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Nov 2, 2024 – Jan 26, 2025

Getting at and removing the alternator on a Honda ST1300 is not for the faint of heart. The charging system is nestled snugly down in the mysterious depths of the infamous “V” of the ST frame — literally the heart of the machine. You have to dig under the tank, under the air box, under the delicate throttle body assembly, and below a tangle of coolant hoses to finally expose enough of a pathway to remove this unsightly, if necessary hunk of metal, wire, and plastic. However, as I’ve tended to find with most new wrenching I’ve tackled, finding trusted instructional resources, with a step-by-step process to follow, along with having the right tools for the job — these do wonders for your confidence. As usual I found that in the Honda shop manual and on the  st-owners.com forums.

It was early November, some two weeks after our anti-climactic return home from Arkansas, before I felt willing or able to start physically working on the motorcycle. I spent some time online in the meantime, researching the problem symptoms, getting familiar with the scope of work ahead of me, and formulating a plan of attack. As a final test before starting disassembly, I attached another known-good battery to the bike. Alas, there was no improvement with the voltage output while running, so as with most jobs on the ST, I started removing plastic.

The following day, with all the standard cowls removed, I proceeded with removal of the main tank, first snapping a quick shot of all the hose connections to its underside, for later routing and reconnection.

I’ve had the airbox off many times before, so I proceeded next to that task, which involves a lot of screws. No big deal, especially with the tank out of the way. Before long, I was looking at the familiar sight of the exposed throttle bodies assembly, and pondering the great unknown to come. From this point forward, I’ll be on unfamiliar ground, since that rather delicate and intricately-connected mechanism needs to come OUTTA THERE.

Aside from the various electrical, fuel hose, and throttle cable connections that all need to be carefully undone, the throttle bodies (TB) are connected to the top of the cylinders via four squat, thick rubber boots. These boots are notorious for becoming rather firmly attached to the assembly over time, making it all but necessary for most DIY mechanics to basically pry the thing up. And this is not a part you want to bend or damage in any way. There are several horror stories on the forums of over-enthusiastic pressure being applied and borked parts as a costly result.

Prying is definitely not the recommended procedure, with use of compressed air being the likely best solution. But a big problem with a complex and rarely removed part like this, is it’s hard to see exactly how things are attached and how to relieve the attachment pressure in the gentlest fashion. Once you’ve done it once and understand how it all fits, everything seems obvious in retrospect. 🤷‍♂️

After loosening some very awkward-to-reach clamp screws on the upper end of the boots, I spent time working gently at the boots, where I could apply some pressure to unstick them from the metal. Trying to wiggle the TB out of there, it just doesn’t seem like it’s moving at all and you’re just not sure how much force you can safely apply. So, for better or worse, I followed the example in a forum report from a well-known forum member, who I know to be careful and sensible about these types of jobs. The main idea is to try to apply pressure directly upwards, using a large lever and a strap, rather than prying directly on the TB itself.

I used the handle from my motorcycle lift and a thin nylon tie-down strap to get leverage on the recommended spot on the TB that wouldn’t bend any fuel lines etc. With multiple attempts at gradually increasing lift and no violent movements, I was finally able to get the TB wiggling around a bit within the sleeves. Finally, with one final lift of the bar, one side popped gently free at last. Whew, certainly the worse is over now, right?!

Revealed at last is my target and the likely reason for all of this. Nestled down snugly within the V-shaped recess in the motor atop the bike frame, sits the ST’s alternator. However, getting it out of here is still a fair bit of work to come. I got a head start on it by flushing the coolant, then removing the radiator and thermostat housing

The following weekend, I picked back up where I’d left things, having read and re-read the shop manual and most relevant forum articles and comments multiple times, for tips and advice. First, for due diligence, I testing out the wiring harness with a multimeter, per the recommended troubleshooting steps. All that tested out fine.

All of the coolant hoses and attachment points need to be removed from “the V” in order to extract the alternator, so I planned to replace all of the OEM rubber bits that I could. Hopefully this would be the last time that I’d have to dig this deep into the guts of this particular machine! I took lots of photos and tried to keep the old hoses roughly in position so I’d be able to easily replace each one with new, using proper routing through the surrounding components of the bike.

Finally, everything was removed except the damn little oil pressure sensor that threads down into the engine from the top. Some people said it was necessary to remove it while others claimed not. I generally try not to touch or remove any part that isn’t 100% necessary for the job at hand, especially this being a pretty important and sensitive part for operation of the motor and getting to it again would be a royal PITA! Somehow, some way, I managed to twist and wrench that big ungainly blob of machinery (the alternator) out past the sensor at last, though I damaged the special rubber cover for the sensor’s electrical harness in the process. Of course they don’t sell THAT separately — you’d have to replace the entire wire harness! Gorilla glue to the rescue. But at least the alternator is out!

A new alternator isn’t cheap, especially considering the age and mileage of the motorcycle, so I was holding out hope that I might be able to identify one of its subcomponents, some which are offered as separate part #’s from Honda, that might be faulty. The brushes definitely appear worn, but based on my (admittedly novice-level) troubleshooting with a multimeter, I concluded that the rotor, one of the major sections of the device was kaput, and most of the diodes failed their continuity test. This apparent hard evidence, along with my reluctance to ever open this thing back up again, made my decision for me — a new alternator it is!

I had my parts ordering list ready to go. I found the best deal on a new alternator from a Honda dealer selling through Amazon. The rest — hoses, clamps, o-rings, doo-dads — all came from my usual online Honda vendor, Partzilla.com. That done, I spent the rest of the weekend on cleanup of the engine V. Years and miles of accumulated dust along with telltale signs of minor coolant leakage required quite a bit of elbow grease and it didn’t even really look that great when I was done. But it was cleaner, and I have a much better mental picture now of my bike’s innermost recesses. Oh la la! 😳

The following weekend, mid-November arrived, along with all my ordered parts, surprisingly quick with no backorders! First up is replacing the thermostat and all the smaller coolant hoses that feed into the different sections of the motor.

I spent several hours of my Saturday just replacing these damn hoses. Two of them, in particular, that run to the oil cooler on the back of the engine block, in a very hard-to-reach-and-see location, were absolute knuckle-bleeders! Tears of frustration were shed and salty language issued forth! A trip to Harbor Freight to get The Right Tools for the Job was in order. In this case, that meant some hose pliers and a handy set of 45-degree long-handled pliers, along with a 1/4″ elbow socket adapter for a later step.

More hours were spent on Sunday for hose replacement, even with the new tools. But finally all those coolant lines were replaced. I followed that up with installation of the alternator itself, almost easy after going through “hose hell”! I did end up having to remove that oil sensor to get the damn bastard wedged back in there however. 🙁  Some Permatex Black sealant was applied to the sensor’s threads for the re-install.

My new fancy Breeze constant-torque hose clamps had arrived today, recommended by the ST community to help mitigate the common coolant leaking for the large diameter hose elbows within the V. Apparently, they apply pressure more evenly around the entire hose diameter and are commonly used in the community for this particular purpose. So I got to work on the thermostat and larger hose connections, following a photo from the forum in order to ensure the new larger clamp bolts wouldn’t interfere with any other parts as I continued reassembly.

The following weekend, just prior to Thanksgiving. It was time to re-install the throttle bodies. Much easier than removing them, especially once you’ve seen how it all goes together underneath! My new socket elbow adapter made the boot clamp bolts more accessible, and I’d created a homemade gap-measuring tool out of an old gift card (per forum tip) to ensure I didn’t tighten them too snugly. Working methodically with many references to the manual and forum, I reattached all electrical connectors, fuel hoses, and cruise control cable to the TB

Unfortunately, I got some extra practice with removing the throttle bodies right away, when it became clear that I hadn’t routed the cable to the idle adjustment knob properly and it was caught up. I tried (too) hard to shift it into proper position below the TB, but there just wasn’t enough space to do so. I worried that I was putting too much strain on the cable and could damage the end connecting to the TB, so I ended up removing the entire assembly once more with the big lever. This time, I didn’t disconnect everything and it was definitely easier the second time. Got the cable relocated and everything buttoned up for a second time. Then moved on to the radiator and upper fuel tank.

The following day, I filled up the oil and coolant. Fired the bike up for the first time in weeks to run another voltage test with the bike running. 14 beautiful Volts baby — we are charging!

The rest of the day was spent on reassembly, plus bolting on some new ST-specific fork light brackets from Twisted Throttle. I felt lucky to have noticed an old photo of these somewhere online, as they are now discontinued. A call to the company several months ago had turned up a few left in their warehouse, so I’d ordered a set for both of my STs. I was looking forward to having properly-mounted fork lights that don’t keep dipping down after large bumps.

The next weekend, the weather was still holding up and I managed to get out for a quick 30 mile test right with no salt on the roads. The motor was having issues getting to the expected fast idle mode when first turning over from a cold start. Uh oh. I was now concerned that I’d done some sort of damage to relevant parts when initially trying to force the idle adjustment cable into position.

It broke my heart to do it, but that evening I tore the bike right back down to the throttle bodies, though I didn’t remove the fuel tank this time. At this point, i just had to leave things be for a while, being physically and emotionally drained from spending all my November weekends (and then some) on this repair.

 

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I spent some time around the holidays and through January learning more than I wanted to know about the thermal wax valve that Honda uses to auto-adjust the idle on this engine. Essentially, the valve connects via small rods to the TB. The bike starts and goes to a “high-idle” mode while the wax inside the valve is solid. As the engine warms it up, the wax liquifies, releasing the rods and closing small fuel flaps within the TB, so the engine settles down to a “normal idle”.

Towards the end of January, I finally felt ready to tackle this again. Starting with some basics, I checked the vacuum hose connections to the TB assembly and found a few of them quite loose. The five-way vacuum connector joint (a common source of idle issues) was clean, so I decided to just replace these hoses as well while I was in here, using the proper 3.5mm Honda hose I’d found in bulk on Amazon, to ensure a snug fit.

Using my newly acquired knowledge of the fast idle valve, I fiddled with the connecting rods manually, to ensure nothing was sticking. Taking any and all suggestions from the forum, I also dripped some Marvel Oil into some of the tiny orifices atop the TB, to hopefully clear out any possible junk blocking the sensitive passageways. This felt a bit like resorting to snake oil, but I was willing to try almost anything! 😀

The bike started, choked a bit, then finally found the high idle that I was expecting to hear. I was able to eyeball the wax valve mechanism as the bike warmed up, also using a small bolt held up against certain gaps as a measuring indicator that the valve was operating as intended, slowly closing as the wax heated up, bringing the bike to standard idle. I lubed the valve rods with Syl-Glide for good measure to avoid any stiction and tested starting the bike several more times from cold start.

While still not going to fast idle as smoothly as before this whole mess, the engine is more or less completing the fast idle cycle now as it should, with just an extra throttle twist or two needed to help it along. Good enough for now, and maybe it will “settle in” and just get better as I use the bike. I was just relieved that I hadn’t permanently damaged anything expensive!

Before buttoning her back up, the following weekend I synched up the throttle bodies using my new Carbtune Pro (right tool for the job!). This also improved the starting process and overall sound of the motor.

The roads were salty, and with plenty of winter weather in the forecast, I wouldn’t have much opportunity to really get out on any long rides before my planned trip to Jacksonville in March. But after several cold start cycle testing and a few quick laps around my neighborhood block on dry pavement in between storms, I finally called this job done, if not “well done”!

Special word of thanks to all the st-owners forum contributors on this topic, including but not limited to: karaszp, Sennister, dduelin, IGOFAR, and of course Mellow for keeping the forum up and running.