Stihl FS85T cylinder/piston upgrade

[Noah8888]

I recently purchased a project FS85T trimmer and the compression seems to be low in it. I figure, if I have to replace the cylinder and piston, I might as well attempt to upgrade the horsepower on this machine. How could I do that? Would a piston and cylinder from a more powerful model work? Thanks!

 

[Fish]

The only compatable models were the fs75, 80, and fs85.

 

[Fish]

Take off the muffler and take a peek at the piston.

 

[Fish]

Here is a tech bulletin on a cylinder change that they did.

 

[Noah8888]

The only compatable models were the fs75, 80, and fs85.

I know those are the only ones that are stock compatible. I’m looking to increase the displacement. For example, my brother replaced the piston and cylinder on his ms290 chainsaw with the piston and cylinder for a ms391 and saw a major increase in horsepower and torque. Could I do something similar with the smaller FS85T motor?

 

[Fish]

my brother replaced the piston and cylinder on his ms290 chainsaw with the piston and cylinder for a ms391

How in the world did he do that?

 

[StarTech]

I thinks he means he replaced the MS290 46mm PNC with a MS390 49mm PNC as if he went with the MS391 there was major changes to the intake requiring a completely different carburetor.

 

[Fish]

I would think so..

 

[Noah8888]

Yes, I’m sorry, I intended to say 390. He did it a while ago and he is much more mechanically savvy than me.

 

[Fish]

Yeah the ms290, ms310, ms390 are pretty much identical except for piston size.