Pull cord jams/locks up intermittently. Even with plug removed.

[Bat135]

Hi

I have a Stihl av 038.

When it pulls over it fires….

But it’s rare to be able to pull it over, because the pull cord locks up.

I have tried everything… flywheel ok, pull cord and assembly ok, piston and rings look intact from exhaust and carb port.

If I undo pull cord assembly and turn the flywheel with spanner it frees up again… untill it jams/locks up again.

Everything else is working. Good compression ect.

Even with spark plug removed… still locks up every rotation or other one.

What could it be? Tearing my hair out here. Lol

 

[Bob Hedgecutter]

Pretty simple engine- everything rotates around the one axis of the crank- so you start eliminating components.
Personally I would start at the flywheel, remove it and see if there is not a bolt worked out of somewhere and is now residing behind the flywheel and jamming between wheel and crankcase. By far easier to remove with a puller- buy a copy cat one or take the saw to a shop- there are other ways to remove flywheels- but if not experienced- other ways can cause damage.
Then go to the other side of the case if nothing is found under the flywheel, or rotation of the crank without the flywheel is still binding- remove clutch and oiler- rotate the crank.

If after that it is still binding with no flywheel and no clutch/oiler- then the problem is internal and expensive- like a blown apart bearing and bits of it in the crankcase catching between case and crank lobes.

 

[Bat135]

I don’t think it is anything stuck in crank as there are no rattles when I shake it and I can actually free it up with force on the flywheel… only for it to jam again.

I have removed flywheel… nothing there.

Not tried other side (clutch side). Maybe it’s the clutch side bull race bearing that has been mentioned.

Is it a pain in the proverbial to work on the other side? Opp the flywheel side?

There is the sprocket and a split pin sort of thing holding in all in place… should I work on that side?

 

[Bob Hedgecutter]

If you have had the flywheel off and crank rotation shows the same problem- then yes work on the power take off side.
Remove the E clip, washers, drive sprockets, clutch bell- could be the clutch needle bearing, the oil pump.

Could also be internal- bits that have been smashed by crank lobe rotation often embed into the case wall under force and dont rattle.

 

[Bat135]

All very helpful advice.

Definitely things to check. Otherwise it’s a nice saw so worth having a go.

The other issue is, as my first point of call to check was the area under the piston/con rod, is that I can only get three of the head hex bolts out… one of them has rounded… not the thread but the hexagon that the Allen key fits into has rounded. So can’t get head off…

 

[Bob Hedgecutter]

Being Stihl and 038- it should not have hex drive cap screws holding down the cylinder- it should have Torx bolts requiring a T27 driver- if you are using a hex, that is why perhaps it is rounded off?
If it doesnt come out with a T27 driver after using all means deemed necessary to remove any crud in the driver pocket of the bolt, you cannot get heat and or penetrating oil to it and it still wont drive out- you might need to drill the head off the bolt remove the cylinder, remove the bolt stub and find a replacement bolt- or all 4 bolts even better.

 

[Bat135]

Ok great… yes, they are the wrong bolts… it has a larger cylinder and piston fitted with after market bolts. So will drill it.

 

[Bob Hedgecutter]

Ok great… yes, they are the wrong bolts… it has a larger cylinder and piston fitted with after market bolts. So will drill it.

Oh great- so it has been given the Asian upgrade? If it is running an aftermarket crank or main bearings- willing to bet there is your problem.
If they are hex, if they are metric- you can try smacking in the next size up in imperial driver into the rounded out hole in an attempt to remove it, metrics jump a whole millimeter between sizes, imperial give you like half sizes.