-SG- Valve springs during the twenties were not wildly reliable and Nortons included in their tool kits for OHV machines a cunning device to enable a valve spring to be changed without removing the cylinder head. Basically this used the twin plug holes in the heads of the time, into one of which a cranked and adjustable bar was inserted, to hold the valve concerned in place, while in the other a spring compressor was mounted whereby the spring could be compressed and removed/replaced.
Where have they all gone to? Have come across two over the years but that's all. Here's a photo of one in use, and another showing the various components making up this tool kit item. This one is SOLD