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Hello everyone...

I recently purchased this lovely 1975 T140 Bonnie.. Just spent a fortune on getting it tuned and it now runs like a dream..
I have replaced the battery to pass the roadworthy test. On a 100km trip yesterday I noticed that the indicators stopped working and that the front light went from it's usual yellow white to a brown yellow. Very surprised that I made it home alive in the dark to be honest.. Where should I start testing for possible charging problems?
 

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Beautiful bike

Is the bike using the original rectifier and Zener Diode? Or has it been converted to use a modern combined Rectifier/Regulator?

If your not sure then take a pic under the seat of the battery and coils area, we might be able to see.
Do you own a voltmeter or digital multimeter? It will help with diagnosing the fault.

In any case, have a good look at the visible wiring under the seat and make sure there are no loose snap connectors.

I’m sure Stuart will be along shortly to give you some more detailed advice and tests to do.
 

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Hi,

Firstly, welcome to the Forum. :)

runs like a dream
replaced the battery to pass the roadworthy test.
check the charging system first
Uh-uh, check the battery first; not only is it the last thing you replaced, it's a good battery that's required to run the electrics, never assume "new battery" = good battery.

However, also, is the headlamp bulb standard? Standard on your bike was either 45/40 (Watts main/dip) or 45/35, depending on who you believe (respectively Lucas or Triumph). Not only are some later replacements 48/48, they're all super-crap BPF (British Pre Focus) and the headlamp is often upgraded to modern 60/55. Problem with higher-Watts bulbs is the standard charging system struggles if you don't use plenty of revs. all the time, including cruising.

Testing the battery/charging system
Trickle-charge battery overnight, reconnect it to the bike, turn ignition switch on briefly, turn off - this'll dissipate any misleading 'surface charge' that can be present after charging.

All switches on the bike turned off, connect a well-calibrated Volt- or multi-meter one meter lead to each battery terminal.

Assuming standard lead-acid-type battery (liquid acid, AGM or gel), good battery, well-calibrated meter should read 12.6V (higher Volts is not 'better', it's just a poorly-calibrated meter :().

Lower than 12.6V after overnight trickle-charging might also be a poorly-calibrated meter, but it might also be a bad battery; return to the supplier for verification?

Assuming the meter displays 12.6V with everything switched off, turn on just the ignition, the meter display should change very little; even a drop to 12.5V isn't good with a new battery.

Assuming little or no change in the meter display with just the ignition on, turn on all the lamps; the meter display will change a little but shouldn't drop as low as, say, 12.3V (unless the headlamp bulb is actually some fantastic-Watts floodlamp ...? :cool:).

Assuming only a little change in the meter display with both ignition and lighting turned on, leave the bike that way (engine not started) for either half-an-hour or 'til the meter display falls to 12.3V (battery half-discharged), whichever is the earlier.

Assuming the battery isn't half-discharged in about five minutes (suspicious), recharge the battery.

Battery recharged and reconnected to the bike, start the engine, reconnect the meter across the battery, raise engine rpm slowly, meter reading should rise with engine rpm to ~15V @ 3,500~4,000 rpm then remain steady even when rpm are raised further. Volts should only fall when rpm falls.

Btw, when charging the battery, I always take it off the bike. On the bike, the fuse must be removed but, in any case, does not offer any protection if, say, the open seat closes and the pan comes into contact with the charger terminal in the battery -ve terminal. (n)

Hth, post how you get on? Also look out for a PM ("Started a conversation" in this Forum's software vernacular).

Regards,
 

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Hi,
If you have a working charging system, the headlight will get slightly brighter as you rev up from idling rpm.
It was getting duller on his trip home
Sounds like charge not reaching the battery.
Dud battery can absorb the alternator's output but simply turn it into heat.

I'm not saying the problem is definitely the battery but, given:-
I have replaced the battery
... it'd be dumb to assume it's a charging system fault without checking the battery ...

Hth.

Regards,
 

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Stuart, have you ever written a blow-by-blow process for checking out a charging system? It seems to be a common problem with old bikes and there are a number of potential issues that could cause a system to not charge or act like it is not charging. It might be a good thing to post here as a sticky. Manuals tends to treat the reader like a seasoned mechanic. Where if you wrote it assuming the reader was relatively new to motorcycle electrics, it would probably go a long way in helping them be better informed while solving their issue. Just a thought. So many are intimidated by electrics when they are really pretty simple and very logical if you know a few rules.
 

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I agree with StuartMac, you have to start with verification of the battery's integrity and inspecting all electrical connections before testing for stator output and rectifier function. Once you know the battery is a good one, you can start troubleshooting other areas of suspicion, such as weak rotor magnetism, malfunctioning rectifier, and other voltage drains, like a poorly adjusted or stuck-on brake switch . When I worked at an H-D dealership, we had a Midtronics battery charger and load tester that would print out a reading of the CCA at the end of the charging session. Was pretty surprising how many newer batteries tested weak, or even failed. Best of luck in sussing out the issue!
-Dave
 

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Hi Rob,
have you ever written a blow-by-blow process for checking out a charging system?
I've considered it, but I find a given OP's problem and/or understanding aren't always the same as the previous OP I posted for. Plus, if two are somehow so similar I could post the same, I can simply link a thread for the second OP. :)

Regards,
 
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