Crankshaft and connecting rods

Both crankshafts have a certain number of removable sprockets and bearings which have not previously been discussed in other sub-sections. On the Twin it is quite simple. On the dynamo end there is the starter sprocket which sits behind the starter freewheel. Starter freewheel removal has already been covered in the Maintenance section as has starter chain removal in the Electrical section. Obviously that sprocket is part and parcel of the starter freewheel. It rotates on a needle bearing which is lubricated from the crankcase and simply pulls off once the starter freewheel is removed. External to it is an oil seal, while inside is another one which sits in the crankcase. Both seals should be renewed, if extensive work is being undertaken, and they can be renewed without splitting the crankcase. At the other end of the crankshaft is the primary drive sprocket which splines onto the crankshaft. Obviously no oil seal is fitted to it. That pulls off as previously described with primary drive removal.

The outer bearing at the dynamo side is a ball bearing (the SFC uses roller), the one at the outer primary side is a roller (early Twins were ball here too). Neither should have any play. Both will have to be pulled off the crankshaft with a proprietary sprocket puller.

The two inner main bearings, between the flywheel balancers are roller bearings. Crankshaft main bearings cannot be reconditioned by anyone other than the factory and its representatives (even they send them back).

The Triple crankshaft is longer but very similar even having just four main bearings: outer primary — roller, outer alternator — ball, both inners — roller or ball. (Roller up to late 1978, ball from 1000 frame no. 6204 and 1200 frame no. 1833). All the components have already been discussed except for the crankshaft starter sprocket, which like the Twin is associated with the starter freewheel but unlike the Twin runs on a ball bearing. That sprocket is easy to pull off the crankshaft.

Once again the outer bearings can be easily pulled off with a sprocket puller but the main inners cannot. The crankshaft must be returned to the manufacturers or their representatives and an exchange undertaken. You cannot split the crankshaft yourself without wrecking it.

Big end bearings, their pinions and connecting rods can be replaced by anyone who has the machinery to pull apart, press together and then align and balance the components. It's skilled and expensive work — but cheaper than a new crank assembly. If you suspect bearing failure or a bent rod consult your dealer.

If small end bush wear is suspect then you should measure them for ovality with a pair of calipers and then check the measurements with the Specifications. Small end bush replacement is not easy. The end of the connecting rod must be heated and the bush then pressed out. The new bush must be drilled for its oil hole and once fitted, it must be reamed to size. All this work is best done by an automotive engineer with the proper equipment.

If connecting rod straightness is suspect, you can check this by replacing the gudgeon pins without the piston and then checking their straightness on the surface edge of the crankcase. Two pieces of wood or metal which are exactly the same size, both having parallel edges can be used. Sit them at right angles to the gudgeon pin; sitting on the crankcase.

NOTE: Although crankshaft bearing vear is very unusual, you should check that each one does run freely and has no slop whatsoever.. Effectively the crankshaft operates without end float.

Whenever you replace oil seals. ma«.e sure that the lip of the seal is facing the proper way so that sealing takes place. That's with the sealing, or open face, facing the flow of oil. When refitting the gearbox sprocket make sure the beveiied edge of the sprocket centre engages the shaft first (facing the crankcase). Do NOT force the sprocket onto the splines — you could do damage to the primary shaft — it must be a smooth, easy fit.

0 0

Post a comment