stihl bg 75 sheared flywheel key

[columbo]

hi all. i have a stihl bg 75. couldnt get it to start. good compression. had spark. and rebuilt carb still no spark. i pulked flywheel as last resort and found cast flywheel key. sheared.
tried to realign flywheel to crank and sprayed gas in carb. but still no start
thinking i need to align flywheel better
any ideas how to get it close enough to start
thanks

 

[buzz sawyer]

I'm not familiar with that particular saw but what I have done on others is: Make a mark on the end of the crank threads and flywheel in line with the key and slot. Line them up when assembling. Make sure the crank and flywheel tapers are smooth and clean of all oil/grease.

 

[columbo]

I'm not familiar with that particular saw but what I have done on others is: Make a mark on the end of the crank threads and flywheel in line with the key and slot. Line them up when assembling. Make sure the crank and flywheel tapers are smooth and clean of all oil/grease.

i have it lined up with tdc. but can not even get a pop out of it. spark seems good. i am using just a quick spray of starter fluid
btw. its not a saw. its a leaf blower. thanks

 

[columbo]

i have it lined up with tdc. but can not even get a pop out of it. spark seems good. i am using just a quick spray of starter fluid
btw. its not a saw. its a leaf blower. thanks

also compression is 120 +

 

[Bob_w]

From picture 2 above, it appears that the notch for the key in the flywheel, is 20 degrees to the right of your marker mark. Is there a black mark on top of the flywheel? of you don't have a key, even if you do, you need proper torque. verify marks line up after torqueing.

 

[buzz sawyer]

OK, leaf blower, my bad. First, use a shot of mix, not starting fluid. The oil in the mix can actually increase compression. Starting fluid can wash oil off, maybe cause a problem. 120 seems a little low but it should start on that. Are you pulling until the gauge stops rising? If your marks are lined up and you're getting spark, it should at least pop. Sorry, can't help much more than that without seeing it in person.

 

[columbo]

OK, leaf blower, my bad. First, use a shot of mix, not starting fluid. The oil in the mix can actually increase compression. Starting fluid can wash oil off, maybe cause a problem. 120 seems a little low but it should start on that. Are you pulling until the gauge stops rising? If your marks are lined up and you're getting spark, it should at least pop. Sorry, can't help much more than that without seeing it in person.

ok. i will try using mix. and yes 120 should be enough for at least a pop. i pulled it til it stopped rising. about 5 pulls got it to 120
and i tried to line up the flywheel with coil. at tdc. and tried to a few degrees both directions with no pop.
also. i just snug flywheel bolt . not sure if or why that would make a difference. thanks for advice.

 

[singinwoodwackr]

What is the part# on your flywheel. I may have some spares from dead blowers

 

[Oletrapper]

hi all. i have a stihl bg 75. couldnt get it to start. good compression. had spark. and rebuilt carb still no spark. i pulked flywheel as last resort and found cast flywheel key. sheared.
tried to realign flywheel to crank and sprayed gas in carb. but still no start
thinking i need to align flywheel better
any ideas how to get it close enough to start
thanks

Good morning Columbo, I have to ask, how did the key get sheared? Possibly using it as a vacuum and sucking a walnut into it? I can think of no reason for the flywheel key to become sheared unless possibly the flywheel nut vibrated loose and constant back and forth eventually sheared the key. Just curious. The line up of the key to the crankshaft is critical. 120psi is okay but if spark is at the wrong time= no fire. Also, from the pics posted, it appears that the coil may be too far from the flywheel. Other than that, I would just replace the flywheel. Stihl part number should be 1127 400 1200.
Let us know what you find. OT

 

[stihltech]

Yes, I have seen those shear the key. Pretty old unit.
Pull the muffler and inspect the piston. Stihl actually said to roughen the taper with a little valve grinding compound, clean, then reassemble by lining up the marks.. Check for spark.
If that does not start the unit, look elsewhere for the issue.
Don't let one issue keep you from looking at the whole unit.

 

[columbo]

What is the part# on your flywheel. I may have some spares from dead blowers

part # is 4137 400 1200a. it seems like the shear pin was cast into the fly wheel. thanks

 

[columbo]

part # is 4137 400 1200a. it seems like the shear pin was cast into the fly wheel. thanks

Good morning Columbo, I have to ask, how did the key get sheared? Possibly using it as a vacuum and sucking a walnut into it? I can think of no reason for the flywheel key to become sheared unless possibly the flywheel nut vibrated loose and constant back and forth eventually sheared the key. Just curious. The line up of the key to the crankshaft is critical. 120psi is okay but if spark is at the wrong time= no fire. Also, from the pics posted, it appears that the coil may be too far from the flywheel. Other than that, I would just replace the flywheel. Stihl part number should be 1127 400 1200.
Let us know what you find. OT

good morning Ole. and the flywheel nut was loose. the coil is a business card away from flywheel. and spark is good. i was tryi g to line up the flywheel and crank best i could. thanks

 

[columbo]

Yes, I have seen those shear the key. Pretty old unit.
Pull the muffler and inspect the piston. Stihl actually said to roughen the taper with a little valve grinding compound, clean, then reassemble by lining up the marks.. Check for spark.
If that does not start the unit, look elsewhere for the issue.
Don't let one issue keep you from looking at the whole unit.

i did pull muffler and there is some light scoring. but i have seen running saws with worse and still ran. and spark is good compression 120.
buzz sawyer suggested using gas mix instead of starting fluid. which i will try. thanks for advice

 

[singinwoodwackr]

All I have is a 4140 400 1200 and a 4241 400 1200 so no help
these are off a b85 and a b86

 

[columbo]

All I have is a 4140 400 1200 and a 4241 400 1200 so no help
these are off a b85 and a b86

thanks for checking

 

[columbo]

thanks for checking

update. i picked up a flywheel from ebay and it started right up. thanks for help.
i guess i just kept missing the right spot
i did try to line it up at tdc a bunch of times

thanks again

 

[Oletrapper]

update. i picked up a flywheel from ebay and it started right up. thanks for help.
i guess i just kept missing the right spot
i did try to line it up at tdc a bunch of times

thanks again

Good deal and thanks for letting inquiring minds know. OT