Saturday, May 10, 2014

Picking up again.

On Monday I got my cylinder head back from a machine shop that the Thomasdunstall guys recommended and I'm pleased to say it looks like they did a good job truing the mating surface:

Now I can bolt this sucker down knowing that the mating surface is actually flat. Yes I know there are some casting imperfections in the alloy, but this is by no means unheard of with these things. I'll seal it as best I can and see what happens.

Before fitting the cylinder block, I had mocked-up all the parts, both for the new cylinder and head, as well as for the display engine (we'll get to that in due course); this was to find out exactly what was missing before I went any further: it'd be easy at this point to get caught up in the enthusiasm only to find work grind to a halt for want of a 50p washer... So, I came up with a relatively short list of fasteners and gaskets that I got from Andover: an absolute pleasure to deal with, very fast and the real deal when it comes to spares. Accept no substitute. There are also a few decals for the side panels and tail fairing, since the whole bodywork will need to go back to Toni for some minor repairs and a conservative re-spray.

One thing I'll be fitting this time is the heat insulating washer under each valve assembly, just to be safe. I will check the installed height before I bolt down the head, of course, but again the only way to know for sure if something works is to try it. You can do all the calculations you want, but in the end you need to slowly rotate the engine by hand and stick a feeler gauge in there to make sure the springs don't end up a coilbound disaster when the camshaft is at maximum lift. With a 4S camshaft the problem could be the intake valves, as lift is higher than with a standard camshaft, however the exhaust should be the same, and that's where you really need the insulators. Anyway, if there is enough clearance, I'll leave the washers in everywhere.

I've also decarbonised the valves, real bloody drudgery but it has to be done. Even so, I did the absolute minimum, but it's definitely good enough. The build-up of carbon especially on the intake valves was pretty horrendous and betrays the sort of carburation nonsense that had been going on before. Here's some before and after:
Next up, actually assembling the valvetrain!


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