Magneto belt drive conversion

Information relating to the Matchless G80 or AJS Model 18 500cc Heavyweight.
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Re: Magneto belt drive conversion

Postby Mick D » Sun Jun 02, 2019 12:36 pm

Hi

I find it interesting that a belt drive has been developed - to me it's another case of a solution searching for a problem.

The chain drive is one of the most efficient forms of drive and certainly more efficient than a belt drive.
The chain drive is also much stronger and less liable to break, therefore more reliable - yes it needs to be lubricated but I would counter this with the life of a chain compared to that of a belt.

Belts are used because they are:
Cheaper - but the manufacturers don't have to absorb the cost of replacements.
Quieter - not really a consideration on a classic motorbike for me.
Lighter - ditto the above.

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Re: Magneto belt drive conversion

Postby 56G80S » Sun Jun 02, 2019 7:40 pm

Agree with Mick on all points - but did have a dynamo chain let go in the relatively early days of ownership (so a very long time ago). Probably me not having lined up the chain runs properly. If it had been a belt the consequences would've been much less although of course poor maintenance is no reason to make alterations to original.

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Re: Magneto belt drive conversion

Postby Jdraper » Tue Jun 04, 2019 9:38 am

So the consensus is that the conversion is an interesting exercise, but not a must have. There must be quite few of them running around out there as the kits were on sale for some time (about £50 IIRC). No-one has owned up to using one yet!

Perhaps more useful was the comment about a conversion for the dynamo and the potential for removing a clash of chains in the event of a break. Its also worth noting that the tension for a toothed will put a lot less strain on any bearings than some chains (my experience working on fragile motors). Chains re-used from old motors that have sat for a long time get tight/loose spots making the correct slack setting difficult. Both dynamo & magneto rebuilds are getting expensive, so anything that makes their life easier is OK by me.

Jeremy

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Re: Magneto belt drive conversion

Postby Jdraper » Sun Jun 23, 2019 9:18 am

Just a bit of an update on this thread. I was cleaning the insides of the timing chain cover (sad) and found this old damage.. The chain must have been hellish slack for this to happen. I wondered why there was a weep from here.

Also found some pics on line of the belt conversion..

Jeremy
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Re: Magneto belt drive conversion

Postby thornebt » Sun Jun 23, 2019 9:40 am

The toothed rubber belt looks a bit flimsy compared with a chain? I'm not a big fan of rubber belts though. For this reason I always buy cars with camchains. Cheers. Bruce.

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Re: Magneto belt drive conversion

Postby 56G80S » Sun Jun 23, 2019 1:30 pm

Good pick on that, I had the belt go on my Lucida (Previs) and wrecked what was a sound engine; I'd had the belt replace at the due time and it was only half way through it's planned life.

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Re: Magneto belt drive conversion

Postby Jdraper » Sun Jun 23, 2019 4:19 pm

You should see what happens when a chain goes, or is a bit slack. It makes the damage in the pictures I uploaded pretty mild. Cam chains/belts is one thing and the conversion here is another. Cam belt failure only causes a problem in engines where the valves & pistons have to occupy the same space, albeit at different times. I run a classic car with a cam chain and the thought of that going is horrendous. Jap engines with slack cam chains seem to produce aluminium soup when they have not been adjusted properly. Replacing a cam belt is just another maintenance item that should be done - yes they can fail, but nothing is perfect, even chains. Check out the failure rate of cam chains in Vauxhall Corsas.... and others.

If the belt in the picture went, what is the worst that can happen? How easy to fix if you carry a spare? If chains clashed in the primary chain case, what would the outcome be? If (I know unlikely) the timing chain snapped, what would the outcome be? I suspect the chain would bunch up and the cog would mash the chain though the alloy destroying the timing cases and probably the cam & sprocket. Failure analysis as a thought experiment is a powerful tool for understanding the consequences of any component failure. The picture showing the nibbled case suggests that some owners are less rigorous with their maintenance and the bikes are now getting on.

I am returning to classic bikes with a eye to what can make life easier for us. Some things seem to work, others not. My original question was to seek feedback from anyone who had tried the timing belt and what they perceived as a benefit. So far no one has given any feedback, so I remain open minded. The bike in the picture is a 350, so I may open the thread in that forum to see if any one there will own up to having a belt fitted.

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Re: Magneto belt drive conversion

Postby ajscomboman » Mon Jun 24, 2019 7:03 am

There are people out there using belt drives coupled to electronic ignition. I know of 1 in India and the other in Denmark neither of whom are club members so I've no way of contacting them. Both carried out the work out of necessity as original spares are not in abundance and the modern parts were. Lots of engineering work required but the final outcome was very successful.

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