Black Dog Classic Motorcycles

MY BROUGH SAGA

Part Three

A new headlamp rim had been purchased, the crutch splitter from the old rim being soldered to the new rim. Now, the best bit, strip down and sand all parts ready for powder coating and chroming. While these are away, I can play with the best bits (engine and gear box). I also decided to re-condition the horn and speedometer to cut down on the cost. The speedo was stripped, with the mechanism being cleaned in white spirit and blown dry with low-pressure air. I oiled it with some clock oil, fitted a new rim glass and needle and was amazed when it worked first time. The original horn was stripped and cleaned, this also worked after some fiddling with the tone screw.

The engine. An uneventful re-build, nothing much wrong with the engine. I completely stripped it and cleaned all components. The cylinders needed honing, due to rust, the valve guides being badly worn, the pistons were O.K. but the rings worn. Cams and followers O.K. but with some surface rust. Big end was fine but the timing side bush needed renewing, a new drive side bearing came with the bike. After removing the cylinder base oil valves I found the oil ways completely full of hard packed sediment, the cylinder bases must not have received any oil for hundreds of miles, but, the pistons were free from score marks. The pistons are the original split skirt type, I cleaned these well, and checked for cracks, these pistons can crack from a drilling at the top of the slot in the front of the piston, up to the oil scraper ring groove. It may be necessary to use a magnifying glass to see this, if you put a piece of thin plate in the slot and twist it you may see the crack open. I like this type of piston, as you can run them to a tighter clearance in the cylinder bore, theory being that, as the piston warms up and expands, the slot gets smaller, whilst the piston diameter does not change much, this gives a quiet engine. Do not ask me for boring clearances; everyone I talk to gives a different figure. I once bored a Velocette 86mm cylinder to fit an original Wellworthy split skirt piston to a .003” finish size, the Velocette has done several thousand trouble free miles since, with a very quiet engine. Back to the 80, as I said earlier the spacers were missing from the camshaft rocker shafts and the valve lifter shafts.

I turned a long piece of EN8 bar and bored it to shaft size clearance, experimenting with parting off different lengths, so as to have the cam followers running centrally on the cams. I use a dental mirror for this type of work; they can be purchased from most tool suppliers

(Or, you could try asking your dentist?). The spacers were flame hardened and tempered, only after I had tried on the cover, to make sure everything went round and round as well as up and down, as it ought.

The rest of the engine went together fairly well; the only things found damaged being the two oil pump end plates, both of which were cracked. These are the same end plates as the 350 singles, so there was no problem finding more at an auto jumble.

The gearbox was dismantled when I got the bike; I had checked the main shaft before purchase to find if it was the correct length and not from a 16H. The shell was damaged around two of the end studs; these I had welded and then re-tapped the holes. New sets of bearings were purchased as well as some oversized pivot pins for the external selector linkage rod. Some ex. W.D. selector springs were found at an auto jumble, still wrapped in heavy grease paper, after fitting these on assembly and with the gearbox in the vice, all gears could be selected with ease. The main shaft end float was adjusted with shims behind the clutch worm nut. New rubber inserts were needed for the clutch shock absorber and new inserts for the clutch drum, all these being fitted whilst the box was still in the vice.

Home Dogs Motorcycles