Monday, October 21, 2013

Building a T100R Daytona Engine

It's a '67 Triumph T100R Daytona, 500cc twin but the principles apply to any engine.  The owner wanted the engine properly rebuilt, blueprinted and cosmetically restored.  His orders were to "build it like it was my own", music to the ears of the OCD sufferer.

Let's start from the top (of the engine).

Valves, guides, springs and seats were completely worn out and there were a few decades worth of baked-on oil everywhere.  These photos show the bare head, I've already removed the valves, springs and the guides.

Making the oil's return trip a bit easier.

The cylinder head all cleaned with the new Kibblewhite valves and guides ready for installation.

The guides installed and ready for honing to size, also note the oil drain-back area.

Guides honed to size and now the seats can be cut.  Getting ready to true the seat with a Neway 45 degree cutter.

A nice 45 degree cut, the 60 and 30 degree cuts will come after.

All of the seats are cut and the head gasket surface and rockerbox landings have been trued.  The next step will be to measure the volume of each combustion chamber in preparation for making them identical to each other.

Measuring the chamber volume.  The left chamber measured 62.4 cc and the right measured 62 cc, since it is much easier to remove material than to replace it, the smaller chamber's valves will be sunk in order to match the volumes to each other.

With the head ready to go to the flowbench it's time to turn to the pistons.  Contrary to the belief of most "mechanics", they are not ready for use out of the box.  The first step is to contour and remove all toolmarks from the domes because sharp edges do not help combustion chamber turbulence and toolmarks are always potential stress-risers.

With both domes done, now I compare their volume and make sure that they are the same. 

The domes were within 0.2 cc of each other, good enough even for me.  Next the pistons are weight-matched.  The right piston was 1 gram heavier, it only took a little hand-scraping (their is an area of extra material under the skirt which is there to facilitate balancing) to match it to the left.

I took no photos of honing the cylinders (it's a filthy job and I didn't want to handle my camera while doing it) or of filing the ring end-gaps (because it's boring to look at).

Time to rebuild the connecting rods.  First they are checked for straightness (bend and twist) and the wrist pin bushings were also measured and inspected and found to be serviceable. Again toolmarks are the enemy, especially here. 



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