STIHL 034 Seal Problem

[J Arnold]

I was gifted a Stihl 034 after a local shop gave the owner "too high an estimate for repairs". The shop told the owner that the piston was scored and that he had probably run the saw on straight gas. I looked in the exhaust port and the piston was scored but not as bad as some I have seen from straight gassing. I ran a pressure test on the saw and found that it would not hold pressure. I then did the soapy water routine and found the culprit seal on the flywheel side. It was blowing bubbles. But now comes the issue, the bubbles were without a doubt coming out between the metal body of the seal and the boss in the housing that it was pressed into. I figured a previous seal repair had gouged the seal boss in the housing. After carefully pulling the seal with a seal puller, I found the problem. There is a very slight, looked machined, groove in the boss. The grove had to have been done during manufacturing. It is extremely shallow and perfectly straight, but it allowed air in through it. The seal itself has a corresponding buildup of residue in a perfectly straight line from the years of leaking. See attached photos. It was next to impossible to get a good photo of the groove in the boss of the case, but the grove can be detected in the second photo directly opposite the tapped hole on the right side. After doing some measurements I think I can press the new seal in deep enough in to get it to seal, almost to the bottom of the boss. The question is how far in is safe? My measurements will keep the seal from contacting the bearing. Has anyone else had such a problem and does anyone have any recommendations on how to repair it other than replacing the case? Thanks to all for your help.

 

[lone wolf]

I was gifted a Stihl 034 after a local shop gave the owner "too high an estimate for repairs". The shop told the owner that the piston was scored and that he had probably run the saw on straight gas. I looked in the exhaust port and the piston was scored but not as bad as some I have seen from straight gassing. I ran a pressure test on the saw and found that it would not hold pressure. I then did the soapy water routine and found the culprit seal on the flywheel side. It was blowing bubbles. But now comes the issue, the bubbles were without a doubt coming out between the metal body of the seal and the boss in the housing that it was pressed into. I figured a previous seal repair had gouged the seal boss in the housing. After carefully pulling the seal with a seal puller, I found the problem. There is a very slight, looked machined, groove in the boss. The grove had to have been done during manufacturing. It is extremely shallow and perfectly straight, but it allowed air in through it. The seal itself has a corresponding buildup of residue in a perfectly straight line from the years of leaking. See attached photos. It was next to impossible to get a good photo of the groove in the boss of the case, but the grove can be detected in the second photo directly opposite the tapped hole on the right side. After doing some measurements I think I can press the new seal in deep enough in to get it to seal, almost to the bottom of the boss. The question is how far in is safe? My measurements will keep the seal from contacting the bearing. Has anyone else had such a problem and does anyone have any recommendations on how to repair it other than replacing the case? Thanks to all for your help.

Put some sealant on the seal when installing. As far as installation depth goes, was it flush when you pulled it out, most are that's where I would install it. The sealant will work if you allow it to dry. When retesting pressure if it leaks in the same spot you can put more sealant on the outer rim until it stops.

 

[J Arnold]

Put some sealant on the seal when installing. As far as installation depth goes, was it flush when you pulled it out, most are that's where I would install it. The sealant will work if you allow it to dry. When retesting pressure if it leaks in the same spot you can put more sealant on the outer rim until it stops.

The seal was flush when I removed it. I had considered some kind of sealant but was hesitant to try it. What type of sealant do you recommend? Thank you for your quick reply and suggestions.