but a sheared pin or spindle can pass unnoticed until overheating occurs.
However, the pump is more prone to leak rather than to fail altogether and a leak can develop at the pump housing joint. Lubrication starvation can cause pump failure at the bearing, but greasing can be overdone and excess grease forced out of the bearing chamber along the spindle into the water chamber, where it is going to do a lot more harm than good in the form of clogging and consequent overheating.