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post #1 of 47 Old 03-04-2016, 05:04 PM Thread Starter
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kick back when starting

I've just got an HM80-155128E back together. When I tried to pull started it the engine kicked back and yanked very hard on my arm. I got it started and it runs ok but most of the time I that tried restarting it would kick back and really yank. I 'm thinking it fires at the wrong time. I've have had the flywheel off to clean and paint the rusted blower housing baffle and then torqued it back on and the key seemed fine , although I didn't examine it that closely. It seemed to line up ok but I now wondering if it was loose. History of the main repair is that it was given to me by a friend who told me that it had just stopped. When I took it apart there was small screw from the throttle plate that had got sucked up and bounced around on top of the piston and even bent the exhaust valve.

Unless someone can give be me more of a solution I thinking I need to take the flywheel off again and check the key/keyway as a starting point?

Thanks for any input
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post #2 of 47 Old 03-04-2016, 05:26 PM
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That kind of kick back often points to a flywheel key that's sheared resulting in overly-advanced spark timing.

It can also point to excessive carbon in the combustion chamber. If this happens when the engine is hot it might mean that some of this carbon is glowing hot enough to ignite the charge early (preignition); this can also produce a nasty kick.

I'd start by re-checking (and replacing) the flywheel key.
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post #3 of 47 Old 03-04-2016, 05:57 PM
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Another vote for checking the flywheel key.

When you reinstalled the flywheel, did you use a torque wrench to tighten the flywheel nut? If the nut is too loose, you can shear the flywheel key, since the flywheel is largely held in proper alignment by friction against the crankshaft.

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post #4 of 47 Old 03-04-2016, 06:09 PM
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When you figure it out, please post; because I have an HM100 doing the same thing. I have not got back into it deeply, yet, because I need it to move snow with it....but I used a torque wrench; that much I know. Once it starts, it runs great. But it will kick back a good number of times before it does. I am talking about a kick back that will draw an Ariens ST1032 clear off the ground, if you are holding on good. It also totally destroyed an aftermarket starter handle, from being whipped against the recoil housing a few times.
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post #5 of 47 Old 03-04-2016, 07:20 PM Thread Starter
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Originally Posted by bwright1818 View Post
When you figure it out, please post; because I have an HM100 doing the same thing. I have not got back into it deeply, yet, because I need it to move snow with it....but I used a torque wrench; that much I know. Once it starts, it runs great. But it will kick back a good number of times before it does. I am talking about a kick back that will draw an Ariens ST1032 clear off the ground, if you are holding on good. It also totally destroyed an aftermarket starter handle, from being whipped against the recoil housing a few times.
Yes, a very hard yank! I started mine 3 times and it kicked back a couple of times before each start. I think it could easily break the recoil starter plastic parts inside.
I used a torque wrench and had the head off and cleaned carbon deposits,flatten the head , lapped the valves, ground the clearances, and cleaned the carburetor and adjusted air gap clearance (it has solid state ignition).
It had an electric starter on it but that was shot when I got it.
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post #6 of 47 Old 03-04-2016, 07:43 PM
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If you cleaned off the carbon, and it also happens when cold, then there should really only be 1 cause that comes to mind, the spark firing too early.

That would be either the flywheel key being sheared for some reason, or the ignition timing otherwise being off. But it's hard to think of why the timing would be off, apart from the flywheel key. The coil position typically isn't adjustable. Unless somehow failing ignition components could make it fire early, but that doesn't sound likely to me.

The kickback sounds nasty, though, sorry I've been lucky, I haven't had an engine do that do me; it sounds like that could do something unpleasant to your shoulder. Good luck, please let us know what you find.

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post #7 of 47 Old 03-04-2016, 08:14 PM
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im a two stroke guy, so this question is fwiw....could a tooth out on the cam timing cause kickback?

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post #8 of 47 Old 03-04-2016, 09:12 PM
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Originally Posted by nwcove View Post
im a two stroke guy, so this question is fwiw....could a tooth out on the cam timing cause kickback?
I don't think so.

If the valve clearances checked out correctly, then the compression release should presumably be working properly.

Even if the compression release wasn't working right (such as the cam timing being off), resulting in full compression while pulling the cord, I'd expect that the result would just be that the cord is harder to pull. You'd be fighting full compression, rather than the typical reduced compression that is courtesy of the release.

But even at full compression, the fuel charge shouldn't just self-ignite, it should still require the spark. If full compression alone was enough to make it self-ignite (pre-detonation, or pinging), then the engine would be doing that constantly while running, since the compression release is disabled at operating RPMs.

Merely my ....

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post #9 of 47 Old 03-04-2016, 10:01 PM Thread Starter
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Quote:
Originally Posted by RedOctobyr View Post
If you cleaned off the carbon, and it also happens when cold, then there should really only be 1 cause that comes to mind, the spark firing too early.

That would be either the flywheel key being sheared for some reason, or the ignition timing otherwise being off. But it's hard to think of why the timing would be off, apart from the flywheel key. The coil position typically isn't adjustable. Unless somehow failing ignition components could make it fire early, but that doesn't sound likely to me.

The kickback sounds nasty, though, sorry I've been lucky, I haven't had an engine do that do me; it sounds like that could do something unpleasant to your shoulder. Good luck, please let us know what you find.
I do remember torqueing it, and I took the key out but didn't closely examine it ( wish now I had ) and then later stuck it back in with shaft groove being up - seemed to fit ok, then stuck on flywheel and torqued it. I bet the next time I'll make sure how good it all fits. Hope to pick a new one up tomorrow . Should know more next week. Thanks
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post #10 of 47 Old 03-04-2016, 10:32 PM
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Merely a guess on my part, but I'd think that if the flywheel key didn't look obviously distorted when you removed it, then it was probably OK at the time. If it was only a little bit distorted, but not obviously, that might equate to maybe 1 degree of timing, if even that?

Don't get me wrong, definitely check the key. I'm just thinking that the problem is probably not because you didn't put the key on a granite surface plate in order to perfectly check its flatness It still could have sheared due to something else.

This is probably old news, but when torquing a bolt, it's best to tighten it all at once, as you approach the intended torque. If you need 50 ft-lb, but stop temporarily at 40 ft-lb, you may not get an accurate result. The coefficient of static friction is almost always higher than the coefficient of sliding friction. So if you torque to 40 ft-lbs, then stop twisting, the nut/bolt will stop turning. When you twist the wrench again, the nut/bolt not may not actually start to move again before the wrench reaches 50 ft-lb. But you've really only effectively torqued it to 40 ft-lbs, despite the wrench reading 50 ft-lbs. As it starts to tighten up, try to keep the nut/bolt moving until you reach the desired torque.

I had an old Simplicity like the one in your profile pic. That thing was a tank, the geared transmission was my favorite part. No slipping, ever, and with chains on the solid tires, it was almost unstoppable. Too bad mine was a tired 5hp, with a lot of worn parts, leading to reliability problems.

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Last edited by RedOctobyr; 03-04-2016 at 10:38 PM.
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