Jonsered 920 air leak- need help

[A_sharp]

Hi everyone. I am relatively new to rebuilding chainsaws and after spending countless hours on this site I finally started to rebuild this 920 I aquired about 15 years ago. The saw had an air leak at the shaft seals so I replaced them, cleaned up the cylinder and installed a new piston. I did another air test and still had a leak whick I could not find, so plugged all the holes and dipped in a bucket of water. What I found was a bit of a surprise. The leak was right below the bar studs around a small pin in the case. This pin is folded over kind of like a cotter pin but really small and is loose in the case. I have attached a pic with a black arrow pointing to this pin. Anyone have a similar problem? Any help is much appreciated!!

 

[Johnwell]

I’ll check my 930 over tomorrow evening—I don’t think it has a pin there. Maybe the casting had a hole there and the factory plugged it with a pin? You could probably jb weld it to seal it up.

 

[SteveSr]

Hi everyone. I am relatively new to rebuilding chainsaws and after spending countless hours on this site I finally started to rebuild this 920 I aquired about 15 years ago. The saw had an air leak at the shaft seals so I replaced them, cleaned up the cylinder and installed a new piston. I did another air test and still had a leak whick I could not find, so plugged all the holes and dipped in a bucket of water. What I found was a bit of a surprise. The leak was right below the bar studs around a small pin in the case. This pin is folded over kind of like a cotter pin but really small and is loose in the case. I have attached a pic with a black arrow pointing to this pin. Anyone have a similar problem? Any help is much appreciated!!

Is this possibly a vent for the oil tank and is there a leak between t he crankcase and oil tank?

 

[cbfarmall]

Here's the backside of the split crankcase. You should see if air is leaking out of the oil cap as well. Confirm what Steve suggested. Fortunately, aftermarket gaskets are available.

 

[Bob Hedgecutter]

The cotter pin is the vent for the oil tank as suggested above- if the saw is showing an air leak from the engine internals exiting this point then yes (as also stated above) you have an internal leak from engine interior into the oil tank interior.
Likely to be a failed gasket- but not impossible for it to be a hole in the crankcase if something hard got lodged between crank lobe and case at some stage- something hard like a bit of bearing- ball, needle or race.

 

[heimannm]

I had a 920 in early last year with exactly the same symptoms. The owner decided not to proceed with repairs and took it home partially assembled.



Mark

 

[A_sharp]

I had a 920 in early last year with exactly the same symptoms. The owner decided not to proceed with repairs and took it home partially assembled.

View attachment 1235306

Mark

Thanks everyone for the replies, looks like I have more work to do! The air leak is not that severe so am hoping it is the gasket and not a hole in the case. If it is a hole in the case I would assume it is not repairable??

Thanks again,
Harry

 

[Johnwell]

…If it is a hole in the case I would assume it is not repairable??

Thanks again,
Harry

I’ve fixed aluminum-cased two strokes (lt500r) that had a hole in the case from the piston skirt breaking up; just had to find a good welder.

I’ve heard you can weld magnesium but I have never attempted it; and somehow you’d have to keep it from catching on fire. I’m sure it could be done. Probably easier, cheaper, and safer to buy used cases on e-bay.