# MTD Governor Spring problem



## luciferX (Jun 25, 2008)

My mistake, I pinched the governor spring when reassembling a craftsman rebranded MTD snow thrower. The spring's OEM part number is a 751-10654. I ordered it and they shipped me instead the "official replacement": part# 951-10654. This is all well and good except the new spring is noticeably shorter. Installed the engine revs WAY too fast. In the picture it is the darker black spring attached to the governor half way down the lever, not the lighter spring at the end of the arm.

The snow blower is a Craftsman #247.88970, the engine is a ZS370-SUA (both the craftsman and the MTD engine numbers appear to be the same).

My question is this: Should I loosen and reposition the governor arm? Is there a better way? Does MTD often update parts without reason or a note about implications? Grrr...

The thing appears in the MTD repair manual in the attached picture.


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## Don L (Jul 14, 2012)

Does MTD often update parts for no reason?They probably have a reason but
it's a mystery to me.My favorite theory is since MTD stands for Modern Tool and Die they must have lot's of mechanical engineers who have to justify their existence by reinventing the lawn mower at least once a year.(I used to be a job shop Tool and Die Maker and I still like to get in jab at the engineering department every now and then.)
They seem to use 7 and 9 like they are the same number so I doubt the actual part changed.This gets very confusing when a dealer has a lot of parts in stock and they change the first digit of the part number.To make matters worse theres a good chance they'll change it back next year.


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## luciferX (Jun 25, 2008)

I shopped around for someone that listed the original part so I might get the actual part. They still substituted it "for me". The spring is a good half inch or more too short. It isn't something you'd miss holding them next to each other.

The governor arm doesn't look keyed. I bet if I loosen it I can reposition it clockwise to compensate for the difference in spring length. The question is whether this will have any other implications (internally).


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## Don L (Jul 14, 2012)

That wo'nt work.The way a mechanical govenor works is with centrifigul force.When the engine speed increases the govenor tries to slow it down.The govenor spring counteracts this.If you put more tension on the govenor spring the engine will run faster,less tension and the engine will run slower.


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## luciferX (Jun 25, 2008)

Thanks Don L. I appreciate the info. I'm just not sure I understand.

The arm that the governor spring attaches to is just clamped onto the shaft going into the engine. If the shaft remains as is and the external arm is repositioned relative to it, what internally will change? I am thinking to loosen then rotate the external arm to be at minimum tension with the new, shorter spring from where it was at minimum tension with the old, longer one. The shaft going into the engine will remain where it was. There might be less travel possible but with a smaller spring, that seems unavoidable.


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## luciferX (Jun 25, 2008)

So the other attachment on the arm would be affected. Hrmm....

So how am I supposed to use this new spring size? If it came with a different arm I could see it. As is, I am at a loss on what to do.


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## Don L (Jul 14, 2012)

I went to Jack's Small Engine website and found the same part number (951-10654).I think this must be a misprint.I looked at a 2010 model 247.889702 and it showed a 951-11935 govenor spring,$3.59.It might be worth trying.
The throttle return spring (951-10664) is shown next to the govenor spring so I thought that might have caused a mix up.
The shorter spring is overiding the govenor causing it run too fast.Normaly the engine speed is adjusted by bending a tab that the govenor spring is attached to but obviosly that wo'nt work if the spring is a half inch too short.
Best of luck,keep us posted.


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## Don L (Jul 14, 2012)

I just looked a the photo in your original post and see that your engine looks like it has an adjustment screw to vary the tension on the govenor spring (on the thottle control) but I doubt that it would have a half inch adjustment.


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## 30yearTech (Sep 14, 2006)

luciferX said:


> I'm just not sure I understand.
> 
> The arm that the governor spring attaches to is just clamped onto the shaft going into the engine. If the shaft remains as is and the external arm is repositioned relative to it, what internally will change?


The reason this will not work is because the length of the rod that attaches to the carburetor from the governor arm will still be the same length. The way a mechanical governor works requires that there is no clearance between the governor spool and the governor shaft internally inside the engine. The governor shaft that extends through the engine is operated by the spool pushing on it so that it rotates and moves the arm that the spring and the rod that attaches to carburetor to control the throttle position and limit engine speed. 

The tension on the spring cannot be changed without also changing the position of the throttle shaft in the carburetor, and affecting the engine's speed. If you reposition the the throttle and do not maintain the zero clearance internally on the governor assembly, the engine will race and over speed. The static governor adjustments is the same on all internal mechanical type governors regardless of the manufacturer. 

The are several ways that you could achieve lower tension on the governor spring, but the easiest way would be to just stretch the spring a little at a time and keep checking to see when you have the correct rpm's. This would be a stop gap measure as stretching out the spring could ultimately affect the throttle response, but for your application may still be alright.

I hope this clears it up a little for you, it's the best description I could put in words.


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## luciferX (Jun 25, 2008)

So is there a good source for springs of this tension of varying lengths? Does anyone know where to get this spring with the ends not yet hooked so I can do an arbitrary length? The rate is the question and I can't just go to the home depot and expect to find anything close.

Alternatively I was thinking about just taking a piece of a tin can lid, cutting out a 1/2" round piece and using a nail to put two holes in it. One for the spring (now shorter) and one for a buss wire to connect it to the old governor arm. Seems awfully sketchy but desperate times and desperate measures and all.

Don L, great idea. I will take a look today.


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