ChrisW wrote: Fri Dec 13, 2024 6:33 pm
This one had everything - a simple quest at the beginning, dragged ever more complex. Highs, lows and a cliffhanger for the next episode.
Well, we have some answers- if not all!
The mystery of the origin of the mashed nut-thing was bugging me, and sad as it sounds, and probably is (
) it kept me awake that night so as soon as I could I poured over every engine exploded diagram/parts fiche to try and work out what it could be.
there really aren’t that many pieces in one of these engines, relatively speaking, and I very quickly came to the conclusion that the only thing it could possibly be (apart from big-end cap nuts, which I’d already ruled out), was the nut holding the alternator drive gear onto the alternator- #29 in this pic
For anyone who doesn’t know, on these old oil-cooled Bandit/Gixxer motors, the alternator sits up behind the barrels rather than on the end of the crank, and gets it’s drive from a gear on the back of the clutch basket.
It’s a 2-minute job to changeit on these, so, back into the garage I went, whizzed out the three bolts that hold it to the crankcase, and pulled it out
- it came straight out but its drive gear didn’t, so that’s one mystery solved!
Having said that, there was, however, no sign of the washer that should be behind the nut ( #28 in the diagram) so that gave me another bit of head-scratching as it definitely hadn’t been in the sump with its nutty friend.
Anyway, I was resigned to doing a full engine strip and inspection, so my thoughts were that it will turn up , assuming it was ever there of course.
This is what the end of the alternator looks like-
As you can see there's damage to the threads, I’m guessing (but I am of course not certain), that was caused as the nut made its way off, unless someone had previously had it off and crossed it or something putting it back -who knows
Otherwise, I struggle to understand why the nut came off, as they are peened over at the factory, as may be seen below – this is my “spare” that I’ve now taken off the original engine, and will be using
IMO It says something for the design that it ran like that without causing any real damage, and that's due to both the fact that the back of the clutch keeps it in place, and also the helical nature of the drive gear pulling the gear towards the alternator, as it’s not on a taper.
This is a shot looking in at the back of the clutch with the alternator removed- the gear on the end of the alternator is driven from the smaller gear in the pic
And this is the back of the alternator gear, which shows the cush drive .
I then removed the clutch casing and the clutch, which allowed me to properly inspect the alternator drive gear, the area of the crankcase that it runs within, and of course the clutch itself
Everything looks pretty much tip-top, which is good, and nothing short of a miracle IMO, but there was still no sign of that missing washer!
Next up I went underneath and removed the oil pump pickup- basically the tube with a gauze on the end that extends right down into the sump and sucks up the oil .
The gauze had a few small bits of steel on it, still no sign of the washer though, until I took it apart, and this dropped out, yay!
I guess that when the nut parted company with the shaft, the washer followed, and somehow managed to miss getting caught up in any of the many drive gears on its way down into the sump- feck knows how, as there are so many moving components on the way, but thankfully it then got sucked into the strainer with some oil and wedged up in a corner of the housing.
Aside from a little bit of surface marking where it has obviously rubbed a bit on the back of the clutch gear, the washer looks pretty much brand new, and it is all quite astonishing to me that it’s managed to make its way to where it has and not lock up the motor or damage anything on it's journey.
So, that’s the mystery of the mashed nut and missing washer solved, but still no sign of the missing cam sprocket bolt.
I have however, been doing a lot more thinking on that, and have changed my mind , I really don’t think it can have ever been there.
I say that for the following reasons-
- With the clutch and sump etc off, and my endoscope and thin extendable magnet I can get to just about every place that the missing bolt could possibly be, and it’s not there.
- More than that though, I fail to believe that it could have come out and not caused any damage to the rockerbox cover, head, valves, or not got wedged in between the cam chain and crank, or crank and crankcase.
The inside of the rockerbox is immaculate
And there really isn’t any space down here, which is where it would have most likely fallen, assuming that it didn't come to rest somewhere under the cams in the head ( which it definitely didn't)
The only slight anomaly is the (very small) scrape on the head that I showed in my last post, that looks as though it would have been caused by a cam sprocket bolt, but I really can’t explain that other than it has to be a hangover from a previous event?
Anyway, I am now confident that there is no loose cam sprocket bolt lurking anywhere in the motor , and no real damage to anything else in there so although I am still not completely 100% decided, my current thinking is that this is as far as the engine strip goes and I’m don't bother removing the engine and splitting the cases after all- although a 100% strip would fully satisfy that tiny (0.01%) doubt that there may be something more to find, it’s a fair bit more grunt work, so unless I change my mind over the next few days, or am convinced otherwise by any of you lot, from here on in it’s re-assembly time.
The head and pistons will get a de-coke, valves lapped in , re-shimmed and re-assembled with new stem seals , and we should be good to go for another season ….
)
