Best Timing Method Model 7 with Mag

Brooking 850

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Helping a friend with a 1951 Dominator 7 500 twin.
Mag totally rebuilt great spark.
The owner has an old paper style manual which indicates to time off the RHS with mechanical marks all aligned.
Double checked mechanical marks and they are good with 6 x plates between the cam sprocket and the intermediate sprocket with intermediate gear and crank pinion aligned as per factory specs.
That manual indicates the points should be in the 9 o'clock postion just about to open.
I have another hard cover book which indicates to time off the LHS (this is what Im used to having had older 500's in the past) and that puts the points at the 3 oclock position when comparing with the first manual.
I used the LHS retimed the mag points and it fired although never ran.
Rear HT lead to LHS plug.
I checked the plugs , great spark although looked very short in the threads.
Replaced with some B7ES to get the spark further down the hole, still no luck.
Forum thoughts please
Regards Mike
 
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BP7ES will get you a bit further into the combustion chamber, P stand for Projected.



But that does not sound like your issue, when you take the plugs out after unsuccessful firing is there any sign of unburnt petrol on the plug. What else was done to the engine and was the carb left with fuel in it while the mag was away being rebuilt.
 
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In my experience, anything between 38 degrees BTDC and 12 degrees ATDC will start a Norton. Never tried more wrong timing than that. Of course not running very well, but still running. So I presume that if you don't have timing totally wrong, your problem is something else.
Two weeks ago started a Yamaha cross bike which had stood with petrol in it for four years. Drained tank and filled with fresh petrol. Too lazy to drain the carb, I feeded it with start spray for a minute running until it started to on the fresh petrol. Start spray could help you.
 

texasSlick

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I am not familiar with the early twins, but if at all similar to my Atlas, aligning the timing marks on the RHS, puts the engine at TDC. The points are in the 3:00 position, and the rubbing block is about the 5:00 position. The rear HT lead goes to the left cylinder.

On an Atlas or Dommie with an AAU, when properly timed, the points will be open at TDC, having opened at 8 degrees BTDC. This 8 degree statement is true if the AAU is in the retarded position.

Using a degree wheel and timing from the LS is preferred.

I agree with Mike40M. Anything close should start the engine, although it may run poorly.

Slick
 
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Manually or automatically, timing should always be set on FULL advance at 32 degrees with a timing disc on crankshaft. (Low compression engines) Also check the other cylinder is firing exactly the same whatever ingition system you have, or you might find yourin some expensive troubles, trust me from someone who knows. . . . .
 

Bodger

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I asked because I was wondering if the OP inadvertantly set the timing with mag on retarded instead of full advance. If manual, it sets with lever (no personal experience), if automatic by jamming or otherwise locking the counterweights in the full advance position.
 
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The Norton Owners’ Club think a 7 takes HS short-reach plugs. Are they stupid?
Don't think so. Took a walk to the barn and found an iron Norton twin head. Though the bad light there, I'm certain that it is considerably shorter than 3/4".
 

Brooking 850

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Thanks guys, owner had jammed open full advance AAU when setting the ignition timing and there is also a handlebar lever to operate points advance/retard.
After a few kicks , checked the plugs for fuel, and yes unburnt fuel.
Big blue spark at the plugs every kick.
Yes the points were at 3 Oclock timed off the RHS, 9 0 oclock timed off the left hand side.
I will spin it up on my race bike roller later in the week.
Fuel is not old, carb in very good condition.
With the timing cover off to check the mechanical timing, we undid the AAU bolt to rotate the points to the correct position, is this any way different from loosening the points centre bolt to rotate the points system when the timing cover is on?
Regards Mike
 
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Have you tried swapping the plug leads over, just in case you are timing 360 degrees out? Also you shouldn't have manual advance and automatic advance. Should be one or the other and given the age of a Model 7 I would think it had manual advance when new. If you want to use the automatic advance, I would fix the manual advance somehow and remove the cable.
 

texasSlick

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Here is a tutorial on setting up and timing a K2F ...


Slick
 

Brooking 850

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Thanks guys, yes did swap plug leads to check that.
Ill go back and have another look and yes agree that when I was a teenager dealing with mags there was either handlebar lever or AAU , not both although owner seems to think otherwise.
Ill remove the handle bar unit and lock the points accordingly.
Regards Mike
 
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Which ever direction the points friction block points is the (slip ring )plug wire to be ignited. obviously it therefore goes to the cylinder under compression.
Iron heads take short plugs!
The AAU unit is far superior to make better spark. Moving the cam ring per cable type mag is definitely not as good because the magnetic field collape is reduced from optimum.
I will be doing the exact thing building my 88SS which originally was a cable pull advance. I will install a AAU and use the cable for minor tweeking. and for show.
 
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It satisfies me for the AAU ease of starting and running performance.
It satisfies me and the rivet counters for the timing cable on a 62 88SS. The magneto function and part# IS a manual advance type.
Makes people ask questions...
 
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You can fool them all as they cannot see the a/r with the timing cover on.
But if you just happend to suffer from brain fade one day, you might just confuse yourself.
 

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