Valve Spring Dimensions 1935 250 JAP Engine

[CPR]

Hi.
I need some information regarding valve springs for my 1935 twin port 250cc JAP engine.
I need the dimensions of the length, inside and outside diameters and the wire diameter of the inner and outer springs. I’m not sure if it matters which way round they are wound.
I am having to get the springs made as I am unable to find any to buy.
Can anyone help?

Thanks Chris R

[cottonjo]

Hi Chris,
I may be able to help if they are the same as my 1932 350 JAP. Although I have been using Velocette valves that have a slightly larger diameter stem than the originals. I think my springs are from a BSA C15. I will see what I have and report back.
Paul

[chris1]

In the early days of my Blackburne engine I needed to replace the springs which were far too weak and there was also no data available. In the end I had a new set made the same as the old weak ones so I knew the material was good and then made spacers (against the head) to replicate the forces quoted in Tuning for Speed. This is 100 lb closed and 160 lb open. I measured this by making a crude scissor arrangement out of wood which crushed the spring by the amount of the valve travel and measured it on a spring balance. I always meant to get full springs made one day but its been good for about 10 years now and theres no valve bounce at full revs.

[CPR]

Thanks Paul and Chris1 for replying to my post. Here is an update on the valve spring problem.
I tried a dealer in Sheffield but he was unable to help. So I contacted Active Springs in Studley Warwickshire. They have been very helpful. They have contacted the National Motorcycle Museum and other contacts in the hope they have the details of the VS71 Terrys springs I need. As yet they have drawn a blank.
If all else fails I think I will follow something along the lines that you suggested Chris.

Chris R

[CPR]

I have found the dimensions of JAP engine valve springs.
I've listed them in a spreadsheet for those interested.
Hopefully attached to this post.
 
Chris R

Attachments:

JAP Motorcycle Valve Spring Dimensions.pdf (64.6 KB)