This is my third time replacing the cylinder already and I still can't get the original head bolts to fit. 7mm x 1.5 TORX is quite too big for the first 2 cylinders, now it's a little small for the third. What to do? Can you recommend specifically for the Stihl MS290?
Replacing the cylinder of my Farm Boss
- Thread starter J1GSAW
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Vorhi-heesy1985
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- May 2, 2025
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I ran into this exact headache helping a friend rebuild their MS290 and we learned the hard way that aftermarket cylinders often come tapped for 6mm x 1.0 bolts instead of the original 7mm x 1.5 self tappers. If your new cylinder is already threaded, grabbing 6mm bolts should do the trick. If not, you might need to tap it youself or see if the original bolts can thread in without stripping anything. Have you checked if the cylinder has pre-tapped holes?
Cuttingranger
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It seems like you're dealing with a combination of OEM and aftermarket cylinder threads. The MS290 typically uses self-tapping IS-D6x52 screws, but a lot of aftermarket cylinders come pre-tapped for M6 x 1.0 bolts. Make sure to check if yours is pre-threaded. If it is, you'll want to toss aside the original screws and get some M6 x 1.0 bolts in the correct length. I've been through it myself, it's a simple fix once you find the right match
Hmm, that's odd, have you tried using a slightly different size bolt or checking if the threads in the cylinder are damaged? it could the head bolts have been swapped out before?
HArborist2
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- Apr 25, 2025
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I've been in that situation before, the MS290 actually requires 7mm x 1.0 self-tapping bolts, not 1.5. Most aftermarket jugs come pre-threaded for 6mm x 1.0 bolts. You need to either match the bolt to the threads on the cylinder or just stick with OEM or Meteor cylinders that are designed for the 7mm self-tappers. If you try to force the wrong size, you'll ruin the bore threads pretty quickly.
