Making an brand new 32A crank

I wanted a more robust crank and one that had a bit more weight, higher primary compression, and longer drive shaft to fully support a belt drive pulley. That was the spec. I also determined that I wanted to use a Maico con rod with its 25mm big-end and the standard full circle Alpha cranks do not have enough "meat" in them to support that diameter of big-end pin.
This is what is looks like at the moment, yet to be used in anger. I am hoping that it will give me a very good primary compression ratio, 1.6:1 is the magic figure at which high rev delivery ratios are achieved. If you don't understand about inlet delivery ratios and how much it affects power, then read a good book.

I have modified the crankcase slightly. The crank is 3mm larger in diameter than the standard Alpha and 1mm smaller than the later square section Alpha flywheels and that is primarily to put enough metal on the flywheel to support a 25mm crank pin properly. Not only have I enlarged the crankcase but I have revised the location fixing of the outboard drive side bearing. The standard method is by circlip and shim. The space between the inner and outboard bearings is filled with a spacer to keep primary compression up, I have revised this by making this spacer now a screw in collar that holds the outer bearing tight. Oil from the transfer port is directed down channels. The primary drive is to be belt and I wanted a longer drive side shaft to support the pulley for its full width.

The crank flywheel pictured left takes a substantial effort to make, but that is what you have to do. I choose a balance factor of 79% based on previous experience in racing 250cc Villiers motors using different weight pistons. The balance is achieved by removing metal from the top half of the flywheel (to be replaced by aluminium to preserve primary compression) and adding lead inserts in the bottom. the standard outer drive-side bearing is used but the main roller bearings are slightly larger in diameter and are of the roller/sleeve type (as you can see). oil seals are off-the-shelf components, slightly larger at 42x30x7 and they do not run direct on the shaft but on hardened steel collars. The collars are the Villiers component that you will find on the high sleeve gear in the gearbox, part number E9644, and you can find it on the exploded 9E gearbox diagram item(7).

I start by gently squeezing the flywheels together on the crank pin in a vice, maybe just 1/16" or 1/8" and then use a square to set the alignment by eye. Now transfer to "between centres" or roller knife-edges and measure various points with a micrometer. I use a vice and tyre levers to get the flywheels parallel. Then rotate to see how much they are skewed, and strike "smartly" with a copper hammer to correct.

You just work out where it is most out and "give it some hommer". You work out where the skew is by how the dial gauges move. When it is pretty close, not more than a couple of thou' then press the "just nipped up" crank in about half way and repeat. Each time you press the crank on further it becomes *much* harder to correct any misalignment. When it is less than 2 thou' press it all the way home and make final correction, you are aiming for less than 1 thou' run out (0.001"). That process just described could easily take you several hours unless you are quite practiced. Working out what the dial gauges are tell you when you have slight amounts of both skew and parallel alignment can make you weep.
Drop the bearings into the crankcases, fit is about 0.002". We did try more but the pressure crushed the bearing rings sufficiently that assembly was not possible.
Ready to assemble crank into the crankcases. On the left you can see the timing-side oil seal and the hardened ring on the crank. On the right, you see the drive-side ball and roller bearings and the screw in spacer/sleeve.
The crankcases are assembled and tightened up, then the crank-crankcase clearance is measured with feeler gauges, then a gasket is cut of the correct thickness to give the desired running clearance. My choice is 0.015" (15 thou). Of course, you have to have this in mind when you make the crank and machine the crankcases. I did not say that this is easy, some people just naturally take this in their stride, others struggle. I struggle. I make the gasket by tapping the paper with a plastic hammer and then cut with a scalpel. The holes are punched out with a "hole punch" and you can buy bundles of these at the autojumbles, they are inexpensive. See my "Tools" section for pictures if you want to see what they look like. You can see in the picture of the assembled crank why the new crank had such an extended drive-side, it is to fully support the belt pulley. Below you see the gearbox and clutch loosely fitted and a steel rule between crankcase and gearbox while is just belt tension. Eventually steel, alloy or paper gaskets will be made.

Next step is top-end and fit to frame. Next report will be from the dyno room. What is primary compression ratio? Does it rev? Is it any better for all this effort? What is the meaning of life? .....

I wanted a more robust crank and one that had a bit more weight, higher primary compression, and longer drive shaft to fully support a belt drive pulley. That was the spec. I also determined that I wanted to use a Maico con rod with its 25mm big-end and the standard full circle Alpha cranks do not have enough "meat" in them to support that diameter of big-end pin.
	This is what is looks like at the moment, yet to be used in anger. I am hoping that it will give me a very good primary compression ratio, 1.6:1 is the magic figure at which high rev delivery ratios are achieved. If you don't understand about inlet delivery ratios and how much it affects power, then read a good book.
	I have modified the crankcase slightly. The crank is 3mm larger in diameter than the standard Alpha and 1mm smaller than the later square section Alpha flywheels and that is primarily to put enough metal on the flywheel to support a 25mm crank pin properly. Not only have I enlarged the crankcase but I have revised the location fixing of the outboard drive side bearing. The standard method is by circlip and shim. The space between the inner and outboard bearings is filled with a spacer to keep primary compression up, I have revised this by making this spacer now a screw in collar that holds the outer bearing tight. Oil from the transfer port is directed down channels. The primary drive is to be belt and I wanted a longer drive side shaft to support the pulley for its full width.


	The crank flywheel pictured left takes a substantial effort to make, but that is what you have to do. I choose a balance factor of 79% based on previous experience in racing 250cc Villiers motors using different weight pistons. The balance is achieved by removing metal from the top half of the flywheel (to be replaced by aluminium to preserve primary compression) and adding lead inserts in the bottom. the standard outer drive-side bearing is used but the main roller bearings are slightly larger in diameter and are of the roller/sleeve type (as you can see). oil seals are off-the-shelf components, slightly larger at 42x30x7 and they do not run direct on the shaft but on hardened steel collars. The collars are the Villiers component that you will find on the high sleeve gear in the gearbox, part number E9644, and you can find it on the exploded 9E gearbox diagram item(7).


	I start by gently squeezing the flywheels together on the crank pin in a vice, maybe just 1/16" or 1/8" and then use a square to set the alignment by eye. Now transfer to "between centres" or roller knife-edges and measure various points with a micrometer. I use a vice and tyre levers to get the flywheels parallel. Then rotate to see how much they are skewed, and strike "smartly" with a copper hammer to correct.

	You just work out where it is most out and "give it some hommer". You work out where the skew is by how the dial gauges move. When it is pretty close, not more than a couple of thou' then press the "just nipped up" crank in about half way and repeat. Each time you press the crank on further it becomes much harder to correct any misalignment. When it is less than 2 thou' press it all the way home and make final correction, you are aiming for less than 1 thou' run out (0.001"). That process just described could easily take you several hours unless you are quite practiced. Working out what the dial gauges are tell you when you have slight amounts of both skew and parallel alignment can make you weep.
	Drop the bearings into the crankcases, fit is about 0.002". We did try more but the pressure crushed the bearing rings sufficiently that assembly was not possible.
	Ready to assemble crank into the crankcases. On the left you can see the timing-side oil seal and the hardened ring on the crank. On the right, you see the drive-side ball and roller bearings and the screw in spacer/sleeve. The crankcases are assembled and tightened up, then the crank-crankcase clearance is measured with feeler gauges, then a gasket is cut of the correct thickness to give the desired running clearance. My choice is 0.015" (15 thou). Of course, you have to have this in mind when you make the crank and machine the crankcases. I did not say that this is easy, some people just naturally take this in their stride, others struggle. I struggle. I make the gasket by tapping the paper with a plastic hammer and then cut with a scalpel. The holes are punched out with a "hole punch" and you can buy bundles of these at the autojumbles, they are inexpensive. See my "Tools" section for pictures if you want to see what they look like. You can see in the picture of the assembled crank why the new crank had such an extended drive-side, it is to fully support the belt pulley. Below you see the gearbox and clutch loosely fitted and a steel rule between crankcase and gearbox while is just belt tension. Eventually steel, alloy or paper gaskets will be made.