Magneto removal

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
User avatar
Rob Harknett
Member
Posts: 11236
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: Magneto removal

Post by Rob Harknett »

You should use only the correct puller, one that does not fit properly could cause damage. I often use a small washer to 2 to protect the armature. It only needs a slight pull to break the contact on the tapered shaft and it will fall off. Soaking in Pernatrol for a few days will help. But I keep repeating myself. I would not consider a mag overhaul until first checking everything else, that could cause no spark at the plug. Have you made sure, brush spring move freely and make contact, wire makes good contact, pick up not cracked, plastic fitting you screw in to tighten the lead fully tight threads not damaged. Plug & lead. Now for the mag if no luck. Have you had the points off to properly reface them and correctly assembled ? If SR1 mag there's lead joints to check and check fibre washers are in the correct place. ( done that many times and still manage to get one in the wrong place ) Change condenser if SR1 mag. Other mag condensers are not easy to replace. Now's the time to let an expert check the mag for you. If you do that, get the mag back and it still won't spark. Its back to the start to discover what you have not done correctly. Please do let us know when you succeed. Even if its perhaps your fault you have not checked a simple thing correctly. It does warn others what to look for. I think I have mentioned most that I have come up against.
willowbedone
Member
Posts: 191
Joined: Mon Nov 16, 2015 6:08 pm
Location: east sussex

Re: Magneto removal

Post by willowbedone »

Hi Roger
If I were you I would check and do a few more things before trying to start an engine which has been standing for 50 years .Yes I agree with mag rebuild but also remove sump bung and let all oil drain .think about oiling the bore through the spark plug hole kick it over a few times with fresh oil in it Clean the carb jets.And when it starts make sure you have a good oil return to tank .Yes the mag might spark with a points clean and last a while but piece of mind when it's been rebuilt There are many clevererer people on here than me but don't ruin an engine by cutting corners
SPRIDDLER
Member
Posts: 8542
Joined: Wed Sep 01, 2004 1:00 am
Location: WEST SUSSEX UK

Re: Magneto removal

Post by SPRIDDLER »

Welcome Roger. Plenty of help on here.
Agree with all above, plus, after 50 years unused, new tubes and tyres.
If you don't have them, the original Owners, Workshop, and Spares manuals are here under 'Books':

http://archives.jampot.dk/
'There is a tide in the affairs of men
Which taken at the flood............'
Mick D
Posts: 2886
Joined: Mon Mar 24, 2014 5:44 pm
Location: Aberdeenshire

Re: Magneto removal

Post by Mick D »

Hi

I can understand your enthusiasm to get the bike running again but I would counter it with the potential for damage you could generate by starting / riding it after 50 years without a bit of investigation.

I'd strip the bike completely and rebuild, it doesn't take many tools and at the end of the process you'll understand the bike as your Dad did.

I'm with Rob - have a good look, do a bit of research and don't just assume everything will need extensive refurbishment - these old bikes are surprisingly resilient.

Have Fun Mick
RogGillingham
Member
Posts: 19
Joined: Sat Feb 16, 2019 7:56 pm
Location: Essex

Re: Magneto removal

Post by RogGillingham »

Thanks again one and all. As in life you ask ten different people and you'll get ten different answers!! I am going on the thought that if I want to ride it it's best to get the magneto refurbed for the long term by someone who knows what they are doing. I am very happy to tinker and no doubt will as I get familiar with the bike but life has taught me to know my limitations! I have a list of things to go over and do before I ride it but getting it going is first with new plug, HT lead, refurbed magneto, new oil etc. Then it will need new tyres, brakes looked at, cables checked, battery etc etc. I will no doubt be back on here as things progress. I have found someone to help with the puller so that should let me remove the magneto. Owners club were very helpful on first visit but will need to get to know people and their various knowledge and experience. I find I'm about midway between two clubs so might tap the potential of more members! I have the original receipt when Dad bought it from Hallams in Cambridge (they are still going I believe) and original maintenance manual and spares list. It will be something special for me when I ride it down the road for the first time - something to look forward to, I'm going to take my time and any advice I can get.
Thanks. Roger
If no reply - Gone fishing!
User avatar
Rob Harknett
Member
Posts: 11236
Joined: Mon Jan 01, 1990 12:00 am
Location: ESSEX UK

Re: Magneto removal

Post by Rob Harknett »

Mick D wrote:Hi

I can understand your enthusiasm to get the bike running again but I would counter it with the potential for damage you could generate by starting / riding it after 50 years without a bit of investigation.

I'd strip the bike completely and rebuild, it doesn't take many tools and at the end of the process you'll understand the bike as your Dad did.

I'm with Rob - have a good look, do a bit of research and don't just assume everything will need extensive refurbishment - these old bikes are surprisingly resilient.

Have Fun Mick
I took a chance on one of my prewar bikes that was found in a field. When looing for bits I put them on loosely. I had not touched the engine or mag. I found most of the carb, just air slide to find. Carb was cleaned with petrol, loosely fitted nut by hand. Petrol tank was not even fitted. I give thing a kick, as I was being called for lunch. BANG, made me jump, wife said what was that bang. It fired only sniffing petrol I cleaned it with. I quickly fitted any old bits to make it ride able. Been no trouble for the last 32 years. Not used done so many miles, years ago now I checked when MoT came round, I had done over 10,000 miles. That's a lot of little runs out with the lads etc. I did rebuild wheels, new tubes & tyres, bearing all cleaned and greased. Brakes relined. All sorts of S/H Clutch plates used. Rewired, two new dynamo bearings, as shaft was very loose. New chains. Rewired. Few new nuts & bolts. Usual service done oil grease etc. Everything else either on the bike, or S/H off a jumble stall, untouched. Total cost I seem to recall under £800
( 1986 prices, but still a cheap bike, I reckoned it worth £2,500, VMCC valued it at £4k for insurance.)
User avatar
Duncan
Member
Posts: 2118
Joined: Thu Jul 10, 2003 1:00 am
Location: HAMPSHIRE UK

Re: Magneto removal

Post by Duncan »

ajscomboman wrote:
Duncan wrote:Roger, it is usually easier to remove the bottom cam sprocket first, I use a tyre lever about 10" or 12" long with a ? shape on one end, it usually pops off after applying leverage in a couple of locations behind the sprocket. Sound move getting the ancient magneto refurbished at this stage as it will only let you down later as the capacitor/condenser fail and the shellac melts in the windings.
Animal! You're such a cheapskate Moss! Get the correct tool, a nice little 2 leg puller does the job without the need for levers, if it's slim enough it'll slide behind the chain and just pop the whole lot off. My one does anyway. However when I can't find it, have I mentioned tyre levers work quite well. :rofl: :rofl:
Only follownig the manual:
51 TO RE-TIME THE IGNITION
The maximum advance is ½".
Have available a stout screwdriver, or an old type tyre lever with turned up end, and a bar of metal about ¼" diameter and 5½" long.

Unscrew, several turns, nut retaining magneto sprocket to camshaft. (No need to remove nut).
Lever off sprocket until it is loose on the taper of the shaft. (Use stout screwdriver or old type tyre lever).


I should add that I found most two leg pullers will not fit in the gap between the sprocket with a chain on and the inner timing case (and is it good practice to use the puller on the chain?) so by removing the lower sprocket the chain can be worked off of the mag sprocket and the puller inserted in the wider gap.
User avatar
ajscomboman
Member
Posts: 3963
Joined: Mon Jan 01, 1990 12:00 am
Location: HAMPSHIRE UK

Re: Magneto removal

Post by ajscomboman »

Duncan wrote: Only follownig the manual:
51 TO RE-TIME THE IGNITION
The maximum advance is ½".
Have available a stout screwdriver, or an old type tyre lever with turned up end, and a bar of metal about ¼" diameter and 5½" long.

Unscrew, several turns, nut retaining magneto sprocket to camshaft. (No need to remove nut).
Lever off sprocket until it is loose on the taper of the shaft. (Use stout screwdriver or old type tyre lever).


I should add that I found most two leg pullers will not fit in the gap between the sprocket with a chain on and the inner timing case (and is it good practice to use the puller on the chain?) so by removing the lower sprocket the chain can be worked off of the mag sprocket and the puller inserted in the wider gap.
It'll do no harm to the chain using the correct type puller. I agree the manual states using a bent screwdriver but that's just downright crude! I'll bring the puller to clubnight along with the carb body.
Locked