0340100 JOHNSON CYLINDER HEAD, All 25 and 50 models

start by:a) remove oil pan1. The main bearing caps are installed with the part number toward the front of the engine. Each cap has a number on the bottom of the cap which is the same as the number on the camshaft side of the cylinder block. 2. Remove the bolts that hold main cap (1). Remove bearing cap (1) and the lower half of the main bearing.3. Remove the bearing from the cap. 4. Turn the crankshaft until tool (A) can be installed in the oil hole in the crankshaft journal. Install tool (A). Turn the crankshaft in the direction which will push the upper main bearing out, tab end first.
If the crankshaft is turned in the wrong direction, the tab of the bearing will be pushed between the crankshaft and the cylinder block. This will cause damage to the crankshaft and block.
5. Install lower bearings in the bearing caps.6. Install upper bearings in the cylinder block with tool (A). Be sure the tab on the back of the bearings fits in the groove of the caps and cylinder block.
When bearing caps are installed, make sure the caps are installed with the part number toward the front of the engine and the number on the bottom of the cap is the same as the number on the camshaft side of the engine.
When the bearing clearance is checked and the engine is in a vertical position, such as in the vehicle, the crankshaft will have to be lifted up and held against the upper halves of the main bearings to get a correct measurement with Plastigage (B). The Plastigage will not hold the weight of the crankshaft and give a correct indication. If the engine is in a horizontal position, such as on an engine stand, it is not necessary to hold the crankshaft up. Do not turn crankshaft when Plastigage is in position to check clearance.7. Check the bearing clearance with tool (B) as follows: a) Put tool (B) and cap (1) in position and install the bolts. Tighten the bolts to a torque of 120 10 lb.ft. (160 14 N m).b) Remove the bearing cap and measure the thickness of the Plastigage. The main bearing clearance must be .0030 to .0066 in. (0.076 to 0.168 mm). The maximum permissible clearance is .010 in. (0.25 mm). 8. Put clean engine oil on the bolt threads and lower half of the main bearing. Put bearing cap (1) and lower half of main bearing (2) in position on the engine. Install the bolts. Tighten the bolts to a torque of 120 10 lb.ft. (160 14 N m).9. Do Steps 1 through 9 for the remainder of the bearings. When a replacement of the thrust plates on No. 3 main bearing is made, install the thrust plates with the identification "BLOCK SIDE" next to the block. 10. Check the crankshaft end play with tooling (C). The end play is controlled by the thrust bearing on No. 3 main bearing. The end play with a new bearing must be .0025 to .0190 in. (0.064 to 0.483 mm). The maximum permissible end play for used bearings is .035 in. (0.89 mm).