Pulling Stilh MS270 cylinder/piston

[diymarketing]

I have a 20+ year old Stihl MS270 chainsaw. After changing out the coil and carb, still no start so I invested in a Mityvac compression tester. Got about 120 psi, which from what I have seen, is probably the culprit. I am trying to remove the top end and find the 4 T25 bolts to be resistant to my efforts. Usng a drill/driver. Tried a little heat to see if that would help, assumng there is threadlocker on the bolts, but no success. Looking for any advice to disassembly. Thx

 

[atpchas]

Try a T-handle T27. With luck, the T25 didn't FUBAR the bolt. A good T-handle gives better control and more feedback than s drill/driver.

 

[diymarketing]

Try a T-handle T27. With luck, the T25 didn't FUBAR the bolt. A good T-handle gives better control and more feedback than s drill/driver.

Try a T-handle T27. With luck, the T25 didn't FUBAR the bolt. A good T-handle gives better control and more feedback than s drill/driver.

Thanks much! Thought it was a T25. Will be getting a T27.

 

[stihltech]

Before disassembly, invest in a vacuum and pressure tester. It will tell you what else you may need.
120 psi? Not bad in day to day. Never stopped on from running. Take a look in the exhaust port. That may tell the story.

 

[diymarketing]

Thanks Stihltech. For a non-expert I always find the diagnoses to be the hard part. I have taken off the exhaust and can see the piston, but not sure what it should look like. Piston does not seem to have obvious scoring, but perhaps a bright light would show some defects. Is there something in the port I should be looking for?

I assume from your comments a vacuum tester and a pressure tester is different from a compression tester and I will look into those tools. I am no tfamilair with them.

I thought 120 psi was a bit low. It won't start. Spark tester shows spark. New carb and injecting fuel into cylinder does not get it running. Learning as I go and know I can get this running again.

 

[atpchas]

Re: "I have taken off the exhaust and can see the piston, but not sure what it should look like."

This handy reference should give you an idea of what to look for.

 

[AnthemBassMan]

A pressure/vacuum tester gives you the readings of the crankcase. It will detect bad crank seals or other leaks. A compression tester only tests the cylinder compression. You can have great cylinder compression but it won’t run or run badly if the crank seals are bad.

L8R,
Matt