Magnet for engine

[Harold in CR]

Yeah, it's for the ignition on my Honda sawmill engine. How to identify a ceramic magnet from a Neodymium magnet ?? Mine is shattered in 2 pieces plus a hundred smaller pieces.

What I'm trying to deduce is, curved magnets are listed by outside and inside dimensions. I have no idea how to figure the radius. I just laid the cover piece of metal on a wooden bowl I turned, and, it nearly sits completely down on the 8" dia bowl, so, I'm thinking a 7 7/8 " radius would be very close. ?? I'm thinking a motor magnet might be just what I need ??

Even better is, this magnet is mounted on the OUTSIDE of the flywheel, so, IF I can find one, I will proceed to drill a center hole, and, if need be, cut it down to size, to fit the depression in the flywheel edge where it passes by the coils.

Reason I posted here is, There has been some random posting about guys reworking magnet sizes to fit their needs, if I need to go that route, any info on cutting magnets would be appreciated. There are none available in Costa Rica, from Honda ??????

ANY info would be greatly appreciated.

 

[spinningmagnets]

8" circle diameter is a 4" radius. If you get a curved magnet that is even close to the proper shape it should work fine. I'll bet the magnet is a common ferric magnet, I don't think there is really a need for a neo in that application. However, if you find a cheap curved neo in the correct size/shape, it also should work fine. I could be wrong, best of luck...

 

[Harold in CR]

Judging by the way it broke, I would think a ferric ? magnet would work fine. This one is pretty strong for it's size.

I typed in the wrong description I wanted regarding the curvature. Sometimes magnets are listed as ?? forming a circle, so, just under 8" will work perfectly.

Now, to just find such a critter.

 

[Thud]

I am with Spin, Good luck finding something to fit....but for future referance, heres a handy equation for calculating an unknown radius. (straight out if an old machineries handbook)

 

[Harold in CR]

Thanks Thud.

Question, I have 2 large pieces of this magnet. I also have some Hematite sand granules. I also have some damn good epoxy. I'm thinking about mixing some hematite into some epoxy and gluing this magnet back together ??? Small pieces keep flaking off as I handle the pieces. Epoxy will stop this. I also have a small piece of broken magnet here, that I could put between the broken pieces ???

Am I completely crazy ??

I would also stick it fast to the Cast Iron flywheel and the curved metal piece that holds, clamps the magnet to the flywheel. If I then pour some more epoxy around the magnet, it will encapsulate it in the depression of the flywheel.

Will the magnet work as I described, by adding the hematite to bridge the small gap ?? I KNOW I can repair it, but, will it affect the making of the spark for both coils ???

 

[Thud]

Other than time lost, I would think you have nothing to lose attempting the repair.
did the maoto take a hit to break the magnet in the 1st place? if it just flew aprart that would be a bad thing..(i assume its a governed engine running well below any max rpm level its capable of)

 

[Harold in CR]

Thud, the magnet sets over a brass pin that evidently screws into the flywheel. The head has a phillips cross in it, but, the head is worn off. That magnet must have been loose for quite a while. It simply decided to fly off, I reckon.

Us rednecks don't NEED no stinkin Chinese magnets. Just send me a shovel full of that rare dirt, and send in your order. I did the repair.

Here are some photos. First one is the broken pieces.



Next 2 are the ingredients.

View attachment 6

Hematite is magnetic sand, so, I mixed a LOT of it into the epoxy, trying to maintain the flux path of the magnet.

This epoxy says usable in cold or hot conditions

This one is showing the curve that is needed for the magnet to sit tight in the pocket of the flywheel.

View attachment 4

Next is the repaired magnet. Note the stick in the center. That was placed so I could have access to the center hole to grind it to fit over the pin.



Next is showing the curve as I have started cleaning up the excess Epoxy. It was a real experience to keep that hematite from crawling all over the whole magnet, until it finally started to set up.

View attachment 2

Next is showing how much was needed to make the repair. It is the part in the center area. Note the slight misalignment. It was a bear to hold the 2 opposing magnetic pieces together, while waiting for the epoxy to set. It still separated a little. This is why I used the Hematite for a filler.





After much sanding and grinding, I have the magnet and metal cover plate epoxied in place. Later tonight, I will go out (if it's not lightning and thundering), and flip the flywheel past the magnet. IF I get spark to the plugs, I will pour some epoxy all around the magnet, to try to secure it in place. I might need to adjust the coil laminations clearance. Then, I should be good to go ??

I need to brad the top of the pin, but, I COULD break the magnet, so, I will force epoxy into the hole around the pin, and hope that holds. I might even wrap a length of fine copper wire around the top of the pin, under the head, so it's larger than the hole, then try to brad it a little, as the wire is softer.

 

[John in CR]

If that doesn't work out, we may be able to make a magnet to size from a larger one. I was testing with a grinder today to see if I could round off the sharp corners of the magnets I'm going to use as choke cores, and none of the pieces broke. I used both a grinding disk and a lap disk. If you want, I'll see how drilling a hole works out.

 

[Harold in CR]

This one seems to have enough spark. The engine will run pretty nice at idle, but, it just blows black smoke at higher throttle. It never even tries to get up to speed, as I open the throttle a little at a time. I'm going to put in 2 new spark plugs and see what that does.

I tried to clean the carb, but, the jets are very hard to get to. Besides, someone has tried to remove them, before using pointed screwdrivers and cold chisels, looks like.

On the original magnet, it was damn near impossible to grind it down a tad thinner. Only shined it up. Cutting on the edges, to remove sharpness, resulted in tiny flakes being cut off.

If you can drill a hole, I would be interested in trying to make a new one. It will need just under an 8" diameter curve, to fit in the pocket.The hole is metric, around ¼", and, the magnet is ¼" thick.

Appreciate you trying to redneck a magnet for me, John. 8) 8) :lol: :lol:

EDIT: Whatever you do, DO NOT Use a regularly sharpened drill bit to try making a hole. I never tried to drill a magnet, but, IF you get a catch, it will probably break and throw chunks.

I used to drill thousands of holes in Plexiglas-Lexan. Sharpened the bit, then, ground straight down the cutting edge, to make a "Scraper" edge. Worked a treat. There are also glass drill bits. Might have to try one of those ??? They LOOK like scraper edges on those, also. They are a spade (flat) bit.

 

[Hillhater]

...The engine will run pretty nice at idle, but, it just blows black smoke at higher throttle. It never even tries to get up to speed

Yep, carb / mixture problems.... too rich off idle
Make sure the choke is not stuck on
Air cleaner ok ?
look for a mix adjuster screw
Remove, strip, clean and rebuild carb, fit new jets if they have been tampered with
If all else fails , try another carb off any other similar small motor !

 

[Harold in CR]

Choke manually held open.
Air cleaner off the engine.
No visible adjustment screws.
No other engines available.
Had carb apart. No significant amount of varnish or debris inside the carb.

Engine was running fine, then, POP POP POP and ran down to a stop with NO sound of trying to fire. That's probably when the magnet broke.

 

[Hillhater]

what model /size honda is this ?.. G, GX , GH, ??
What make /model carb ?.. Mikuni ?
holding the choke butterfly open may not be enough !
Is the float and needle valve function properly ?

 

[Harold in CR]

Engine ran, then died.

Metal cap on top of the magnet, flew off, knocking off the fuel line and small air tube for the rebreather. Magnet is still 905% good. Small pieces of the magnet or epoxy repair pulled off with the metal cap.

Honda does NOT sell the magnet. They sell the whole damn cast iron flywheel, but, no one has one in stock.

Question. Would this magnet be magnetized end to end or through the thickness ??? North on one end, South on the other, or North on the outside radius and South on the inside radius ???

It snapped down tight to the flywheel when I installed it ???

IF I try to remove it, it will go into a hundred pieces or more. ??? Suggestions ??? All motor magnets I find, online, are magnetized through the thickness, North on outside radius, South on inside radius.

Anybody got a good 10HP 240V single phase motor for sale ???

 

[salty9]

Did you try drilling the flywheel so as to form a undercut dovetail like recess and potting the magnet in with epoxy? I know this is a Rube Goldberg solution but it seems like most of my repairs are like this.

 

[Harold in CR]

No room to maneuver to cut into the flywheel with any hand held machine. The magnet is still epoxied into the recess. It's the metal cap that didn't stay bonded with the epoxy.

The Pin that is supposed to hold this stuff tight, is brass, and I didn't want to chance breaking it off, the first time around.

I smeared epoxy all around and under the steel cap piece, then shoved it down into the epoxy and wiped off excess that oozed out of the hole, around the pin head. Hoped it would form a "Rivet" type head. Wasn't strong enough.

I need to see about brazing it, but, I will bet it will ruin the epoxy bond that I already have.

Only hope was to find a magnet that I could adapt, break off that pin along with the old magnet, and go from there.

NO MAGNET that I can find. An arched motor magnet could be modded, BUT, that's why I asked about the magnet poles. When I epoxied the 2 larger pieces together, they were opposing each other. I just can't get my brain to function and figure out if they are outside-inside or end to end charged ???

 

[liveforphysics]

That magnet is a little ceramic ferrite POS crap magnet.

Simply find the largest Neo magnet that you can glue into that area and still have it physically clear the magneto. It doesn't matter if it's only 1/5th the size or whatever. It's still going to perform better.

 

[fechter]

It is most likely a ferrite magnet. Neo magnets generally can't survive the heat. If you try a Neo magnet, it needs to be the highest temperature rated type.

When a magnet breaks, the pieces will repel each other, so it's hard to hold them in place to glue them together.
Most likely the magnet is magnetized through the thickness.

It may be possible to make a replacement from several bar shaped pieces tiled together. Again, this is difficult as the pieces will repel each other and try to flip over.

If the magnet is not strong enough, it may not be generating enough voltage. The voltage required to fire a spark plug increases with cylinder pressure (throttle), so if it runs at idle but not with throttle, this could explain things.

 

[Harold in CR]

Thanks guys. This broken-glued together magnet DID run the engine, until speed threw the metal cap off. Unless John knows of a supply that has magnets, I will have to find something online and have it mailed down.

Thanks for that Magnet information. First time I ever saw one pinned on the outside of the flywheel ??? Now, I have a much better idea of what I can use.

Really appreciate the advice. 8)

 

[fechter]

Epoxy generally isn't very strong when it gets hot. They do make high temperature versions.

You might be able to use a pair of smaller bar magnets on either side of the hole, then use the hole to hold a plate on top of the magnets to keep them from flying off. The combination of epoxy and a plate should hold them.
If you use high temp Neodymium magnets or Cobalt-Samarium ones, they could be a lot thinner than the original magnet and still have plenty of power. This would allow flat bars to fit within the radius of the opening.

How about a picture of the flywheel where the magnet goes?

 

[salty9]

I have an old generator that is going to have to be scrapped. I'll check the size of the magnet and get back to you.

 

[Harold in CR]

About to go get a photo or 3 and, it started pouring and lightning. BYE.