Magneto drive sprocket

Niall

Thanks for your reply. Your mention of two types of sprocket and request for pictures made me go and have a closer look at my A/R unit. Of course the drive sprocket is incorporated into the unit. Must have had a bit of a senior moment! I need to look at the parts more closely and I think that the parts that I have are correct for my bike.  I've attached the pics that I took. At least I haven't ordered a new sprocket. I am more used to distributor systems with the A/R incorporated into the housing and had assumed that the magneto also needed a separate sprocket. I need to sort out the ignition timing now which is a little different with a mag. Thanks for your help.

Tony. Thanks for this tip. I have managed to tighten the nut using a short, angled spanner although it wasn't that easy. Without the oil tank and battery case on the bike access is a little easier but won't be once the rebuild is more advanced. I have seen this extended bolt mentioned elsewhere and will probably get one from Feked before I put more of the bike back together. 

Allan

I treated myself to an extended magneto bottom bolt and thought I would get a stainless one from Stainless Classics rather than the mild steel one from Feked.  Unfortunately it does not fit. The extended shaft of the bolt hits the lip where the two halves of the crankcase are joined. I think that without machining the crankcases it will be a no go. The threaded end is also too big for the bottom magneto bolt. This is a double sized bolt, plain 5/16" under the head and 1/4" threaded. part no. 067906. The threaded end on the extended bolt is 5/16"BSC. If I could sort out the crankcase issue I suppose I could use a suitable length 5/16 bolt instead. I think that I will have to see if Stainless Classics will take the part back. If not I have an unused stainless part available.

Does anyone know how I could fit this bolt without having to modify the crankcase. Maybe it will fit on some dominators but not a 650SS. 

Managed to fit the magneto using the short Norton designed bolt and have fitted the camshaft, intermediate and magneto sprockets. However, the tension on both the timing and mag chains is far too loose, about 3/4" on the mag and 1/2" on the timing chain despite the tensioner plate being at maximum. I have obviously done something wrong but don't know what. The bike had been converted to coil and distributor ignition when I bought it and apart from the replacement mag and A/R I am using the sprockets that were on the bike when the distributor was fitted. I thought that the timing side components were the same but will I have to replace components to get the right chain tension. The chains were ok when the distributor was fitted. Any ideas as to what I may have done wrong?

Howard

Thanks for your suggestions. I have rechecked the tensioner assembly. The fishplates were fitted with the right orientation but I have found that the plates have been apparently put on back to front with the thin plate first and the thick plate on top of the tensioner plate. The parts diagrams in both the Norton spares parts list and on the Andover Norton site both show the thick washer installed first. This seems to have been the setup 0n my bike when it left the factory as the thick plate is the only one with witness marks from the star washers. I have tried the reversing the plates as per the diagrams but this makes no difference to chain tension. I have also tried to move the magneto as far from the timing cover as I can but there seems to be very little adjustment on this. I note that new chains are described as suitable for either a mag or distributor so there can be no difference to the drive sprocket for these two systems. I am a little reluctant to purchase new chains if this is not the problem. The amount of chain movement is much more than I would expect from simple chain wear.  I am at a loss as to know what else I can do.

Howard

The upper studs are the waisted type with the bottom fixing being a dual 5/16;1/4 bolt. Despite this there is still very little movement of the mag to allow adjustment. Certainly not enough to take up the slack in the chain. The tensioner plate is pushed up as far as it will go with the cam chain still too loose. I think I will have to bite the bullet and buy new chains but I am a bit reluctant to part with £40 or so only to find I still have the same problem. The bike was running OK when last used 20 years ago and the old chains have been sitting in a box since then. I can't work out how both of them have stretched. 

Thanks again for trying to help

Thanks for your suggestions. The chains are continuous so I would have to use a chain splitter to lay them out to check for wear. I also marked the chains and sprockets when I dismantled the bike to help with valve timing when I rebuilt it so the sprockets and chains have gone back the same way they came off. One thing that I have changed from the bike as it was is a pair of replacement crankcase halves. When I dismantled the bike in the 1980s I noted that one of the main bearing housings was damaged. I exchanged the damaged set for a reconditioned set. Don't see how this would make a difference to chain tension unless there are slight differences int he crankshaft/camshaft housings with different cases. Anyone come across this before?

David 

A bit of confusion here. I meant that the drive chain was the same for both magneto and distributor ignition sprocket to intermediate sprocket. Didn't mean that the camshaft chain was the same as the ignition. These are of course different as you have described. Sorry if I didn't make myself clear.

As you say these chains run in an oil bath and shouldn't wear that much. There is a very small amount of play on the links of my camshaft chain which I would have thought should be easily accommodated by adjusting the chain tensioner. Virtually no play on the magneto chain which is the one with the most movement and least opportunity to adjust tension. Either the chains are too long which seems unlikely as they worked before the bike was dismantled or I have somehow replaced the magneto, intermediate spindle and camshaft incorrectly. If so don't know how I have done this or indeed if this is possible. When I turn the camshaft nut all the timing case sprockets, crankshaft and mag turn easily even with loose chains. 

Howard

The hole for the magneto in the crankcase seems to correspond to the size of the flange on the magneto. There is a very small amount of lateral movement when it is in place. I think my cases are from a '62 650SS so not the later model but there is no number on the cases so I cannot check the age exactly. I think that they were a replacement set rather than from a running machine hence no numbers. Don't know if the hole ids the big or small one but I have attached some pics.

Paul; thanks for your comments. I think that the 650SS/Atlas cases are slightly different from earlier Dominator models. Either that or I have incorrect set of cases. There is no way that the extended bolt would fit on my cases without removing material from the centre flange and adjacent case. There is no space otherwise for the bolt to fit. I discussed cutting a slot in the bolt to make more space with the supplier but he wasn't keen on that. Thought that the bolt would not cope with the torque during tightening and snap.

I have ordered a new set of chains from Norvil. At least with those I will know if it is chain wear or some other issue.

Howard;  Thanks for the suggestion but I swapped the cases 30 years ago and exchanged my old cases for the replacements so don't have them for comparison. I had thought that Norton introduced the two studs and bolt arrangement when they introduced the 650SS in 1962 but I've just looked on RGM's website and they state that the bottom waisted bolt was introduced in 1964. So it looks like my cases are not a 1962 vintage but later. RGM describe the waisted bolt as a magneto fixing bolt and I think that magnetos were used on the SS model until 1967 when all models were converted to distributor/coil.  So it's possible that cases with the 2 stud/1 bolt configuration like mine could still have had a magneto originally. I have still got the Lucas distributor and its drive sprocket so I will fit that to the case and compare the chain tension with that and see what the new chains do when they arrive. 

Thanks again for your advice. Allan