Stihl TS400 Rebuild Issues

[SawDocAZ]

I have been buying and selling TS400’s as a hobby. I have mostly just been replacing heads and carbs and having luck. Due to an increasing number of saws with bad bearings, I’ve decided to start replacing bearings rather than selling the saw for parts. I bought a small shop press to assist me. After removing the old bearings and crank seals, I clean the crank case halves, great then and press in the new bearings and seals with no heating or cooling. I then grease the crank and then press the case halves back together with a new gasket and seal with the screws. I’ve done 3 saws this way and the bearings seem solid with no play, but I am not having any luck starting the saws once reassembled with a new carb and head. I am getting minimal firing with lots of back firing through the exhaust or no firing at all. I am confused as to what my issue is as I seem to have good spark, compression, and fuel. Any help would be greatly appreciated!

 

[Woodslasher]

I have been buying and selling TS400’s as a hobby. I have mostly just been replacing heads and carbs and having luck. Due to an increasing number of saws with bad bearings, I’ve decided to start replacing bearings rather than selling the saw for parts. I bought a small shop press to assist me. After removing the old bearings and crank seals, I clean the crank case halves, great then and press in the new bearings and seals with no heating or cooling. I then grease the crank and then press the case halves back together with a new gasket and seal with the screws. I’ve done 3 saws this way and the bearings seem solid with no play, but I am not having any luck starting the saws once reassembled with a new carb and head. I am getting minimal firing with lots of back firing through the exhaust or no firing at all. I am confused as to what my issue is as I seem to have good spark, compression, and fuel. Any help would be greatly appreciated!

I don't see how bearings would affect how saws run, have you pressure/vacuum checked them and made sure you correctly aligned the flywheel?

 

[Ozhoo]

Welcome to AS.

Any saw taken down that far should be vacuum a pressure tested after reassembly. Also, check the flywheel key... having a cast in key makes it a bit more expensive to fix. You've got to clean and re-clean the crankshaft and flywheel before crunking them down.

 

[lone wolf]

I have been buying and selling TS400’s as a hobby. I have mostly just been replacing heads and carbs and having luck. Due to an increasing number of saws with bad bearings, I’ve decided to start replacing bearings rather than selling the saw for parts. I bought a small shop press to assist me. After removing the old bearings and crank seals, I clean the crank case halves, great then and press in the new bearings and seals with no heating or cooling. I then grease the crank and then press the case halves back together with a new gasket and seal with the screws. I’ve done 3 saws this way and the bearings seem solid with no play, but I am not having any luck starting the saws once reassembled with a new carb and head. I am getting minimal firing with lots of back firing through the exhaust or no firing at all. I am confused as to what my issue is as I seem to have good spark, compression, and fuel. Any help would be greatly appreciated!

Is the flywheel key sheared?

 

[SawDocAZ]

I don't see how bearings would affect how saws run, have you pressure/vacuum checked them and made sure you correctly aligned the flywheel?

Thank you for the reply. Aside from bolting the flywheel back on as normal and gapping between the flywheel and coil, I do not do anything special. I am finding instances where the flywheel hits the coil even after bearings and gapping. Any pointers on how to actually align the flywheel? Also, how do you do a vacuum test? I’ve seen that mentioned several times.

 

[cscltd]

Have you mixed up the coils and flywheels. There is a 3 bolt coil and a 2 bolt coil that use different flywheels. Do you have a mix of ts400s and took them apart and mixed parts up

 

[keithto]

I have been buying and selling TS400’s as a hobby. I have mostly just been replacing heads and carbs and having luck. Due to an increasing number of saws with bad bearings, I’ve decided to start replacing bearings rather than selling the saw for parts. I bought a small shop press to assist me. After removing the old bearings and crank seals, I clean the crank case halves, great then and press in the new bearings and seals with no heating or cooling. I then grease the crank and then press the case halves back together with a new gasket and seal with the screws. I’ve done 3 saws this way and the bearings seem solid with no play, but I am not having any luck starting the saws once reassembled with a new carb and head. I am getting minimal firing with lots of back firing through the exhaust or no firing at all. I am confused as to what my issue is as I seem to have good spark, compression, and fuel. Any help would be greatly appreciated!

I had a similar problem rebuilding fs90r series motors. which is totally different because I just swapped out whole cranks with good bearings. After I put everything back together I could not get them to run. valves were good. compression was good and, everything was sealed and the fly wheel was good but I got no spark. I never figured out what was wrong so I stopped rebuilding the motors with bad bearings. I know that doesn't help you at all but was wondering how many of the three had zero spark? I think that has something to do with it because of the problem I had. It just dawned on me that I think the fly wheel has to make proper contact with the crank to produce spark but I am not sure. I can't wait to find out the solution.

there are 2 different types of fly wheels. one for a 2 bolt and one for a 3 bolt coil. the 3 bolt fly ends in 1200 and the 2 bolt coil fly wheel ends in 1201. I am assuming the 1201 is the newer model.