If you've been pushing your saw through some heavy oak and suddenly it loses power, a fresh ms291 cylinder kit might be exactly what you need to get back in the woodpile. It's a pretty common story for anyone who uses their Stihl MS 291 for more than just light pruning. These saws are absolute workhorses, but they aren't invincible. Whether you accidentally ran a tank of straight gas or the engine just got too hot during a long summer afternoon, a toasted top end doesn't have to mean the end of the tool.
Replacing the cylinder and piston is a big job, sure, but it's honestly one of the most satisfying repairs you can do. It feels like you're giving the saw a second life. Instead of shell out several hundred dollars for a brand-new unit, you can spend a fraction of that on a kit and an afternoon in the garage.
Why your MS 291 needs a new top end
Usually, the need for an ms291 cylinder kit comes down to one of two things: heat or lubrication (or a lack thereof). The MS 291 is a stratified scavenging engine, which is a fancy way of saying it's designed to be cleaner and more fuel-efficient. However, that also means it runs a bit leaner and hotter than the older 029 or MS 290 models.
If your air filter gets clogged or there's a small leak in the fuel line, the engine can start running "lean." When that happens, the temperature inside the combustion chamber skyrockets. The piston starts to expand faster than the cylinder wall can handle, and before you know it, you've got scoring. If you pull your muffler off and see vertical scratches on the side of the piston, it's game over for that set. You'll lose compression, the saw will be a nightmare to start, and even if it does run, it won't have the torque to pull through a log.
Picking the right kit for the job
When you start looking for an ms291 cylinder kit, you're going to see a massive range in prices. On one end, you've got the OEM (Original Equipment Manufacturer) parts from a dealer. They're expensive—sometimes so expensive you wonder if it's worth the repair. On the other end, you've got the super cheap aftermarket kits you find on big auction sites.
If you're a professional logger, you might want to stick with the high-end stuff. But for most of us cutting firewood or clearing brush on the weekends, a solid aftermarket ms291 cylinder kit is a perfectly fine choice. Just make sure you're buying from a reputable source. You want a kit where the plating inside the cylinder (usually Nikasil or a similar chrome coating) is smooth and consistent. If the coating is thin or flaky, the saw won't last another season.
Most kits come with everything you need: the cylinder "jug," the piston, the rings, a wrist pin, and those tiny, annoying circlips that always seem to fly across the room. Some even throw in a spark plug and a set of gaskets, which is always a nice bonus.
Getting started with the teardown
Before you even touch your wrench, give the saw a good cleaning. There is nothing worse than dropping a piece of sawdust or a grimy wood chip into the crankcase while the cylinder is off. If that grit gets into the bottom bearings, you're looking at a much more expensive repair than just a top-end swap.
To get to the ms291 cylinder kit area, you'll have to strip the saw down a fair bit. You'll need to remove the top cover, the air filter housing, and the muffler. The MS 291 has a bit of a "clamshell" design compared to the pro-grade saws, which means the engine sits in a cradle. It's a little different to work on than something like an MS 261, but it's totally doable for a DIYer.
Take your time with the bolts. Stihl uses Torx-head screws (usually T27), and you don't want to strip them. If a bolt feels stuck, don't just crank on it. Give it a tap or a little heat to break the bond.
The tricky part: Rings and Circlips
Once you've got the old cylinder off and the new piston ready to go, you've reached the part of the job that tests everyone's patience. Installing the rings onto the piston is delicate work. They're brittle, and if you try to stretch them too far, they will snap. You want to gently walk them down into their grooves, making sure they're seated over the tiny locating pins.
Then come the circlips. These little wire loops hold the wrist pin in place. If one of these isn't seated perfectly and it pops out while the engine is running at 12,000 RPM, it'll turn your new ms291 cylinder kit into scrap metal in about half a second. My best advice? Stuff a clean rag into the crankcase opening before you try to click them in. That way, if a clip jumps out of your pliers, it won't fall down into the bottom of the engine.
Reassembly and the "While You're In There" list
As you're putting the new cylinder over the piston, use a little bit of two-stroke oil to lubricate the walls. You don't want that first start to be "dry." Slide the cylinder down carefully, making sure the rings stay compressed and don't get snagged on the ports.
Since you already have the saw apart, it's the perfect time to check a few other things. How does the fuel line look? If it's stiff or cracked, replace it now. It's a five-dollar part that can save you from burning up your brand-new piston all over again. Check the intake boot too. If there's a tear in that rubber, air will leak in, the saw will run lean, and you'll be right back where you started.
The first start and break-in
Once everything is bolted back together and you've confirmed you have spark, it's time for the moment of truth. Don't be surprised if it takes a few extra pulls to get the fuel moving. When it finally fires up, it might smoke a bit—that's just the assembly oil burning off.
Don't just go out and bury the bar in a massive log immediately. A new ms291 cylinder kit needs a little time to "seat." The rings need to wear into the cylinder wall to create a perfect seal. Most guys recommend running a couple of tanks of fuel through the saw at varied speeds without putting it under extreme load. And for heaven's sake, make sure your fuel mix is fresh and accurate. A little extra oil in the first tank doesn't hurt.
Keeping it running for the long haul
To make sure you don't have to buy another ms291 cylinder kit in six months, pay attention to how the saw sounds. If it starts "screaming" at high RPMs or won't idle right, stop using it and check the carb settings. Keep that air filter clean, and always use high-quality bars and chains. A dull chain makes the engine work twice as hard, which creates more heat, which well, you know how that ends.
Repairing your own equipment is a lost art for some, but there's a real sense of pride in hearing that MS 291 bark back to life after a rebuild. It's a solid saw, and with a fresh top end, it's got plenty of years left in it. Just take it slow, keep your workspace clean, and you'll be cutting wood again before you know it.