4.236 & T4.236 DIESEL ENGINES Section H: Crankshaft and Main Bearings Caterpillar

Section H: Crankshaft and Main Bearings
1.1. To Renew the Thrust Washers
2.1. To Remove the Crankshaft
3.1. Regrinding the Crankshaft
4.1. Crankshaft Regrind Data
5.1. To Refit the Crankshaft
6.1. Rope Type Rear End Oil Seal
7.1. Lip Type Rear End Oil Seal
8.1. To Fit Lip Seal in its Housing

Some crankshafts can incorporate forged in balance weights whilst others do not have balance weights.

When replacing a crankshaft, always ensure that the correct type is fitted.

The crankshaft runs in five pre-finished replaceable shell bearings lined with aluminium tin.

End float is controlled by four thrust washers which are located on both sides of the centre main bearing housing 0.0075 in (0,19 mm) oversize thrust washers are available which may be combined with standard thrust washers to give an adjustment of 0.0075 in (0,19 mm) or when used on both sides of the bearing housing, give an adjustment of 0.015 in (0,38 mm).

The main bearings are located in position by tabs fitting into slots in the bearing housings.

The tabwashers as originally fitted to the main bearing cap setscrews on 4.236 engines, have now been deleted, see Page B.2 for Recommended Torque Tensions.

Because Tufftrided crankshafts are fitted to some engines it will be necessary to identify the shaft before commencing regrinding operations.

It is important that the information on Page H.2 headed Regrinding the Crankshaft relevant to the Tuffriding process is adhered to.

To Renew the Thrust Washers

Renewal of thrust washers can be carried out without withdrawing the crankshaft, as follows:-

1. Remove the sump, sump strainer and the oil pump suction pipe (Page L.2).


2. Remove the centre main bearing cap containing the two bottom half thrust washers (see Fig. H.1). The two top half thrust washers should be removed by sliding round from one side. Identify each thrust washer half to its relative position.

3. To refit the thrust washers, liberally oil the two upper halves and slide them into the recesses provided on either side of the main bearing housing.

The steel side of the thrust washers should be towards the bearing housing and the cap. Refit the cap with the lower half bearings, secure with the setscrews tightened to the torque given on Page B.2.

NOTE: Later type thrust washers are non reversible and are not interchangeable with the earlier type. Replacement thrust washers must be of the same pattern as the originals.


4. Check the crankshaft end float for a clearance of 0.004/0.015 in (0,10/0,38 mm), Fig. H.4.

5. Refit the oil suction pipe to the oil pump.

6. Refit the sump strainer and sump.


To Remove the Crankshaft

It will be necessary to remove the engine from the vehicle or application.

1. Remove the sump, sump strainer and the oil pump suction and delivery pipes.

2. Remove the timing gears and timing case (Section K).

3. Remove the flywheel and flywheel housing.

4. Remove the connecting rod caps and big end bearings (Page F.1).


5. Remove the rear main bearing oil seal housing (Fig. H.8).

6. Take off the rear main bearing bridge piece.

7. Remove the oil pump (Page L.2).

8. Remove main bearing setscrews.

9. Remove the main bearing caps and half bearings.

10. Lift out the crankshaft and remove remaining half bearings.

Regrinding the Crankshaft

Before commencing regrinding operations, examine the crankshaft to see if it has been hardened by the Tufftriding process. The shaft may be identified by Part No. which will be found on the front end or on No. 1 web.

If the crankshaft is identified as a Tufftrided shaft then it will be necessary to re-Tufftride it regardless of the diameter to which it is reground.

If facilities are not available for re-Tufftriding a replacement shaft should be obtained.

Before regrinding the crankshaft it should be crack-detected.

Demagnetise the crankshaft after crack detecting.

The main journal and crankpin diameters should be checked to ascertain the next size to which the crankshaft can be reground, i.e., -0.010 in (-(0,25 mm), -0.020 in (-0,51 mm) or -0.030 in (-0,76 mm). If it requires to be reground below -0.030 in (-0,76 mm) a new crankshaft must be fitted.

After regrinding, the sharp corners on the oil holes should be removed and the crankshaft crack detected and demagnetised.

NOTE: It is important that the radii on the main journals and crankpins are maintained.

The crankshafts of engines fitted with Lip Type rear oil seals have a rear flange with an extended width of over one inch (25 mm) to provide a seat for the lip seal (Page H.5). If all the three positions for this seal have been used, the sealing area of the flange may be reground to a minimum diameter of 5.243 in (113,17 mm), leaving an unmachined diameter for a distance of 3/16 in (4,8 mm) from the rear end.

Only the minimum of metal should be ground off to ensure removal of the seal wear grooves and the surface finish should be the same as the crankpins and journals.

It is not necessary to re-Tufftride the flange after this operation.

Crankshaft Regrind Data

To Refit the Crankshaft

1. The oilways in the cylinder block and crankshaft must be free from obstruction.

2. Check the main bearing setscrews for stretch or damage. Only setscrews supplied by the engine manufacturer should be used as they are of a special heat treated high grade steel.

3. Clean the bearing housings, place the top half bearings in position and liberally oil.

4. Position the crankshaft.

5. Oil the two upper thrust washer halves and slide into the recesses provided on either side of the centre main bearing housing.


6. Liberally oil and fit the lower halves of the main bearings to the bearing caps. Fit the caps to their respective positions so that the lower halves of the thrust washers are correctly positioned on either side of the centre main bearing cap. The main bearing caps are numbered, No. 1 commencing at the front of the engine. Each cap is also marked with a serial number as stamped on the cylinder block bottom face. These should read in line (Fig. H.2).

7. Fit the setscrews. Shim washers originally fitted between the setscrew head and the main bearing cap have now been deleted.

8. Tighten the main bearing setscrews to a torque given on Page B.2.

9. Check the crankshaft end float for a clearance (Fig. H.4).

10. Refit the connecting rod caps and big end bearings (Page F.5).


1. Bridge-piece.

2. Bridge-piece End Seal.

3. Joint (if fitted).


11. Refit the rear main bearing bridge piece to the cylinder block (Fig. H.5). The rear face should be flush with the rear face of the cylinder block (Fig. H.6).

12. Fit new seals in the rear main bearing oil seal housings and refit the housings as described in "Crankshaft Rear End Oil Seal".

13. Refit and correctly align the flywheel housing (Page P.1). Refit the flywheel.

14. Refit the oil pump, timing case and timing gears (Page L.4 and Section K).

15. Refit the sump, sump strainer and the oil pump suction and delivery pipes.

Rope Type Rear End Oil Seal

The housing consists of two halves bolted around the rear of the crankshaft which has a shallow spiral oil return groove machined in it to a depth of 0.004/0.008 in (0,10/0,20 mm). The bore of the housing accommodates a rubber cored asbestos strip comprising two sections.

When fitting the seal the following procedure should be adopted:-

1. Set up a half housing in the vice with the seal recess uppermost and settle approximately 1 in (25 mm) of the strip, at each end, into the ends of the groove so that each end of the strip protrudes 0.010/0.020 in (0,25/0,50 mm) beyond the half housing joint face.


2. With the thumb or finger press the remainder of the strip into the groove, working from the centre. Use a round bar to further bed in the strip by rolling and pressing its inner diameter (Fig. H.7).

3. Fit the sealing strip to the other half housing in a similar manner.

4. Fit a new joint using jointing compound applied both sides.

5. Spread a film of graphite grease over the exposed inside diameter surface of the strip.

6. Assemble the half housings around the crankshaft rear journal and fasten together (Fig. H.8).

7. Swivel the complete seal housing on the shaft to bed in the strips and to establish that the assembly turns easily on the shaft.

8. Bolt the seal housing to the block and rear bridge piece.

Lip Type Rear End Oil Seal

Later engines will be fitted with a circular spring loaded lip seal that locates around the periphery of the flange of the crankshaft. The seal is designed to function correctly with the direction of rotation of the engine and for identification purposes the seal is marked with an arrow.

The lip type oil seal assembly and its counterpart crankshaft are not interchangeable with previous types.

This seal is easily damaged and extreme care should be taken when handling and fitting it. Any visual damage across the lip of a new seal will cause leakage and prevent bedding in of the seal.


Earlier seals have a flat rear face as shown in Fig. H.9. Later seals have a protruding dust lip from the rear face as shown in Fi.g H.10.

To Fit Lip Seal in its Housing

On production, the old type seal was fitted flush with the rear face of the housing (Fig. H.9) but the new type seal is fitted deeper into the housing at 'A', Fig. H.10.

In service, when a new seal is fitted to a worn crankshaft, it should be pressed further into the housing. In the first instance it can be pressed in to 1/8 in (3,2 mm) for old type seals or position 'B' for new type seals or, if this position has been used, to 1/4 in (6,4 mm) for old type seals or position 'C' for new seals.

If a new type seal is used in place of an existing old type seal, position 'C' should be used if the old seal was fitted 1/8 in (3,2 mm) below the housing face.

If all three positions have been used, it may be permissible to machine the worn sealing area of the crankshaft flange (See Page H.2).


When a new seal is fitted to a new or reconditioned crankshaft in service, it should be fitted in the production position, but if the latest seal is not to be used in a wet back end application, it can be fitted flush with the housing rear face ('D', Fig. H.10).

When pressing in the latest type seal, ensure that the adaptor has a suitable recess to clear the protruding dust lip. Tool PD145C can be used with both type seals.

Before fitting the seal in the housing, carefully examine the seal for damage especially on the lip and outside diameter.

Using clean engine lubricating oil, lubricate the outside diameter of the seal and the inside diameter of the housing.

Press the seal into the housing to the required position, taking care that the seal is entered and pressed in squarely, otherwise damage to the outside diameter of the seal may occur or, if it is not square in the housing when fitted to the engine, it may leak.