Putting the Triumph Pre-Unit Engine back together pt 3

Published on 8 January 2024 at 10:34

As I had identified that I was not getting a spark I took the timing cover off with a view to removing the magneto - first thing you need to do is remove the magneto drive gear. There are two sorts - a fixed gear and a variable timing unit that adds advance as revs increase, mine turned out to be the fixed type, which makes sense on a drag bike that always runs at or near max revs. I expect the timing will be about 32 degrees or so btdc. I will have to get a timing disc to verify that.

I was not expecting to see what I saw when I took the cover off, all the gears are lightened racing jobs, maybe I should have guessed as the internals I had already seen were all polished and lightened too. Somebody spent a great deal of time and effort making this bike quick.

The timing marks make no sense to me whatsoever, I watched a video that seemed to make some sense right up until the part when he explained that the timing marks are only correct upon initial installation and then are only correct every 96th rotation of the engine. I am still trying to get my head around that one. The marks on mine are nothing like the marks in any video I have found so I remain confused. There are a couple of paint marks on the exhaust and inlet cam gears and numerous punch marks on the intermediate gear. I can see one punch mark on the crank gear but nothing really seems to line up right now so I need to look further in to that.

It was while I was messing about in this area that I suddenly had an idea with regards to the magneto. There are two pickups that mount one each side - they allow the ht leads to be connected to the magneto, they have spring carbon brushes that conduct the high voltage pulses from the magneto armature to the ht leads. I just suddenly got this impulsive urge to remove them and check them for conductivity - both were open circuit. Now I am not saying this will fix my problem but they are definitely faulty so they need replacing, I have 2 on order. I am hoping it will fix the problem, if not I will progress to taking the mag off - I will make all new timing marks on everything before I touch anything.

In the mean time my car has failed it's MoT big time so I have to fix that before I do any more on the Triumph, there is a few days work to be done and much money to be spent. I don't suppose I will get much done for a good while, unless I end up waiting for part for the car.

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