Question 1

Bar mount torque — and how little of it is actually published

Accepted Answer

Less is published here than the internet suggests. Husqvarna’s workshop manuals for the 435, 440, 445 and 450 contain no guide-bar-nut torque at all. Stihl does not specify a "bar nut" either — it specifies a collar screw or collar stud, and the figure varies by model rather than by saw size: 16 N·m (12 ft-lb) on the MS 210/230/250, 23 N·m (17 ft-lb) on the MS 261 or 30 N·m on its quick-tensioner variant, and 16 N·m on the MS 271 C/291 C. Echo is the one brand that publishes a straightforward bar-nut figure, 20-23 N·m (about 15-17 ft-lb), and it is the same on the 40cc CS-400 and the 59.8cc CS-590 — bar torque does not scale with engine size. That puts the 20-30 ft-lb figures that circulate for bar nuts at or above the top of the published range: Stihl’s highest bar figure is 30 N·m, which is 22 ft-lb, so the upper half of that circulating range exceeds anything any of these three manufacturers prints for the joint. Whatever your saw specifies: tension the chain first, tighten the two nuts evenly in an alternating pattern, then re-check tension, because tightening usually takes up slack.

Question 2

The clutch is a left-hand thread, and the highest torque on the saw

Accepted Answer

Stihl lists the clutch carrier as M12x1 L across the MS 210/230/250, MS 261 and MS 271 C/291 C — left-hand thread, loosens clockwise — at 50 N·m, about 37 ft-lb. Echo’s trimmer cutter fastener is the same story: LM10, left-hand, 28-32 N·m, the highest figure on the machine. That combination of highest torque plus reverse thread is why this is the fastener most often destroyed, and forcing it counter-clockwise only tightens it further. Two things worth separating: the clutch carrier is not the flywheel nut (28 N·m on those same Stihl saws, roughly half), and on Husqvarna the centrifugal clutch is specified as a minimum — "min. 20 Nm" — rather than a target band.

Question 3

Spark plug torque follows the plug thread, not the saw size

Accepted Answer

This is the figure most often got wrong on a 2-stroke, in both directions. Every Stihl chainsaw powerhead with a published table specifies 25 N·m (18 ft-lb) on its M14x1.25 plug — the MS 210, MS 230, MS 250, MS 261, MS 271 C and MS 291 C all print the same number, small saws included. Husqvarna specifies 20 N·m (15 ft-lb) for the 435 through 450. Echo’s CS-400 and CS-590 both give 15-17 N·m (about 11-12.5 ft-lb), and its M10 trimmer plug drops to 10-15 N·m. So the spread is driven by plug thread — M14 versus M10 — not by displacement, and the common advice that small 2-stroke plugs want a light 6-7 ft-lb is roughly a third of what Stihl actually specifies for exactly those saws. Torque cold, on a clean seat. With no wrench that reads the figure, seat a new plug finger-tight against its washer and add about half a turn.

Chainsaw Bolt & Torque Specs

Bar mount torque — and how little of it is actually published

The clutch is a left-hand thread, and the highest torque on the saw

Spark plug torque follows the plug thread, not the saw size

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