Knocking / rattling inside primary drive case + backfire
- Thread starter M-Hawk
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Shims cut from milk cartons seem to be a popular idea here 
marshg246
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Try these:
1) With the stator off, make sure there is nothing protruding into the gap. You can sand it out a little if the encapsulation seems to be.
2) Try the three spacers in different locations.
3) With the nuts just snug hit the center of the stator 180 degrees from the tightest spot.
If those don't work, you need to open the holes a little, but I don't recommend drilling as I've ruined a couple of stator trying to drill them (the laminations separate).
marshg246
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Take the stator and rotor off and make very sure that the front sprocket is locked to the crank taper.
I could easily be wrong, but I don't think the rotor is touching the stator. As much as the chain is jumping it might be the only problem. The front sprocket is keyed, but on a Norton, the key should be thought of as a locator - the taper is what matters.
It's also possible that your drive-side main bearing is going.
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So, interesting thing. As I rotate the engine, the part with the narrow gap moves. Meaning, the part that is almost touching the rotor is in a different place depending on the position of the crank.
This surely means the spacing can’t be resolved by shimming the spacers or moving the studs. Doesn’t this mean that the rotor itself is somehow misshapen? If the spacing problem was because of stator misalignment wouldn’t the tight spot always be in the same place?
I’m a bit scared to remove the rotor unless I absolutely have to, due to the torque settings involved. Also the timing seems good and I don’t want to mess that up.
This surely means the spacing can’t be resolved by shimming the spacers or moving the studs. Doesn’t this mean that the rotor itself is somehow misshapen? If the spacing problem was because of stator misalignment wouldn’t the tight spot always be in the same place?
I’m a bit scared to remove the rotor unless I absolutely have to, due to the torque settings involved. Also the timing seems good and I don’t want to mess that up.
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Timing won't be affected.......
marshg246
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Means that the rotor is cocked or the crank is bent. Don't worry about the rotor torque - you can make it tight enough, and timing won;t change.
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No, the crank is bent on the end but not enough to affect anything but the rotor to stator gap. So you are going to have to open up the gap all the way round so the tight spot is 10 thou all the way round. So get the rotor OD skimmed or the ID of the stator to get 10 thou at the tight spot.
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Rotor centre seemed solid (not loose).
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I've removed the rotor and stupidly (getting tired), I forgot the rotor key would drop out. I'll have to figure out how it all goes back together later! I.e. which way around the key goes. Also, whether the collar/shim goes behind or in front of the rotor spacer.
I then mounted a DTI to see if the crank is bent. It's definitely not 100% true but I don't know what the tolerances are. I think it's deviating about 0.1mm. Is that normal?
Not sure what else to look for while the rotor is off. The sprocket seems to have a very small amount of play to it. Also, not sure if that's normal. I'm favouring Kommando's suggestion that the crank must be slightly bent, and a rotor skim could be the solution.
In the meantime, I've tightened the primary chain to a smidgen over 3/8's (preferring to err on the side of loose than tight).
I then mounted a DTI to see if the crank is bent. It's definitely not 100% true but I don't know what the tolerances are. I think it's deviating about 0.1mm. Is that normal?
Not sure what else to look for while the rotor is off. The sprocket seems to have a very small amount of play to it. Also, not sure if that's normal. I'm favouring Kommando's suggestion that the crank must be slightly bent, and a rotor skim could be the solution.
In the meantime, I've tightened the primary chain to a smidgen over 3/8's (preferring to err on the side of loose than tight).
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marshg246
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OK, I'm getting nervous for you. You are left with:
1) Bad rotor (I've never seen one that wobbles). Probably not causing the noise.
2) Bent end of the crank. Probably fixable but not sure I would try in the engine. Probably not causing the noise, but hard on the crank and main bearing.
3) Loose front sprocket (Very unlikely). Could cause the noise.
4) Bent crank which has caused the main bearing to start to go. You need a crank and main bearings and if you can't do it, help. Could cause the noise.
5) Bad main bearing. Could cause the noise.
6) Loose conrod and the noise is not actually in the primary.
7) Combination. Could cause the noise.
It is difficult to tell from the video. I guess I would tighten the chain and then listen again. If you still have the noise, then start on the list above.
marshg246
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Good! Now you can upload pictures directly.
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...Curved edge into the crank slot:
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I can only suggest you buy the crank sprocket removal tool (that's assuming the engine sprocket is actually tight on its taper?) and clutch spring diaphragm compressor and strip the primary drive. The crank sprocket should definitely not feel loose.
marshg246
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You can. Just be sure the key stays in place when you push it on, and don't worry about torque too much - just make it real tight.
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The engine sprocket fits on a taper on the mainshaft and normally grips so tight people post asking how to get it loose even with the proper puller. If its loose then hopefully its due to dirt/grit or a bad burr on the taper stopping it from making full contact, it has to come off for checking.
