Demoder recently posted a great video of changing the timing belt and related parts. See https://www.rav4world.com/forums/94-...ml#post2690655
. In this video demoder demonstrates how to remove a particularly stubborn crankshaft pulley bolt. An AC electric impact wrench rated at 450 ft-lbs would not get the bolt off. At one point in the video demoder has a neighbor come over to help in the problem-solving. The neighbor and she discuss what is going on. They point to one of the reasons the pulley bolt is sometimes so hard to free is the pulley bolt's washer. The washer has a lot of area, and it is highly compressed. When the pulley bolt is torqued to 80 ft-lbs, I figure the compressive force applied to the washer is on the order of 12,000 pounds. When trying to free the bolt, one is largely fighting the friction of the washer's area, with said washer compressed tightly against its mating surfaces. A few observations to support this:
-- Threads that are galled result in a bolt that is a battle to rotate for many revolutions. By contrast, the crankshaft pulley bolt always seems to come nearly hand-loose (or small ratchet-loose) after only a quarter revolution or so. This points to the threads in fact not galling.
-- When the bolt is super tight and so hard to remove, people (incuding myself) have reported a cracking sound and a little cloud of dust when the bolt finally frees. The threads never look beat up or otherwise disturbed.
-- Others I know have reported steel bolt heads galled to steel washers in the past.
-- Engine heat and vibration may cause the galling between the washer's mating surfaces to worsen with time. In my experience, it does seem like crankshaft pulley bolts left in place a long time are more likely to be a battle to remove. Of course, as demoder and her neighbor point out, the cause of a super hard to remove pulley bolt might also be that the previous technician overtorqued when re-installing the bolt, via say an impact wrench.
-- If the pulley bolt's threads were galled (seized) into place, then I think people would be reading of crankshaft pulley bolt heads snapping off. On old rusted suspensions on my Honda Civics, I have snapped off several large bolt heads. The suspension bolts' threads were corroded into place. But I do not think I have ever read of a crankshaft pulley bolt head shearing off. This is despite the massive torque that occasionally is needed to free the bolt.
-- Googling on "torque to overcome friction" yields numerous scientific-engineering web sites that report that about half the torque needed to free a bolt is dissipated in overcoming the friction between the bolt under-face and the surface to which the bolt underface mates. E.g. see Tightening using the Bolt Head or Nut
-- Whew, this was the subject of a big debate at a certain Honda Civic forum years ago. No one felt 100% sure of the explanation. Now I do. Good job, demoder.
-- What about that cracking sound and small could of dust that often accompany the freeing of a super tight pulley bolt, followed by the torque required to continue removing the bolt being way less? I am guessing this is the crystalline surface of the washer suddenly un-meshing with the underside of the bolt. It's the noise of a lot of friction? Or the compression of the washer is suddenly released, exactly like a very tight spring, and pushes free a bit of corrosion in the area?