Lots of progress over the last week. My new built wheels seem in-line with the frame etc, so I must have got the off-set correct. Plunger rear end and fork all done and mudguards in:
Number plates done. Handlebars on. And bottom half of engine and gear box in the frame:
P.S. Make sure you put the breather pipe and union on the engine before putting the gearbox and/or engine into the frame
. Otherwise, you'll have to make up a special spanner to get to that union hex head...
Barrel on with no broken piston rings:
Having read about John Davies recent problem on his 4G with oil spewing out of the magneto sprocket crankcase aperture, I carried out the same modification I did on my SF31 Sloper in 2012. Having measured up, I use exactly the same seal: a Viton 20 x 26 x 4 garter seal. Back in 2012, I initially used a bog standard Nitrile seal but, due to the heat, it became hard and brittle quite quickly and started leaking, so I switch to the more expensive Viton seal which can withstand much higher temperatures. BTW: you'll not find this Viton 20 x 26 x 4 seal on any website but they are available to special order.
Using a reamer, I opened up the aperture to 26mm; this provides a tight push fit for the seal but I'll also use some Loctite 480 to bond the seal to the case. On the sprocket, I turned down the worn out scroll, and then sleeved the boss with some phosphor bronze I had lying around. The sleeve is 638 locited on, turned down to 20mm and serves two purposes. 1) the boss on the sprocket was not deep enough for the 4mm seal, so the sleeve extends the boss all the way back to the face of the magneto and 2) it provides a nice polished surface for the seal to run on:
'28 Model B (future project), '30 Model F, '31 SF31, '35 4F, '38 VB (abandoned project), '39 4G (current project), '46 VH, '48 KG