AJS & Matchless Owners Club

Hi

Went out on a bike today for the first time, for a socially distanced coffee with a mate. It was his first ride on his AJS 650 since getting it up and running. Turns out it's not charging. It's a 6v 3 wire alternator model. Putting a meter across the battery with the engine running shows crazy readings, occasionally negative. I'm guessing this suggests that the rectifier is at fault? It's what appears to be a bridge rectifier, about 30mm square. If is that, any recommendations for a replacement? Thanks.

Malc

I fitted one of these to my alternator G80 several years ago - its been perfect ever since. Alan is also very helpful when it comes to identifying problem and giving advice.
http://www.aoservices.co.uk/a_reg.htm

Steve

hi malc ;
i find it better to use an older analogue style multimeter with a moving coil needle type display to do any alternator readings because a digital meter will tend to show wild fluctuations or erratic readings .

you should see somewhere around 6 - 8.5 votls swinging of the meter when running engine and increasing revs a little .

read from the alternator directly using AC setting and change to DC after the bridge rectifier or rectifier/voltage regulator .

must admit i have an ariel leader with basic alternator and rectifier and batteries dont last too long on it i find , so think i will get one of the A-reg alternator regulators that steve put the link up for and swap that for the rectifier and see if it improves matters .

i think the leader alternator is same one as used on many AJS and matchless .

i found my alternator worked but i suspect it has tenedncy for overcharging and losing electrolyte in the process, and it needs regular checking of electrolyte level . .

i have to keep a decent topped up battery and charging system on it otherwise i will find the engine misfires after a while .

funnily though my ajs mod30 with dynamo and DVR2 regulator seems to last forever with the same battery , now 5 years on it .

hope you get it sorted easily .
ian

Hi

Steve, thanks for the link; that's the sort of thing I think he needs.

Ian, good point about using an analogue meter. I've ordered one, as they're always useful, especially in cases like this. I have a DVR2 on my Model 31. It works well, but I do get intermittent charging problems. However, I think I've now tracked it down to the lighting switch. Typically, the last thing checked!

Malc

Hi

I have now managed to test my mate's alternator twin's charging using an analogue meter. With engine off and a fully charged battery, measuring at the battery shows about 6.3 volts. With the engine running and the meter still set to DC, the reading is the same, with no movement on the dial as you raise the revs slightly. With the meter on AC the reading goes up to nearly 12v. This suggests to me that AC is being fed to the battery and the bridge rectifier isn't working, but I'd like to know what more knowledgeable people think.

Thanks,

Malc

MalcW wrote:but I'd like to know what.................. people think.

I think I've offered assist with this query before - I suggested measuring the output from the rectifier.

It's probably better for all if you don't split queries over more than one thread.

Regards Mick

And maybe have a read of this (or one of the similar sources):
http://www.aoservices.co.uk/info/ALTERNATOR_COLOURS.pdf
I'd probably start with the alternator output. If there is some, that's great . . . If there isn't - bad luck and 'Do Not Pass Go' as they say. But if there is, then see if there's DC coming off the rectifier or not as Mick has said x2 now.
If there is a working DC feed with the engine running but no charge at the battery, then check the ammeter / switch connections.

My money is always on junking the original three wire arrangement, getting an A Reg 6 or A Reg 1 (if going 12v) from Al Osborne or via Paul Goff, and simplifying the whole kit and caboodle. Either by doubling up on stator leads on a three-wire alternator that's proven to work, or by replacing the necessary bits with a 2 wire job. Then, you can get the harness, barring extras, down to a dozen or fewer wires with very few possible points of failure. The nett of it is that it's often quicker and easier than messing with what was originally there.