# Tecumseh HM80 Flywheel Key Sheared



## MrChooks (Apr 19, 2008)

I need to remove the flywheel from my Tecumseh HM80 as the key has sheared.

I tried to budge the flywheel with a small gear puller - but being too small - the puller broke without shifting the flywheel at all.:banghead:

The key is a 1/2 moon Woodruff key & I can see the broken key inside the keyway.

Given that the Woodruff key has sheared and is now fowling the crank / flywheel join - I expect that it is going to need a lot of force the free the flywheel / jammed sheared key free from the crank

I have a 8" 3-jaw gear puller on order and propose to torque that up and gently tap on the puller's center bolt then torque up again and repeat the exercise until the flywheel comes free.

Given how tight the flywheel is & I don't want to break the flywheel - does anybody out there have any alternative suggestions / tips or "old war stories" on how they removed a jammed on flywheel?

P/S Hey Basementgeek - any thoughts / suggestions


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## Basementgeek (Feb 7, 2005)

Cast iron correct? HM should be. 

Put your puller on it, tighten it up then use a propane torch around the center, try not to heat the shaft.

If it had holes (3) in the fly wheel I would have used a different puller. I use a puller that is made for cars.

Good seeing you after 2 years.

BG


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## MrChooks (Apr 19, 2008)

Tks BG - I knew you would have some usefull tips. 

Yes - it's a cast iron flywheel and it doesn't have any drilled puller holes - so I can't see I have any choice but to have a go with a 3-jaw puller and hope & pray the rotten thing comes free. 

As I no longer have my oxy/acetylene kit - do you think that I could heat up the flywheel with my electric paint stripper gun - it's sorta like a giant hair dryer on steriods!

& Yes - I've been a bit busy for a while - surgery on both hands is a total PiA  but sutures are out and the casts are off - but am still a bit tender in the palms which doesn't help with this SoB Tecumseh problem


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## Basementgeek (Feb 7, 2005)

I don't think heat gun would do it, the time it took the flywheel to get fairly hot, the shaft would be hot too. The idea is to get the flywheel hot to expand but keeping the shaft cool.

I would pick up a propane torch.

Glad you are on the mend.

BG


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## MrChooks (Apr 19, 2008)

Tks BG - will let you know how I get on with this rotten flywheel


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## Basementgeek (Feb 7, 2005)

Don't over heat it, remember you have to keep the shaft from heating up to much.

BG


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## MrChooks (Apr 19, 2008)

Tks BG - Promise I will be "kind & gentle" with the "flywheel cook up". 

Am still waiting for the 3-jaw puller to arrive - hope to get the puller by the week end and get on with the job and get this damned thing going before Monday when I go back to see "Dr Chop" again :frown:


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## Wrench97 (May 10, 2008)

When you get the puller on and tightened up tap on the top of the center bolt with a brass hammer while turning with a wrench sometimes the shock of the hammer blow will jar it loose.


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## k2skier (Sep 30, 2008)

Use a dead blow, rubber hammer, 2lbs or 1kilogram, hit perpendicular to the crank. The other method would be nut flush on end of crank and hit on nut with metal hammer with 2 pry bars behind flywhell. I have seen may broken flywheels using a jaw type puller. Always use lapping compond to seat the crank and flywheel together, cleaning it like a surgen hwen done.


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## MrChooks (Apr 19, 2008)

Tks Guys - all great thoughts.

My original plan was to follow Wrench97's plan - as I hadn't thought about K2S's suggestion of hitting the flywheel with a "soft" hammer pependicular to the shaft - so great thoughts guys & think I will ty a "combo" of both.

K2S - I can't get pry bars behind the flywheel and apply sufficient force without distorting a light metal backing plate located between the block and flywheel - hence my initial attempt with the (now broken:angry small 2-jaw puller. 

So I think I will have to use the 3-jaw puller - but if I tension up the centre bolt then tap the centre bolt with a small steel hammer as well as giving the flywheel outer perimeter a few blows with a soft hammer before further tensioning the puller's centre bolt - I am hoping to be able to "tease" this rotten thing off by simply repeating the cycle and being patient with it - (not so easy for an old "rip n tear merchant" like me - but I will try to be good)


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## Basementgeek (Feb 7, 2005)

You can be firm, but be gentle. Don't over do it. Here is an example of what the wrong puller can do. I sort of did on purpose the engine was trashed anyway:

BG


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## MrChooks (Apr 19, 2008)

EEEkkk :hide: I can see how that would happen with a perimeter puller on a light die cast flywheel - but am hopefull that as mine is a "bloody great lump" of cast iron - the 3 jaw puller + judicious application of heat + some light taps with a steel hammer on the tensionsed puller's centre bolt + as suggested by K2S, a few solidish blows with a soft hammer on the flywheel perimeter I will be able to tease this rotten thing off.

Of course if Tecumseh had simply provided a few threaded puller holes around the inner of the flywheel - all this would have been a "no-brainer" - BUT they didn't:banghead:


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## Basementgeek (Feb 7, 2005)

No holes are cheaper, maybe that is why Tecumseh went out of business a couple of years ago. 

If it does not "Pop" for you, leave it set over night with some pressure on it, maybe use some penetrating oil in the center. 

BG


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## MrChooks (Apr 19, 2008)

Tks BG - a good plan to tension up and leave the flywheel for a while to "think about coming free" then repeat if nothing has happenned. 

It will tax my natural impatience - but I will just have to be good else I can see this all ending in tears


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## Wrench97 (May 10, 2008)

A propane torch may also loosen it just enough.


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## MrChooks (Apr 19, 2008)

Tks Wrench - yes a judicious application of gentle heat on the inner boss area of the flywheel is part of the plan - now just waiting for the mailman to turn up with my new 8" 3-jaw puller - seems this whole task was designed to stretch my "natural impatience" to its absolute limits!!


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## k2skier (Sep 30, 2008)

Duh, I forgot about these, used them quite regularly. Knockers for 5/8 thread. You dont need a lot of pry behind the flywheel and the tin will straighten easy, breaking the flywheel with a jaw puller will be ugly. The aluminum flywheels would always break before a properly seated flywheel will come loose. 2 pry bars and a knocker and your set.

Warning, if this has points behind the flywheel I would caution the use of heat, tho I do love heat for breaking things loose, I dont mess around and go straight to oxy/acetylene!


Tecumseh Flywheel Puller Knocker 5/8" Thread Brigg 670314 *New* | eBay


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## MrChooks (Apr 19, 2008)

K2S -are those "knockers" just a long nut to protect the crank thread - if so, I could turn one up from a lump of hex bar I have in my workshop.

Fortunately, my flywheel is a big lump of cast iron so a bit stronger than those light die cast jobs and the ignition is a solid state unit mounted on the outside of the flywheel - so easy to remove so it wont get "hurt"

Agree about the oxy/acetylene - only problem is I turned in my bottles about 2 weeks ago - got sick of paying the $300 / year bottle rent when I hardly ever used it. - Ain't it the way - the minute you get rid of something - you find you need it big time


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## k2skier (Sep 30, 2008)

Yes, doesn't matter what the stock you use is, just something to get a wrench on. You srcewed it on all the way and backed it off about 1 full turn. No bending or damaging the crank. Just another idea to try. Approx 2" (5cm) long.


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## MrChooks (Apr 19, 2008)

Tks K2S - it's worth a try - I think I am going to need every trick in the book for this one


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## SABL (Jul 4, 2008)

How far out of line is the keyway?? Is there any way to use a piece of wood and tap the flywheel back towards proper alignment?? Maybe a 1" X 1" x 8"-10" piece of hardwood and a decent size hammer can relieve some of the extra bind caused by the sheared key. If you can catch a solid point on the outer portion of the flywheel to place the wooden 'punch' against and give it a few good hits (opposite the direction of shear), it may persuade the parts to line back up for easier pulling. Just a thought.....but I've done it before.


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## MrChooks (Apr 19, 2008)

OK everybody - its off & many thanks for all your help and suggestions

K2S - I turned up a knock-off tool and tapped it @ 7/16 UNF - Did wot you said and the flywheel came loose on the 3rd wrap with a hammer. - Tks for the tip

So now I have a brand new 8" 3-jaw puller on its way in the mail - but no work for it :facepalm:

For those interested - the woodruff key was sheared completely through - needed a pin punch to extract the remanant from within the crankshaft slot.

Will shoot over to the mower shop this afternoon to see if they have a replacement woodruff key.


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## Basementgeek (Feb 7, 2005)

Don't forget to torque the nut down.

BG


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## MrChooks (Apr 19, 2008)

:dance: All is back together and running fine & many thanks to all those who provided such helpful advise - we can mark this one as "Solved"

It took longer to put the throttle / governor linkages back than it did to fit the new key and re-assemble the engine. I took BG's sticky tip and had photos of the linkage set up, but this rotten thing has a small helical spring that operates against the governor to set throttle position - and it didn't show up on my photos, so I had 3 goes at getting that bit right. Next time I am going to tape up all connections in their respective positions before I remove the throttle control assembly.

I will compile list of all the steps and tips I took from flywheel removal to job completion, as the info & tips might be helpfull to others with a sheared flywheel problem. 

Maybe BG, K2S, Wrench or SABL can edit and post as a sticky - coz I don't know how to do that


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## MrChooks (Apr 19, 2008)

OK - BG, K2S, Wrench & SABL - As I mentioned in my earlier post & in case these steps might help others - Here is a distillation of all the very welcome tips and advice I received from you all of what I did once I got the flywheel free.


1 Recover the broken piece of woodruff key from the flywheel and set aside
2 Using a pin punch with slightly smaller diameter than the key thickness – tap out the remaining sheared off piece of woodruff key from crankshaft. Don’t use a screwdriver or cold chisel as it is very important that the woodruff keyways are clear, burr free and undamaged
3 Fit the 2 broken pieces of key back together the correct way round and stick them down on to a piece of sticky tape – this allows you to take the broken key and flywheel to the mower shop to get an exact replacement key – (They are so cheap I bought 2 – so I would have a spare)
4 The woodruff key is a slight interference fit in the crankshaft and a sliding fit in the flywheel keyway, so the keyways need to be perfectly clear and clean before installing a new key – Using a small, sharp flat needle file – carefully dress any burs and broken key remnants from edges of the crankshaft keyway and make sure that the new key will slide nicely along the flywheel keyway.
5. As the crankshaft / flywheel woodruff key is positive and accurate locating devise and *NOT a power transmission devise *– it is critical that the taper fit between the crankshaft and flywheel is as near perfect as possible. 
So, this is probably the most important step in the process. Using #1 cut / coarse lapping compound, lap the taper of the flywheel and crankshaft together until they are clean and without any ridges whatsoever. If there are a few minor gouge marks from the damaged key moving on the taper that’s not a concern – it’s the ridges that must be completely removed to ensure a tight taper fit.
6. Thoroughly wash all the remnant grinding compound from the tapers on crank and inside the flywheel with diesel or kerosene and use an old toothbrush to scrub away all remaining grinding compound until it is spotlessly clean & dry.
7. A very fine film of grease or “Neversieze” applied to the new woodruff key makes it easier to install and remove if it needs replacing again at some point in the future. The important point is that no grease or Neverseize finds its way onto the taper fit – as you need a tight interference fit between the male and female tapers and any lubricant on the tapers can allow the shaft to slip and the key will shear all over again.
8. Using a small hammer – tap the new key carefully into position in its keyway ensuring that it is all the way home and centered in its half moon cut keyway.
9. If the new woodruff key is properly home in its place on the crnkshaft – the flywheel will slide easily back onto the crankshaft and slide virtually all the way home without any force. Once in place, pull the flywheel home using its retaining nut and just nip up to tight then remove the retaining nut again and inspect the final position of the flywheel to ensure that it has engaged the crankshaft taper over its full length.
10. Once satisfied the flywheel is fully home, reinstall the retaining nut, lock washers etc and torque up tight and it’s all done- now you just have to put all the cowls, linkages and fuel lines back and job’s finished.


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## k2skier (Sep 30, 2008)

success without breakage=happiness!


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## MrChooks (Apr 19, 2008)

Yes & I owe it all to the help I received from my TSF colleagues. - Tks again

What's more, the engine is running better than it had for years, which I put down to a now accurate ignition timing.

My 1" diameter crankshaft only needed to deform the woodruff key by about 3/64" or 1mm to throw the timing out of manufacturers spec by over 4 degrees

No wonder it seemed to have a bit of a knock in it - as the key gradually failed I assume the ignition timing was gradually advancing beyond specs - until it finally sheared and the flywheel moved a full key thickness resulting in about 13+ degrees advance in ignition timing - so little wonder it wouldn't start and kicked back like an angry bull.


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