Help Suzuki GSXR 250 (GJ72A) Flywheel

Hello,

I'm in the process of rebuilding a Suzuki GSXR 250. I have found the flywheel to be damaged...

Three of the magnets are broken in multiple pieces. I tried to find a new unit, but it seems to be no longer available.

Therefore I'm reaching out to see if anyone here have a unit laying around. It does not matter if it suffered the same fate as my own, maybe i can use the parts to rebuild a new one.

If anyone knows of other flywheels that fits the GJ72A engine, I'm very interested to hear from you.

The inside diameter of the flywheel is 111mm. Outside is 117,5mm & the circle the magnets create is 94,4mm.

 

I tried all sites that even mentioned 31402-05C00, but no one is selling it... I even reached out to some Japanese sites to see if they could get hold of the part, but to no avail..

I ended up doing it myself.. Hold on, this will be a long one..

I found out the a Suzuki GS 500 E flywheel, had the same overall dimensions (ID & OD) as the GJ72A flywheel. I hoped this meant that the magnets would be the same size. I ordered a second had flywheel for the GS 500E to investigate.

When i got the flywheel, I put it on the gas grill (at low heat) to loosen up the old glue. 3 of the 6 magnets were broken, probably due to old age.. I needed 3 magnets for my own flywheel, so i pressed on.

When i removed the magnets i found that the magnets ID, OD & thickness & length were a match for my flywheel. The only issue was the hight.... They were too high.

After some thought, I thought to myself; 'what do I have to loose?'. i measured up a cutline on the magnets with the GJ72A's magnets as reference & found the anglegrinder.

I managed to cut the magnets to the shape of the original magnets (Make sure to take your time & let the magnets cool in between cuts so they do not overheat & loose their magnetism) if you rush it you will breake the magnets - I tested on broken ones first.
Next up were to measure the weight of the magnets to make sure that they would balance OK in the rebuild flywheel. I used the kitchen scale to measure the original magnets & the 'new' magnets (i used a plastic cup to raise the magnets from the scale, so the magnetism would not interfere with the scale).

Then i used the angle grinder to grind away slowly the magnets, until they weight the same as the original magnets. Original magnets weigh 48g.

Next up i needed to know the spacing of the magnets in the flywheel. Since all the original magnets were loose, i did not know the original spacing. I used my printer & placed an original magnet on the scanner, with a ruler as this would give me a reference. I used the scanner as it does not distort the image the same way a camera does.

With this image, i loaded the scan into my 3D modeling software. This way i could find how many degrees one magnet would occupy in the flywheel. From this information i calculated that for 6 magnets & a internal diameter of the flywheel of 111mm the spacing would be 5,13mm.

I then proceeded to 3D print 6 spacers that were 5,13mm. See picture below for reference.

Now that i had the spacing, I rough up the flywheel surface with some sandpapir & cleaned the flywheel with acetone. I was now ready to glue the magnets.

I found some industrial grade epoxy that was meant for gluing magnets. I glued this with the spacers in place & applied pressure with a clamp until the epoxy was cured.

As a preventative measure, I used some epoxy putty inbetween the magnets to make sure that they would stay put. I sanded the putty to make it level with the magnets surface.

I let it cure for some days & assembled the bike. The bike started on right up & there were no noises or vibrations. I tested that it was charging the battery. I saw 14V & climbing, so i was happy!!

My concern is that any imbalance in the flywheel may rip the engine apart over time. But then again, otherwise I had a two wheeled paper weight on my hand..

Now it runs & there is no noticable vibrations even at 16000rpm. I could not be happier!