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 ‘ ?