What causes the pull start to rip back at you?

[napalmfire]

I was driving out to lunch today, just left my house. This guy maybe 5 houses down from me was wheeling out a rather new looking Craftsman chopper/blower machine with a nice yellow FREE sign on it. I stopped and asked "Youre giving that away?" and he said yep! Tossed it in my car and went home with it.

Whole thing was a mess but it worked great. Cleaned it up and replaced the oil, etc.

When I tried to start it up again, it took one pull and revved up to idle. I turned it off and went to start it again and when I pulled, the pull start just (under its own power) ripped out of my hand and wound it self back up. The motor somehow pulled the pullstart back and I have no idea why.

Does anyone know what would cause this?

 

[Affair_driven]

Two possibilities.
Defective recoil.
Sheared flywheel key.
Both easy fixes.
What engine does this thing have?

 

[napalmfire]

Its a nice Craftsman 5hp ohv.

When I took it apart to clean it up, it didn't appear broken at all. I checked everything on it to see why the heck the guy was getting rid of it. Didn't want to break it even more than if it was ever malfunctioning in the first place..

When I started it while still attached to the blower, it didn't have the rip back problem.

 

[dpaxson]

it's most likely the teeth on the pull start engaging at the wrong time. normally kickback is a sheared flywheel key but i don't think it would have started up at all with a sheared key. you could always check it though it's not too hard to remove a flywheel

 

[Kaptain Krunch]

Thats a tecumseh, but ****! free, thats a nice find. you got all the luck, duel hydro trannys, brand new engines...

 

[Affair_driven]

Craftsman could be Briggs or Tecumseh.
Got a model number?

 

[Kaptain Krunch]

same gastank and carb setup as my tec.

 

[napalmfire]

plenty of houses around and its the end of bulk trash time around here.. so much stuff to sift through.

I'll have the model number in a little bit. The inside of the head looked like a briggs I took apart last week from that timecutter. I'm leaning towards it being that.

 

[napalmfire]

Heres the engine info:

Engine Model: 143.985005
Engine Family: STP172U1G1RB
Displacement: 172
D.O.M. - 7227B

Google search of engine model shows it is a Tecumseh

 

[napalmfire]

http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_47861_47861

Looks just like mine except I think mine has a 1" shaft.

Ok back to the original question.. Stupid pull start really rips itself out of my hands.

 

[Affair_driven]

Ok, definitely Tecumseh.
Check pawls and starter cup for rough edges and/or burrs.
If these items look OK, then most likely key has sheared which requires removal of flywheel.
Your description is the very definition of advanced timing.

 

[napalmfire]

What do I look for with a sheared key? Would I be able to replace it easily? Could this have had an advanced timing to begin with? The chopper wheel/blower wheel weighs a good 15-20lbs and is solid metal. Pulling the pull start up to speed once with it in place would turn over the motor about 3 more times.

I just read this.. Good chunk of info. I'll have to do it later though. Heading out in about 5 mins

http://www.freeengineinfo.com/sheared-keyway.htm

 

[Affair_driven]

What do I look for with a sheared key?

When flywheel is removed...you'll know.
Link supplied is partially bogus.
Do not apply heat and prybars are a definite no-no.

 

[slideways]

If the key isnt sheared the compression release on the cam may have broken. There is a little spring to keep the valves from closing completely at very very low rpm (or while pull starting) to make the engine lose compression a little bit.

If it were me i'd roll the motor over slowly to the compression stroke and just pull it quick from there. That's what you have to do to a racing kart engine to prevent kickback.


That is an OHH50 model Tecumseh.. FYI

 

[Affair_driven]

One thing that should be looked into before engine is disassembled.
If this engine has a light flywheel, this could also cause symptom you describe.
If this is the case, nothing can be done except to replace with a heavier flywheel.

 

[Kaptain Krunch]

its only a 5hp 200cc block (around that), it shouldnt have enough compression to yank the cord back that much.

 

[Affair_driven]

it shouldnt have enough compression to yank the cord back that much.

I'm not talking about compression and it doesn't enter into the problem.

 

[Kaptain Krunch]

I know, but thats what Sideways was suggesting.

 

[Affair_driven]

Cool.
It comes down to inertia.
Take the blade off of a vertical shaft (rotary mower) engine and the same thing happens.

 

[BAMBY]

100% POSITIVE!!!

It's a sheared flywheel key. i know from experience as this just happened to my minibike engine. it would rip that cord away from me so hard i got bruised from it whipping back around toward the engine.

its deffinitely the flywheel keyy.
goodluck
BAMBY