Crankshaft

For main bearings and oil seals click here; for alternators and fittings click here.

Do not try to remove the crankcase end doors without the correct tool as this is virtually impossible without it, click here. We also stock a hand reamer for replacing the small end bushes, click here

Exchange Crankshaft Assemblies.

As well as the obvious wear that takes place in the big end bearing of the Arrow and Leader crankshafts, wear is usually also found to have occurred on the mainshafts where the main bearings and the centre oil seal run. Once the bearing becomes loose on the shaft, wear is accelerated, vibration increases and primary compression is lost as the seals wear. Replacing the seals and bearings does not cure the problem as they just wear out again, in some cases as soon as 2,000 miles.

To check for wear, slide a good, preferably new, bearing onto the shaft to its correct position. It will probably be quite tight to fit initially on the unworn portion of the shaft but slide on easily as it arrives at the portion of the shaft where it usually sits. If it slides by hand or the inner race can be turned on the shaft it has failed the test and should be exchanged for a reconditioned crankshaft. Also check the left half of the right hand crank where the centre seal runs as the oil seal will wear a groove at this point and this should also be repaired. Also do not forget to check the loose collar for the right hand outer seal. 2 stroke engines depend on good primary or crankcase compression provided by the crankcase oil seals.

Wear in the big end bearings is usually easy to detect but it should not be possible to feel any up and down movement. Some rocking from side to side is permissible. If in doubt as to the condition of your crankshaft we will gladly inspect and advise without obligation.

All exchange crankshafts are pressed together and trued with new big end assemblies and good shafts. As very few shafts arrive that are the correct size the exchange shafts have almost always been reclaimed by grinding undersize and plated with hard chrome before being ground to close tolerances. This ensures that the bearings are a perfect fit and the engine will work properly and last for years.

We can overhaul your own crankshafts if wished but this may take some time while we wait for the next batch of shafts to be done. We can also just replace the big ends and true the assemblies without replacing the mainshafts.