lotty Posted October 8, 2011 Posted October 8, 2011 Took the dt 175 to quarry to scrub land for a quick do. The danm thing stopped. Its normally ok. I had a new plug, but nothing, just a tantalizing little rev and then nothing. I had to push it back, a steep hill which I had to tack up for a long way. It nearly put my lights out, so I quickly bought a long-overdue trailer. Got one of those that break down in mins to go in the car, can be single or double, very good. Anyway, I gets around to looking at the job. Firstly, sometimes spark then not. So whipped the flywheel off. The points were deep pitted. I trimmed em back to shape with a diamond file, getting then even, but still the same. I soldered on a new condenser. The spark seemed much better. So I whipped it in the head and it revved into life......for about 10secs. Whipped plug out and there was no spark. and on and on it went, then one time it gave a couple of backfires. I whipped the flywheel off and the first thing I noticed was the little semi-circular thingy that fit in a slot which lines the flywheel up right had......sheered in half like it was best butter! I will make one of those, no prob, and am jus about to fit a new set of points, so I'll have to see how that goes. But in the meantime I am wondering about something I saw when I took the flywheeel off. The cam is like a tube which slides onto the middle of the inside of the flywheel. and at the bottom of it there is a little slot into which fits a little arm which is fitted with a spring. All this is in the flywheel. I took it apart and cleaned it and oiled it, noticing that it was very worn through lack of oil (the bike is 1975). In fact, the pin on which it moved was so worn at one side that this 'thing' was able to wobble a bit, and so much so that it may not have been able to do its job properly. I made a very thin little washer and put it under the little circlip, and it seemed to level it up. I oiled it and it seems to move and return ok. All it seems to do is move the cam 'sleeve/tube' a tiny bit. Can anyone tell me wht this thing's function is? I just inagined that a cam would be enough to open and close points, so why this little thing, and is its unworn functioning very necessary to the job. Does it halt the points open for a moment or something. Perhaps this is the trouble. I'll know more when I've made the thing that broke and when the points are in. But what is that rocking thing in the bottom of the flywheel? The manual doesn't show the flywheel inner. The last points I set was 32 years ago on my AP 50. I think that could be done with the flywheel off. This sucker is difficult working through the slots in the flywheel. Anyway, the girlfriend has just stirred upstairs......X-Factor must have finished, so I'll be signing off for today but will look back to this and bump it up if anyone can shed any light on the matter. What is that damn thing? Puzzling.
Moderator Cynic Posted October 8, 2011 Moderator Posted October 8, 2011 The half circle 'thing' is called a woodruf key and normally if they shear its due to the flywheel being loose. The other item is the advance retard unit that adjusts the spark automatically for engine speed. TBH if its a quarry bike and it causes issue lock it up in the mid position and it will be ok.
lotty Posted October 9, 2011 Author Posted October 9, 2011 Thanks. Yes, the woodruf key would have been loose, though I didn't realise it. I pretty much just took the nut to the split washer to finger tight.....it all seemed firm enough for point setting and kicking it over a few times, but when spinning fast, well, that's another thing. It was because I'd had the damn thing on and off so many times that it seemed pointless to arrest the flywheel and tighten it fully up. I'll try it all tightend up from now on. Thank you very much. I would have carried on doing the same thing. Thanks. So the thingy is the advance retard unit. I thought it would do something like that. The bike is a damn good specimen of its type, so I will certainly get it all working perfectly. Once again, thanks for clearing that up. We all have to learn, eh.
Moderator Airhead Posted October 9, 2011 Moderator Posted October 9, 2011 yeah the loose flywheel has sheared the key, in normal use there is no stress whatsoever on it because the taper locks solid. The key is only there for positioning. a new one will be very inexpensive...try yambits
lotty Posted October 9, 2011 Author Posted October 9, 2011 Yes, It's probably best to get one. I'll do that. It's amazing how much you begin to learn by getting stuck into a challenge like this one I have. I'm actually really enjoying the challenge rather than it frustrating the hell out of me. It's all the more pleasurable to be able to chat about the job. I should make this a regular haunt......even when my bike is running, not that i feel i have much in the way of helpful advice or hints to give, but it is good to be a part of the group. Keep up the good work, Cheers.
lotty Posted October 12, 2011 Author Posted October 12, 2011 Yes, Colne in Lancashire. We have chatted before, about 3 years ago. I think you said that you had been through Colne on your way to The Lakes once?
lotty Posted October 13, 2011 Author Posted October 13, 2011 Well, I've got the new points in and everything set and tightened up, and am getting a good healthy spark. It started first time, as it always (normally) has, and ran well, but again, only for about ten seconds. I took the plug out to check the spark, but nothing, the plug was wet, so I checked with a new plug and there was a good spark and it ran again, but for ten seconds. I have taken the plug out and left the pot to breath for a day, and will give it another go later......it was 1am when I got it running, so I couldn't keep trying. In a way, this is basically where I was when the thing stopped in the quarry. I was getting a spark then...but, as i'd kicked it over a fair few times, when I took the plug out I expected it to be drenched, but it was dry! The points were in a bad way, so it is all better now, but basically the same thing seems to be happening as when it cut out in the quarry, I could manage to get it running for a few seconds and then it just dies. In the quarry, when the plug was dry, I naturally thought it was the carb, which i took off and checked over and put back on. I am thinking that it could be something to do with the carb being set up wrong, or the throttle cable not beind right (affecting the needle not being right position in the carb, perhaps). I'm going to wait until Saturday pm when i can get it outside and, if it starts, which it should, keep the revs on for a good long time, if I can. But, it baffles me because these things are essentially so simple that it should work without any mysteries. Why is it running for only 10 seconds and yet coming out with a wet plug, so there must be petrol? Perhaps there is too much petrol going in, and maybe this could be the needle in the carb letting too much in.....this may sound daft, but I'm a beginner, really, in the scheme of things. I could take it to someone, but I want to learn, and I want the challenge. Anyway, I'll have another bash tomorrow. But if anyone has any suggestions they are certainly most welcome, and don't assume that I will have covered obvious bases. I could be missing something really basic, so any suggestions are welcome.
lotty Posted October 19, 2011 Author Posted October 19, 2011 Well, I'm just bumping this thread up to say how i got it going, as it may help someone. I was a bit stumped. I noticed the battery was down so thought I may as well charge it. As I was doing this a connector dropped down the air intake, and it got me thinking about air. The filter was all ok, but I decided to screw in the air screw on the carb, and then wound it out again between 1.5 to 2 turns (which is what the book says). I then decided to take the back of the exhaust off to check the baffles, which were ok, but I noticed some play in the exhaust, finding that it was a bit loose at the engine pot, so I fit a new gasket and kicked it over and it ran fantastic. It is a good bike. I think that it was just suffering from some neglect in terms of keeping it serviced and everything set correctly. Oil was certainly needed in the flywheel's moving parts, especially the rocking thing, as it was wearing away. I suppose it is true what Fred Dibnah used to say, 'All you need is one little tiny drop of oil, but if you haven't then you are f********'.
Moderator Cynic Posted October 19, 2011 Moderator Posted October 19, 2011 Many people underestimate just how vital the exhaust seal is on a 2 stroke. The intake charge does leach out into the expantion chamber and then gets drawn back as the engine fills with the next charge, if that seal is broken then you suck air and run dangerously lean. Glad you sussed it.
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