Stupid problem with FS 91

[Blue Moon Mountain Farm]

Hello experts. After using my FS 91 for 3 years and being thoroughly satisfied, I made a stupid mistake made in haste. After using a metal brush cutting blade, I changed over to the line trimming head. Later, wanting to reinstall the metal blade, I inserted the anti-rotation pin, hand rotated the head but could not drop the pin to lock out rotation. Debris...no, pin damage...no. Checking the parts for the metal blade, I found that I did not install the thrust plate. This plate has the hole to allow the anti-rotation pin to drop into place.
So now I am seeking advice as to how I may stop drive shaft rotation so that I may unscrew the line trimmer head.
Do I need to open the gear box and block gear rotation, or is there some simpler method?
Thanks

 

[upupandaway]

Do you have some space between the trimmer head and the body of the trimmer head? I would get a wide piece of metal 1/16"ish think min and cut a wide 9mm???(measure the thrustplate you have removed) slot on it to catch the flat spot the thrust plate fits.
If you don't have any space where the thrust plate went originally, last resort, you could vice grip the square end of the drive shaft.

 

[StarTech]

It would simpler the remove the gear head box, pull the drive shaft. Insert the drive shaft into the gear head box. Now using a pair vise grips clamp on to the drive so you can hold it. Now you should be able to remove the head, making you are turning it in the right direction for removal which opposite of the normal way it turns. Be careful as you could strip the bevel gears.

Also note where the spacer is normally at is splined so just inserting something there usually will not work as there is no flat spot.

 

[upupandaway]

It would simpler the remove the gear head box.... you could strip the bevel gears.

Which is why I use this route as a last resort.

 

[StarTech]

Understood but sometime it is a necessary route and just repair the damage if done. But you must how to get the bearings and gears out. So far I have been lucky and not to have damage the gears.

And I have rebuilt several of these gear boxes after bearings have failed so I keep the bearings in stock but no bevel gears replaced except one hedger head attachment. The customer ran it until he destroyed the gears. You know it does help to things greased.

 

[Fish]

Take the gear head off, and buy a foot of keystock that fits in the hole. Lock it in a vice, and with a chisel, tap the trimmer head lightly in the direction of removal. Several taps should get it loose again.

 

[Blue Moon Mountain Farm]

Thanks to all replies.
I was able to source .25"x .25"x 12" steel keystock from local Ace Hardware.
Removed the line trimmer head from the shaft. Inserted the keystock into the female coupling of the trimmer head, clamped a large vice grip onto the keystock, held firmly and twisted the line trimmer off.
I"ll not make that mistake again (tho there may be others).