It always annoyed me that flatheads weren't flat. Recently I read someone moaning that they should be called 'under-head valves' which I liked. Anyway I took mine down to Barry at precision engineering and played with his mill.
Barry, the master.
Before & After
The heads are both similar number 5's but one had a lot more flaws in the casting. The aluminium was also thinner where the bolt passes through: 30.5mm compared with 34.5mm on the better head which meant the bolts stuck out at different heights, another thing to fix. I later found that one of the bolt holes on this cursed casting didn't even line up with the cylinder hole, about 1mm out. Odd as they looked like a perfectly matching pair.
It also annoys me how the alloy heads are bigger than the cylinders. The top profile of the cylinder has these beautiful curves and scalloped sides but the alloy heads have straight sides so they overlap and look like an oversized mushroom head. The iron-heads are curved to match the cylinder.
So, getting a bit carried away, we cut some scallops out of the sides to give a more curved profile.
Filed the corners a bit.
Polished the cut edge with a flap disc. Parkarised head bolts.
Reading an Italian bicycle blog I found a post about my very own bicycle! The picture is when the last owner had it, he's a Hungarian racer and sent me that very pic when we were e-mailing.
It's an Italian Pinarello Prologo (Lo-Pro in English) track frame. The smaller front wheel design is for time trials and gives better aerodynamics. The curved tubing is for sex-appeal. Speaking of which, donne nude..
1. Buy some Mullins 35mm trees and ebay some forks. Add to frame and congratulate yourself on having great taste when it comes to narrow front-ends.
2. Apply ruler between forks. Accompany ruler round swapmeets, scrouge ebay, wrangle advice until realisation that the only drum your ruler vaguely approves of is from a cub 50 scooter which has an axle diameter of about 6.734 mm.
3. Decide: brakes or suspension. Or machine your own hub but by that time you've already laced a Kempton found drum to the Borrani rim even though you knew it wouldn't fit but it was a twin leading shoe and you got carried away. Brakes over suspension it is.
Chop (all important word) the fork tubes.
This is actually the first part I ever made on a lathe.
Milling in the lathe.
At this point I drilled and reamed a hole. Actually I snapped the pilot drill half way but seeing as it took me like two days making this part and working out how to use the lathe, I alternated. Plunged an end-mill in about 2mm (the snapped drill bit rising into the hole in the end-mill), oxy-acetylened it, hammered protruding drill bit flat, plunged the end-mill another 2mm, repeat 10 times until mad with the world then enlarge messy hole to correct size.
Make a little axle.
Trim the fork tube caps.
OPTIONAL: Advise all comfort cynics that you spent everyday for the last four years riding a completely rigid bicycle with 19mm cross-section tubular tyres at 180psi around crappy, pot-holed, English roads and you only had to see the doctor about an embarrassing lump on your anus once. This should distract them from knowing best about vibration damage, cornering-grip, and other borings.