I would be as careful using (on an engine) a Harbor Freight torque wrench as I would be using a loaner from a parts store (how often do you think that would be calibrated)?
Two years ago, I checked a 5 year old Harbor Freight torque wrench against a newly calibrated Snap-On torque wrench. We did not do a carefully scientific study but the Harbor freight wrench seemed to be about 5 ft-lbs over torque for head bolts.
I like (and use) my Sears "beam wrench" but it has not been calibrated since I bought it about 40 years ago.
