A MAINTENANCE HINT.
Page 19
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Opinions of an Expert on a Case of Excessive Oil Consumption.
ONE of our readers recently purchased an R.9 Pierce-Arrow, and is seriously troubled owing to the excessive oil consumption. The front pair of cylinders are often covered with oil, and so much of this passes the pistons that there is a considerable quantity of oil in the valve caps after a day's run.
About two gallons of oil are used for a day's run of about 50 miles, and the trouble was thought to be due to missing baffle plates, bad rings or scored cylinders, but on lifting the front block the baffle plates were found to be correct, and both the cylinders and rings were in perfect condition.
Another driver had informed him that the trouble was probably due to the gudgeon pins, as he contended that these should be hollow and capped at both ends, but the pins on the vehicle in question were not so capped.
The trouble is only with the front block of cylinders ; the rear block keeps perfectly dry.
As a result of this letter, we wrote to Messrs. George Bright (distributors for the Pierce-Arrow Motor Co.), West Heath Yard, Mill Lane, West Hampstead, London, N.W.6, and we have received a most comprehensive reply, from which we extract the following details:—
The chief complaint seems to be excessive oil getting past the pistons Nos. 1 and 2 in the front cylinder block. It is possible that your correspondent has an 11.8 model which has been converted to an 11.9-type force-feed lubrication. A number of these conversions have been made by people not having a full understanding of the requirements, and, in consequence, customers have had considerable trouble.
Mr. Bright stated that he would personally be only too pleased to inspect the lorry and tell whether it was a genuine 11.9 or not.
The fact that Nos. 1 and 2 pistons oil up and that no trouble is experienced with Nos. 3 and 4 would indicate that either the bores of the front cylinder block are worn oval and the pistons are a sloppy fit or the rings have not been lapped in properly.
If, upon further examination of the cylinder, the bores, pistons and rings are found to be in perfect condition, he has suggested that the baffle plates be removed.
Regarding the pistons, R.9 pistons have oil-relief holes drilled through the bevelled surface on the outside edge of No. 3 ring to take care of excessive oil getting into the cylinder bores. The holes in the tops of the connecting rods should be plugged. The gudgeon pins are not capped, and R.9 gudgeon pins have no holes in them, as in the _R.8 type supplied for the gravity-feed system. The oil is fed by a small pipe from the big-end bearing to the small-end. As the pressure varies between 3 lb. and 20 lb., it is essential that no hole be provided for the escape of this oil which runs into the bushes, the excess finding its way down inside the postons.
The 11.9 engines are not fitted with baffle plates, although in some instances they have been put in. In the circumstances it would appear that the trouble is possibly due to the 11.8 gudgeon pins being used instead of the 11.9.
The following are adjustments of the oil pump on the 11.9 engine. The oil pressure is altered by two regulating valves on the pump, the low-speed pressure adjustment being obtained in the following manner :— First, with the engine hot, back off on the small highspeed adjusting valve, which will be found at the side of the pump next to the crankcase, until the valve is wholly open. Then throttle the engine down to its lowest free running speed and adjust the low pressure by the outer regulating valve, which is the larger one. Then tighten the locking nut on this valve. To make the high-speed adjustment, allow the engine to run at its highest or governor speed when, by turning down on the high-speed valve, the desired pressure of 20 lb: can be secured. Then screw up the lock-nut. Adjustment should not be changed unless absolutely necessary, possibly after overhauling. The oil strainer is located in the sump. it should be removed and cleaned at least every 1,000 miles. If the oil pressure drops below normal while there is ample oil, it may be that the strainer is clogged.