SECTION 2-E 1950 BUICK REPLACEMENT OF ENGINE PARTS LIKE CRANKSHAFT AND CONNECTING ROD BEARINGS, PISTONS AND RINGS

2-21 REPLACEMENT OF CONNECTING ROD BEARINGS

A connecting rod bearing consists of two halves or shells which are alike and interchangeable in rod and cap. When the shells are placed in rod and cap the ends extend slightly beyond the parting surfaces so that when rod bolts are tightened the shells will be clamped tightly in place to insure positive seating and to prevent turning. The ends of shells must never be filed flush with parting surface of rod or cap.

If a precision type connecting rod bearing becomes noisy or is worn so that clearance on crankpin is excessive, a new bearing of proper size must be selected and installed since no provision is made for adjustment. Under no circumstances should the connecting rod or cap be filed to adjust the bearing clearance.

Inspection of Connecting Rod Bearings and Crankpin Journals

After removal of lower crankcase, disconnect two connecting rods at a time from crankshaft and inspect the bearings and crankpin journals. While turning crankshaft it is necessary to temporarily reconnect the rods to crankshaft to avoid possibility of damaging the journals through contact with loose rods.

If connecting rod bearings are chipped or scored they should be replaced. If bearings are in good physical condition check for proper clearance on crankpins as described in subparagraph b, below.

If crankpin journals are scored or ridged the crankshaft must be replaced, or reground for undersize bearings, to insure satisfactory life of connecting rod bearings. Slight roughness may be polished out with fine grit polishing cloth thoroughly wetted with engine oil. Burrs may be honed off with a fine oil stone.

Use an outside micrometer to check crankpins for out-of-round. If crankpins are more than .0015″ out of round, a proper adjustment of connecting rod bearings or satisfactory life of new bearings cannot be expected.

Checking Clearance and Selecting Replacement Bearings

Service bearings are furnished in standard size and several undersizes, including undersizes for reground crankshafts.

The clearance of connecting rod (and crankshaft) bearings may be checked by use of Plastigage, Type PG-1 (green), which has a range of .001″ to .003″. Plastigage is manufactured by Perfect Circle Corporation, Hagerstown, Indiana, and is available through Buick parts warehouses under Group 0.093.

  1. Remove connecting rod cap and wipe oil from bearing and crankpin journal, also blow oil out of hole in crankshaft. NOTE: Plastigage is soluble in oil.
  2. Turn crankshaft so that crankpin being checked is approximately 30 degrees before bottom dead center. In this position the clearance will be checked at point of least clearance if crankpin is worn out of round, and the Plastigage will not be at oil hole in crankshaft.
  3. Place a piece of Plastigage lengthwise along the bottom center of the lower bearing shell (fig. 2-24, view A), then install cap. Tighten bolts to 40-50 ft. lbs. torque on Series 40-50 engine, or to 60-65 ft. lbs. torque on Series 70 engine. NOTE: A ridge formed on edge of cap and a boss formed on web of rod above the bearing must be in line and toward rear of engine when cap is installed.
    1950 Buick Checking Bearing Clearance with Plastigage

    1950 Buick Checking Bearing Clearance with Plastigage

  4. DO NOT TURN CRANKSHAFT with Plastigage in bearing.
  5. Remove bearing cap. The flattened Plastigage will be found adhering to either the bearing shell or the crankshaft. Do not remove it.
  6. Using the scale printed on the Plastigage envelope, measure the width of the flattened Plastigage at its widest point. The number within the graduation which most closely corresponds to the width of Plastigage indicates the bearing clearance in thousandths of an inch. See figure 2-24, View B.
  7. The desired clearance with a new bearing is .0008″ to .0015″. If bearing has been in service it is advisable to install a new bearing if the clearance exceeds .022″; however, if bearing is in good condition and is not being checked because of bearing noise, it is not necessary to replace the bearing.
  8. If a new bearing is being selected, try a standard size, then each undersize bearing in turn until one is found that is within the specified limits when checked for clearance with Plastigage. NOTE: Each undersize bearing shell has a number stamped on outer surface on or near the tang to indicate amount of undersize.
  9. After the proper size bearing has been selected, clean off the Plastigage, oil the bearing thoroughly and reinstall cap. Tighten connecting rod bolts to 40-50 ft. lbs. torque on Series 40-50 engine, or to 60-65 ft. lbs. torque on Series 70 engine. Tighten Pal-nuts just enough to lock securely.
  10. With selected bearing installed and bolts tightened, it should be possible to move connecting rod freely back and forth on crankpin as allowed by end clearance. If rod cannot be moved, either the bearing is too much undersize or a misaligned rod is indicated.

 

2-22 REPLACEMENT OF CRANKSHAFT BEARINGS

Crankshaft bearings are the precision type which do not require reaming to size or other fitting. Shims are not provided for adjustment since worn bearings are readily replaced with new bearings of proper size. Bearings for service replacement are furnished in standard size and several undersizes, including undersizes for reground crankshafts.

Under no circumstances should crankshaft bearing caps be filed to adjust for wear in old bearings.

A crankshaft bearing consists of an upper and a lower half or shell. In Series 50 engines the upper and lower shells are interchangeable. In Series 40 and 70 engines the shells are not interchangeable since the lower shell has a short oil groove and the upper shell has full length oil groove across the middle, and an oil hole. When the shells are placed in crankcase and bearing cap the ends extend slightly beyond the parting surfaces so that when cap bolts are tightened the shells will be clamped tightly in place to insure positive seating, and to prevent turning. The ends of shells must never be filed flush with parting surface of crankcase or bearing cap.

Inspection of Crankshaft Bearings and Crankshaft

After removal of lower crankcase, oil pump and flywheel lower housing (syncro-mesh) or bell housing cover (Dynaflow) perform the following removal, inspection and installation operations on each crankshaft bearing in turn so that the crankshaft will be well supported by the other bearings.

  1. Since any service condition which affects the crankshaft bearings may also affect the connecting rod bearings, it is advisable to inspect connecting rod bearings first (par. 2-21). If crankpins are worn to the extent that crankshaft should be replaced or reground, replacement of crankshaft bearings only will not be satisfactory.
  2. Remove one bearing cap, then clean and inspect lower bearing shell and the crankshaft journal. If journal surface is scored or ridged, the crankshaft must be replaced or reground to insure satisfactory operation with new bearings. Slight roughness may be polished out with fine grit polishing cloth thoroughly wetted with engine oil, and burrs may be honed off with a fine stone.
  3. If condition of lower bearing shell and crankshaft journal is satisfactory, check the bearing clearance with Plastigage as described for connecting rod bearings in paragraph 2-21.
  4. When checking a crankshaft bearing with Plastigage, turn crankshaft so that oil hole is up to avoid dripping of oil on Plastigage. Place paper shims in bearing caps of adjacent bearings and tighten cap bolts to take the weight of crankshaft off the lower shell of bearing being checked. NOTE: Arrow on cap must point to front of engine.
  5. If the bearing clearance exceeds .002″, it is advisable to install a new bearing; however, if bearing is in good condition and is not being checked because of bearing noise, it is not necessary to replace the bearing.

Selection and Installation of a New Crankshaft Bearing

  1. Loosen all crankshaft bearing cap bolts 1f2 turn, and remove cap of bearing to be replaced.
  2. Remove upper bearing shell by inserting a suitable tool in crankshaft oil hole and turning crankshaft to push shell out. Tools for this purpose are available through automotive jobbers. If a tool is not available, a 1/8″ x 1 1/2″ cotter pin with ends bent to lie flat against crankshaft journal may be used. CAUTION: When turning crankshaft with rear bearing cap removed hold oil seal to prevent it from rotating out of position in crankcase.
  3. The crankshaft journal cannot be measured with an outside micrometer when shaft is in place; however, when upper bearing shell is removed the journal may be checked for out-of round by using a special crankshaft caliper and inside micrometer. The caliper should not be applied to journal in line with the oil hole.

If crankshaft journal is more than .0015″ out-of-round, the crankshaft should be replaced or reground for undersize bearings since the full mileage cannot be expected from bearings used with an excessively out-of-round crankshaft.

  1. Before installation of bearing shells make sure that crankshaft journal and bearing seats in crankcase and cap are thoroughly cleaned.
  2. Coat inside surface of upper bearing shell (full length oil groove in Ser. 40-70) with engine oil and place shell against crankshaft journal so that tang on shell will engage notch in crankcase when shell is rotated into place.
  3. Rotate bearing shell into place as far as possible by hand, then insert suitable tool in crankshaft oil hole and rotate crankshaft to push shell into place. CAUTION: Bearing shell should move into place with very little pressure. If heavy pressure is required, shell was not started squarely and will be distorted if forced into place.
  4. Place lower bearing shell (short oil groove in Ser. 40-70) in bearing cap, then check clearance with Plastigage as previously described.
  5. The desired clearance with a new bearing is .0008″ to .0015″. If this clearance cannot be obtained with a standard size bearing, insert an undersize bearing and check clearance again with Plastigage. NOTE: Each undersize bearing shell has a number stamped on outer surface on or near the tang to indicate amount of undersize.
  6. When the proper size bearing has been selected; clean out all Plastigage, oil the lower shell and reinstall bearing cap. Tighten cap bolts to 90-100 ft. lbs. torque. The crankshaft should turn freely at flywheel rim; however, a very slight drag is permissible if an undersize bearing is used.
  7. After bearing is installed and tested, loosen all bearing cap bolts 1/2 turn and continue with other bearings. When all bearings have been installed and tested, tighten all bearing cap bolts to 90-100 ft.lbs. torque.

Installation of Rear Bearing Oil Seals

The rear crankshaft bearing is sealed against external leakage of oil in the following manner:

  • An oil slinger machined on the crankshaft rotates in a groove formed in crankcase and bearing cap just to rear of the rear crankshaft bearing. This oil collecting groove drains back into the crankcase.
  • Braided fabric seals are pressed into grooves formed in crankcase and bearing cap to rear of the oil collecting groove. See figure 2-25.