Sunday, 7 October 2018

The new TR1 engine - learning from mistakes (part 30)

As the saying goes: you can't make an egg, without breaking some omelettes – the same applies to make go-fast-engines. By now roughly 1200km have been clocked up and a flaw of the welded up heads has reared its ugly head. The engine has got a ferocious appetite for spark plugs. I mean, when it runs, it just runs. It goes. It really does. Until it doesn't.

So it was time to take things apart, swap back to the somewhat tried and tested setup of 700/750 heads as the Tractor isn't referred to as the "Everyday TR1" without a reason. Piston and head show no obvious signs of mishap. Some carbon buildup as is to be expected with my bad habit of using lots of oil on first assembly and rings that had to bed in. All in all (even though AFR said otherwise), it looks a lot like a rich condition. As such my hypothesis goes along the lines of some weird turbulence or flow issues? Contrary to that the carbon buildup on the piston shows an almost perfect swirl pattern.

Either way, I need a second daily bike to complement the Dre-XT-Stück and that's what the Tractor is there for. (Actually the Dre-XT-Stück is meant to complement the TR1, but digress...) Luckily I still had a set of XV700 heads, with some transportation-damage. Welding the fin back on was terrible, not being helped by the fact that I was "a tad" pressed for time.

The combustion chamber on these is again a bit smaller than on 750 heads, mainly due to the additional squish area near the sparkplug. A very knowledgeable friend talked me out of these originally and suggested I should go with the bigger port, welded up heads.

The heads overall were in pretty good condition, but the usual re-threading of all studs and threads was due, as were new valve stem seals and lapping in the valves. 

The procedure should be quite well known by now - strip the bike back to the engine and rear wheel.

Unfortunately my supply of good Gen1 cams and rockers is a bit limited so I had to remove all the bits from the welded up heads to use them on the new heads, which added a bit of extra work.

I've had to look it up so often, that I finally decided to simply write it on the engine, which mark is which.

Behold the mighty throttle-cable-oiling-spider that lurks next to the door...

Oh and the carb-fairy dropped off two uber-sweet TM38-86. Why new carbs? Simple: these fit the same inlet manifold rubbers as the older VM38-9 roundslides and as such allow back-to-back testing. Also they are somewhat better affixed in the rubbers as the TM38-85 in the stock TR1 rubbers. Additionally I am using 45 degree cable bends, as I saw that in the original XS650 kit the throttle cables come from, these are used as well and guess what: No more shortening of cables necessary.

Jetted: #22.5 (pilot, stock), #175 (mains), Needle in mid position (stock) and air-screw 1.5 turns out (stock) the bike is an absolute beast. I hate to admit it, but I am not sure it was really much faster with the bigger ports. It now cleanly revs to my hard limiter at 8000rpm and pulls all the way. The #22.5 is a tad richer than I'd like it to be, but the needle is too rich one notch up and with the #20 pilots there's some slight detonation, when the bike is really hot. I still may try to go back to #20ies once more and just retard the max. advance by one or two degrees, but as you should be able to read out of this, it's really close.

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