Winter Project... at least a short term spa treatment and repair.

One of our forum members and a good friend of mine had his alternator go out on his bike. Didn't have time to get into the job about a month ago when it happened, but I did rescue him from the side of the road. Fast forward and now his bike is in my shop in pieces. Seems that the regulator went out. There is a little more to this job than is obvious.
The first thing I noticed was there was a rather profound leak from the left valve cover gasket. Oil and road grime was pooling in the top vee of the engine. It was about 2" deep and had the consistency of hot asphalt! It was so deep it did not allow access to the bottom bolt of the alternator! It also completely buried the temp sensor on the top of the block. Wish I had taken pictures of it... all I have now is the cleaned up engine.
Parts are on order along with coolant hoses and thermostat, new valve cover gasket, etc, etc..

I would suggest to replace the complete alternator especially if it has been that contaminated with oil. Recently I had mine go out after doing that job where I replaced brushes as a preventative measure. Shortly after the alternator packed it in and rotor windings went open circuit. The individual components for it are prohibitively expensive and I believe false economy to repair. I replaced it with brand new unit. Also check the condition of those inlet port boots mine were hard, cracked, and leaking.


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We had the discussion, Geoff. Trying to save him some money. Replacing the entire unit was my first suggestion. He may end up paying me twice to mess with it.

A good auto electric shop should be able to check it out and rebuild it , good as new since there is nothing magic about a ST1300 alternator. Parts such as the regulator and brushes, etc. aren't unique parts and a good auto electric shop can even rewind a rotor or send it out to be re-wound. May be much cheaper than a new alternator. Worth it to check-out.

Jim Van said:

A good auto electric shop should be able to check it out and rebuild it , good as new since there is nothing magic about a ST1300 alternator. Parts such as the regulator and brushes, etc. aren't unique parts and a good auto electric shop can even rewind a rotor or send it out to be re-wound. May be much cheaper than a new alternator. Worth it to check-out.

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Good suggestion... parts will be here tomorrow. Not familiar with a good auto electric shop near by... but I am going to check. Thanks

This project is being wrapped up now. It turned out to be the regulator inside the alternator. Approx $200 part verses almost $600 for a complete alternator.
Since most of the cooling system had to be removed to access the alternator, we gave that a complete overhaul, as well as replacing the leaky left bank valve cover gasket.
The clutch circuit got a good flush and cleaning and we addressed some wiring issues. I think Greg will be a happy rider now.

If you want a possible big surprise, take the old regulator to your local auto electric shop and ask them if they can get you one and get a price ......... I bet it's the same regulator used in many Japanese alternators that they see. And I'm betting the cost would be about $75 or less. May be helpful to know for others on this Forum. Or if you would send it to me ( I'll pay postage ) I can take it to my local shop. Send me a pm for my address.

Jim Van said:

If you want a possible big surprise, take the old regulator to your local auto electric shop and ask them if they can get you one and get a price ......... I bet it's the same regulator used in many Japanese alternators that they see. And I'm betting the cost would be about $75 or less. May be helpful to know for others on this Forum. Or if you would send it to me ( I'll pay postage ) I can take it to my local shop. Send me a pm for my address.

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Thanks, Jim! As it would be... I found it on Amazon after the fact.

https://www.amazon.com/Denso-Voltage-Regulator-Alternator-2005-2009/dp/B01ITNMQYM/ref=sr_1_fkmr0_1?ie=UTF8&qid=1516490075&sr=8-1-fkmr0&keywords=Denso+D2+voltage+regulator

Oh well! Now we know. This regulator is used in some Moto-Guzzi

Good to know.. I bookmarked the info, but will probably forget when / if I need the info ..

The saga continues.... seems the regulator was taken out again. After removing the alternator for the second time... we took it to a very repeatable auto electric shop. They bench tested it and said the rotor was bad. They also said it is a common failure for the smaller Denso alternators. When trying to look up the part, they informed me they had no source for that particular rotor because of the size of the spline end. (Probably proprietary Honda)
We ordered another alternator from Ma Honda and it will be installed today. Yes, we are aware that you can order individual parts for the alternator... but as you are also aware, the sum of the parts is worth more than the whole.
This way we know everything is fresh and should be good to go.

Well, that's a bummer! At least you'll get it taken care of and not have any more problems! We Hope! 4:

SupraSabre said:

Well, that's a bummer! At least you'll get it taken care of and not have any more problems! We Hope! 4:

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Yes, we hope. Got a couple of hours work in it this morning... about one hour of that was looking for one of the small hose clamps for the 1/2" hose mated up to the thermostat housing. The new alternator was a bit touchy on the alignment. Actually had to remove the Oil pressure sensor to insert the new alternator, whereas the old one slipped out and back in without having that big of an issue. The neighbor needed some help with his building project, so I left the ST there partially completed. Will put some more time in after dark. I was thinking... if I take an ST apart another time or two, I may start teaching the blind to do it. I imagine, Bob, as many times as you have taken one down, you could probably do it blind folded.

vinny said:

... I imagine, Bob, as many times as you have taken one down, you could probably do it blind folded.

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Nah, that will never happen, I have to see the part so I know where it goes!