I'm Sat Waiting On Postman Pat

[BTDT]

The HW50 piston weighs 186 gm, the HW55 163 gm. The HW55 piston head is aluminium, and extends back into the piston, giving available length for the compressed mainspring of 95.6mm in the 55, against 108mm in the 50.

I suspect that if Venom used the HW50 piston in their 55, it was as much for the extra spring room as the mass.

[evert]

The HW50 piston weighs 186 gm, the HW55 163 gm. The HW55 piston head is aluminium, and extends back into the piston, giving available length for the compressed mainspring of 95.6mm in the 55, against 108mm in the 50.

I suspect that if Venom used the HW50 piston in their 55, it was as much for the extra spring room as the mass.

I really need to open up a few of the ones we have in the family, we have to different 55's and several different 50's, would be interesting to see if there are even more variations between them.

[T 20]

The HW50 piston weighs 186 gm, the HW55 163 gm. The HW55 piston head is aluminium, and extends back into the piston, giving available length for the compressed mainspring of 95.6mm in the 55, against 108mm in the 50.

I suspect that if Venom used the HW50 piston in their 55, it was as much for the extra spring room as the mass.

Cheers for that, Jim.

I'm now looking at making a custom piston using a threaded 77 latch rod, by doing this I can have the minimum wall thickness between the front of the spring and the rear of the seal, giving the maximum Spring room.

I've found some Titan springs in my pile with a 19mm OD made from 3mm wire which I think will fit the bill, by using one of these I can increase the wall thickness of the piston to bring the weight back up to make up for the lighter front end.
If I can manage to keep a decent wall thickness at the rear of the piston then I can fit a bearing to it to make up for me using mild steel for the piston body.




All the best Mick

[TonyL]

Hi Mick. Back in the early 80s Venom would use the piston from the HW50 and use it in their HW55 conversion. As the 55 piston was to lite. Hope that helps in someway? Regards Mach 1.5

The HW50 piston weighs 186 gm, the HW55 163 gm. The HW55 piston head is aluminium, and extends back into the piston, giving available length for the compressed mainspring of 95.6mm in the 55, against 108mm in the 50.

I suspect that if Venom used the HW50 piston in their 55, it was as much for the extra spring room as the mass.

Brilliant information.