Timing woes

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Sep 14, 2006
OK, 74 850 Commando, points.

I need info on how to time the machine from scratch. My haynes manual is too vague for me to follow. I'm a 53 year old HVAC mechanic. I've done most of my own car/bike work all my life. I hate to admit defeat, but this thing has got me pulling out what's left of my hair. I just don't get it. Can ANYONE point me to a step by step guide to timing this thing? I'm trying to avoid taking it 120 miles away to a decent Brit Bike guy. Why does the AAU have to be locked in full advance? CCW, I think.

Any help here will help me get a few days riding in before the long Vermont winter sets in.

Thanx in advance for any help.
Timing article

There is a timing article "timing"posted july 2nd 2006. The reply by Norbsa48503 deals with getting right back to initial setting up of points using a dead stop tool and degree wheel. This makes sure the timing graduation marks inside the primary cover are accurate. then the points are set to start opening at this 28 deg btdc fuly advanced mark.
The automatic advance bobweights are held fully advanced because this is the position needed for the spark to happen at 3000 rpm and higher when the timing is fully advanced by the bob weights. If you don't advance the points cam and open the points at 28 deg then the timing will be right out of the ball park.
I've just made a dead stop tool and will let you know how i go with using it if your interested.
Get a mug of your favorite beverage and calm down!,
Your Commando should have the 10 CA contact breaker assembly,a circular base plate with independent contact sets mounted on it,elongated slots in the base plate allow equal movement of BOTH contact sets,either adavance or retard timing on both cylinders by an equal amount.
To set timing from scratch -- remove spark plugs,adjust the gap on both sets of contacts -- the contact set should be mounted on the tapered camshaft nose,a small mark located near the lubrication slot on the ignition cam indicates the highest lift point,rotate the engine until the mark aligns exactly with the nylon heel of the contact breaker,at this position the points are fully open,the gap should be .015",if the gap is something other than .015" you will need to slacken the contact breaker fixing screw -- the one that attaches the contact to the base plate -- the gap is altered by using a small screwdriver to move the contact plate to obtain .015" gap.
Now for timing -- remove the centre bolt from the auto advance unit,a special washer is required for the following procedure -- any washer that will clear the bolt diameter and tighten against the face of the ignition cam will work -- place the washer on the bolt, turn the auto advance unit to full advance position and tighten the bolt to hold the AAU in position -- the AAU will only rotate one way --CCW I think.
Timing the LEFT side cylinder,rotate the engine until piston is at TDC and both valves closed,the yellow / black wires are to the left side cylinder contacts,rotate the engine backwards until the timing mark on the rotor aligns with the 28deg. mark on the indicator plate in the primary case,at this position the points for the left side cylinder should just begin to open,this is correct timing,if the points are not opening at 28 deg. you will need to loosen the TWO attaching screws in the elongated slots and move the whole base plate so that the points begin to open -- a piece of cigarette paper or similar gripped between the face of the contact points should just release as the points begin to open,tighten the screws.
For the RIGHT hand cylinder,turn the engine as before, RH piston at TDC,valves closed,turn engine backwards until mark on the rotor is at 28 deg., RH points black/ white wire, should just be open,if not, loosen the screw on the sub plate and turn the eccentric screw so that the points just begin to open,tighten the attaching screw. Remove the special washer and replace the stock washer and bolt.Your Haynes manual should show the points diagram and identify the screws that I have mentioned here.
I hope that I have not confused you even more,I have a Boyer unit on my bike so I have not set up points in quite some time,hopefully I have guided you correctly.Good luck, ride safely. James.
PS. Frank Holmes of Franks Brit Bike Barn is in New Hampshire -- Chocorua -- great fellow, does all Brit bike work, phone # 603-323-8310.
Thanx for the info. I hope I can get to work on it tomorrow. Franks Brit Barn is where I plan to take it if I just can't get it going. I will post here when she fires up. Now, for that beverage

I made the Dead stop tool described by Norbsa and finally had a day to myself to play around with a timing Wheel. I Printed off a 360 degree wheel and fixed it under the points cam fixing bolt. This meant every time the motor did one revolution the timing wheel did half a rev so each degree mark on the wheel is 2 degrees on the crank.
Found the top dead centre wound the crank back to what should be 28 degrees and low & behold the marker plate is out by four degrees.
I left the machine overnight and started again to make sure i had my thinking straight and again came up with the same answer. Set the timing at 32degrees before top dead centre according to the timing marker plate set up new points and started it up. Engine sounds a lot crisper and idling is slower and even. Top end speed is more responsive ( don't know what i was doing because the speedo is out of action) Since then I have had five or six great runs. The Norton feels like it ought too. Thanks Norbsa for the info.
Last run to work the left hand Throttle slide stuck. idling at 3000, I spoke too soon. I must get those brass slides. Might try a bit of 2 stroke oil in with the petrol.
Thanks again for the timing information. :lol: :D
Check the carb body for being out of round. Sometimes you can squeeze them back to rounder with slip joint pliers padded with a rag. They make a 720 degee timming wheel with all the right studs and spacers for all english bikes for about 30.00 US dollars. You will find it real good for strobe timming on that side.
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