Trying to torque harmonic balancer but keeps turning. Engine is in the truck, so, can't block the flywheel.

Any tips? Thanks!

 

A few ideas.

If manual transmission put it in high gear with emergency brake on or wheels blocked.

A stout strap wrench on the damper or pulley can help.

Use strip steel to fabricate a holding tool using two of the pulley bolts on the damper. I have used retired garage door opener arms for this purpose. They already have extra holes and curves which is handy. This is my favorite.

If you pull the cover you may be able to catch and block the starter teeth on the ring gear. There are tools for this or improvise with a helper... just be careful so teeth are not damaged.

A bit risky yet has been done more than once... use an impact gun with capacity roughly equal to the torque required. You really need to know the gun you are using to get enough torque but not so much that something strips or stretches.

Good luck!

 

I've used just two longer bolts in the hub with a stout pry-bar between them to hold it while pulling the torque wrench.

 

Yep! Quickest and easiest way I've found to do it as well.