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Sheared key & slipped flywheel (probably)


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#1 bobl OFFLINE  

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Posted February 05, 2011 - 08:53 AM

Was snowblowing weekend before last (MF1650 with Kohler M16 engine that had been put in by a PO), just finishing the driveway when the blower belt slipped off the pulley & jammed. After I got the belt loose & stated the tractor back up it ran real rough & I barely got it back to the shed. As I shut it down I noticed it ran a bit smoother as I closed the throttle.

Last weekend I went out to check it out. Most I could get out of it was a few seconds of idle with choke & throttle closed. Checked spark, compression, fuel flow, carb & valves, all seem OK. After a bit of research it seems likely the problem is a slipped flywheel due to sheared key, throwing the timing off.:mecry:

I remember how hard it was to get in there to replace the ignition module a while back... am I gonna have to pull the engine to fix this? Any tips would be appreciated, thanks.

#2 mikebramel OFFLINE  

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Posted February 05, 2011 - 09:06 AM

I would verify first that the timing is off. Just rotate the engine, with the ignition on or kill switch disconnected and how relative it is to the timing marks.
To replace the key you would have to remove the engine to get the flywheel off unless you are good with a breaker bar and a strap wrench

#3 FirefyterEmt OFFLINE  

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Posted February 05, 2011 - 12:35 PM

Mike, unless I am wrong, the timing marks are internal on the cam / crank. You can "kinda tell" by the flywheel magnet, but if it's running at all, the key is probably just kinda sheared, and the flywheel is moved so little you can't tell. You are going to need to pull the flywheel and while you are there, just replace the key anyway. Given your symptoms, this is the very first place to look to.

Access to an impact gun and the proper flywheel puller makes this a simple job if you have room to work. If not, you may need to yank the motor.

#4 mikebramel OFFLINE  

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Posted February 05, 2011 - 03:19 PM

youre propably right. i was thinking you could set the engine to tdc, mark it and see where it went off

#5 FirefyterEmt OFFLINE  

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Posted February 05, 2011 - 09:20 PM

On a car, you are correct. But there are no adjustments for the timing on most small engines (None that I have ever seen anyway) You will typically have two dots to line up, one on the crank gear, one on the cam-shaft gear. The flywheel is locked in place by the key. You might be able to get a little something moving the coil, but they typically only have a little height adjustment, not side to side if any. But for having a typical TDC gauge and pointer, I do not think any of the small engines have them because there is no adjustment for the timing like on a car. (Even that is going away with newer computers and advanced computer adjusted timing on the fly)
Given what you did, and what it's doing... you may not of sheared the key off, but I am willing to bet it dis-formed it and it's pushed the key maybe 1/3 to 1/2 of the key width off to one side. It's very common, and really, what the key is designed to do. That is why you NEVER exchange it with a steel key. Kind of like how you never put a grade-8 bolt in place of the sheer pins on a snow blower!

#6 bobl OFFLINE  

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Posted February 05, 2011 - 10:03 PM

Thanks all. Should I be able to see the key and see if it's bent or broken by getting the cover off and having a peek?

#7 mikebramel OFFLINE  

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Posted February 05, 2011 - 11:14 PM

I wasnt saying to adjust the timing with the electronic ignition. But he could check the timing to see if the flywheel and key was off of where it was supposed to be. If that makes sense. Like youre saying though there are propably no external marks to check it against

If its your first time Id say youre gonna spend a couple hours pulling the motor and popping the flywheel off to get to the key. Maybe less. Im a pretty slow worker lol

#8 FirefyterEmt OFFLINE  

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Posted February 06, 2011 - 09:27 PM

That's the problem Mike, because it would be off so very little, it would be very hard to see it without marks.

If you pull the blower cover off and then remove the nut and washer that hold the flywheel on, you "might" be able to see the keyway well enough to tell if it has slipped. The flywheel will have a clear view of the keyway, but it depends on the way the thread is cut and where the key way starts. There is a bevel just after the threads to lock the flywheel to the shaft. I think that because of this, you may not be able to see the keyway on the crank to line it up with the flywheel, but I could be wrong!
  • bobl said thank you

#9 bobl OFFLINE  

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Posted March 12, 2011 - 08:39 PM

Finally got back to this last weekend and today (no heated space to work in). Got everything apart with some difficulty (followed by borrowed & bought tools). Turned out the flywheel key was fine. I'm thinking it's either the valves or I don't know what. I have had a problem with the intake valve - every time I check the clearance it's too much, because the adjuster that screws in & out of the top of the tappet is too loose. Also the rotator on that one broke & came off a while back. I've bought a new rotator, keepers and tappet, but I'm thinking maybe I can make it better by just replacing the adjuster screw instead of the whole tappet, since it seems like I'd have to take the whole engine apart to replace the tappet.

#10 MH81 OFFLINE  

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Posted March 13, 2011 - 09:50 AM

Sorry to hear it wasn't just a key. Good luck with the valve.

#11 bobl OFFLINE  

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Posted March 21, 2011 - 09:55 PM

Well, didn't get the tappet adjuster fixed - I'll have to do that when I'm up to taking the head off (otherwise valve doesn't quite raise enough to unscrew the adjuster all the way). Good news is that once I got it put back together it started & ran fine! Other than check the flywheel key, I had thoroughly cleaned the carb and, while the engine was out, adjusted the coil-flywheel gap and valve gap more accurately than I had managed before with engine in. I suspect now the problem was just an overdose of ice in the carb after that snowblowing sesssion, just happened to coincide with the jammed belt.

On that adjuster, I'm wondering if some version of loc-tite could be used on the threads to keep it from slipping?

#12 MH81 OFFLINE  

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Posted March 22, 2011 - 11:13 AM

Good news on it running again. As for tha loc-tite, IDK what would hold up there, I hate using the red Because it'll never come loose again without heat, but I don't think the blue will do it. Anyone use the green enough to know if it'll hold up under these temps?

#13 Texas Deere and Horse OFFLINE  

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Posted March 22, 2011 - 11:20 AM

Green Loctite is a bearing retaining compound, It will take a lot of heat before coming loose. Ussually it takes a torch to get the bearing race to come out after it's been applied.

#14 MH81 OFFLINE  

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Posted March 22, 2011 - 11:28 AM

Green Loctite is a bearing retaining compound, It will take a lot of heat before coming loose. Ussually it takes a torch to get the bearing race to come out after it's been applied.

Thanks Brian.
It it better or worse than the red stuff in this application?

#15 Big John OFFLINE  

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Posted March 22, 2011 - 11:38 AM

Bobl, if your engine was running rough it was probably carb icing. My old tractor MF14 ran rough once
while plowing snow. I took out the air cleaner & it ran fine.




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