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The second rebuild pt2

It must have taken me hours of checking, measuring and template cutting to work out the rear engine plate design and also the position of the crossover shaft which would be mounted to and run through the plates themselves. It was very tight. I got some steel tube and a 3/4" die and threaded the ends. Terry Mead made up the cross over shaft to go through the tube. The shaft was brazed to a brake pivot bracket from a Yamaha XJ750. The T140 brake pedal was reshaped and shortened and a nicer XJ750 'plate' fitted to the end.

 

I was really excited when I went to fit the crossover set-up. But that excitement was short lived when I realised to my horror that I hadn't taken into account the final drive chain. The shaft went smack into the side of it! So now I had to move the shaft back and up to clear the chain run. This not only meant new outer engine plates but the modified brake pedal that I'd had chromed for £75 was now too short. The air in the garage went a bit blue that day.

Right from the off I was starting to regret going down the unit 750 route. As mentioned, it started with the engine plates, followed by my miscalculation of where to place the cross over shaft so as to avoid the chain run. It got worse when I went to collect my crankcases from the blast cleaners. They hadn’t told me that they had stopped vapour blasting anymore. Instead they had sand blasted them, so now I had a dull grey set of cases with a horribly rough surface finish. Great.

However, all was not quite lost. In keeping with my idea of building a slightly less ostentatious bike I decided I would paint the cases with black crinkle finish VHT paint. So after lots of careful masking and several coats, I achieved a most impressive finish.

Thus began the long awaited engine rebuild. All went to plan (more or less) and I managed to get the completed bottom end into the frame. A lot more convoluted than might be expected as certain bolts had to put in before others. Anyway, tightened everything up and put some oil into the cases. Had a break.

Disaster!
With a feeling that I was at last making progress I came into the garage the next day only to be confronted with a pool of oil underneath the half built engine! I couldn’t believe it. I had used the excellent Wellseal on the case joints and I had been extra careful and thorough in its use. But then my to my horror I discovered it wasn’t the crankcase joint at all. I wearily took out the engine and dismantled it to confirm my worst fears.

It all came back to those wretched Converter engine plates. In order to get the front plates to run parallel, and so fit the engine, it required about 1/8th” of alloy to be removed from each side of the lower engine boss. I thought I had been extra careful but obviously not. The alloy on the underside of the cases was thinner than I’d reckoned and on dismantling the engine I found a tiny hole, no bigger than a pin prick. So now I had to get the hole welded up which, of course, destroyed the paint. I couldn't face masking and painting it all again so I laboriously stripped off all the paint and got the cases bead blasted. Although not quite as good as vapour blasting, it at least brought them up to a finish similar to what I originally wanted.

So the engine build started again, but now yet another problem reared it's ugly head. This time in the building of the top end. After fitting the pushrods, pushrod tubes and rockerboxes I couldn't work out why the valves weren't closing properly when the crank was rotated. After exhaustive examination and numerous attempts at assembly it transpired that the problem lay with the alloy pushrod tubes. Despite the fact that they were CNC machined, it turned out that they were not only slightly longer than the original steel type (so affecting the crush on the lower seal), but they were too narrow inside leading to the pushrods binding on the inner lip of the tube. This was eventually fixed by purchasing original spec tubes from LF Harris. A lesson learnt using pattern parts!

Crinkle paint finish was not part of the original plan, but looked great until a pin hole was discovered in one of the case halves!

Crossover shaft to allow use of excellent BSA single sided brake and QD wheel with left hand Triumph gearchange

RHS rear engine plate showing threaded crossover shaft tube (centre of picture)

LHS rear engine plate showing crossover shaft tube retaining nut

Here we go again .... repaired and re-blasted cases and the engine build can restart. But now it's the pushrod tubes which cause a headache ....

.... CNC alloy tube v original. Too much crush on oil seal meant it kept popping out. Narrow inner diameter meant pushrod would stick and valve not fully close

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