# OHSK120 Extreme Kickback



## JB1212 (Sep 18, 2020)

Hi Everyone,

I have recently gotten into working on older Ariens (80s-00s) and currently have a ST1236 (924076) with an *OHSK120* motor.

When i went to buy it i gave the cord a big pull and it ripped the handle right out of my hand and i thought it took my arm with it. Arm was sore for a week. Eventually got it started and it runs fine once its going. Clearly the previous owner also had issues as the electric starter gear is completed stripped and won't engage at all.

My first thought was the exhaust valve lash so when i got it home i brought it to TDC and checked the lash and sure enough it was .013" when spec is .004" so i thought that's definitely the issue and because it was so far out the compression release was not engaging on the compression stroke. Brought the lash to .004" and gave it another pull and this time it ripped the handle out of my hand and broke the handle and a part of the recoil starter on the kickback.

Scratching my head i double checked the lash and it was correct (.004). I've never heard of a snowblower having a sheared flywheel key, but know that can cause kickback on mowers so i took the flywheel off and checked the key and it was completely fine so the timing should be correct. I then gapped the coil with a business card and put it back together. I fixed the broken recoil starter and gave it another pull and it still kicked back.

I talked to a small engine shop owner and he suggested bringing the exhaust valve lash to .003 (spec is .004) so i did that and then pulled the recoil over with the valve cover off and i can see the exhaust valve *every so slightly* bumping during the compression stroke, not sure if its enough to lift it off its seat to reduce compression or not. Attempted to start it again and it still kicks back!!

Pretty stumped at this point and curious if anyone has any familiarity with this engine. There does not seem to be much info on it out there. I did see one forum post that someone said tecumseh had advanced timing issues with this engine from the factory and *the fix was to retard the timing one tooth* and that actually resolves the issue without reducing power as they had over advanced the timing in the original design. Has anyone else heard of this? Any other thoughts on what could be causing the kickback?

I did read a few people said leaky carbs can cause hydrolock. Is this possible?

Thanks in advance!!!


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## Kiss4aFrog (Nov 3, 2013)

Welcome to SBF JB1212









IF it was hydrolock you'd yank the cord and it would stop abruptly. The raw fuel wouldn't be able to ignite as it would foul out and ground the spark plug. If it did pull over there would be gas coming out the exhaust.
Hopefully one of the guys more experienced with that OHV might have a solution.


.


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## JLawrence08648 (Jan 15, 2017)

Welcome to SBF! Lot of smart and knowledgeable people on here. Hope someone has your answer. Your making the right steps except .003 & .004, Come on Man, Really, .001, doesn't matter, he gave you bad advice. 

I had that problem with the fresh gas I bought, same kickback, cord handle hit my knuckles, pain. I put that gas in 5 mowers and did the same thing, I wish I was ambidextrous. I went to a Top Tier gas station with an empty gas can, drained the gas from 5 mowers, and all of them started fine.


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## JB1212 (Sep 18, 2020)

Thank you both for the responses, i appreciate it! Definitely a lot of good knowledge here.

The gas tank did have some debris in it when i got it so i took the tank off, cleaned it, replaced the fuel line and put new fuel in it and still have the issue unfortunately :/. I have run the same fuel in another blower without issue.


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## ChrisJ (Nov 27, 2014)

Makes me think of advanced ignition timing.


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## JB1212 (Sep 18, 2020)

ChrisJ said:


> Makes me think of advanced ignition timing.


Hi Chris, any ideas of what else could cause advanced timing other than a sheared flywheel key, which i already ruled out? I wouldn't think a bad coil could cause advanced timing, but could it?


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## ChrisJ (Nov 27, 2014)

JB1212 said:


> Hi Chris, any ideas of what else could cause advanced timing other than a sheared flywheel key, which i already ruled out? I wouldn't think a bad coil could cause advanced timing, but could it?


On a car, yes.
On these engines I have no idea, but I have very little experience with them so it doesn't mean it's something bizarre.

Are you sure it kicked back, as in literally fired and pushed the piston back down. Or is there a chance the compression release simply isn't working?

Its hard to know what you experienced via text. I have an 8hp briggs that doesn't have a compression release and I have no idea how I don't break the string pull starting it. But I know what to expect and make sure I pull hard.


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## ST1100A (Feb 7, 2015)

The breaker point gap can change the ignition timing to cause that, even faulty points and condenser will cause the 'Kick-Back' problem on an engine that uses points.
An older 'Electronic' ignition coil can also do that when the 'Pick-up' sensor in the ignition coil goes bad and throws the timing out of spec.
By replacing the coil with a new one, it usually stops the 'Kick-Back' problem at start up.
The air gap between the ignition coil/armature and flywheel can change the ignition timing a little bit, but usually not enough to cause the kick-back that severe unless it is way out.
Some electronic ignition coils use a 'Pick-up' or 'Signal coil' to tell it when to fire, others use a 'Zenor' type diode to sense change of direction of the magnetic field when the magnets of the flywheel pass the legs of the coil and as soon as it changes direction, the 'Zenor Diode' signals the main ignition coil to 'Fire' because the 'Charge' is at its 'Peak'.
If the 'Zenor' diode goes bad, that will throw it out of 'Time' and cause a 'Kick-back.


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## ChrisJ (Nov 27, 2014)

ST1100A said:


> The breaker point gap can change the ignition timing to cause that, even faulty points and condenser will cause the 'Kick-Back' problem on an engine that uses points.
> An older 'Electronic' ignition coil can also do that when the 'Pick-up' sensor in the ignition coil goes bad and throws the timing out of spec.
> By replacing the coil with a new one, it usually stops the 'Kick-Back' problem at start up.
> The air gap between the ignition coil/armature and flywheel can change the ignition timing a little bit, but usually not enough to cause the kick-back that severe unless it is way out.
> ...




I'm curious how a bad condenser could cause it?


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## JLawrence08648 (Jan 15, 2017)

How do you tell if you have a Zenon diode? Is there a physical difference? What engines use a Zenon diode? More specific to certain equipment?


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## ChrisJ (Nov 27, 2014)

I haven't looked but I assume it's a zener diode. They're basically voltage sensitive diodes. 









Zener diode - Wikipedia







en.m.wikipedia.org


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## JB1212 (Sep 18, 2020)

ST1100A said:


> The breaker point gap can change the ignition timing to cause that, even faulty points and condenser will cause the 'Kick-Back' problem on an engine that uses points.
> An older 'Electronic' ignition coil can also do that when the 'Pick-up' sensor in the ignition coil goes bad and throws the timing out of spec.
> By replacing the coil with a new one, it usually stops the 'Kick-Back' problem at start up.
> The air gap between the ignition coil/armature and flywheel can change the ignition timing a little bit, but usually not enough to cause the kick-back that severe unless it is way out.
> ...


ST1100A, thank you. I really appreciate the feedback. I did not realize that could happen. My thought was if the coil started to go bad it would retard the timing if anything and not advance it.

My machine does have a solid state ignition (PN 35135B). I am going to order an aftermarket coil on amazon and give it a try! I will report back with results. Thanks again.

Amazon Coil Link


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## ST1100A (Feb 7, 2015)

A bad condenser could discharge at the wrong time by 'Leaking',causing an 'Arc' at the breaker points, making the engine miss fire or fire before it is supposed to.
A Zenor Diode is built in to the coil as part of its 'CDI' or 'Electronic' discharge system. The Diode is one part of what makes it work, there is a condensor, a capacitor, and a 'Thyristor' or another word for it is a 'Signal Switch' to make it discharge or spark.
Most small engines have all of that built into the ignition coil, some use a little box mounted separately as on some Kawasaki engines.
Motorcycle engines have a separate box, usually called the 'Black Box' that houses all the parts in an epoxy so they are not visible, and isolates them from vibration and helps insulate them from heat.
There are a lot of videos explaining how electronic ignitions work. Some are called 'CDI' some 'TPI', DTPI' and other names. The 'CDI' is the most common name.


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## JB1212 (Sep 18, 2020)

So I finally got around to replacing the coil tonight and unfortunately it still kicks back :/.

it does not kickback when I unplug the spark plug and pulls over with relative ease so that makes me believe the compression relief is doing it’s job. I also pulled it over with the valve cover off and I can see the exhaust valve bumping on the compression stroke.

I’m at the point where the only advice I have left is the post below (see pic) that states these engines came with advanced timing and the resolution was to retard the timing one tooth. I’m going to give that a try at some point this summer and will report back.


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## Oneacer (Jan 3, 2011)

Interesting.......


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## deezlfan (Nov 8, 2017)

> I did see one forum post that someone said tecumseh had advanced timing issues with this engine from the factory and *the fix was to retard the timing one tooth* and that actually resolves the issue without reducing power as they had over advanced the timing in the original design.


If that was true, there would have to be a factory service bulletin available somewhere that would confirm and/or instruct as to what needed to be done. 'Til then I would look elsewhere.


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## JLawrence08648 (Jan 15, 2017)

This is very interesting. Please get back to us. It seems strange ths only happening with the 12hp. I would thing the timing of all these OHV engines would be the same, especially 8hp-10hp, and using the same parts for the timing. Maybe the flywheel is a different size thus the imbedded triggering magnet is taking longer to get around?


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## cpchriste (Jan 19, 2014)

JB1212 said:


> So I finally got around to replacing the coil tonight and unfortunately it still kicks back :/.
> 
> it does not kickback when I unplug the spark plug and pulls over with relative ease so that makes me believe the compression relief is doing it’s job. I also pulled it over with the valve cover off and I can see the exhaust valve bumping on the compression stroke.
> 
> I’m at the point where the only advice I have left is the post below (see pic) that states these engines came with advanced timing and the resolution was to retard the timing one tooth.


Or perhaps someone has been inside this motor and didn't reset the timing correctly.
Do you have a timing light?


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## JB1212 (Sep 18, 2020)

cpchriste said:


> Or perhaps someone has been inside this motor and didn't reset the timing correctly.
> Do you have a timing light?


That’s definitely a possibility. I will check the cam and crank marks to see if they are aligned when I open it up.

How would a timing light help on a small engine? I’ve never seen one used on a small engine before.


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## Oneacer (Jan 3, 2011)

I have never heard of a timing light on a small engine either .... ??


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## JB1212 (Sep 18, 2020)

Finally was able to crack the case and take a look inside of the engine. Everything looked good and i verified a few things. First, the compression release mechanism was intact and functioning properly.

Second, the crankshaft and camshaft timing marks were lined up properly (see first pic). This being the case i decided my only option was to go with @94EG8 advice from his post back in 2016 to retard the mechanical timing one tooth. When reassembling the engine i retarded the camshaft one tooth (see second pic). I sealed the engine back up and gave it a pull... started right up without any kickback at all! The engine seems to be running strong. I readjusted the governor and set the RPMs to ~3,550. I then shut it off and re-started it 5+ times and there is no longer any kickback. The true test will be when the snow flies to see if i lost any significant power by retarding the timing one tooth, but it seems promising. 

I currently have the blower fully torn down to repaint and rebuild. I will report back after the first snow to let everyone know if there is any noticeable power loss or if this solved the problem. Thank you 94EG8 for the suggestion!


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## Shaw351 (Nov 15, 2016)

That's great !!! 1 less project to bring to my shop !!! 
When your done with that..... I've still got another 2 big 36" machines that need some love.


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## JB1212 (Sep 18, 2020)

Shaw351 said:


> That's great !!! 1 less project to bring to my shop !!!
> When your done with that..... I've still got another 2 big 36" machines that need some love.


Should have this one done in a week or two! Look forward to jumping on those 36s soon!


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## 94EG8 (Feb 13, 2014)

JB1212 said:


> Thank you 94EG8 for the suggestion!


You're welcome! Glad you got it fixed. You won't notice any loss in power. If anything they seem to work better after doing this which I've never really been able to understand. The exhaust doesn't seem to get so hot either.



deezlfan said:


> If that was true, there would have to be a factory service bulletin available somewhere that would confirm and/or instruct as to what needed to be done. 'Til then I would look elsewhere.


There is a factory service bulletin on this. Bulletin 219 from 1989


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## JB1212 (Sep 18, 2020)

Tested it out in the snow 2 weekends ago and it worked great. Thank you again @94EG8 !!


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## harry398 (Jun 22, 2021)

thats something.......tells me that the mark on some camshafts may have been marked off spec- or the cam ground off spec...

I never experienced that one, but sure as Heck have on many Honda gx's....


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## 94EG8 (Feb 13, 2014)

harry398 said:


> thats something.......tells me that the mark on some camshafts may have been marked off spec- or the cam ground off spec...
> 
> I never experienced that one, but sure as Heck have on many Honda gx's....


I remember my boss telling me that only about 90% of those engines were affected, which is a really odd statistic. They got it right 10% of the time. Most them were fixed early on I would guess, because quite frankly most people can't start them with the recoil otherwise. A lot of people got broken wrists, some ended up with broken jaws, and even heard of one shop owner that got a severely bruised stomach from the kickback. If you've never experienced starter kickback one of these it's something else. You can wrap your fingers as tight as you want around that Tecumseh mitten grip™ as tight as you want and it's still going to rip it out of your hand.


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## JB1212 (Sep 18, 2020)

94EG8 said:


> I remember my boss telling me that only about 90% of those engines were affected, which is a really odd statistic. They got it right 10% of the time. Most them were fixed early on I would guess, because quite frankly most people can't start them with the recoil otherwise. A lot of people got broken wrists, some ended up with broken jaws, and even heard of one shop owner that got a severely bruised stomach from the kickback. If you've never experienced starter kickback one of these it's something else. You can wrap your fingers as tight as you want around that Tecumseh mitten grip™ as tight as you want and it's still going to rip it out of your hand.


Completely agree. I thought I tore a muscle in my arm.


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## ChrisJ (Nov 27, 2014)

94EG8 said:


> I remember my boss telling me that only about 90% of those engines were affected, which is a really odd statistic. They got it right 10% of the time. Most them were fixed early on I would guess, because quite frankly most people can't start them with the recoil otherwise. A lot of people got broken wrists, some ended up with broken jaws, and even heard of one shop owner that got a severely bruised stomach from the kickback. If you've never experienced starter kickback one of these it's something else. You can wrap your fingers as tight as you want around that Tecumseh mitten grip™ as tight as you want and it's still going to rip it out of your hand.


This is the reason when cranking a car you always pull up on the crank with your thumb off to the side. Never ever push down.
Many were seriously injured by kickback from forgetting to retard the timing and pushing down on a crank.

I'm surprised a little recoil starter could break someone's jaw though.


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## 94EG8 (Feb 13, 2014)

ChrisJ said:


> I'm surprised a little recoil starter could break someone's jaw though.


If I remember correctly what happened in those cases is the rope snapped the customer's punched themselves in the jaw. I know of at least one that ended up with a severely bruised stomach that way too.


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