Time to do the alternator?? 1991 ST1100

Mark2864

Mark2864

Joined
May 15, 2022
Messages
38
Age
58
Location
Shelton, CT
Bike
1991 ST1100
Hey all,
I think it may be time to do the alternator if I can’t track down my electrical issue. Hopefully it’s just a bad/dirty/corroded wire.
Anyway, what are all of the parts I’ll need to do it?
(i.e. O-rings, special plate(?), special shaft, new 40 amp alternator, etc…?)
While I have the rear wheel and swingarm off to access the charging system, I’m addressing the rusted swingarm ☹️. Will probably try to find something on eBay and/or find someone to weld up my old one.
Any tips or tricks are appreciated!! I haven’t changed an alternator on the ST before!!
Thanks ✌️
 

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Your only bet on all the parts for alternator is ebay as the shaft and base plate are no longer available from honda.There is a guy fz750 on here that makes the base plate but you still need the shaft. Also while shopping ebay look for the sub harness for the 40 amp as it will make the wiring a plug and play.
 
I have a clean swingarm off a '98, that I'll send you for free if you pay the shipping. And, its your lucky day because I just happen to have an old box that fits it perfectly. The estimated shipping cost is around $30, so I'm guessing you're not going to beat that on Ebay.

And, mine is clean and straight, so no worries about its condition.

I don't know if the '91 and '98 use the same swingarm, anybody here know?
 
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tnbill said:
Your only bet on all the parts for alternator is ebay as the shaft and base plate are no longer available from honda.There is a guy fz750 on here that makes the base plate but you still need the shaft. Also while shopping ebay look for the sub harness for the 40 amp as it will make the wiring a plug and play.
Click to expand...
Good to know, thanks! I see the base plate and alternators on eBay. I’m unsure where to get the shaft. I’m assuming the shaft for the 40 amp alternator is different than the shaft for the original alternator? I’ll need some o-rings too, correct? I’m trying to watch all of the videos on YouTube. I don’t really want to pull the engine to do it!
 
dwalby said:
I have a clean swingarm off a '98, that I'll send you for free if you pay the shipping. And, its your lucky day because I just happen to have an old box that fits it perfectly. The estimated shipping cost is around $30, so I'm guessing you're not going to beat that on Ebay.

And, mine is clean and straight, so no worries about its condition.

I don't know if the '91 and '98 use the same swingarm, anybody here know?
Click to expand...
Thanks! I’m not sure if ‘91 and ‘98 swingarms are the same. If they are, I might take you up on the offer!
 
I checked the fiche for both years, regular and CA models, and they all appear to use the same part number.
 
On the 28 amp the shaft is also the rotor so yes they are different. I would be looking for a complete assembly and that is what most will be selling. You can get the 3 bolts, both O rings and the seal from honda. You don’t have to remove the engine to do the alternator but you will need the tool kit that is on loan from another member. Also it is a real trick to get in in place.
 
Thanks. What’s the tool kit I need? I might just replace with a 28amp if that’s easier. We shall see!
 
tnbill said:
On the 28 amp the shaft is also the rotor so yes they are different. I would be looking for a complete assembly and that is what most will be selling. You can get the 3 bolts, both O rings and the seal from honda. You don’t have to remove the engine to do the alternator but you will need the tool kit that is on loan from another member. Also it is a real trick to get in in place.
Click to expand...
If I can’t find the shaft that’s needed for the 40amp upgrade, I may be forced to just replace with a 28amp alternator.
 
Mark2864 said:
If I can’t find the shaft that’s needed for the 40amp upgrade, I may be forced to just replace with a 28amp alternator.
Click to expand...
I don't believe the 28A alternator is available any longer, the parts fiche I use says its unavailable, and I think that's what I recall others here saying.
 
The 28 amp alternator has not been available for the last 4-8 years. Attempts have been made to rebuild it, but to the best of my knowledge it hasn’t been successful.
You may be able to get the shaft from a wrecked post 96 ST1100.
The clock will start ticking once the 28 amp alternator starts leaking oil, if that happens your riding days are numbered.
The voltage regulator/rectifier is also prone to burning out, that usually happens before the alternator, check the condition of that first if you notice a charging issue.
Consider disconnecting one low beam headlight, that will reduce the load on the charging system. I believe the gen one ABS bikes functioned with one low beam. In some European countries that was the law when the bike was introduced.
 
ST1100Y said:
With the wiring exit (an stator terminals) sealed with resin a difficult task...
Click to expand...
I believe that’s where the root of the problem lies. That cap has come undone and there’s some oil leaking. I’ll try to clean it up if possible and do some checking! Got the swingarm, and tank off so I can get a better look soon! MAYBE it can be rebuilt. I just don’t know yet…
 
kiltman said:
The 28 amp alternator has not been available for the last 4-8 years. Attempts have been made to rebuild it, but to the best of my knowledge it hasn’t been successful.
You may be able to get the shaft from a wrecked post 96 ST1100.
The clock will start ticking once the 28 amp alternator starts leaking oil, if that happens your riding days are numbered.
The voltage regulator/rectifier is also prone to burning out, that usually happens before the alternator, check the condition of that first if you notice a charging issue.
Consider disconnecting one low beam headlight, that will reduce the load on the charging system. I believe the gen one ABS bikes functioned with one low beam. In some European countries that was the law when the bike was introduced.
Click to expand...
I believe it has started to leak oil, sadly. I’ve got the swingarm and tank out to get a better look. If I need to replace or upgrade the alternator, I need to start looking for parts!
 

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OK, I've been reading a few posts here that keep mentioning the alternator shaft, and was wondering about that part.

When I parted out the '98, I just pulled the alternator out of the engine block, without reading the Honda manual.

Now, I looked at the manual and see I was supposed to rotate the alternator clockwise and insert an 8mm bolt to retain the shaft in the engine.

Since I didn't do that, and presumably have the entire alternator with shaft attached as a spare part, how hard will it be with it off of the engine to rotate and remove the shaft?

I don't have the part in front of me, but from the diagram in the manual it looks like there's a plate with the same 3-bolt pattern as the alternator, that rotates and then the shaft will come out of the alternator?

The reason I ask is since I have a '97, and am keeping the alternator as a potential replacement part, I don't think I'd need the alternator shaft if I ever need to use the spare part, right?

If so, then I'd be willing to let go of the alternator shaft for someone to use on a 28A upgrade.
 
You can get a new alternator off of eBay. They are a Chinese knock off and are reliable. I purchased one for my 97. Do a search on the site for the plate. The shaft….well you may have a contact for that. ;)
I strongly recommend a new boot for the swing arm, that will make it easier to reassemble, though it’s still a pain to install.
Fitting the 40 amp alternator will be a challenge as the frame has an extra brace that the post 96’s do not have. If I recall you may need to trim the cover of the alternator to get it to fit. It’s like fitting a USB plug into a charger…you end up turning it three or four times before it goes in ;)
With patience it will come together and you will have many fine years of riding once it’s done.
 
kiltman said:
You can get a new alternator off of eBay. They are a Chinese knock off and are reliable. I purchased one for my 97. Do a search on the site for the plate. The shaft….well you may have a contact for that. ;)
I strongly recommend a new boot for the swing arm, that will make it easier to reassemble, though it’s still a pain to install.
Fitting the 40 amp alternator will be a challenge as the frame has an extra brace that the post 96’s do not have. If I recall you may need to trim the cover of the alternator to get it to fit. It’s like fitting a USB plug into a charger…you end up turning it three or four times before it goes in ;)
With patience it will come together and you will have many fine years of riding once it’s done.
Click to expand...
Thanks for the encouragement! It’s driving me nuts…just so sad to see the bike in pieces. I don’t want to give up on her yet! Yes, that shaft may be most difficult thing to find. I see the alternators and the plate on eBay
 
kiltman said:
You can get a new alternator off of eBay. They are a Chinese knock off and are reliable. I purchased one for my 97. Do a search on the site for the plate. The shaft….well you may have a contact for that. ;)
I strongly recommend a new boot for the swing arm, that will make it easier to reassemble, though it’s still a pain to install.
Fitting the 40 amp alternator will be a challenge as the frame has an extra brace that the post 96’s do not have. If I recall you may need to trim the cover of the alternator to get it to fit. It’s like fitting a USB plug into a charger…you end up turning it three or four times before it goes in ;)
With patience it will come together and you will have many fine years of riding once it’s done.
Click to expand...
I’m even starting to look at other ST’s! But like I said, I’m not ready to give up yet. This is my other “pride and joy”. 1990 KLR650-B Tengai
 

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