Post by 78sr on Oct 30, 2008 8:23:41 GMT -5
Weather permitting, I ride my 78 SR500 back & forth to work nearly every day. My last ride was about 3 weeks ago. I got ready to ride home, ( jacket, helmet & gloves ) & my bike wouldn’t start. This bike almost always starts on the first kick so after it hadn’t fired in 6 or 7 attempts I knew it was a lost cause. I pulled the spark plug, grounded it to the block & kicked. No spark. A friend had a spare CDI box which I installed the next day but still no spark. After much shop manual reading, along with visits to various forums & a lengthy session with my ohm meter, I determined that a coil on my stator had failed. My first thought was ebay but that turned up nothing. Someone mentioned a company in Canada so I contacted them. They will rewind the offending coil for $200 plus shipping both ways. I didn’t want to spend that much so I tried to find some do it yourself info. I didn’t find much & only 1 pertaining to the SR500 & it was on this forum, but it was written in such a manner that it left me wondering what I had just read. Too confusing for me. I decided to figure it out for myself and have a go at it. My theory is, it doesn’t work anyway so I have nothing to lose by trying to repair it. I bought a flywheel puller from ebay (27 mm left hand thread). I can’t imagine trying this without the proper puller.
1. After pulling the flywheel, unbolting a clamp that helped secure the wiring & moving an oil line out of the way, I was ready to unplug the 2 stator plugs & take it off. I marked the engine & stator so I could put it back in its original position.
2. I removed the three screws & pulled the stator off. My tests had shown that the large stator coil had failed. Apparently a common failure & the one whose repair I will try to explain. The stator is now off the bike.
3. There are 3 screws holding the stator to its backing plate. Remove & store these screws. On the backside of the coil portion of the assembly that you just seperated from its aluminum backing plate, you will see where the winding for this coil starts. Mine had a short section of black insulation over the wire between the coil and the lug to which this wire is soldered. Save this piece of insulation. You will re-use it later. On the front side of the stator, buried in a layer of epoxy is the other end of the coil wire & it is soldered to a much larger gauge wire. This completes the circuit on this coil. Once enough epoxy is removed you can unsolder the connection & proceed to remove the broken coil wire by whatever means you find work for you. I used a sharp chisel & pliers to strip mine down to the core. Be patient. Mine came off in little bits at a time & since it was dipped in varnish at the factory, the wires were all stuck together. I spent about an hour cutting & pulling till I was down to the core.
4. If you manage to get yours stripped without chipping any epoxy on the core you did good. I wasn’t that lucky. I sanded the core with emory cloth & smoothed it with JB Weld. Just enough epoxy to smooth it so your new wire isn’t damaged when you do the rewind. I bought a spool of 34 gauge wire from ebay. The wire measures .0063. It’s really thin but pretty strong.
6. The larger of the 2 stator plugs has 5 wires that may or may not match the colors coming from the CDI. Make a schematic that reflects the colors from the CDI onto the actual stator plug so you can read the proper wires. Readings should be as follows + or- 30%. White/green-black 90 ohms. White/red-black 16 ohms. Red- brown 5 ohms. Brown- black 330 ohms. Red- black 335 ohms.
7. Find a piece of brass or aluminum tubing no larger than 1/16” in diameter. I read an article that said metal tubing was forbidden so I used plastic tubing when I did mine. It didn’t take long for the wire to saw through the end of the plastic tubing and start snagging. If I were doing this again I would definitely use brass or aluminum unless it somehow damaged the coating on the wire. Space becomes a real issue toward the end of the wind so this small tubing is necessary. Smooth any burrs on the ends of the tubing, inside and out so as not to scrape the wire coating. Scraping the coating off the wire is not acceptable.
8. I placed my spool of wire on an old turntable, (record player, not running) but anything that allows the wire to feed out easily is ok. The wire needs to be free to come off the spool easily. The spool placed upright on the center of my record player proved to be a good way to go.
9. It would be a good idea to give your wire a good pull just to see where the breaking point is so you’ll have an idea of how tightly you can wrap the core. You DO NOT WANT TO BREAK THIS WIRE! Do this a couple of times just to be sure you have a feel for the strength of the wire.The wire is fed through the tubing & any kinked or damaged bits need to be cut off. You are now holding the tubing kind of like you would hold a coffee stir stick with the wire coming out the end.
10. Find the solder lug on the back side of the stator. Slip that little piece of black insulation back on the wire, scrape off a small bit of coating, and solder the wire to the lug. On my bike the wire wraps counterclockwise. I suspect yours is the same but check it out. Very carefully start winding (stirring motion) from the bottom to the top of the core. Bottom to top to bottom & round & round. Not brain surgery. Keep winding & keep it relatively tight but not tight enough to break it. Be patient. You’ll get there. After a couple of hours I couldn’t get any more winds. That’s why it’s so important to use small, smoothed metal tubing. The wire will saw through plastic so don’t be tempted to use a straw or stir stick like I did.
Small tube & tight wind = more wire= more resistance= good
You’re shooting for 330 ohms = or- 30% which is 231 to 429 ohms. I had 221 ohms when I finished which is below the acceptable limit but I couldn’t get any more wire on the core. I simply ran out of room.
11. I soldered the end of this wire after I had cut it, to the larger gauge wire that I had unsoldered earlier.
12. I coated all exposed wire & soldered areas with epoxy to protect it. After all this, you don’t want anything disturbing the wire or permitting moisture in.
13. I carefully put the stator back in its original position & tightened the screws. I routed the wiring & secured it. Installed & tightened flywheel.
With the lower than normal ohm reading, I had no idea what to expect. Choke on, ignition on & kick. Mine started on the first kick in spite of the low readings. I don’t know how low your ohm reading has to be not to work. All I know is mine works & I have the satisfaction of having done it myself.
It cost me a few hours of time and $31 for the flywheel puller & the wire, & I’m running.
If you are having the same issues I had & this writing makes any sense to you, go for it. What do you have to lose? Look at the knowledge you’ll gain. Another big gun in your arsenal. Enjoy
1. After pulling the flywheel, unbolting a clamp that helped secure the wiring & moving an oil line out of the way, I was ready to unplug the 2 stator plugs & take it off. I marked the engine & stator so I could put it back in its original position.
2. I removed the three screws & pulled the stator off. My tests had shown that the large stator coil had failed. Apparently a common failure & the one whose repair I will try to explain. The stator is now off the bike.
3. There are 3 screws holding the stator to its backing plate. Remove & store these screws. On the backside of the coil portion of the assembly that you just seperated from its aluminum backing plate, you will see where the winding for this coil starts. Mine had a short section of black insulation over the wire between the coil and the lug to which this wire is soldered. Save this piece of insulation. You will re-use it later. On the front side of the stator, buried in a layer of epoxy is the other end of the coil wire & it is soldered to a much larger gauge wire. This completes the circuit on this coil. Once enough epoxy is removed you can unsolder the connection & proceed to remove the broken coil wire by whatever means you find work for you. I used a sharp chisel & pliers to strip mine down to the core. Be patient. Mine came off in little bits at a time & since it was dipped in varnish at the factory, the wires were all stuck together. I spent about an hour cutting & pulling till I was down to the core.
4. If you manage to get yours stripped without chipping any epoxy on the core you did good. I wasn’t that lucky. I sanded the core with emory cloth & smoothed it with JB Weld. Just enough epoxy to smooth it so your new wire isn’t damaged when you do the rewind. I bought a spool of 34 gauge wire from ebay. The wire measures .0063. It’s really thin but pretty strong.
6. The larger of the 2 stator plugs has 5 wires that may or may not match the colors coming from the CDI. Make a schematic that reflects the colors from the CDI onto the actual stator plug so you can read the proper wires. Readings should be as follows + or- 30%. White/green-black 90 ohms. White/red-black 16 ohms. Red- brown 5 ohms. Brown- black 330 ohms. Red- black 335 ohms.
7. Find a piece of brass or aluminum tubing no larger than 1/16” in diameter. I read an article that said metal tubing was forbidden so I used plastic tubing when I did mine. It didn’t take long for the wire to saw through the end of the plastic tubing and start snagging. If I were doing this again I would definitely use brass or aluminum unless it somehow damaged the coating on the wire. Space becomes a real issue toward the end of the wind so this small tubing is necessary. Smooth any burrs on the ends of the tubing, inside and out so as not to scrape the wire coating. Scraping the coating off the wire is not acceptable.
8. I placed my spool of wire on an old turntable, (record player, not running) but anything that allows the wire to feed out easily is ok. The wire needs to be free to come off the spool easily. The spool placed upright on the center of my record player proved to be a good way to go.
9. It would be a good idea to give your wire a good pull just to see where the breaking point is so you’ll have an idea of how tightly you can wrap the core. You DO NOT WANT TO BREAK THIS WIRE! Do this a couple of times just to be sure you have a feel for the strength of the wire.The wire is fed through the tubing & any kinked or damaged bits need to be cut off. You are now holding the tubing kind of like you would hold a coffee stir stick with the wire coming out the end.
10. Find the solder lug on the back side of the stator. Slip that little piece of black insulation back on the wire, scrape off a small bit of coating, and solder the wire to the lug. On my bike the wire wraps counterclockwise. I suspect yours is the same but check it out. Very carefully start winding (stirring motion) from the bottom to the top of the core. Bottom to top to bottom & round & round. Not brain surgery. Keep winding & keep it relatively tight but not tight enough to break it. Be patient. You’ll get there. After a couple of hours I couldn’t get any more winds. That’s why it’s so important to use small, smoothed metal tubing. The wire will saw through plastic so don’t be tempted to use a straw or stir stick like I did.
Small tube & tight wind = more wire= more resistance= good
You’re shooting for 330 ohms = or- 30% which is 231 to 429 ohms. I had 221 ohms when I finished which is below the acceptable limit but I couldn’t get any more wire on the core. I simply ran out of room.
11. I soldered the end of this wire after I had cut it, to the larger gauge wire that I had unsoldered earlier.
12. I coated all exposed wire & soldered areas with epoxy to protect it. After all this, you don’t want anything disturbing the wire or permitting moisture in.
13. I carefully put the stator back in its original position & tightened the screws. I routed the wiring & secured it. Installed & tightened flywheel.
With the lower than normal ohm reading, I had no idea what to expect. Choke on, ignition on & kick. Mine started on the first kick in spite of the low readings. I don’t know how low your ohm reading has to be not to work. All I know is mine works & I have the satisfaction of having done it myself.
It cost me a few hours of time and $31 for the flywheel puller & the wire, & I’m running.
If you are having the same issues I had & this writing makes any sense to you, go for it. What do you have to lose? Look at the knowledge you’ll gain. Another big gun in your arsenal. Enjoy
