Who calibrated your digital unit?I do check mine with a digital torque adapter. That how found out how lousy HFT torque wrenches were. One was nearly double the torque setting before it clicked. No wonder I was snapping bolts
Also you should unload the torque wrenches when you not using them as leaving them loaded can cause the calibration to become un-calibrated.
Tap Magic doesn't work very on aluminum. I have tried it then my machinist suggest the alcohol.I recall AlumaTap when I worked in machine shops. If you used Tap Free on Aluminum it would turn it black. Back in the day. Now they have tapping fluids that claim to work on all metals. Tap Majic.
That is what happens when they make a product that accommodates too many options. Too many compromises. It does not work well at anything while claiming it can do everything.Tap Magic doesn't work very on aluminum. I have tried it then my machinist suggest the alcohol.
Or in the case of the old Kohler K-series it was recommended to replace the head bolts. The understanding was the bolts were designed to expand and contract with the aluminum, but were basically a one time torque to yield bolt.I recall the cast iron engine days of book specific head bolt torque values and "by the book" was the rule.
When aluminum heads and blocks came out, the game changed due to dissimilar metals and a high coefficient of friction. Steel bolts and aluminum components have different rates of expansion and contraction with changing temperatures.
To resolve issues many manufacturers switched over to angle torque settings and torque to yield one time use bolts. That was mainly critical on the automotive engine designs due to higher engine compressions and longevity.
On the small engine side, they mostly still relied on fixed torque settings, but all the head bolts required a very thin coat of lube to prevent excess friction during the bolt torque process.
The whole idea of properly torquing bolts is providing the proper bolt clamping force and gasket crush to ensure proper long-term sealing.