Wow! thanks guys!
Lars; that BSA of yours looks nice enough to eat! That looks a lot like an A10 rather than an A7 head there. You do know those are worth
good money, dont you?
You might be interested in the story of my little bobber I built a few years ago:
http://www.customcycledevelopments.com/BSA_bobber.htmlI used parts from as many different bikes as I could there!
On with the story...
It was at this point that some money became available
. I had been building a '79 Trans-Am with a 540 inch BBC for some time. It was progressing slowly what with all this LSR stuff. So when I got a reasonable offer for the uncompleted car, I reluctantly went for it (I've never had a really massive big-block before - dont suppose I will now)
So with this windfall, I asked Dave Branch if he'd do me a billet crank, and he agreed to take it on. In doing this, I was able to specify a few things that the Norton crank didn't have.
Anyway, with some customer work out of the way I was able to get stuck into it again.
I needed to assemble a mockup engine assy, so I resumed work on the barrel casting. Sadly, our Julian never came up with the drawings for David to CNC them, so I did it the old fashioned way.
Took the top-end off the Bobber and plotted the top & bottom bolt patterns. The stock barrel was all over the place! fortunately, when BSA designed the A10 they mostly used rational measurement units - sixteenths of an inch here! So figuring out what the dimensions should be was easy.
Top bolt pattern - tapped the holes 10mm rather than 3/8 BSF:
Bottom holes:
And doing the spigots on the ol' rotary:
The rearmost bottom holes ended up too far back and so I'll need to build it up with weld.
The last bit is the hardest; doing the cam-follower bores and the pushrod tunnel.
Doing the cam follower bores was a bit heart-in-mouth as screwing it up would junk the whole job.
First thing was to bolt the stock barrels onto the cases with a pointer in a lifter bore to check for misalignment:
Not too bad, maybe ten thou out.
Set the mill up using the stock barrels. Drilled the angle plate so I could bolt the stock set on and then the ally casting in the same place:
And there's the followers in place! Got the fit just about right...phew!
Time to do some ally welding. Built up the rear barrel flange and got started on ol' Muskys head.
Added bosses for exhaust studs. Dont think shove-in pipes will work with a turbo! Also welded up one of the exhaust valve-guide holes as it was hugely oversize, and plugged up some damage to the gasket surface.
While it was cooling down, I set up the cases and bored out the cam tunnel. Our superduper cam was too big for it!
Thought I'd let that ally welding age for a few days. Plenty else to be getting on with.
Before I could set up the engine/gearbox I needed to know primary length. Primary drive was something that could be done in a number of ways.
Definitely wanted belt drive; could have spent north of £400 on a Commando kit, but with the billet crank, I have the option to have a splined sprocket shaft (which I certainly will choose! - hate tapers)
Also, the Commando clutch was good in its day, but there is better stuff. Such as the Kawasaki GPZ1100 clutch I've had kicking about for decades!
The good thing about the Kwak clutch is that both the basket and the hub are rivetted to their respective drive parts. So grind off the rivets and you can attach it to anything..well almost.
I bought some blank pulleys and a 2" belt from Bearing Boys along with some bearings & circlips. Here, I'm measuring the installed length between centres:
Sadly, the big pulley wasn't solid, but was webbed with big centre bosses, so I machined the middle out and turned up some steel:
Then welded it all up and machined it:
Completed:
End of August, it was cylinder head time, amongst other things...
Wasn't looking forward to doing this! All the valve guide holes were tapered and well oversize, and the valve seats were for the small A7 valves. Too small for our SRM Rocket Gold Star valves.
I'd already welded up the worst guide hole (over 1/16" oversize!).
I set the head up on the adjustable angle plate...
..And remachined the guide holes and machined out the seats. A horrible job; the stock seats are cast-in and are an irregular shape. They're also pretty hard.
This meant that some of the old seat material was still present in the finished insert bore. The hard seat material cut smaller than the remaining ally. I got it as good as I could by taking many small cuts.
Heres the head ready for the new seats:
before doing this, I did all the port-enlargement that I needed to do in the valve-bowl area. A lot easier without the guides in.
Putting new seats in an ally head is a bit fraught at the best of times. You need 7-8 thou interference fit or they'll come loose. This means getting the casting bloody hot (or chilling the seats in liquid nitrogen - not something I happen to have!) And then pounding them in.
Got 3 of them in, but broke one insert so had to take a ride down to Cambridge Rebores on Friday morning to get another.
This of course meant having to re-heat the head. So in the meantime I got the new guides ready.They had to be custom-sized, so I turned the exhaust ones from a small bar of Colisbro and made the intakes out of some Rowe shovelhead ones. made them with 4 thou interference. Probably a bit too much as they were a bastard to get in there! They're not coming out!
Guides in:
Seats in:
Once cool, I had to ream the guides to size. There was about 10 thou to come out of the exhaust ones and it soon became clear that my little adjustable reamer wasn't going to do the job. This Colisbro stuff doesn't like being cut, and tends to machine undersize & sieze the tool. I actually broke the reamer.
I do have a 5/16 machine reamer but was scared I'd get too much clearance, so I tried it on an offcut and it came out just right. Fortunately, I'd left the mill setup from when I'd machines the seat & guide holes, so it was simple to bolt the head back in and run the reamer thru. Came out spot-on. TFFT!
Next day I finished blending the new seats to the ports and then got the ol' valve-seat cutting gear out to finish the valve-job. Did a 3-angle job on the intakes (I already did the first angle in the lathe before I fitted the seats). On the exhausts, I had bored them to the max size I could, so no room for a 60-degree cut. A bit of lapping, and its good to go, apart from some port opening-out on the intake side.
Checked valve-stem protrusion expecting to have to cut the seats some more to get them to spec, but found they were all within 5 thou of each other! They're actually about 40 thou less than what I think is stock (1.8") at 1.760" I most definitely wont be sinking the valves deeper to get the 1.8" spec!
There it is done:
Next; setting up the drivetrain...