Friday, 1 June 2018

The new TR1 engine - welding up and machining heads back down (part 21)

Now you can't make an omelette without breaking a few eggs (a lot actually). With the fixture done, the next step was to put it to good use. But first a base-value for the cylinder head volume had to be established and yes, a TR1 head has actually got a chamber volume of 54cc.

To maintain repeatability, I marked out the lines I wanted to meet on a headgasket.

Welding the heads up with MIG and a spool of AlMg5 is messy, but works beautifully. It has to be noted, that you get so much heat into the heads that pre-heating had little effect on the final outcome as I found out on some test pieces.

One of the locating dowels was one hell of a stubborn b*st*rd, but it had no chance against a TIG used in anger and a bolt. (Some hammers and rods were part of the equation as well...)

Pre-heating the head on an old hot-plate.

The first head was milled to size before flycutting, but it turned out, that it was easier to first skim the head and then mill the wedge to size, as this helped a lot with accurately aligning the head gasket with the cylinder head.

No photoshop trickery here: With a nicely balanced flycutter, a large flightpath and high rpm a nice finish was really simple to achieve.

CC'ed the new chamber and et voila: 47 to 48cc. Which means, now I will end up with the same 10.5:1 compression ratio as with 750 heads. 

At the time of this posting another set of cylinder heads will have been fabricated as these had a little more material removed than I would have wanted as the heads themselves were a bit warped. This unfortunately also means, that the piston to valve clearance is reduced, which is not a big issue with stock cams and stock squish-height. Two other issues that will be addressed very soon in the course of this build.

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