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now this is odd!

now this is odd!

Postby john robert bould » Sat Jun 21, 2014 5:27 am

Ok this is not a Norton...my grandad allways spoke the truth!

But i am sure this is common to a commando..
I strobed my friends Bsa Rocket three yesterday ..becase the bike runs rough at tickover.
What i saw flashing up the snapon strobe ..confused me a bit...why do i see two marks approx 20 mm apart...surly i should see only one? Is the boyer dicky?
The rota as three lines 120 degrees apart its only a 1 inch window ..so impossible to see the other two when one appears.
I know the plugs all fire together ..but how on earth can i see two lines lit up 20mm apart?

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Re: now this is odd!

Postby texasSlick » Sat Jun 21, 2014 5:59 am

john robert bould wrote:Ok this is not a Norton...my grandad allways spoke the truth!

But i am sure this is common to a commando..
I strobed my friends Bsa Rocket three yesterday ..becase the bike runs rough at tickover.
What i saw flashing up the snapon strobe ..confused me a bit...why do i see two marks approx 20 mm apart...surly i should see only one? Is the boyer dicky?
The rota as three lines 120 degrees apart its only a 1 inch window ..so impossible to see the other two when one appears.
I know the plugs all fire together ..but how on earth can i see two lines lit up 20mm apart?


There are two possible explanations:

1) the electronic ignition is firing twice in quick succession .....not likely, or even possible for the coil energy to rebuild so fast.

2) the ignition is firing a few crankshaft degrees differently on successive revolutions of the crank. likely explanation, but why becomes the next question. Such a difference would explain the rough tickover.

I would guess it is more likely an erratic variation of case 2) above....example, let's say one of the lines is 5 deg BTC, and the second, 10 deg BTC. The engine is firing 5,5,5,10,5,5,10,5,5,5,5......etc

Check the ignition sensor or points for any looseness in the mount.

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Re: now this is odd!

Postby dave M » Sat Jun 21, 2014 7:54 am

Some of the Lucas rotors have the timing marks scribed on a slightly raised section you may be seeing the shadow produced by the edges of this raised section which are indeed about 20 mm apart. I generally mark the timing line with coloured paint then there is no mistaking anything else for the mark.

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Re: now this is odd!

Postby john robert bould » Sat Jun 21, 2014 8:17 am

I think mayby the coil/ coils are triggered twice one post is in a differant place [very close to the first] does that make sence? due to the three coils [boyer] or a post in the wrong place...if the boyer plate as its posts set at ,0 then 100 ,then 140 ,back to 0 will this strobe as two lines slightly apart?

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Re: now this is odd!

Postby L.A.B. » Sat Jun 21, 2014 11:40 am

dave M wrote:Some of the Lucas rotors have the timing marks scribed on a slightly raised section


However, all BSA/Triumph triple alternator rotors have a flat machined surface with three (later, six) scribed lines, if there is a raised pad then the rotor is either fitted back to front, or it's the wrong rotor.
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Re: now this is odd!

Postby john robert bould » Sat Jun 21, 2014 2:21 pm

Correct LAB the rota is flat with 3 groves ..well they look like sharp chisel indentations ..this two strobe "appearances" [two groves 20mm apart] is very odd, i am thinking the three poles in the boyer are not 120 degrees apart...? would this produce the double lines?

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Re: now this is odd!

Postby L.A.B. » Sat Jun 21, 2014 2:54 pm

john robert bould wrote:this two strobe "appearances" [two groves 20mm apart] is very odd, i am thinking the three poles in the boyer are not 120 degrees apart...? would this produce the double lines?


I couldn't say for sure, although it seems rather unlikely unless the pickup plate was damaged perhaps, but I thought you would have checked something like that?

The only other 'Boyer' thing I can think of, is to check if the Boyer rotor is running out of true?
Or, perhaps the alternator rotor body is loose or is otherwise moving on the crank so the timing mark is constantly shifting about?

Did you use a separate power source for the strobe (assuming it's a 12V strobe)?
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Re: now this is odd!

Postby ashman » Sun Jun 22, 2014 3:51 pm

Is the centre on the rotor worn as I had that trouble many years ago when I put the timming light on it I was gettting 2 marks, but found out my rotor was worn and was moving back and forward, had to get a new centre fitted.

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Re: now this is odd!

Postby kerinorton » Sun Jun 22, 2014 4:48 pm

L.A.B. wrote:
john robert bould wrote:this two strobe "appearances" [two groves 20mm apart] is very odd, i am thinking the three poles in the boyer are not 120 degrees apart...? would this produce the double lines?


I couldn't say for sure, although it seems rather unlikely unless the pickup plate was damaged perhaps, but I thought you would have checked something like that?

The only other 'Boyer' thing I can think of, is to check if the Boyer rotor is running out of true?
Or, perhaps the alternator rotor body is loose or is otherwise moving on the crank so the timing mark is constantly shifting about?

Did you use a separate power source for the strobe (assuming it's a 12V strobe)?

If that was the case, you would see the timing mark jumping around, but not 2 marks, [ at idle revs that is. the apparent 2 marks may be visible at high revs though . the movie projector effect].
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Re: now this is odd!

Postby john robert bould » Tue Jun 24, 2014 1:00 am

I"m looking today at the issue, I have a inkling the magnet screws are rubbing on the back plate...touching the soldered "blobs" I guess this would cause some ill effect?

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Re: now this is odd!

Postby L.A.B. » Tue Jun 24, 2014 2:59 am

john robert bould wrote:I"m looking today at the issue, I have a inkling the magnet screws are rubbing on the back plate...touching the soldered "blobs" I guess this would cause some ill effect?


There are normally pins projecting from the coils on the reverse side of the plate, so if the magnets are touching something it's more likely to be those pins.
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Re: now this is odd!

Postby john robert bould » Tue Jun 24, 2014 2:03 pm

Thanks Lab for your imput, I have found out the problem :oops: It was just sods law i had viewed though the timing window one single timing mark . eased the engin over to see another mark...had i done this again ,there appeared two marks :evil: ...why there are two approx 15mm, not twenry as first stated..god knows :!:
So the strobe was flashing up all the marks..two single and one double. this is what i see kicking l..........l.........ll........l.........l.........ll
At 5000 i see ll........ll.......ll........
Live and learn :oops:

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