Not everything goes according to plan ….and this was one of those instances. I was hoping that KTT 305 would start as easily as KTT 55 but this was not to be. This is a short clip of the first attempt at starting the bike.
Hmmmm! Not exactly the result I was hoping for.
If this was a bike that had been up-and-running in the past and then dragged out of a shed after being stored for a few years this narrows down the possible causes of not starting - it’s invariably either a fuelling problem or a “sparks” problem. This is not the case with a new-build as there are many other things that could have been screwed up during the build. And so, it was back on the bench and some of basics were checked again – ignition timing, valve timing etc. Everything here was in order and so it’s back to either fuelling or “sparks”,
There was plenty of fuel (wet spark plug) and although the carburation will almost certainly need some setting up when the bike is running, if fuel is present then it’s not usually the cause of an engine not starting at all. A closer look at the video shows that the bike is “trying” to start and appears to get an occasional successful ignition followed by a bunch of non-firing cycles and this points to an ignition problem. So, time to check the output from the magneto.
Before checking the magneto on the bike, I first checked the spark plug itself. The short video clip below shows the plug used on the bike with another magneto on the bench.
Absolutely fine. I removed the magneto chain on the bike and, with an electric drill on the magneto shaft (making sure it’s running anti-clockwise!) this was the result.
Almost certainly the cause of the problem. This magneto had been rebuilt, including armature rewind, remagnetised etc before it was put on the bike so why would this happen? I can’t remember when this particular magneto was rebuilt – probably 2 to 3 years ago around the time I started these projects and this is the clue to the problem.
The original contact breaker points, which would have been fitted nearly 100 years ago, would have been made of a platinum-iridium alloy for the contact surfaces whereas the replacement points that are now available use tungsten. The original platinum-iridium material does not oxidise whereas tungsten forms a very thin oxide film that gives an electrical resistance and this is the cause of the intermittent sparking.
There is an easy fix: remove the points assembly (it’s held in with one screw on a small keyed and tapered shaft),
remove the moving “point” (on the right in the above picture) and gently polish both contact surfaces with a clean piece of fine emery cloth, reassemble and test.
A spark every time and so after refitting the timing chain and checking the ignition timing I was now more optimistic that the bike would start. And, sure enough…..
Borrowing a phrase from NASA’s Apollo era ….We have Ignition
There was one last problem and it’s seemingly always the little things that can be really frustrating. I was aware that the bike was wet-sumping and although there is an oil tap to prevent oil getting into the engine when the engine is not running it only take a very slightly leaky tap – a drip every minute is enough – to allow oil to fill the crankcases and then find its way out via the drive-side main bearing and end up on the floor over a period of time.
As I was about to go on holiday to the Peloponnese for some late summer sun and to visit some ancient Greek sites, I left a clean container under the engine (the bike is up on the bench) and when I got back the entire contents of the oil tank were in the container. It seems that my supplications to Hephaestus in Greece had been unsuccessful and I would have to fix it myself. KTTs have a large oil tap – see here for repairs that I had already carried out to both the tap and the tank on this bike, but I had not done anything specific to address the sealing of the tap.
It was therefore stripped
and the taper lapped with fine grinding paste followed by Autosol. Rather than refitting the tap and refilling the oil tank to test the outcome, which would be rather tedious to continually repeat, the sealing can be tested by inverting the tap, holding it gently in the vice, putting a small amount of oil into the downstream end and leaving overnight. After a few attempts and adjusting the pressure of the taper with the securing nut so that it showed no leakage the tap was refitted to the oil tank and then left for a week with the crankcase drain plug removed for final testing.
Finally, the oil pressure was set to 12 psi – same as KTT 55 - and that’s about it for the moment. Both KTT 55 and KTT 305 are up and running and the last one, the DOHC 250, will soon be up for its first start.
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