Vintage Dirt Bike Q & A

Howdy fellows of Vintage Dirt Bike forums! Thank you for the add . I figured I'd give a brief introduction of my self and general description of my bike. My name Is Ven and I live in Atlanta, GA.

I recently purchased a 1976 Honda MR175 and its in pretty awesome shape for the year. I was able to get it registered for street use in Atlanta after undergoing a inspection process offered here for vintage bikes older than 1980 and sometimes you get lucky and since the bike has a visible head light and tail light, I did! I'm pretty excited to start riding it around and making it my daily commuter.

I've added a handful of images of my bike. I just need to figure out why the lights wont turn on. None of the 3 lights (headlight, tailight and gauge light) power on. All the switches are there and the bike starts up fine. Wiring looks to be spot on perfect from the diagram I got from the mr175 1974 service manual. Doesn't look to be molested or messed with very much at all. The bikes vin is different from the number on the motor, and I'm not sure if this is the norm? As for the lights I'm guessing it's got to be something loose on the stator? I'm not the best at electrical. Any help would be greatly appreciated.

Cheers.

Hi Ven,

Wow, that bike looks great! That may be the cleanest one I've ever seen. I'm amazed at the mileage on some of these bikes, like they were used for a few months and then parked in the spare bedroom for 40 years. The chassis and motor VIN's are very often (always?) different.

Re the lights - if the bulbs are OK, the first place I'd look on your bike would be inside the headlight switch assembly, which was removed and reinstalled incorrectly when the bars were replaced (originals were chrome) - it should be between the clutch-lever mount and the grip. I'd take it apart and check it out, especially the on/off switch section and the wiring connections to/from it. It's surely a good idea to check the wiring harness too; a bunch of wires are usually packed inside the headlight shell and behind the side cover on the left. If the bulbs / switches / wiring's OK, then I'd suspect the stator. Bear in mind the flywheel can be a nightmare to remove even with the correct puller (which in my opinion is a must-have).

Do you have a meter? Ohm checks on the bulbs and AC voltage checks on the wires could save you a bunch of time.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Hey Ray thank you so much for your response! I've seen you post alot of helpful info on this forum and have read through many of your past posts. I will check the switch and also get the correct placement on it. The bulbs are all brand new so I don't believe they are the issue. I will check with a meter this evening also.(I'm kind of just learning my way around using the multimeter.) Does the bike have to be running to do the voltage check?

I've gone through all the wiring inside the headlight and on the entire bike(with the exclusion of connections behind the actual stator and inside the switch)and everything looks to be done correctly.

Wouldn't the taillight and speedo light still turn on regardless of whether the switch is hooked up properly? I am looking inside the flywheel and I'm not 100% sure, but I think the brown fabric colored wire that I believe houses the yellow wire going to the lighting coil looks to not be disconnected. My guess is this is what may be my issue? If so, do I just have to pull the flywheel, and solder this wire back into place? Also is there anything I should keep in mind if I do this?

I don't have any original Honda workshop tools to hold the sprocket in place to remove the retaining nut on the flywheel. Could a piston stop work? I think can track down a puller. Correct me if I'm wrong but is it a reverse threaded 27mm x 1.

Thank you!

Sure, no problem at all. With the main lighting switch off on a stock MR175, no bulbs should light up at all.

For go/no-go situations like yours, I'd start with resistance checks with the motor off. The stator failures I've seen all involved breaks and/or shorts in the actual windings and not the end connections, although that's certainly possible.

If your meter has multiple ohm settings, set it to the lowest one, preferably 100 ohms or less. Connect one lead to a good ground on the motor cases (this isn't always as easy as it sounds). Unplug the ignition/lighting cable from the motor to the wiring harness, and take readings from the two contacts inside the motor cable's end with the other meter lead; I used a small screwdriver into the contact and connected the lead to that. You should get roughly 1.3 ohms for the yellow (lighting) wire, and 3.3 ohms for the black/yellow ignition wire. Your readings need not be identical to these, but if you get less than .1 or more than 50 ohms on the yellow wire there's likely a problem.

While you're at it, take a reading from the harness connector's yellow-wire contact, leaving the ground lead connected. With the main lighting switch off you should get an open-circuit reading, as this wire is connected to nothing with the switch off. Then I'd turn the switch on and note the readings on both low and high beam (all readings should be quite low, but not zero).

The best way to hold the flywheel during nut removal is to use a big pin spanner into the flywheel slots, but the rear brake is strong enough to hold the sprocket if you want to try that method. As you mentioned, the correct flywheel puller (K&N 82-0150, Moose 28-1953) has 27x1 LH threads that screw into the flywheel center; you then hold the large hex section with one wrench and use another smaller one to turn the center push bolt in, hopefully popping the flywheel off. It's not a bad idea to pre-heat the flywheel center with a small heat gun and grease the center bolt's tip, and also a few hammer taps can help pop it off once the center bolt's real tight (you probably know all this already).

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Thanks for the info! I'm still waiting to get the tools for the flywheel removal but went a head and tested the wires from the motor with the multimeter.(lowest setting on this one was 200 ohms.) I got roughly in the range of 2.9 - 7.3(depending on the ground area) coming from the blk/yellow wire, and no change at all for the yellow wire coming from the stator.
I attached a pic of the multimeter and reading from the yellow wire.

Does this verify that I am indeed looking at either a break or short in the windings on the lighting coil, or possibly bad end connection?
If so I found this write up for rewinding the coil: http://www.kdxrider.net/forums/viewtopic.php?t=10226

I'm thinking thats what I'll have to do if it isn't the end connection? Whole Stators on ebay at $100+

Well, it looks like your original diagnosis was correct, and your lighting coil or lead has a break in it somewhere. Sometimes these occur because something small gets loose inside the flywheel and cuts the wire. I fixed one once by cleaning the break and the adjacent wires and soldering them together - the output voltage was reduced a tiny amount by the shorted turns, but it worked fine. Once you get the flywheel off you'll know more - it could be something as simple as the coil ground connection getting loose.

Re the stator - I'm about 90% certain the MT125 stator uses the same ignition and lighting coils as the MR175, plus an extra battery-charging coil (the MR stator just has the lamination stack for this coil, w/no windings). I don't know if you want to get into any electrical mods, but the MT stator has the potential for 12V output using both the lighting and charging coils in series, which could power a super-bright LED headlight bulb if they're available for the MR socket.

http://www.ebay.com/itm/75-Honda-MT125- ... 6f&vxp=mtr

I'd avoid going the rewind route if possible - it looks easier than it is. You might want to check out Ricky Stator, he should be able to hook you up:

http://www.rickystator.com/product/stators/honda

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

Awesome! I'd totally be interested in getting my lights brighter. So running the 2 coils in series turns the system into 12v? I'd imagine this would require me changing the taillight and speedo setups as well and getting a 12v rectifier?

I'm going to get behind the flywheel this weekend and see whats up there first. At least get lights period and see what they're like before I go brighter. Thank you again for all the helpful info. I appreciate it. I'll update here how it goes.

Cheers.

Ven

Ven,

Yes, you'll have to change all the bulbs to 12V, but they should be much easier to find than 6V ones. I'd also suggest a 12V rectifier/regulator, as you'll most likely be getting all kinds of AC voltage with the series connection that you'll want to convert to a steady 12-14VDC. Current will be limited to the capacity of the lowest-current coil, which is generally determined by wire gauge and hard to determine from the photos I have. If you go with an incandescent headlight you'll be happy to have every last watt of power this setup will deliver, but with LED's you'll mainly just need the voltage unless you go with a serious LED array. I'm a big fan of LED lighting; I've got flashlights and worklights that are brighter than practically any OEM vintage headlight, and will run for days on a small gel-cell battery.

Both MR175 wiring diagrams I've seen (Honda and Clymer) show all bulbs running on unrectified AC power. The rectifier on the airbox is used as a pulse-forming network for the stator's ignition-coil output; if it shorts the motor will not run.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

So I'm actually working on this right now and everything is going smoothly for the most part. I have the flywheel off and can see the disconnected wire From the lighting coil as pictured. I now am having a real difficulty getting the 2 stator plate bolts off. I'm using an 18v impact driver. Lefty-loosey for this right? I've tried spraying it with this product 'bolt off' and even taking a heat gun to it and I am starting to strip the screws a little at this point. Does anyone have any pointers here?

You'll only get one quality shot at getting those screws out, after that it will be damage control.

First, I'd use a flat-tip punch and small hammer to flatten the areas where the Philips slots are starting to deform. Yours aren't too bad, you should be able to bring them back to full functionality several times if needed, then toss them after they're out.

To loosen the threads' grip on the case metal (all of mine have had oxidation on both screw and threads), I'd suggest applying some serious heat to the screws IF you can do so without putting the coils at risk. If it were me, I'd protect the coils with sheet metal while applying heat with a small heat gun, or if you haven't got one, a torch on low heat if you're comfortable with that. The idea is to get the screw nice and hot (maybe 160F to 250F), then let it cool down and try removing it (one or two tries only, then heat it again and use the punch again if necessary). It's also really important to use a Philips impact tip that exactly matches the screws, or is even slightly bigger than ideal; a too-small one will spuzz it right out and you'll end up with a rivet. Be sure to push down hard on that impact driver and use short bursts, obviously.

Using the above techniques I recently removed two butter-soft Allen screws which were Loc-Tited really tight into a small cast-aluminum brake cylinder. I used my handheld impact driver and hammer as I thought the 120V one was too much. It took 3 heat applications, probably 4 or 5 goes with the punch per screw, and a whole lot of medium-hard hammering and twisting, but they came out without damage to the cylinder or mount.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

I Got it! Disconnected a couple of the coil screws and used the heat gun. So looks like the lighting coil wire was disconnected on purpose. Any reason someone would do this? I'm going to reconnect and see if I can get them going again.

Could you check the coil resistance first? It would suck to reconnect an open coil.

Maybe they were looking to decrease flywheel drag or something, but if so they should have removed the coil and lamination stack.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

So just soldered the yellow wire back to the coil. Reconnected to the stator and on 200ohm setting I'm getting around 0.9 - 1.1 reading. i dont know what this means because of my lack of expertise in the electrics, is this good?(fingercrossed)

That seems like it's close enough. Touch the leads together and see what you get for baseline lead resistance (on my meter it's about .3 ohms).

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

For the win! Thanks for all your help Ray.