Rebuilt 10hp Briggs Won’t Start

[Go-Rebels]

Thems very rough figures and we are talking shear strength for keys and torsional shear strength for the crank not tensile strength.
Next a lot of mower cranks are cast malliable iron not forged as the latter are about 6 timed the price of the former.
That was the real problem with the Kohler Courage engines.
At some point the forged cranks ( found on the Commands ) got replaced with the cast crank with corresponding heavier counterbalance and a whole different set of vibrations

Of course these are rough figures and, yes, we're talking shear strength of the key versus shear strength of the crank (their is no such thing as "torsionsal shear" strength; it is just "shear" strength.) And of course we can get a good estimate of the shear strength of steel by multiplying the tensile strength by 0.6 so we're still talking apples to apples. The tensile strength of cast malliable iron is all over the place ranging from 65ksi to over 130ksi. Who knows where my crank is at? The only way to tell for certain what I have is to do a hardness test on the crank. I'll save that for another time...

Is it common for these cranks to fail on these engines?

 

[Go-Rebels]

I checked for piston movement this morning by dropping a weld rod through the spark plug hole and found the piston moving up and down! The tension on the pull cord is erratic through the pull stroke with the plug in place, but not like going through a normal compression cycle. But I'm getting tension on the cord today where I had none a few days ago.

I'm thinking now that I may have a combinaton of a balky pull cord spring mechanism and a dirty carb that needs a good cleaning. I'll check the flywheel key again this weekend. Remember, this motor sat for years before I got around to installing the new crank.

On another point... how is the carburetor removed from this engine? I removed the two nuts that hold on the air filter backing plate and thought I could just pull the carb off the threaded studs (the studs with the male 'star' ends) but found it stuck. I tapped the carb body with a plastic hammer, thinking it was stuck to the gasket but no luck. It's not coming off! Any help would be appreciated.

 

[bertsmobile1]

Of course these are rough figures and, yes, we're talking shear strength of the key versus shear strength of the crank (their is no such thing as "torsionsal shear" strength; it is just "shear" strength.) And of course we can get a good estimate of the shear strength of steel by multiplying the tensile strength by 0.6 so we're still talking apples to apples. The tensile strength of cast malliable iron is all over the place ranging from 65ksi to over 130ksi. Who knows where my crank is at? The only way to tell for certain what I have is to do a hardness test on the crank. I'll save that for another time...

Is it common for these cranks to fail on these engines?

Been a long time since I did any of this stuff in the lab but the shear strengths as measured with a Charpy or Izod were a lot lower than the rotational brittle failures what ever they were called..
An yes it will depend upon what grade of malleable iron the crank was made from .
And for that matter , the forged cranks are probably a fairly low grade steel as well when you consider the price of a crank.
Most of the failed cranks I get my grubbys on have failed on the PTO end, usually a brittle failure initating at the root of the retaining bolt hole.
Never seen a journal let go but then I have not been doing this for all that long.
We had some one here a while back with a classic fatigue failure but can't remember if it was a crank or a spindle.
Interesting units Kilograms / Sq inch ?

Usually if the end of the carb mounting studs has been formed into a torx head then the stud has a lip or boss on it to hold the cab in place so the whole stud needs to come out.
Having said that the only parts list I have for a 205412 shows the number of a plain stud and to check any further we need the 4 digit code number, there were a lot of variations of the 205412 model.

And some of those engines have a rod that is handed so it is possible to fit it upside down and have it foul on the crankcase.

 

[Go-Rebels]

Been a long time since I did any of this stuff in the lab but the shear strengths as measured with a Charpy or Izod were a lot lower than the rotational brittle failures what ever they were called..
An yes it will depend upon what grade of malleable iron the crank was made from .
And for that matter , the forged cranks are probably a fairly low grade steel as well when you consider the price of a crank.
Most of the failed cranks I get my grubbys on have failed on the PTO end, usually a brittle failure initating at the root of the retaining bolt hole.
Never seen a journal let go but then I have not been doing this for all that long.
We had some one here a while back with a classic fatigue failure but can't remember if it was a crank or a spindle.
Interesting units Kilograms / Sq inch ?

Usually if the end of the carb mounting studs has been formed into a torx head then the stud has a lip or boss on it to hold the cab in place so the whole stud needs to come out.
Having said that the only parts list I have for a 205412 shows the number of a plain stud and to check any further we need the 4 digit code number, there were a lot of variations of the 205412 model.

And some of those engines have a rod that is handed so it is possible to fit it upside down and have it foul on the crankcase.

It's interesting that the "brittle failures" often mentioned are really classic fatigue failures where a small crack is formed at a stress concentration then progresses throught the cross section over many cycles.

Remember that the hardness testers measure the deformation (displacement) of a hard tip (ball or diamond) pressed into the surface of a metal using a calibrated load. Then we use conversion tables to estimate the tensile strength, and then multiply by 0.6 to estimate the shear strength.

"ksi" = Thousands of pounds per square inch

I've got a female TORX socket set that I haven't used in over 10 years. I guess there's a first time for everything.

BTW, my 4-digit engine code is -0120-E1

Thanks for all the help!

 

[Go-Rebels]

Another interesting design point... why does B&S put a small tension spring in parallel with the fixed governor rod that runs from the carb lever to the governor mechanism located on the plate that is mounted over the cylinder? Is it meant to take up any clearance in the mounting holes of the fixed rod?

 

[bertsmobile1]

It is a dampening spring to prevent hysteresis with throttle variations.
It must be needed but I see a lot of engines come in without it or with it stretched a long way & I don't notice any difference to the engine operation between the old one & the new one.
It does make a bit of a difference on the bigger Honda engines.
When I am in off peak times I will download the pars list ( you should have done the same ) from Briggs then get the stud number and plug that into one of the online parts retailers web site & see what it actually looks like.

 

[Go-Rebels]

Today’s update:

Checked the flywheel key and sheared it again. This time I actually followed the spec and torqued the nut to 100 ft-lb with a new key. I took great care to torque the internal fasteners to spec but got lazy tightening the flywheel nut.

Lesson learned.

Choke, pull start and it fired right up, running well like it did years ago.

Then I found oil dripping from the engine coming from my crappy weld where I tried to TIG weld the block... probably a couple tablespoons over fifteen minutes run time. Too much to ignore. Next I need to remove the engine from the chassis and lather up the weld repair with some high temp JB Weld. I should have just JB Welded the block in the first place. I’ll re-tighten the head bolts while my hands are dirty too.

 

[Russ2251]

The regular JB Weld will be fine. The high temp stuff is overkill.

 

[bertsmobile1]

If that flywheel key goes again you might need to dress the groove in the crank then lap the flywheel to the crank with some fine valve grinding paste

 

[Go-Rebels]

The regular JB Weld will be fine. The high temp stuff is overkill.

Yup, that’s what I picked up. It’s good to 550F.