Complete Alternator Replacement for CT70 K1

[Thursday]

Hi Everyone,

I just picked up a project bike and I'm going over everything it will need to run.

I believe it is a K1 model. The tag says August of 1971 Serial: (CT70 2001419)

The most pressing item for the engine is a complete alternator assembly.

I have found alternator assemblies on eBay and Amazon. They claim to work for the CT70 but all their compatibility descriptions are vague and generic.

https://www.amazon.com/gp/product/B0787CY3DX/ref=ox_sc_saved_title_1?smid=A31M7FTC4XRLZH&psc=1

I thought I would ask here to see if anyone has used these or can recommend me a replacement?

I noticed these replacement alternators have 6 wire harnesses where my connection seems to be 3 or 4 wires?

I say 3 or 4 because the wiring harness diagram shows 3 (Black, Green, Yellow), but the physical connector I have is (Black, Green, Yellow, Red/White) Shown in the pictures. Not sure why there's a discrepancy?

 

[69ST]

Light green w/red trace is the neutral indicator light lead.

I'd try Northeast Vintage Cycle (hondanuts.com) and chp. Dratv appears to be out of stock. If you're a little bit adventurous, head to ebay. Any K1-79 stator can be used. You may find new, but more likely you'll find used in working condition. There are also a couple of ebay sellers offering CDI conversion kit that will work with your engine. The oldest of these is user ID "xrarespares".

 

[lukelaw1]

the long to the short when it comes to flywheels/magnetos is there are 3 type/styles; 6volt 3 speed (Hitachi), 6 volt 4 speed Hitachi or Mitsubishi), and 12 volt. so in general you need to match flywheel and stator plate to crank shaft taper.

The kit you posted i dont think will work with you bike. the kit listed i think is for a 12volt.

what parts do you need exactly?

 

[69ST]

the long to the short when it comes to flywheels/magnetos is there are 3 type/styles; 6volt 3 speed (Hitachi), 6 volt 4 speed Hitachi or Mitsubishi), and 12 volt. so in general you need to match flywheel and stator plate to crank shaft taper.

The kit you posted i dont think will work with you bike. the kit listed i think is for a 12volt.

The xrarespares kits are tailored to fit the 3-speed and 4-speed; you specify which model you have, the seller tweaks the parts list. 12v conversion is easy...sealed 5.0ah/12v AGM battery, 12v bulbs to replace the 6v.

 

[Thursday]

Light green w/red trace is the neutral indicator light lead.

I'd try Northeast Vintage Cycle (hondanuts.com) and chp. Dratv appears to be out of stock. If you're a little bit adventurous, head to ebay. Any K1-79 stator can be used. You may find new, but more likely you'll find used in working condition. There are also a couple of ebay sellers offering CDI conversion kit that will work with your engine. The oldest of these is user ID "xrarespares".

Thank you for the information.

I guess the alternator I linked on amazon won't work. I'm surprised there are no aftermarket options for an entire CT70 alternator.

I have checked a number of vendors online who specialize in Honda Trail bikes, but none of them seem to have the whole alternator assembly. i have seen stator replacement parts but that is all.

This is what I'm working with.

 

[Thursday]

the long to the short when it comes to flywheels/magnetos is there are 3 type/styles; 6volt 3 speed (Hitachi), 6 volt 4 speed Hitachi or Mitsubishi), and 12 volt. so in general you need to match flywheel and stator plate to crank shaft taper.

The kit you posted i dont think will work with you bike. the kit listed i think is for a 12volt.

what parts do you need exactly?

See photo for what I'm missing. I believe my model requires 6 volt 3 speed. But I don't' mind going to a 12volt if it's all that's available.

 

[Thursday]

The xrarespares kits are tailored to fit the 3-speed and 4-speed; you specify which model you have, the seller tweaks the parts list. 12v conversion is easy...sealed 5.0ah/12v AGM battery, 12v bulbs to replace the 6v.

xrarespares does not have anything listed for sale on eBay at the moment.

 

[lukelaw1]

i dont mean this to be in anyway disrespectful, but from the looks of those pics a stator kit maybe the least of you worries. that crank taper could probably be cleaned up to properly fit a flywheel. I would be more concerned about the internals, connecting rod, bearings, shift forks, gears, jug and head. id start by splitting the motor and see what going on inside and go from there.

 

[cjpayne]

i dont mean this to be in anyway disrespectful, but from the looks of those pics a stator kit maybe the least of you worries. that crank taper could probably be cleaned up to properly fit a flywheel. I would be more concerned about the internals, connecting rod, bearings, shift forks, gears, jug and head. id start by splitting the motor and see what going on inside and go from there.

I agree. Looks to have had the flywheel cover missing and the intake is exposed. The rims may also need replaced. Once they've been blasted, that will be the only way to determine really. You definitely have some good bones to start with and it looks to be mostly there.

 

[69ST]

Your last photo speaks volumes. Based on what can be seen, I second lukelaw1's suggestion.

There are a number of ways you could go with this engine rebuild. And make no mistake, it needs to be opened & inspected...to do proper rebuild. I'm not being alarmist here. There's a chance the internals survived unscathed, if both valves were closed all the years the bike sat. Find out what-all is needed, or you'll end up with what seems like an endlessly-expanding project. Starting with a complete list of what needs to be replaced is not only easier on the psyche, it's more efficient too.

One of the main questions I'd want answered is the condition of the crankshaft. If it needs to be rebuilt...or replaced...that opens a world of possibilities, including going to 12v CDI...using either an OEM crank, or an aftermarket stroker crank in 12v flavor, then sourcing a complete 12v alternator from a known, established, outfit like Ricky stator.

FYI, any pre-1982 CT70 3-speed, or Z50 alternator will fit this engine...and that's a huge pool of vintage parts to choose from...if you decide to go that way. But, again, I think you'll be a lot happier if you know what you're working with first...then making informed purchase decisions.

 

[Thursday]

No offense taken by the comments. This is not my first project bike and I fully understand evaluating the project's scope and direction given the state of the picture I posted.

I have split the case and should be able to get away with nothing more than piston rings and some valve lapping.

That is part of the reason I created this forum post, so that I could compare the pricing of a complete alternator, alternator cover, carb, piston rings vs. a new Lifan 140 engine.

 

[airblazer]

We love progress pics, so it would be cool to see how you’ve begun to bring this crusty fossil back to life. How’s the top part of the frame, in front of the gas cap? It looks like a bad bend/dent in the pic you provided. But you do have the helmet holder, so you got that going for you

 

[69ST]

Best guess is that you're looking at a $300 for the AWOL items. I'm guesstimating $80 for a clean, used, alternator assembly, another $100 for a cylinder + piston kit (I'd go for a 52mm/88cc version), $50 for a reproduction (hondatrailbikes.com) CT70 carb and $50 for a flywheel cover. Don't take those numbers as gospel, they are just educated guesses at the moment.

Last I looked and L140 was a $450 item, exclusive of shipping. You will need some additional items to make it fit: high-flow exhaust w/relocated rear hanger, wider footrest assembly to actually fit the much wider engine, modded brake pedal, 22mm carb + intake w/LH turnout + open element air filter. I could see this as a $700+/- project, which is not bad at all.

That's the best I can do to directly address what you explicitly asked.

If you'd care for some input on what you asked implicitly...read my further ramblings below...

For the sake of pre-planning conversation, let's say there's an expected difference of $350+/-50, at the outset. There are lots of cool stuffs out there: wheels, exhausts, lighting, shocks, brakes, etc. You know, the reasons why true gearhead projects are never truly finished. Back to topic...a $400 bill doesn't mean all that much in 2020, especially when you're going to ride the finished bike. For the sake of objectivity & full disclosure, I remain old-school and on the Honda side of the proverbial fence. That said, the difference between a well-tuned 88cc original engine and 140cc stuffed into the boiler room is going to night & day. That big Chinese lump ought to give you enough grunt to easily keep pace with suburban traffic and exceed every speed limit you're likely to encounter. Seriously, I'd expect 65-70mph top speed potential, minimum. That makes for an apples-to-oranges comparison. The leveler: how you wish to use this bike, a.k.a. your goals. Once you have the ability of cruising along north of 50mph, you can ride just about anywhere that doesn't involve a limited-access freeway...which changes just about everything.

 

[Thursday]

Excuse my absence. Visiting this forum is not yet part of my routine.

Thank you for the information and estimates Racerx.

As I stated earlier this project is a part of curiosity to see what minimal amount I can put into this to have a running motor. Please keep that in mind when viewing the pictures.

I have owned previous CT90's that I completely restored with higher scrutiny. That route quickly adds up after buying all of the parts. This is my first CT70 and I wanted to work with what I have before making my decision in which direction to take this or part ways. As you can see I haven't spent much money, mostly elbow grease and tinkering which I enjoy.

The motor is re-assembled and awaiting a used Hitachi rotor in the mail. I will await deciding until after I have tried to run the motor.

I have worked the dent as best I can with my skills and tools. The harbor freight stud welder didn't work for me. The studs broke off with the slightest impact. I was able to pull it out quite a bit with the Astro slide hammer vise grips and some MAPP heat. However, the seam is fatigued from being gripped and will tear if I work it anymore. I have never used filler (Bondo) before. I would appreciate thoughts on filling the remaining dent. Is that too much filler? Any tips?

Here are some progress pictures (chronological).


https://imgur.com/a/2vhSnAo

 

[69ST]

As bad as this looks, you still have what appears to be solid material, a.k.a. "good bones" to work from.

Getting that cylinder back to uniformly solid metal means taking it out two O/S...minimum. Three wouldn't surprise me in the least. There's no way any hone is going to clean up the deep rust damage well enough for the rings to control oil, let alone hold any compression. I'd have bead blasted the head, combustion chamber & ports, with the old valves left in place, as the starting point; then, it'd be time to cut the valve seats, followed by lapping-in the new valves. With this much rust damage to the top end, these are the minimum repairs...not options.

I'd really want to see what's inside the lower end. It might be fine...or it could be rusted. Nothing inside the engine is impossible, or very difficult, to replace. Bearings and the connecting rod are the most immediate concerns. Any rusted bearing(s) would mean disaster in short order. If the rod is worn, either bearing wear/damage or excessive side clearance, it's gonna rattle.

Not surprised that the crank threads were salvageable, nice job btw. The rust should clean off easily, using a rotary wire wheel.

That frame damage isn't as bad as it might appear. The location is a Mofo to access. A couple of huge C-clamps and various scrap pieces of steel + lumber would be the easiest, most controllable, way to reverse the dents. In fact, a large impact socket might be perfect for the edge dent. I can't tell if there's enough access to fit a 2x2 through the bottom of the frame...to reach the underside of the top seam area. Best guess, there isn't. That top seam, however, can be metalfinished...and it's hidden once the top trim is installed. A 1" wide scrap of 0.060-0.125" plate steel could be welded to the top seam, a small-diameter bolt welded to the other end, for the slide hammer. Then you could dolly-out the top of the frame, cutting-off the improvised tool afterward. Most of the edge damage can be flattened. I'd use metal as the bulk of any filler material needed, following the shiatsu session. There's enough material thickness to MIG weld the area...a little bit of "pave & shave" bodywork. Being a structural location on the frame, I wouldn't want any plastic filler thicker than a few thousandths of an inch. Brazing rod, or body lead, would be ideal materials, if welding comes up a little short.

There are lots of "right ways" of ironing-out these dents. I've only mentioned what immediately came to mind. You're limited only by your creativity...and patience.

 

[Thursday]

Well, I purchased an old Hitachi magneto off eBay. A couple of alligator leads to the ignition coil and a squeeze bottle of gasoline.

 

[Thursday]

Can anyone tell me if the stock airbox will work at the pictured angle/arrangement before I spend money on replacing the rubber pieces for the original airbox?

I'm asking because the carb and intake I purchased are generic aftermarket replacements not necessarily designed for the CT70. Looks a little steep to me but this is my first CT70 so I wouldn't know.

I see quite a bit using the K&N style filters and I'm wondering if that's because of compatibility issues with these aftermarket carbs.

Thanks

https://imgur.com/a/P1wZ2tC

 

[kirrbby]

I don't think that intake will work at all. The carb itself might hit the frame. The float, isn't going to float ...or, won't be able to sink. No way the stock airbox would work. The K&N is about 60 bucks, so you would probably be better off going back toward stock. Get a correct intake, and use the stock airbox for the same money. You really can't go wrong using stock parts.

 

[69ST]

That intake is all wrong for this application. Kirrbby is right, it's gonna be nothing but problems. Save yourself a long nightmare. Used CT70 intakes are plentiful; if you go with this, then a stock airbox assembly becomes plug & play. If you want to run a larger carb and/or an open element air filter, you'll need an intake with LH side turnout, for clearance...one that mounts the carb at the proper angle, i.e. float bowl parallel to the ground. K&N is a great product, top quality. UNI makes a good quality filter, also and for half the price. You pays your money and takes your pick.

BTW, the motor sounds pretty good and didn't appear to smoke, on the bench. It'll be interesting to see what the seat-of-the-pants dyno reveals. A healthy stocker should top-out in the low-to-mid 40s on the flat. If it has a tough time reaching 35mph...or can't even do that...it's likely down on compression and in need of a valve job.

 

[Thursday]

Thank you for the thoughts on the carb intake.

I had looked around on eBay for used intakes and did not find very many results and none with a price I could stomach most were being sold with the original carburetor. If you come across one please send me a message.

I agree the motor seems to be okay considering the condition. I won't know for sure until the butt dyno.