Monday 13 September 2021

The Final Build of the AJS V-Twin: Part 2

Before going any further with the final build there were a few important engine checks that needed to be made; in particular, the crankshaft had not yet been put into the crankcases. It could reasonably be argued that this could have been done earlier in the project (which is true) but the dry build had required the crankcases to be in the frame and as I didn’t want to keep taking the crankcases in and out of the frame I had postponed these checks up to now.

Specifically, the following needed checking before the crankcases could be sealed and tightened up:

1)  The crankshaft end float. This had been determined (by subtracting the crankshaft width across the flywheels from the distance between the bearings) as 0.008” – 0.010” but the crankshaft needs to be assembled in the crankcases for a true determination

 2)  The position of both pistons relative to the top of the cylinder at TDC

 3)  The clearance between the connecting rods and the crankcases as the pistons approach and descend to/from TDC and that the connectings rods are centrally located in the cylinders

The crankshaft was put into the drive-side crankcase for the first time

Both cylinders were added (with pistons but without rings but including the spacers and gaskets under each barrel that give the correct cam chain tension)

and the clearance between the con-rod and crankcase checked on the rear cylinder

and on the front cylinder

 So far, so good.

The next check was the piston positions at TDC. First the rear cylinder:

and then the front cylinder:

…and both pistons were exactly where they should be. It would have been fairly disastrous if they weren’t in the right place as this is not something that could be easily remedied.   

The last aspect to check is the crankshaft end-float. In practice, the only way to determine this in the assembled crankcases is to measure the axial position of the crankshaft when it is pushed one way and then the other. In this instance, it is not practical to put a dial gauge on the end of the shaft and “push and pull” the shaft to take a reading because the shafts are (and should be!) a tight fit in the bearing inner races and whacking one end with a hide mallet to move the shaft would disturb the dial gauge reading.

The alternative that I used is to fix the final drive sprocket in place and to measure the distance between the inner face of the sprocket and the crankcase main bearing boss. It is now feasible to tap the end of the shaft with a hide mallet (not too hard – just sufficient to move it) to put it in its 2 limiting locations and take measurements. This gave an end-float of 0.0115’’; although I had targeted 0.008’’ – 0.010’’ this will do fine as there is nothing in this engine that would suffer from being at either limit of crankshaft axial movement, such as a bevel-drive gear for example.

The crankshaft rotated freely (which also adds confirmation to the run-out measurements) and this, coupled with the other measurements, was sufficient reassurance that the crankshaft/crankcase setup was good.

It is easier to fit the gearbox in place at the same time as the crankcases and the last remaining job to be done on the gearbox was to fill it with grease. There are both grease-filled and oil-filled Sturmey Archer gearboxes.

This is a grease-filled gearbox, evidenced by the integral grease nipple on the filler. I use this grease:

According to Castrol Classic Oils, Castrol E/LPO grease is a Lithium semi-fluid self-levelling grease for veteran and vintage cars and motorcycles, with grease packed axles and gearboxes

The easiest way to put it in the gearbox is to take off the end cover and spoon it in. I use a long handled and rather elegant coffee spoon from my wife’s collection of cutlery. Luckily she doesn’t read my blog and so she’ll never know.

There are a few more little jobs that had been postponed until the final build, such as checking/setting the piston ring gaps, and then the engine could start to be built in the frame.

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