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Jon K.
Jon K., Small Engine Diagnostic Expert
Category: Small Engine
Satisfied Customers: 5818
Experience:  Gold certified Stihl tech, Service Manager for a rental/repair shop.Certified in most small engines
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how do i set the timing as i reassemble my stihl fs 90 bru

Customer Question

how do i set the timing as i reassemble my stihl fs 90 brushcutter
Submitted: 6 years ago.
Category: Small Engine
Expert:  Curtis B. replied 6 years ago.

curtis b :

Welcome to JUST ANSWER small engines, let me try to help you !! This being a two cycle engine, it has no cam to time with crankshaft. The only timing is the flywheel key which is fixed, and the position of the coil . There are no other timing marks.

Customer: This engine is a 4 mix that is ahybrid
Customer: This motor is a hybrid 4 mix and has a cam andh aset fof overhead valves but runs on two strke fuel a new inovation by styhl
curtis b :

You have to love it ! So the cam and crank has to time, and you only have one mark. ?? I will opt out and see if we have anyone else that has one of these apart. Please don't respond as it will lock the question. Sorry.

Expert:  Jon K. replied 6 years ago.

Thank you for choosing Just Answer, my name is XXXXX XXXXX I will do my best to help you find the answer you need to resolve your problem.

 

Timing a Stihl 4 mix engine.

With the rocker arms and cam gear removed turn the flywheel so that the piston is at top dead center. You should see an arrow on the flywheel. This needs to line up with the right hand screw that holds the ignition module in place. You are now at top dead center and ready to install the cam, rocker arms and set the valves.

Turn the engine over and install the cam gear with the lobe facing down there are marks at the 4 o'clock and 8 o'clock position and corresponding dots on the housing. These need to be lined up. Install the cam followers push rods and rocker arms and set the valves to 0.10 ± 0.02 mm (not inches) Once you are there you should be all set and timing in place. You may want to turn the engine over a few times and double check your valve clearances. I like to check mine with one valve open and then do the same to the opposite.

Jon K., Small Engine Diagnostic Expert
Category: Small Engine
Satisfied Customers: 5818
Experience: Gold certified Stihl tech, Service Manager for a rental/repair shop.Certified in most small engines
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