My mate Jims plunger / rigid bobber project

[Briz]

I've known Jim Brown just about forever. He's still got his plunger A10; he's had it since the early 70s. It was in BSH a few months ago. More or less stock, well -ish! Lets say it has evolved over the years.
But He has hankered after a bobber for some time. When I told him I was getting a billet crank made for the racer, and that a modified Norton crank was now spare, he got thinking.
A month or 2 back, he arrived with a heap of parts and asked me to get started when I got some time(!)
I wont have any qualms about modifying the frame front section....



Heres a close-up of the headstock; just butt-brazed together! Whats more amazing is that it hasn't broken!



The rearend is straight though, I wonder if anyone here has a worse one they'd want to swap? I much prefer modifying stuff that needs work than good parts.

[duTch]

 Gee Briz, that's a similar colour to one I saw at a rally at Trafalgar square in 1981.
Was also similar colour to mine at the time.
 Got a pic of it on a picture board left at the ex's house- don't go there much   

 Cheers

[Briz]

Turns out there was a slug...of sorts up that top tube! Not sure it was doing much.


Bored the remains of tube from headstock...

Gotta do the front downtube holes tomorrow.

Ol' Jim wasn't too fussed if the bike was based around a swingarm engine or a plunger one, he provided both sets of cases. But the swingarm ones were mis-matched... and the numbers had been filed off. Plus he had a plunger gearbox. Not a hard choice...



Before I can assemble something I can jig up with...had to weld up a broken lug on the LH case..

[muskrat]

Good one Briz, another A7/10 to be resurrected. This one a little simpler than the last one. I thought you'd be camped in the container with that one.
Cheers

[duTch]

 Guess you need something to stay entertained till you catch up with that boat....!

[Briz]

Not sure I'd use the word 'entertained'! Especially after an afternoons sweat-brazing!

Setting up an old frame like this is always a barrel of laughs. They're always bent in more directions than you'd think possible, especially if they've ever done sidecar duty which many had. Unless you want to re-do every brazed lug you have to compromise a bit.
But this one in the centre tube was probably done to make the rake job line up:


With that straightened and the headstock ready, the top tube was slugged & welded with a new front bit:


And then...as if by magic (but actually a lot of sweating & grunting!)...its done!

[Briz]

This project and my little red bobber are inextricably linked. I'm redoing the engine on the bobber, I bought another ally cylinder casting like the one used on Saltflash, only I'm boring this one to 3" and using 883 sportster pistons which will make for 810cc. I'm also doing a 90-degree crank for it; mainly so it sounds like a V-twin! :lol:
So Jim is having the rotating assembly out of mine and the barrels.
There were always 2 niggles with the red bobber engine, the conrods were about .012" too long so I had to use 2 base gaskets, and the A10 rods were about .060" to narrow for the Norton crank. Not a huge problem until the bigends wore a bit, but then the piston could cock sideways in the bore.
Also, the 883 pistons are shorter than A10 ones.
So 2 pairs of custom length conrods needed. I wasn't going to shell out on buying some; having taken a close look at the billet ones I got for the race bike, I reckoned I'd have a go myself. £100 worth of 7075T6 and a few days turning & milling.......

[muskrat]

G'day Briz.
 There's not much you can't turn your hand at is there? Nice work.
Cheers

[duTch]

 What's your address, and when are you goin' stateside for how long...???