I have spent the last few days working on the late Norman T300 which I bought at the sodbury sort-out.
You may remember that when I got it home it proved to be something of a bitsa, with 'nearly new' bottom end topped with a pair of well used (and abused) cylinders. There was a broken head stud, the gaskets showed signs of having recieved the attentions of a screwdriver or worse and one side had suffered water ingress. The rings on the 'wet' side were corroded solidly into their grooves and could not be salvaged, even when broken they had to be chipped out 1/2" at a time! But after much scraping out of rock hard corrosion, the ring grooves cleaned up ok. Perhaps foolishly I had assumed I would be able to track down RGR Sparks for spares, but no joy and the project stalled. However, thanks to an early Christmas pressie of some useable second hand rings and head gaskets (thanks Roland) the job was back on.
In deference to some of the rings not having seen this particular bore before, I decided a good de-glaze would be in order. This was accomplished with my patent tool consisting of a length of plastic drain pipe with a wide slot cut in one end, into which is stuffed one of those hard foam rubber sanding blocks. With a bit of work both bores cleaned up well and looked at in the right light one might almost imagine that they had a nice cross hatch honed surface, just right for good ring bedding-in.
Both exhaust valves were stuck but didn't put up much of a fight (watch out for nasty little burrs around the cotter hole which snag just when you think you are winning) and the seats looked reasonable with just a little pitting on the 'wet side' exhaust, so I treated them to a light grind and left it at that.
Checked ring gaps (at bottom of both barrels), no figures available but assuming three thou per inch of bore, original rings were spot on and others a bit on the wide side, though not enough to be a problem. I opted to use one original compression and oil control ring on each piston, filling the rest of the positions with the worn set. I know one it not supposed to swap components around like this, but it would somehow have offended me to have a nearly new set on one pot and worn set on the other, anyway I had deglazed the bores.
Time to start bolting bits back together. New cylinder base gaskets cut from stout writing paper went on with a smear of blue hylomar on the crankcase side and grease on the other (that way they should come off intact next time). Heads went on with more blue hylomar (yes I know it doesn't really do much on a cylinder head, but it makes me feel better with past their best copper-asbestos gaskets). Tightened up the head nuts with some trepidation (Roland had observed how easily the blighters break). One had that nasty 'plasticine' feel about it and I expected the worst, but on investigation it proved to be the washer which was too large and had not seated correctly in its recess - phew:-)
Time to turn it over and the first thing I hear is an asthmatic wheeze of compression escaping past 'wet side' exhaust valve - bugger:-( Off with the head again, valve seat looks ok but never-the-less I grind it again, this time using course paste before the fine. A smear of marking blue proves that it is touching all the way round. Before re-fitting the head I try a suck test on the exhaust stub - leaky as a very leaky thing:-(( However by turning the valve round I arrived at a point where the leak disappears - must be bent. Out with the valve and pop it in the lathe - yes there is a slight wobble of the head but the seating itself looks true. so I put it back together selecting the position where it doesn't leak and hope that it will settle down after a run. I checked the other side and the same effect was apparent, though not to the same extent. Again I selected the position where there was no leak and put it all back together. Oh well, no wheezing now anyway.
Now for the easy bit. The engine did come with a very nice Wico A, but as a single cylinder, anti-clock with no impulse, it's not much use on this engine! So I borrow the mag off my T600, should be a straight swap. Turn slowly until the impulse trips and check which cylinder the rotor arm is pointing at - neither, it's right between the two! Hmm, I didn't expect that. Check the valve timing, not so many degrees BTDC and all that just a visual check that something vaguely resembling 'suck squeeze bang blow' is likely to happen, seems ok so I move the magneto driving wheel round until the points release a slip of paper at the appropriate moment. Checking again with he impulse engaged and this time the rotor arm points squarely at one of the pick ups, connect to plugs appropriately.
Drain sump, clean oil filter (full of mysterious grey sludge) and fill with fresh oil. Will it start? Well not quite first time, but a bit of cranking produced encouraging pops (it was dark by this time so, with no exhaust pipes, the pyrotechnic display was quite impressive) and a few more tweaks here and there had it away. Still not quite right as it won't run off the choke (anyone know what the jet sizes are supposed to be?) but satisfying none the less. Without pipes the lowly T300 sounds like an aero engine and the exhaust flames compound the effect - using the choke you can 'tune' them from yellow to blue to bang and stop!
Sorry for the length of this post, if anyone has actually got this far - but I still find it amazing just how much entertainment and pleasure even a humble little engine can give.