PDA

View Full Version : What causes the pull start to rip back at you?


napalmfire
05-31-2009, 03:29 PM
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
05-31-2009, 03:33 PM
Two possibilities.
Defective recoil.
Sheared flywheel key.
Both easy fixes.
What engine does this thing have?

napalmfire
05-31-2009, 03:43 PM
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
05-31-2009, 03:51 PM
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
05-31-2009, 03:52 PM
Thats a tecumseh, but ****! free, thats a nice find. you got all the luck, duel hydro trannys, brand new engines...

Affair_driven
05-31-2009, 03:53 PM
Craftsman could be Briggs or Tecumseh.
Got a model number?

Kaptain Krunch
05-31-2009, 03:57 PM
same gastank and carb setup as my tec.

napalmfire
05-31-2009, 03:57 PM
:-) 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
05-31-2009, 04:39 PM
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
05-31-2009, 04:42 PM
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
05-31-2009, 04:46 PM
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
05-31-2009, 04:53 PM
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
05-31-2009, 04:58 PM
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
05-31-2009, 07:31 PM
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
05-31-2009, 07:34 PM
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
05-31-2009, 07:40 PM
its only a 5hp 200cc block (around that), it shouldnt have enough compression to yank the cord back that much.

Affair_driven
05-31-2009, 07:47 PM
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
05-31-2009, 08:18 PM
I know, but thats what Sideways was suggesting.

Affair_driven
05-31-2009, 08:22 PM
Cool.
It comes down to inertia.
Take the blade off of a vertical shaft (rotary mower) engine and the same thing happens.

BAMBY
06-01-2009, 09:58 AM
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

Affair_driven
06-01-2009, 10:16 AM
100% POSITIVE!!!
Only fools are positive.

A little wager perhaps?
A new clone says I have much more experience than you.

As previously stated, a lightened flywheel would have the same effect.

napalmfire
06-01-2009, 10:26 AM
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

Yea I have a welt on the inside of my left leg from it snapping out. lol..

--

It has a rather chunky flywheel. I'm leaning towards a sheared key as well. I've been reading up on it and it seems to fit perfect with the descriptions i've seen.

I'll head down and pop off the flywheel in a few mins and I'll post back when I'm done.

napalmfire
06-01-2009, 12:02 PM
The key was perfect, as was the pull start.. :huh: :huh: :huh:

Could it be intended to fire this way because of its 15lb chopper wheel it's supposed to have on there?

Affair_driven
06-01-2009, 12:05 PM
Yes, I tried to explain.

napalmfire
06-01-2009, 12:22 PM
So i'll have to live with the hard starting? I'm not quite sure where I could find a heavier flywheel for this. It also runs fine if I can get it going.

Affair_driven
06-01-2009, 12:32 PM
I purposely use the lighter flywheels.
Makes you faster off the line.
You may have to raise the idle speed slightly to help prevent stalling because of lack of inertia.
Once you get used to them, they aren't so difficult to start.
Requires a quick arm, a firm grip, and some muscle to get it started.
Just be ready for it. In other words, "man up".
Please don't forget to torque flywheel nut to factory spec.
If not properly torqued, there is a good chance that key will shear.
No doubt you and Bamby (any others?) learned something today.

BAMBY
06-01-2009, 02:23 PM
wow!!!

thanks affair driven, for putting me in my place...
:oops:
i could have sworn it wouldve been the key... oh well

@napalmfire sorry for leading you down the wrong path...
im glad your engine is in good shape though. should be perty powerfull!

BAMBY

napalmfire
06-01-2009, 04:24 PM
I upped the idle screw and it works a bit better but the idle likes to vary through a pretty wide rpm range. I'm not going to rev it as there is no load yet, but my Honda clone doesn't have this problem. Once the Honda is on, it's on and has a consistent idle. Should I be concerned?

Affair_driven
06-01-2009, 04:28 PM
Should I be concerned?Not at all.

napalmfire
06-01-2009, 04:43 PM
Thanks for your help Affair!

Affair_driven
06-01-2009, 04:58 PM
No prob, it's why I'm here.
If you decide that hard starting is not for you, let me know. I'd be interested in purchase if you are looking to sell.

slideways
06-02-2009, 04:32 PM
Tecumseh carbs are very finicky. All you can do is make sure that every passage is clear in the carb body with pressurized air and possibly some thin wire. Be careful blowing into the main jet/emulsion tube area as there is an o-ring in there that will go into orbit. Same with the needle/seat area.

The main jet has a hole going through it from top to bottom and ALSO from side to side.. this has to be clear to get any kind of reliability and consistency from the motor.


Once again... because this was used on a chipper there may be no compression release on the cam or some case where the flywheel is set up to be used with the chipper wheel. Very slowly roll the motor over until you feel the compression stroke. Just after this stroke is where you wind up and pull. Just expect it to recoil on you every time and you should be ok. I've seen alot of chippers that do this because of the effort required to get the flywheel turning. Also the 12.5hp Briggs motors commonly used on logsplitters and tractors are known for recoil too because of the size of what you are trying to start with a small force.

A better suggestion is to go to TSC or online and buy a "mitten handle" for your pull start. It simply replaces the small handle with a large D shape one that is much easier on the hands to start. All of Tecumseh's Snow King motors came with them because people had gloves on trying to start them.

BradenM
06-03-2009, 01:44 AM
Same thing happens to my engine infrequently. It's the decompression release failing to perform it's intended function. If it's happening to you every time you pull on it, its probably the sheared key.

napalmfire
06-03-2009, 10:56 AM
There is no sheared key. If I recall correctly, the decompression system is on the camshaft, but the camshaft is plastic and has no decompression release system. Seems to be working as intended imo.

And also, affair, how much would you be looking to pay for an engine like this? I might take you up on your offer. Apparently I cant send you PM's so if you want to discuss this you can send me a PM with some contact info of yours.

Kaptain Krunch
06-03-2009, 02:00 PM
Plastic cam :ack2: that sucks man.

Affair_driven
06-03-2009, 02:06 PM
And also, affair, how much would you be looking to pay for an engine like this?I'll get back to you in a couple hours.
Plastic cam that sucks man.Why?
First time I saw one was at least 10 years ago in a Briggs.
Now just about everybody has them.

napalmfire
06-03-2009, 02:30 PM
This engine seems to have quite a few hours through it and there is little to no wear on the plastic cam, or any other parts for that matter. I have no problems with plastic camshafts. Plastic, in the right form for the application, is much more durable than you think.

Kaptain Krunch
06-03-2009, 02:35 PM
I know it can be durable, but metal is just so much better. I understand its standard in a lot of engines, i just never trusted plastic for something that spins that much.

Affair_driven
06-03-2009, 06:11 PM
This engine seems to have quite a few hours through it and there is little to no wear on the plastic cam, or any other partsSorry Napalmfire, I've decided against it after reading above post. I require an OHV Tecumseh that is virgin...meaning never disassembled (other than flywheel). Again, I apologize.

napalmfire
06-04-2009, 09:33 AM
Oh this isnt what youre looking for then. Had to take some stuff off to even get it off of the chipper/blower.

sayre315
06-04-2009, 11:11 AM
the 5hp briggs on my gokart dose that ALOT
always snapping off the handle on the pull string

is it because of the power bc i have quite a bit of high performance parts on there

88s10Durango
06-04-2009, 01:57 PM
Put the blower flywheel thingy back on it , try it , I bet ya it won`t kick back on you ,,it needs that weight on the end of the crankshaft , only other way to fix that is to put a cast iron flywheel on it from say a rotatiller engine , it needs the inertia ,,Bill

Affair_driven
06-04-2009, 02:15 PM
is it because of the power bc i have quite a bit of high performance parts on there
Stater rope is sold in various sizes. Larger numbers = greater strength.
Put the blower flywheel thingy back on it , try it , I bet ya it won`t kick back on you ,,it needs that weight on the end of the crankshaft , only other way to fix that is to put a cast iron flywheel on it from say a rotatiller engine , it needs the inertia ,,BillRead complete thread. We've been all through it.

greasemonkey85
06-04-2009, 05:35 PM
Once again... because this was used on a chipper there may be no compression release on the cam or some case where the flywheel is set up to be used with the chipper wheel. Very slowly roll the motor over until you feel the compression stroke. Just after this stroke is where you wind up and pull. Just expect it to recoil on you every time and you should be ok.

this is the correct answer. you must do this every time. what is happening is instead of starting the engine it is backfiring and making the motor spin backwards and pulling the string back in. we have to do this every time we start our race motors because if not it could break your fingers off. the same reason for kick start dirt bikes, harleys, old hand crank cars and tractors and airplanes. you must get it to a certian part of the compression stroke or timing sequence to get it to start and safely! some engines come with compression release on the head or built into the camshaft. most all 5hp briggs flatheads have a ez start cam. the newer briggs animals dont have either of these and is very hard to bet started by hand with a aftermarket cam. that is why almost everyone in kart racing uses electric starters.

http://i73.photobucket.com/albums/i209/greasemonkey85/gokart.jpg

Affair_driven
06-04-2009, 05:58 PM
Lack of inertia is the simple answer in napalmfire's case. Tecumseh is especially notorious for it.

slideways
06-05-2009, 02:54 PM
Nice Jeep man,

Where do you race your kart?

greasemonkey85
06-05-2009, 03:26 PM
i race at shellhammers speedway in leesport, pa.

yeah that is my other baby. 6" lift and 35" tires many others to list, sees the rocks all the time and is only a year old!

pmat
06-05-2009, 04:54 PM
Leesport? THat aint very far from me...