Engine Bearings

This oil-pressure test has been in successful use in the Air Service and in the maintenance stations of two prominent automobile manufacturers for several years.
If properly applied, it will indicate the following:
1. The condition of the bearings in pressure-lubricated engines, that is, if there is too much diametrical clearance, also if the end clearance is more than the manufacturer's recommendation.
2. Whether or not over-oiling is due to improperly fitted bearings or the cause is in the pistons and rings.
3. If drilled passages of camshaft and oil-distributing line are clogged or partially obstructed.
4. Will serve to check the fit of bearings after over-hauling as well as for inspection before overhauling.
5. Will check the condition or accuracy of the pressure gauge on the car instrument board.

Testing Bearings on a Pressure-Lubricated Engine with Oil under Pressure'
The testing outfit which is shown in Fig. 1 consists essentially of a gallon tank that will stand about 100 lbs. pressure, an air-pressure gauge soldered into the top, an outlet nipple and shut-off valve at the bottom, a tire valve stem, and some form of filling spout with an air-tight joint at the top.
The outlet nipple on the test tank is connected to the oil circuit of the engine immediately past the regular engine oil-pump outlet.
The oil pump of the engine should always be kept out of the circuit, and if there is any difficulty in doing this, follow the oil line to the point where the oil leaves the pump and first enters the crankshaft bearings. Thiswill be the .
point where you will (0 roA/RwRPCr
want to connect the out- TIRE VALVESTEM let side of the test tank..
Fig. 2. The outlet of test tank is always connected to the oil circuit at the point where the engine pump outlet was connected.
When this equipment has been secured, the mechanic is ready to proceed on the test as follows:

1. Drop oil pan from engine so as to expose lower rod and main bearings. Place large drip pan under engine to collect oil thrown off during test.

2. Pour about three quarts of oil into test tank, screw filler cap on tightly, and close lower valve.
Oil used in the test tank should be of the same grade and viscosity as used for lubrication in the particular engine. Very good results will be obtained by using the oil drained from engine being worked on. However, if the drained oil is badly thinned or diluted, use new light or medium grade oil.
3. With a suitable piece of copper tubing or high-pressure air hose, connect the outlet nipple on the test tank to oil-distributing manifold in engine.
If there is any doubt as to where to make the connection, follow the oil line from the outlet side of the pump to the point where the oil first enters the crankshaft or distributing manifold as the case may be. This will be the point where the test tank is to be connected.
1 See also page 806 of Auto Encyclopedia.
4. With a hand pump or compressor attached to the tire valve in the test tank, pump air into it until the gauge shows about 30 lbs. pressure.
If the engine is designed to operate at a higher oil pressure, raise the pressure in the test tank to correspond to the engine manufacturers' recommended average oil pressure.
5. Now open the shut-off valve at bottom of test tank, turn engine slowly by hand, and observe reading on the car instrument board oil gauge and air gauge on test tank. The readings should be approximately the same.
The gauge on test tank should show not more than 5 lbs. pressure increase over that of the oil gauge on the instrument board.
6. Watch underneath to observe the amount of oil coming out of the bearings. There should be a drippage from each, but in no case (except when the previously mentioned metering holes register) should the leakage be in a solid stream.
Exceptions to this are on those engines
where the front end chain or gears are pres sure lubricated, and also on those con-
structions where piston and pin lubrication is accomplished by means of holes in
the lower connecting-rod bearing (Fig. 2 A,
at 8) which register with the metering or supply hole in the crank pin, at which time rig. 2A oil shoots up to the piston and cylinder walls. (A construction of this type is used on Chrysler, Franklin, and Nash engines.) Exceptions also apply to engines using a longitudinally drilled rod, such as Packard 6 and 8 or a piston-pin-bearing oil-supply pipe, attached to side of rod, as on the Velie and Marmon.
In either case when these holes line up there will be a drop in pressure and an excessive amount of leakage from the bearing in the register position.
The maximum and minimum drippage standards indicated in the following paragraphs will enable a satisfactory check of the condition of rod and main bearings. Where the repair establishment is specializing on one certain make of car, it is possible to establish even more accurate standards of oil drip-page by applying the test tank to one of these known to be in perfect shape. By observing the exact number of drops leakage per minute using any given brand and viscosity grade of oil under a given test-tank pressure, the data recorded can be set up as the ideal standard for that make and model.
Similarly if the test is applied to a car of same make and model where it is known that one or more bearings are loose or otherwise imperfect, the amount of leakage indicating the conditions will be set up as the rejection standard for that car.
The ideal contact and clearance exist when the leakage from any rod or main bearing does not exceed 80 drops per minute maximum, and is not less than 10 drops per minute minimum (on Studebaker "Big Six" the manufacturers recommend that the leakage from main and connecting-rod bearings be not less than 20 drops per minute and not fast enough to run in a solid stream).
A stream of oil from any bearing indicates that it has either too much clearance, improper grooving, poorly fitted shims, excessive end play, or a bad joint between the rod and cap.
Any bearing showing more than 100 drops leakage using medium oil, or 140 drops per minute with light oil in test tank should be removed and inspected for one or more of the conditions just mentioned.

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Carburetor Manuals: Engine Bearings