Ariel Motorcycle Club North America Forum

I recently completed installation of new pistons in my 1953 Square 4 MK II.

With guidance from noted Ariel expert Paul Ackerman, I used a completely different procedure than the daunting process suggested in the Ariel factory workshop manual, and found the task to complete without issue.

I have documented the process, with pictures. You can view the document here:
http://blog.auldridge.org/wp-content/up ... UARE-4.pdf

The method described by Phil works, but can be hard work. My normal approach, with the engine in the frame, is to use two bungees wrapped over the top frame tube to support the cylinder. Using piston ring clamps, I then put the pistons in the cylinders one at a time - which you can do easily enough with the weight of the cylinder taken by the bungees, provided that you get the bungees to the right tension.

I have recently had to build two MkII engines without the benefit of a frame tube to use for the bungees. So I went back to the textbook approach of supporting the pistons underneath and resting the cylinder on the ring clamps. You cannot do this without ring clamps, in my opinion. The thickness of the steel / timber strips under the pistons was a problem because in each engine I was using BMC pistons instead of Ariel ones and the skirt length is different. I concluded that the thickness of the support strips is not critical, provided that they hold the pistons square to the bores. What does seem to vary is the position of the cylinder above the crankcase as it may be forward or backward from the correct position, depending on the thickness of supports used. But once the pistons are in the cylinder, you can adjust location easily enough.

Fundamentally, you get the pistons square to the bores at about the correct positions. Then you place the cylinder on top such that the cylinder skirts are all bearing down equally on the piston ring clamps. Then you simply tap the cylinder down gently until all the rings are in the cylinders. Make sure they are far enough in, remove the piston ring clamps and then adjust the cylinder location to suit the cylinder base studs. In practice, this is an awful lot easier than it sounds.

Paul