Britbike forum Forums Thread Like Summary - BSA A10 special

I bought a pile of unrelated parts. A 61 frame, 60 SR crankcase, Triumph rear wheel, mid 60's Bsa single side brake front wheel and enough mechanical parts to built a running bike...
The bike is in mock up fitted with a spare set of welded crankcases...The fork assembly is a 2000 Honda 600CBR...made bearing and yoke stem spacers. Setting up steering geometry at ride height to get rake and trail where it needs to be.
Scrapped the isolastics swingarm bushes and made up a metal bushing set.
The engine has a late 50's alloy head, 357 cam, R&R rods, Kibblewhite line bored timing bushing, IMD flat top pistons. Static compression do to this and that will be 7.8

OE shoes work better than Emgo. Personal observation.

Bars and hand controls and heaadlight mounted.....

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Book weight is 408 - 430 pounds for the SA models, depending on spec, the alloy head saves a fair bit. So theres scope for pruning, depending on choice of running gear, the frame is heavy, but its also very good, handling is great , if you ditch the lights and dynamo that will save a good bit.
Stick with the 357 cam its a tad more fun than the 356, not too rad , idles OK.
look for a 4 spring clutch , the 6 spring can be made to work, the 4 spring is better IMO, adaptors for the conversion used to be common,
The earlier plunger boxes had a splined mainshaft that will take the Norton/ AMC clutch, a good mod.
be careful if you have the crank reground, its imperative to have the radius correct at the fillets, they will break if its not correct.
In Roland Pikes memoirs he mentions the factory peening the fillet radius with a ball bearing applied with pressure, this increased crank life.
its worth reading the chapter in his memoirs " The terrible twins"

To me that rolling chassis says "put a solo seat on me or make me a flat tracker"



Specials talk to me and you have the eye for it, Tony!

Tom

Yes it rolls and has a front brake...I did roll it around ....My shop is in the 35 x 25 house basement, the ground level entry is in the rear...There's a bit of snow and cold....I ain't doing outside photos right now, lol...

and the valve issues continue......The machine shop owner calls and says his man took just a .002 cut using the Newen machine and the exhaust seat is into the aluminum..The cast in insert has a flattened side, stack up of clearances went against it. They do a lot of speciality valve seat replacements, so no big deal for them. ...The only issue will be what's left of the original insert after it's machined for the new seat. It might require more aluminum removal, welding, and more machining..It's just money.....

Ok, staring to make some progress. Mocked up the crank for end clearance check, it was .007" , I shimmed it to .003.
The head got new exhaust seats , I did the guides. The shop has a Newen single axis valve machine that holds very tight clearances, .001 on intake guides, .0018 on exhaust. Valve stem and installed spring heights all came out right on target...

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More .......The rotating parts were balanced, the shop said it was the one of the best original Britbike factory balance jobs....R&R. rods, made in UK IDP pisons with thin metric rings.....the bottom end is ready for the cylinders..
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Checking the cam timing, It's a 0357......Intake centerline is 96.5 degrees...100 degrees would be nicer, I can fabricate an offset key...I notice the cam has lazy initial lift to be more gentle on the valvetrain...

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Yes, alloy head has reduced shanks...I gave it some thought, bought the heavy wall TimeSert repair kit, $120 with extra inserts..I'll pull the barrels ,use a junk iron head as a drill guide and do them all on the drill press. 3/8-24 UNF grade 8 bolts have more than enough torque capacity...

That damn cush drive nut was always undoing on my old one, used to chew
in to the cover.