Alternator - Flashing the field?

talss89

talss89

Joined
Jun 10, 2022
Messages
6
Age
35
Location
New Forest, UK
Evening!

So last week I decided to dust off my ST1300 which had been sat for 5 years (had a break from riding after an aero accident). So far I've rebuilt the front end (brakes, forks, head bearing), replaced the battery and replaced the fuel pump. Today she started and ran beautifully for the first time - straight to a stable idle, but the battery isn't charging. I'm pretty sure it's the alternator, although I haven't done much diag other than battery charge voltage.

My question is - alternators (as used in gensets for example) sometimes lose their magnetism, and can be 'flashed' with a quick DC pulse on the field winding. As the bike was working well before I stopped riding, I was wondering if the ST alternator may need to be flashed. Has anyone done this? I'm aware the alternator includes an in-package regulator, so not sure if all that wiring is hidden away deep inside and is as such un-serviceable.

On a slightly related note, any tips for getting the TB off? I've got the radiator off, fuel disconnected and ready to pull the TB off the intake ports but it's such a stubborn bugger. I'm thinking a plank of wood and ratchet straps possibly.

This is my first post here - I hope it's OK to go straight in with a question...

Safe riding,

Tom.
 
The throttle bodies are stubborn. Lube the rubber tube intake insulators where they slip over the TB. (Honda calls then insulators) I took a longish piece of 1" or so pipe and a soft nylon tie and a piece of flat rubber to pad where the pipe bore on top of the frame. I tied the nylon strap around the pipe and one corner of the TB frame. Using the pipe as a lever to lift up the TB popped it free. Others have used a piece of wood across the frame members and a C clamp to apply lifting force.

Before long someone will warn you of doing thousands of dollars damage to your bike by prying on the TB so take your time and think through what forces are involved and how to apply them. You must use force or else you will not get the TB assembly off. Just be circumspect of how to apply it.

Throttle Bodies Removal | ST1300 Related

Hi, I have a 2003 ST1300. Trying to get to the alternator. I'm down to the throttle bodies. Have the clamps loosened, everything disconnected as per the manual (Haines). I am unable to lift the TB from their position. They feel locked in. Verified clamps are very loose. Manual says it a tight...
www.st-owners.com www.st-owners.com
 
Thanks Dave, much appreciated. I'll stay well away from prying.

Will lube the insulators and give your method a go next week when I'm back at the bike.

Fingers crossed the TB comes off with no damage, and the alternator comes back to life with a flash...

Tom.
 
To answer the field excitation flash question I think an alternator gets what it needs from the bike's battery to wake up and start making current. If the bike has enough juice to spin the starter and pressurize the fuel injectors it should be sufficient to wake up the alternator.

I have heard of wiring a dry cell battery to excite the field on very slow turning vintage boat motors but never in a motorcycle or the ST1300.
 
That's what I thought too, but this youtube video seems to suggest otherwise. Some self-exciting alternators can use a kick in the rotor if they're really dead.

Well, if the windings, brushes and bearings are all OK, I guess that leaves me with the rectifier. I'll be damned if I'm buying a whole new lump of copper if it's all fine.

Appreciate the help Dave, forming a plan for the TBs, will update here with results.
 
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OK - after thinking about the TBs, I used two planks of wood, and two ratchet straps, and lifted it off. Took obscene amounts of force, but nothing is bent or broken. I'd do it that way again - gives a lot of linear lifting force and very controllable. Put planks across the frame, directly over the TB (NOT the fuel piping - use the lattice style brace).

Looks like there's been a huge coolant leak from the cold idle wax thingy, and it's left about 30mm of white dust under the alternator, on top of the 'V'. Everything is really corroded. Managed to clean a lot of it up with a vacuum. The drain hole through to the front of the engine was blocked too. Alternator looks like it was found at an archaeological dig.

Have disassembled the alternator, removed the regulator, brushes and rectifier. Winding continuity and resistance are all OK. Rectifier diodes seemed completely dead until I cleaned the corrosion. Now all seem within spec. There was corrosion on the slip ring where the brushes had been sat for years. Span up the rotor and held some 1500 grit sandpaper to the rings, then tested brush continuity with an oscilloscope - minimal noise - I think it's OK.

Couldn't quite figure out the self-exciting circuitry (not even sure it's there, unless potted under the rectifier), so I flashed 10v across the stator. Instantly got better output from hand spinning the alternator. Put the bike back together and now have 13.8v charging @ 2000rpm.

If you've got good winding resistances, but no output, definitely try it. It saved me a lot of money.

Now onto the rear brakes...
 
13.8V at 2k?.......seems a little low. I'm hoping your battery was a bit down and it's taking the extra power to charge the battery back up. Maybe charge the battery fully first, then start it and check? I thought you were going to say 14.2-14.4V
 
Yes, the battery wasn't fully charged (11.5v ish). I hope it's just that. According to the SM, it's within spec: Battery Voltage < Charging Voltage < 15.5v.

Will put the battery on a charge overnight and see what we get. Thanks for the heads up!
 
After four or so years of issue free riding I experienced the fatal-total-electrical-failure-of-doom thing last Friday on the way into work. Bike has a newish battery and is always hooked up to an optimiser but 42 miles into a 44 mile commute the bike simply died without enough power to even light the dash up. Bike would start fine after an hour or so (battery catching its breath) so when the RAC guy came along he quickly conformed what I already suspected - zero charging to the battery.

I've stripped the TB away (gorrilla bar resting on frame and pushed against the injector bracework) did the job and after disconnecting the throttle cables I seem to have decent space to get at the alternator. Ive already dropped the rad and I'm sure after I've pulled the thermostat housing later in the week I should be able to get to the bottom alternator bolt (someone please tell me if I'm doing anything silly.....)

I'm hoping to God my situation may be as easily fixed as the OP's but I'm not placing any bets on that just yet.......

Question 1: is it the regulator or the rectifier within the alternator housing?
Question 2: can a failed rectifier mimic a totally goosed alternator?
Question 3: can I take it that testing the rectifier is a fairly simple diode resistance check?
Question 4: does anyone know of a rebuild service to help me avoid the £1795 I've been quoted for a new alternator............ (should I need it)
 
Welcome. There is a common issue with STs involving a large group of ground wires near the steering neck.
 
Ah - so you're saying it may be as simple as removing + cleaning the grounds?
Where are they - inside or outside the frame?
 
Many thanks for the heads up. Are the grounds on the inside or outside of the fram? Can you say how many I'm looking for?

Cheers
 
talss89 said:
Will put the battery on a charge overnight and see what we get. Thanks for the heads up!
Click to expand...
Best do a load test on the battery. When they go south on an ST,, they do so with little or no notice. I tend to use the cheaper batteries that I can pick up at the auto parts down the street. They last a reliable 2 years or so. I think I have been stranded twice,,, without much notice either time. CAt'
 
I did not see what bike you have. On the 1300, there is a big 23 pin connector behind the headlight. This is more exposed to environmental damage from rain than the big connector on the left side of the bike that clips into the left middle cowl. I think this (headlight area) is what was suggested above.
 
Many thanks guys.

I continued my quest into getting the alternator out. I'd really love to find the engineer who designed that set up and shake very warmly by the throat.

How the f### am I meant to f####### remove that f###### bottom f####### bolt???????

Approx 7 hours so far - last three hours try to get a 12mm socket onto that bottom bolt and then using the 9 degrees of movement to crack it off. And failing miserably. Mind, these bolts have been in place for 19 years and 60k miles. The top ones took a LOT of leverage. I'll give it another half hour tomorrow then I'm going to remove it using a sledgehammer.

any suggestions?
 
Bike = 2003 1300A. 60k ex police bike.

Bike was running great then simply stopped, not enough battery power to even spin up fuel pump. Came to life after an hour and bike ran for few minutes. No charge at all being supplied from alternator.
 
Mrr1 said:
Many thanks guys.

I continued my quest into getting the alternator out. I'd really love to find the engineer who designed that set up and shake very warmly by the throat.

How the f### am I meant to f####### remove that f###### bottom f####### bolt???????

Approx 7 hours so far - last three hours try to get a 12mm socket onto that bottom bolt and then using the 9 degrees of movement to crack it off. And failing miserably. Mind, these bolts have been in place for 19 years and 60k miles. The top ones took a LOT of leverage. I'll give it another half hour tomorrow then I'm going to remove it using a sledgehammer.

any suggestions?
Click to expand...
Long extension and a swivel socket. I replaced my alternator and that bolt was taken out and put back in with no problems.
 
970mike said:
Long extension and a swivel socket. I replaced my alternator and that bolt was taken out and put back in with no problems.
Click to expand...
Just picked up deep sockets from Screwfix. Already have socket wrenches and breaker bar at home.

Pray for me.
 
Mrr1 said:
Just picked up deep sockets from Screwfix. Already have socket wrenches and breaker bar at home.

Pray for me.
Click to expand...
I have an extension that purposely fits a socket loosely so the socket can 'wobble' a little as it is turned. It's not quite like a swivel joint but it allows a socket to fit onto and drive a bolt or nut that I can't quite get straight onto. I think I used that wobble extension to remove and replace the bottom bolt. It's been a long time but I don't remember that bolt being extremely difficult.
 
Reckon I'm going to have to search harder and find a flexi socket thing. Just spent another two hours on the damn thing to pretty much no effect.

I have to say - this is pretty much the worst job I've ever worked on in 30 years of DIY spanner work.

I'll get a flexi thing and if that doesn't work I think I'll sell the bike as is and just stay away from Honda.
 
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