Elusive 32517 Tecumseh flywheel dilemma HS50 looks like HS40


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As i've posted many times, i'm not a huge fan of HS40. Instead i like the HS50 on my 1970s minibikes, and just make the HS50 look like an HS40 ("the look conversion".) There's a variety of reasons i like the HS50 better. One, the HS50 is just more readily available. Two, it offers more horsepower (we're not 10 year kids any more!) Three, parts are easier to get. Really the only downside to the HS50 is "the look" (it always had the more squared top blower housing) and the flywheel (typically big and cast iron.)

To get around these two issues, I generally look for the HS50 in the "A", "B", or "C" models. That is the HS50 from 1972 to 1979. In 1980, starting with the "D" variation of the HS50, the flywheel taper was changed. So the crankshaft and the flywheel are a bit different. Luckily where i live (midwest) there's an abundance of 1970s snowblowers with the HS50 available for often pretty cheap. I tend to buy these up.

To get "the look" (that is the look of an 1970-1972 HS40), the blower housing needs to be the rounded top variety. These were used from 1968 to 1972 on the HS40, and actually other models too (H30 and H35, among others.) Again i buy these when i see them at minibike swap meets, they are generally fairly priced (and usually missing the serial number tag, which to me, is not important, and in fact beneficial, because the price is lower.)

blower housing comparison, square vs round: http://www.pinrepair.com/minibikes/p/snowblow62.jpg

Unfortunately you can't just bolt the slimmer rounded blower housing on an HS50. It won't fit, because the HS50 flywheel is thicker. A lot thicker. But with the HS50 models A/B/C you can use a 32517 alloy flywheel (the flywheel used on non-lighted HS40 engines prior to 1973.) It will fit right on the HS50 models A/B/C. And it gives a lot of benefits. Because the 32517 flywheel is lighter in weight than the cast iron monster (or even a 1972-1974 alloy HS50 flywheel), the engine will get to high RPM faster than a cast iron flywheel equipped engine. AND with the 32517 flywheel (and proper starter cup), the H30/H35/HS40 rounded blower housing will fit right on the HS50. This give the HS40 "look", with the added performance benefits! it's a huge win all around.

Cast iron HS50 flywheel vs the 32517 alloy flywheel: http://www.pinrepair.com/minibikes/p/snowblow63.jpg

But here's the dilemma... the 32517 flywheel is very elusive today. and generally pretty expensive. but there are other flywheels used on the H30/H35 that are abundant. for example #31332 (H35) and #1267 and #610781 and #610757 (H30.) These are alloy flywheels with magnet positions identical to the 32517 flywheel. Unfortunately, the taper used on the h30/h35 crankshaft is different than the HS40/HS50 crankshaft. So you can't just put one of these h30/h35 flywheel on an HS40 or HS50 engine.

With this in mind, i bought a 610757 alloy flywheel off ebay. Not an ideal flywheel, as it has teeth for an electric start, and it's for an h30 engine. But the core (the part that touches the crankshaft) is aluminum (the 32517 and 31332 have steel cores, which is ideal, more on that in a second.) I figured out the taper used on the HS40/HS50 pre-1980 flywheel, and cut this into the alloy 610757 flywheel. Also re-cut the keyway groove, and remove the outside starter ring teeth from the flywheel on the lathe.

So what did i end up with? a SUPER light weight alloy flywheel "on the cheap" that would fit an HS40/HS50 engine. This flywheel is featherweight, like nearly half the weight of the 32517 flywheel. Unfortunately it has an alloy core, which may not be ideal for longevity. But as an experiment, this flywheel was ideal. AND IT RAN. used an HS40 that i bought today at the minibike swap meet for $50 as the test engine (and set its original 32517 flywheel aside.) And the modified flywheel fired the hs40 engine without issue!

the 32517 vs the modified 610757 flywheel, mounted on an HS40: http://www.pinrepair.com/minibikes/p/tec_flywheelconvert1.jpg

with this in mind, i modified a 31332 flywheel in the same manner (these have a steel core, like the 32517.) And a 1267 flywheel too. so now i have a pile of allow flywheels i can used on the HS50 models A/B/C. Obviously i need to test more, but this looks like a good solution to the elusive 32517 flywheel problem.

The early 1970s HS40 engine with the modified alloy h30 flywheel: http://www.pinrepair.com/minibikes/p/tec_flywheelconvert2.jpg

Next up... modify the h30/h35 alloy flywheels to work on "D" and "E" model HS50 with the changed taper, This would be great to have more HS50 engines i can convert to an alloy flywheel and the rounded blower housing. Could also use that style of flywheel on the "F" and "G" HS50, but those are CDI, so would need a points/condenser magneto to do so. Probably can't go later than "G" model HS50's as there may not be mounts for a magneto on those blocks (not sure about that.) Note modifying the old h30/h35 alloy flywheel to fit on the newer taper 1980 and later HS50 crankshaft may not be possible, because of a lack of flywheel material. I will investigate this and give it a try though.

Comments or ideas?
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The question for me is- I have a late taper CDI engine that has a 12v electric starter and also a lighting/charging coil.
Pretty sweet setup but has cast iron flywheel and i'm afraid of revving it too high.
I'm guessing tecumseh never made an aluminum flywheel for that application?
If anyone would know, i'm guessing you would know.
Thanks and i hope this isn't too off topic.


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Mass, that's why i'm working on modifying the h30/h35 alloy flywheels to run on the HS50 "D" and "E" series engines, cutting the flywheel taper to fit their more shallow taper crankshaft. Still working on that, so i don't have more details. If i can get this to work, then essentially any 1980 or later HS50 engine could have a nice alloy flywheel (providing it has the mounts for points/condenser magneto) and the cool rounded blower housing.


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I’d like to use these on the 76 HS50 I put on that 73 Rupp. It's a 31332 flywheel. The HS50 has a billet rod and no governor. Maybe wind up a little faster and give it that vintage look. Let me know when you're open for business. IMG_4994.jpeg IMG_4995.jpeg
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Well-Known Member
More information on this...

i used an H35/H30 tecumseh 31332 flywheel and a "D" series 1982 tecumseh HS50 motor. And re-cut the taper on the 31332 flywheel to 10 degrees. Remember pre-1980 hs50 engines series A,B,C used 16 degree flywheel taper with a 7/16-20 flywheel nut. But with D/E series hs50 engines Tecumseh changed the flywheel taper to 10 degrees and used a 1/2-20 nut to secure the flywheel.

Re-cut the 31332 flywheel taper to 10 degrees on the lathe, as you would find on a 1980 to 1985ish D and E series HS50 crankshaft. This would allow running these later HS50 engines with a much lighter weight alloy flywheel. Note after 1975 tecumseh stopped using alloy flywheels on the HS50, and most other engine models too. Prior to 1973 tecumseh used the 32517 flywheel on the HS40. This is a really nice flywheel for used on the model A/B/C hs50, as it's much lighter weight than the cast iron monsters. which translates to faster RPM spin up acceleration. But no alloy flywheel will fit on the 1980 to 1985ish points hs50 engines. None as in zero. So these engines are locked into a cast iron flywheel. Hence the idea to re-purpose a 31332 flywheel and re-cut it to 10 degrees, for use on the hs50 models D and E.

However this 10 degree modification is a bit more tricky than the flywheel 31332 change to a 16 degree taper (as i described above in the first post.) With the 16 degree re-cut of the 31332, there was no need to touch the flywheel key. It's already deep enough to accommodate the standard flywheel key. But with the 10 degree cut, the key is too tall. so the flywheel key has to be shaved down just a bit to get the 10 degree allow flywheel to fit on the crankshaft with the flywheel key. Not a big deal, but something to think about.

Next issue is the low profile flywheel starter cup #590416 (which is used with the rounded blower housing.) The original cast iron starter cup can't be used if you want that "rounded" pre-1973 blower housing look. Luckily the 590416 cup is readily available and cheap. but it's designed with a 7/16" center hole, and to fit on the 10 degree crank, that hole must be enlarged to 1/2". The problem is this cup is hardened, and does not drill well. I ended up using my lathe to cut the hole bigger to 1/2". But you could also used a die grinder i expect.

Now my HS50 engine from 1982 series D with a crankshaft cut to 10 degrees for the flywheel is ready to test... and MAN it fires right up in a huge roar! Success.

HS50 from 1982 "D" series with re-cut 31332 flywheel to 10 degrees: http://www.pinrepair.com/minibikes/p/tec_flywheelconvert3.jpg

HS50 from 1982 "D" series with rounded blower housing installed: http://www.pinrepair.com/minibikes/p/tec_flywheelconvert4.jpg

HS50 from 1982 "D" series with rounded blower housing, side angle: http://www.pinrepair.com/minibikes/p/tec_flywheelconvert5.jpg

I would also like to mention i tried this 10 degree flywheel re-cut on the 610757 and 32159 flywheels, mounted on the 1982 "D" series hs50. In this case, the engine would *not* run. it wanted to run, but you could feel the feedback on the pull start, like the timing was off, and ignition was way too early (or late.) I re-checked the point gap and timing on the engine, and it was perfect. Add to that the 31332 flywheel ran *great* on this engine. I'm not sure why these two other flywheels did not work (time right)... i would like to know... Especially since those two flywheels worked on the A/B/C series HS50 with 16 degree taper. Scratching my head on this one...
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That looks great! Amazing job!
I wonder if changing the taper changed the magnet location slightly where the magneto picks them up?
I believe that the 10 degree taper is slightly longer VS the 16 degree taper being slightly shorter?
Just spitballing here man, looking for ideas.
But that is great, wish i had a lathe to do awesome experiments!


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i get what you're saying. it *tries* to run with those other two flywheels. it spuders, but you get that back pull on the pull start like the timing is way off, like the engine is premature firing and kicking the pull start back at you. it's that feeling you get on the pull start like the flywheel sheared the key, and the flywheel shifted, changing the timing. but it has full spark with those two flywheels, but it just won't run. it's kicks serious butt with the 31332 flywheel though!


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did you set the timing at .035btdc maybe try .065 or visy versa. i keep thinking if the points open at .035btdc it's going to be timed right
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