The crankshaft is that part of the engine that converts the vertical motion (The up en down motion of the pistons) into a rotating motion, that can be used by the gearbox and eventually the wheels.

Usually the cranckshaft is located in the bottom end of the engine and is cast out of a single piece of steel. After casting, it is finished so that a few lobes remain that are connected by short, smooth finished shafts.

These shafts form the mountings for the conrods and the fixation to the cylinderblok itself.

In case of the 4A-GE, the crankshaft is connected to the cylinderblok by means of 5 main bearings.

The rotating motion of the cranckshaft is used to power other parts of the engine, like the oilpump, waterpump, camshafts and such.

This is achieved by mounting a pulley or cog to the crankshaft. These drive a belt that will turn another pulley on the external parts.

The cranckshaft has to be very strong because it will be rotating at very high speeds. There is a lot of mass flying around at high speeds when the engine revs to 7500rpm (That is 125 complete revolutions a second!). Because of this, the cranckshaft has to be balanced to rule out any anomalies of the casting process. This will prevent unwanted vibrations. To much vibrations could cause fatigue and eventually the destruction of engine parts. And we certainly don't want that now do we?

In the picture above, you might have noticed that there are a few holes drilled in the shafts where the bearings will be mounted. These are connected with each other with a oil passage that runs through the lenght of the entire cranckshaft. This will supply oil to all the bearings that are connected to the cranckshaft. These bearings would be the mainbearings, connecting the cranckshaft to the cylinderblock. And the conrod big-end bearings to connect the conrods to the cranckshaft.

The cranckshaft, which just found it's way back in to my freshly rebuild 4A-GE engine. All the new bearings are already assembled and everything is connected and torqued down to specifications.

In case of the 4A-GE, if you are looking for a cranckshaft for your engine. Keep in mind that there are 2 different cranckshafts used during the lifespan of the 4A-GE engine.

The first generation 4A-GE engines (Those with the 3-rib cylinderblock) used a cranckshaft that had a 40mm conrod big-end connection. This Cranckshaft is thought to be a bit weaker and is slightly lighter (11kg) than the cranckshaft that Toyota used in all other 4A-GE engines (Those with the 7-rib cylinderblock).

Although I have never heard or came across stories of any 4A-GE crankshaft breaking, Toyota dicided to use a stronger but slightly heavier (11,7kg) cranckshaft. The main difference between the two are the shafts for the conrod big-ends. In the later and stronger crankshaft, these have grown to 42mm in diameter.

Another difference between the two is that the early, lighter crankshaft uses 6 bolts to connect to flywheel. On the later, stronger cranckshaft, Toyota decided to use 8 flywheel bolts.

Something to keep in mind if you are looking for a crankshaft for your 4A-GE.