Flywheel with broken magnets.

Joined
Jan 6, 2011
Messages
24
Location
Eastern Massachusetts
On the first start this summer the engine started fine but would

not come up to speed in the usual way with warm up. It stopped and

would only click versus crank. The flywheel was locked. That

turned out to be loose magnets under the flywheel.

I found two pieces of a magnet inside. A pushed a little on an

attached magnet and it fell off. Then another fell off. I moved

more and found I could lift them a little as the glue soft. Maybe

it softened up over the years. ??

All the magnets are loose and can be lifted.

To repair it it seems I would have to remove all the magnets

and epoxy them in. I use the riding more only for pulling a

small trailer but no mowing so not used much but very handy.

I’d like to have it available but not sure if gluing the magnets

will be worthwhile.

I have some questions about this.

Are the magnets only for lights and recharging the battery?

Can I just charge the battery and run the flywheel with no

magnets? With a decent batter that is charged about how many

starts would I get?



One If I cleaned up the flywheel well I could reglue them. I think

there are 13 magnets. There are some location lines where the

magnets go. My guess is where they go does not have to be

exact but just center each on the two lines.



Two There are 11 complete magnets and two damaged. One of the

damaged ones has a chip broken off and I think that would not

matter. The other is broken. It is in two pieces of about 2/5ths

and 3/5ths. They don’t match as I think one got chipped where

it fit to the other so I would just clue in the 3/5ths one. I think

that would be ok and not cause a problem.



Three Is this a doable task doing so many? I know people

glue magnets back in. Would regluing all 13 work? What

are the issues I could run into?





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Clean everything up carefully, and use REGULAR JB weld along with some form of gentle clamp (plastic) and/or positioning device (maybe wood) to hold them in place. The broken magnet can also be put back in place. That one won't be ideal, but it will work just fine. You could try to carefully epoxy that one back together first before installing. The magnetic flux lines on the broken magnet will be slightly distorted as there will be some leakage at the break. But for this application it really won't matter one bit. It's better in place than not.

Some engines do run the ignition timing off of the magnet position, so position may be critical. Do you see some form of pickup? If so, make sure to put them back in proper positions. Mark a line for position before cleaning.

JB quick will work too, but for some reason, seems to last only about 5 years before magnets come loose again.
 
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I simply thought I'd add that if you epoxy the magnets on top of rust, you will not get many years of service. If it's clean, and treated, it will last forever using JB weld.

Yes, I am aware that JB weld is slightly ferrous, and it will ever so slightly affect the magnet. So what? It's on the order of a fraction of a percent. JB weld is truly an excellent epoxy and worlds better than most other available products, with the exception of aerospace structural epoxies, which can just match JB's tensile strength and thermal characteristics. It's that good.

Just another hint, slow-cure JB weld is regularly used to repair race motorcycle flywheel magnets.
 
I like JB and have plenty.
There are lines between all magnets that were molded when the cast was made so I can just center
them to the lines. Height wise I can just place them as they were. It will just be the pain of cleaning
the thing very well.
On the timing part. It looks like the stock setup with an outside coil triggered by a magnet on the
outside face of the flywheel. There are no ID marks on the engine but I think it is the stock motor that
came with the Husqvarna L111. I could not find the exact docs for the machine or engine but do have
the close models docs. I'll look at the electrical diagram and see if I can spot how the spark happens.
So you did not mention any snags with gluing the magnets back in so I'll likely give it a shot. I'm
at a summer place in Maine so will take it back to Mass where I have solvents, metal brushes, and
etc to deal with it.
Thank you for the infomation.
 
Good luck! There really are no difficult snags when gluing on magnets. You may need to use wood to space them apart, as they can migrate when the epoxy is soft. It should be easy enough to make wood pieces of the proper size. Don't worry too much if some of the wood gets glued in place. Just use care to remove the excess.

I found a youtube video.

 
Does the polarity (orientation of each magnet's poles) of the magnets matter? Looks like the magnets could be epoxied to the flywheel in one of two orientations.
 
Best to replace the flywheel. I wouldn't trust an epoxy job on anything spinning that fast.
 
Best to replace the flywheel. I wouldn't trust an epoxy job on anything spinning that fast.
That's the thing. The glues and epoxies used in production are generally of lesser quality and lower bond strength than JB Weld. Take a close look at the specifications of aerospace grade epoxies. Very few are better than JB. I know it sounds silly to think that a consumer level product is that good. The steel and aluminum adhesion strength remains over 1000PSI, even at elevated temperatures over time!

I noted above that JB Weld is used on racebike flywheels. There is a reason for this. Quite often the higher RPM, torsional crankshaft flex and relentless shifting loosen stock magnets and result in a DNF. For decades now, the reliable solution has been to rework the magnets with JB Weld.
 
Does the polarity (orientation of each magnet's poles) of the magnets matter? Looks like the magnets could be epoxied to the flywheel in one of two orientations.
Yes, sorry forgot to mention that. It's easy to put them in order by sticking them together in a ring prior to installation. N-S-N-S etc.
 
Yes the polarity of the magnets matters. Use a separate magnet for testing, marking one end of the test magnet. You will find that some of the magnets attract that end of your test magnet and some repel it. You need to figure out the scheme used from the magnets still attached and put the others back in places that match.

I'm guessing this is a Kohler engine because I had that happen as well. That engine had 6 large magnets.

The magnets and coil inside the flywheel is the alternator. The ignition coil(s) will be on the outside and have a separate magnet. If it's a mechanical blade clutch you can run without the alternator and charge the battery when done. Electric blade clutches require quite a bit of power and would probably run the battery down during the course of a mowing session.
 
Yes, sorry forgot to mention that. It's easy to put them in order by sticking them together in a ring prior to installation. N-S-N-S etc.
Believe it or not there is an app for identifying magnet poles. At least for iphones. "KJ Pole ID" is free and will tell you which end is North or South.
 
Believe it or not there is an app for identifying magnet poles. At least for iphones. "KJ Pole ID" is free and will tell you which end is North or South.
KJ Pole was iphone only but I found others for android and they work. I also found that by using a magnet you can go around
the flywheel magnets and feel the push or pull of each to see the north and south pattern.
 
A few of the magnets fell of when touched and most of the rest

loose as the glue had softened over the years. The glue behind

the magnets was very hard and well stuck to the flywheel but

the bond to the magnets very weak.



I pulled off all but two magnets and reglued them. The gluing

part was easy. The cleaning part was time consuming. The inside

walls had to be scraped to remove rust and hardened clue. The

magnets had to be cleaned constantly as they kept attracting

small metal particles and screwed up fitting to the flywheel wall.



The flywheel glue job looks ok but I realized that the stator

part may be hosed. I think the chances of success are slim.

I’ll likely lose charging. I can use the riding mower without

charging by keeping the battery on a trickle charger. It is

an old spare machine I use with a trailer and never mow with

it.
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Yes that stator looks torn up. If it doesn't have continuity (less than 1 ohm) between the two wires, or there is a short to ground, it is not going to work at all.

It is completely viable to charge the battery off-line for uses other than mowing. Once started, the engine does not require the battery to keep running (unless there is a fuel solenoid, which would need a small amount of electricity) so if you're not using the blade clutch it will stay charged for a long time.
 
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