Can the ATD unit be removed from the rear of the magneto without disturbing the timing gear which is mounted directly behind it ? Will slackening off the central hex head bolt enable the ATD only to be removed ? The mag is in situ on the bike ( Dominator 99 ) and as the ATD is somewhat sticky the springs do not operate the bob weights which remain in position irrespective of their position.
My understanding that when the ATD is rotated it should snap back in position.
George it will only 'snap back' as you describe it if either of the points cam is not touching the heel of the points. You will need to rotate the engine to a position where the heel is free and then carefully advance the points with a 4BA spanner and when you let go of the pressure, the points should spring back to the retard position. This will not happen if the fibre heel is touching the cam. Also the carbon brush in the brass type points unit can cause resistance to movement if there is a strong spring in it . Basically the engine needs to be running to check the operation of the advance /retard unit but that's an unlikely scenario. To remove the advance /retard unit you will have to remove the timing cover and remove the unit from the magneto using the built in "puller bolt" in the usual way. Obviously the donk will need to be retimed when you have completed your examinations. The springs are quite reliable but I have seen the odd one snap. They are difficult to replace in situ but it can be done. Cheers, Howard
Thanks Howard. Will the ATD come away from the timing gear as a separate unit when undoing the puller bolt ? Also is it located on a key thus maintaining the timing integrity?
No and no... the sprocket is part of it, and there is no key since moving it on the taper is how the timing is altered.
If only! You will have to re-time the ignition if you remove the ATD
No keyway, just a tapered shaft.
No George - the ATD is integral with the timing gear and it is difficult to separate the gear from the device. It is held in place by large peened rivets. As the puller bolt engages you will see it pull the unit from the taper shaft of the magneto. There is no keyway so the action of removal necessitates re-timing the motor.
Thanks to all for the constructive comments. I have checked the operation of the ATD with the points heel clear of the cam and using a 4ba spanner as suggested by Howard , the points do not return back by spring tension.
I assume therefore that the problem is within the ATD unit. The bike was restored some years ago and was kept unused in a collection which is never a good sign. I note that there is no split link in the magneto drive chain ( is that correct ? ) so that to remove the ATD the the main drive chain and gears have to be removed.
No again George - the chain fits over the gear at the rear of the ATD so when you remove it from the magneto the chain just slips off and it can remain on the timing pinion until you refit the ATD. Do the springs on the ATD mechanism look broken or damaged in anyway ? Did you also remove the points to do your spring test. The points are on a keyway so they can easily be removed. Are they the brass set or the more modern steel ones ? You may also need to remove the HT brush holders from the magneto. There are some bad brushes about that have too heavy a spring on them. As well as pressing on the slip ring too hard they eventually cause the fibre to wear away exposing the slip ring and that's bad.......... Cheers for now, howard
I have removed the ATD and on the bench it is as free as a bird ! I suspect that the boss on the ATD is fouling the oil seal which is in a recess. I have gently tapped the o/d of the oil seal to make sure that it is seated fully and on a trial assembly the ATD is better but not fully free. I may file a few thou off the end of the boss to ensure clearance.
Hello - Me again. Is the oil seal to which you refer the one in the drive-end of the magneto ? Usually there is quite a clearance between this seal and the bush at the mating end of the ATD. If the ATD taper is worn sufficiently or has been tampered with it may allow the position too far along the taper. Are there any witness marks on the end face of the magneto ? I don't recall any other oil seals in that area. Bye again , Howard
I am referring to the oil seal at the driven end of the magneto. The points are of the steel type. Whilst there are no rubbing witness mark on the end of the ATD gear boss , the bike has not been on the road since the previous owner restored it so it is unlikely it has had time to develop an witness marks on the end of the boss.
i will see if I can determine if there is any clearance using a piece of blue tack.
Hello again George - If the alloy ring that holds the ATD together has been knocked on the centre bolt too hard there can be resistance to stop the mechanism being free on the bronze bush within. You say that it's not run since it's rebuild. Just make sure that the ring has a little end-float so that it can't jam. Get some light oil inside if the bush is tight to try and free it. The ring is difficult to remove but with a little gentle warming they do come off, if so required. Once off, the whole mechanism will fall apart to check everything. Be careful - use only a small hammer and chisel if you must. Cheers, howard
Thanks for the info., Howard.
I re- assembled the ATD and put some engineers blue on the end of the ATD bushing and gently nipped up the central bolt. After rotating it and checking the end face there was no witness mark so my theory of the end of the boss touching the oil seal was wrong.
I am not sure which alloy ring you are referring to. There is an alloy ring fitted over the end boss but I doubt that you are referring to that. Are you referring to an internal bushing ?
No George - It's on the outside of the sprocket on the ATD. They can be steel. It fits as interference fit on the outside of the central pivot for the advance unit. When removed it allows the sprocket assembly with the weights etc to detach from the advance portion. The bronze bush separates these parts and the special puller/securing bolt passes through the whole assembly. It has on o/d of 1 inch and the i/d of the hole is approx 3/4 inch. It is 1/4 inch thick. Also it is important that the dished washer is fitted and located on the two pegs at the front of the unit and the thick open washer sits against it as the central bolt is tightened. Cheers again, H
Howard, on checking various photos of the ATD I notice that there should be a ‘ C ‘ washer under the bolt head. This is missing which obviously allows the bolt to move further into the magneto. I will get one and perhaps it will make a difference.
Yes George I think you've probably solved the mystery. The C-washer and the large shaped pegged washer are vital in the operation. I'm sorry that i didn't mention them earlier in the thread. Good luck retiming the motor. I usually insert a 5/16 inch nut into one of the ATD arms to keep it fully advanced ( they are just the correct thickness ). When you are satisfied with the points just breaking, a tap with a piece of tubing against the c-washer usually does the trick locking the taper. Don't forget to remove the nut when your refitting the timing cover. A new oil pump oil seal is best fitted as well. 32 deg BTDC fully advanced is good for a Dommie. Cheers, howard
Thanks Howard - your a gentleman of the first order !
After all of the above... Surely the springs do not normally pull the bob weights back. The engine itself does that at low revs. The springs delay the point that the bob weights move out under centrifugal forces. Do the weights go back in when you turn the engine slowly after you pull the weights outwards? If so then it is all OK.
Hello David - I am not really sure about what your question is. Suffice to say that as the engine rotates ( clockwise looking at from the timing side ) the ATD rotates counter-clockwise. This causes the bob weights to be forced outwards against the springs until they reach the stops . This is at the fully advanced ignition timing position. If the springs were removed this would be the permanent position. When the engine is running slowly the springs fight against the outward force on the bob weights causing the ignition to be more retarded. If extremely strong springs were fitted this would be the normal firing condition. ( So would welding the bob weights in the closed position ). The springs are chosen to overcome the force acting on the bob weights up to a predetermined force. When the engine is therefore stationary and there is no other force acting against the springs they should rotate the ATD weights clockwise to the rest position fully retarded. Good luck, Howard
I'm not sure myself, Howard! All I know is that last time I looked at the auto advance it did not seem to behave quite as I expected, but the strobe light showed it to operate OK. If the motor will start, that's the best test.
I think I'd assemble as it is, try it, and then sort out the problem if it really is a problem. Not try to solve a problem which might not exist. The things are very simple and robust after all.
The Brightspark web site says that the forces on the system tend to pull the ATD to full retard. The bobweight centrifugal forces overcome this tendency. So as it slows down the timing goes back to retard without the help of the springs. The springs do not need to actually do it by themselves. So I still suspect there is nothing wrong. But anyone can write anything on the www!
I'm with you David - I too much prefer reading fiction. I was put off reading factual scientific publications when I read that someone is still advocating that the world is round and Father Christmas doesn't exist. Ho hum, ride safe. Howard
As I am going to replace the dished end plate on my K2F magneto , I need to remove the bolt so how is the bolt completely removed ? I have taken the ATD off the magneto and I seem to recall reading somewhere that the bolt also has a l/h thread but I cannot get the left hand thread to engage. Am I having another ‘senior moment ‘ ?
George - I'd suggest you check out the Brightspark web site. It has a vast amount of information about the magneto.
I hope someone else can answer your question about removing the bolt. As far as I remember, the self-extractor bolt should come out in the manner you describe. But if, as you say, the thing is free when lying on the bench, I'm not sure why you want to take it apart. The springs don't have to pull the bobweights back by themselves...
I see Dave Lindsley sells replacement ATDs for several major bike manufacturers. They cost £225 plus VAT, so its a big risk if you damage yours - and it's made a lot more risky by the fact that he does not sell them for Nortons (I think because they turn the opposite way to most others).
I still think you should re-assemble and test with a strobe. More time but a lot less risk. And if it's OK, it's win-win.
Hello again George - the ATD extractor bolt has an external left-hand thread not far below the hexagon. So to engage it you may need to push an alloy or brass drift gently against the bolt from within the ATD. I believe the thread on the magneto is 5/16 inch so as you don't want to damage the internal thread I suggest a piece of 3/16 inch rod. Keep the pressure on the bolt from the inside whilst turning the hexagon counter-clockwise and it should engage in the outer and unscrew from the unit. There is a round-wire spring clip on the shank of the bolt and it is this that pulls the ATD off the taper as it is undone. This clip is usually forced off the shank as the bolt unwinds from the unit. It must be refitted when the unit is re-assembled and it can be fiddly. Do you really need it dismantled ? Good luck, Howard
I have ordered a new C washer, the large end dished washer ( the current one is a bit mishapen) and two new springs. According to Dave Lindsley, the replacement dished washer now has a larger hole which goes over the hex headed bolt so the bolt does not have to removed. The C washer will then be inserted as normal under the hex head and clamps the new dished washer in place.
I will report back in due course.
Hello Howard, I am interested in this round- wire spring clip, I have taken this centre bolt out by turning the hex clockwise (viewed from the top) but haven't seen a spring clip. Thought the bolt engaging in left hand thread that extracted the unit. Could this clip lay unnoticed in the ATD body?
Can you please tell be what to look for?
Best regards, Steve.
hello it seem to me a lot of questions for a simple job bear in mind the ADT as double locking thread inside the bolt in the ADT and removed you have to re-time from the left hand side cylinder to find the left hand cylinder you have to remove both sets of rocker covers the rear one and two front then turn the motor to find TDC on left and side by seeing the left side valves are in fully closed position, then look at you mag points should be looking up-wards so you get your ignition spark from the pick-up lead nearest the battery box the right side ignition lead is the nearest the the rear of the cylinder barrel, now with the points looking up wards you now need a cig paper and turn the points until the cam ell is just going to lift the points and you can just get a cig paper in or a 1 thou feeler then turn back the motor to 32 Degrees Before top dead center now set the point up in this portion and lock up the ATD with the bolt but with the ATD fully advanced bob weights open job done, even i know how to time a norton twin, And we females supposed to be thick blond bombshells! or tidied to the kitchen sink! or are us females stepping into your play pen ! your anna j
Hello Steve and George - I am away for a few days but next week I'll respond properly with a photo if I can do that ....? regards, Howard
That would be great Howard, many thanks. It just so happens that I am in process of rebuilding an auto advance unit at this time with a new centre bolt etc and have seen nothing of a wire clip on the bolt , just the left hand thread so I am concerned.
The reason for the rebuild was that for the first time ever, I had the unit taper stuck on the mag shaft, the self extraction thread on the nut then striped and I had to use an extractor to remove the unit. Maybe there's a lesson for me there and I had over tightened the nut when I last timed the ignition.
I look forward to your photos, and again thanks for your interest and help.
Best regards Steve
Further to my earlier queries and helpful replies, I have completed the timing and got the bike running and idling just fine. The ATD was not stripped down but fully degreased and then lubricated and as previously mentioned it freely operated on the bench. After assembly with a new dished washer and the missing C washer replaced, it was not as positive as I expected when rotating the engine although it did move into its retarded position albeit somewhat slowly. I appreciate that there is some internal friction within the magneto via the carbon pickups and perhaps that is difference in operation compared to separately testing the ATD on the bench.
I timed the engine using a timing disc fixed to the crankshaft nut using three powerful small magnets. The ATD was temporarily fixed in it’s advanced position and the tdc was accurately found by using the dead stop method. ( I modified an old spark plug to make an adjustable dead stop thingy ) . The 32 deg btdc was positioned on the compression stroke by putting my thumb over the near side plug hole to feel the compression and rotating the engine by putting the bike into top gear and rotating the rear wheel. The points were set using a bulb and the ATD finally tightened up and the timing was rechecked after to make sure that the ATD had not moved out of position.
All very straight forward without the need to check the rockers etc. Perhaps my method is an over simplification. Please feel free to make any constructive comments.
Pleased you got it sorted George, all sounds good to me, perhaps it may be worth checking the timing on the other cylinder ( the heal of the contact breaker on the top cam) there is sometimes a few degrees difference in the cams, if this is the case pitch it in the middle or stone the cam.
Sorry to have hijacked your thread with my question to Howard.
Best regards Steve.
hello have you tried starting the bike yet you may if that it will not start as you maybe out with your timing , its no good just feeling for compression you have too know 100% them valve are closed proposition and you have timed the motor the right way round with the left hand cylinder firing first and on the left hand plug lead witch is the rear one on the magento , the right hand side spark plug lead one is the lead next to the back of the barrel and you should be 6 degrees fully retarded by using the good timing plate, made from alloy, good ignition timing is paramount on a Norton Twin, yours anna j
Yes, I have started the bike and it idles ok. As I mentioned previously I timed the ignition using a degree wheel at 32 deg btdc on the compression stroke with the ATD fully advanced. I described finding the actual tdc in my previous note.
hello well done you where luck this time around but next time you may not be so lucky but enjoy your rides out, yours anna j
I do not understand why you suggested that I was lucky . Surely identifying the compression stroke is straight forward as one can feel it with the thumb or am I missing something obvious. I use this method when timing car engines so what is different compared to a motorcycle engine ?Please enlighten me.
Hello again George and Steve - I am sorry to have mislead you about the round wire spring on the fastening bolt of my advance /retard unit. It seems that the clip on mine is there as a repair because the left-hand thread to remove the bolt is stripped. Adding the clip was probably intended as a repair but it doesn't work - sadly. In my haste to describe the unit's operation to George I had remembered the clip but not the reason that it was used. Good luck and ride safe. Howard
Thanks for clearing that up Howard. I have found that some of the the replacement bolts available now are made of much softer material than the original bolts and have a tendency to strip.
Best regards, Steve