Stihl 290 chainsaw

Friend brought me a Stihl 290 chainsaw to fix. Dealer diagnosed needs piston and cylinder. Parts are ordered. I've never done this. Any advice or suggestions I should have before I start?

OEM Parts Manual and OEM Repair Manual would be the place to start. Tom

They are just small engines. Take things apart gently (it was put together in a sequence that was not requiring bending things0 take pictures of each piece removed and track the screws in a piece of cardboard with pencil marks as to where they go. Clean gasket surfaces and do not score with the scraper. They are fine pieces of equipment. You will need the manual! to assure tightening specs. Jim

I would be disinclined to work on anothers equipment if I did not know what I was doing.

That said, you will need a service manual to properly torque fasteners upon reassembly. The service manual should also cover disassembly/reassembly procedures.

Determine how the piston pin is secured in the connecting rod before starting. If pressed in, you will need a press to R & R the piston.

Dean

I've replaced the piston and rings in a few saws over the years. First thing is the clean the daylights out of it. I've taken some of them to the carwash to clean them. Be careful not to get water in it. Just blow off around the body and cylinder.

I'd try to find out WHY it needs those parts so it doesn't happen again right after you "fix" it.

Check the fuel hose for a pin hole.

If this is a MS290, the parts will cost near what a New Saw cost. If you charge a fair labor rate the total cost of the repair will likely be MORE than what a new saw cost. These saw DO NOT have a removable jug. The cylinder is also the upper half of the crankcase. Likely WHY the saw need a new piston and cylinder is 87 octane fuel was used in the saw. YOU MUST USED 89 OCTANE OR BETTER fuel in ALL Stihl equipment.

Kent

It is a pretty basic job. Most fasteners are T-27 torx. Aftermarket jug/piston kits are $50 or less(46mm). You could install a 49mm kit intended for a MS390 if you were so inclined, and wanted more power.

Well Kent I was starting to believe you about the hug and piston then you made the statement about 87 octane fuel.
I KNOW that's wrong. How? I run a 290 and the older 28 on 87 octane with no problem! The real issue is the mix. Use 50:1 and you're asking for problems; use 40:1 and they run forever.

Use caution if you have to put the ring on or put the piston in the cylinder. The rings break easily. 87 octane will pit the top of the piston due to preignition.

Took me long time, age 68, but finally I can say no to some jobs. This sounds like one of them. I no longer tackle anything I don't know inside and out unless it is mine. Dave

Was the saw damaged from running too lean?

Last summer I got a carb overhaul kit for a Stihl string trimmer that I could not get to run right. The owner of the Stihl dealer/small engine repair shop commented that the newer 2 cycle engines have to be set to run on the extremely lean edge right from the factory to meet tight emissions standards. Restrictor caps on carburator needles are fine when the engines are new, but since they only allow 1/4 turn of adjustment they leave no room for error as engines get older. In time the engines run way too lean and fail prematurely.

As machines get older, many owners are reluctant or don't know to pull off the restrictor caps and adjust the carbs properly, so their engines are ruined way too early from running too lean. He said he sells more repair work and replacement machines because of this, but it makes his products look bad. Eventually most small engines will go to 4 cycle and the problems will be reduced.

Before I tore down the carburator I pulled off the adjustment restictors, opened the needles all the way, turned them back to their original setting and tuned the carb again. It runs like a top now, and it doesen't smoke much. The needles are less than a quarter turn past what the restrictors would allow.

I haven't used the $16 carb kit yet, but I feel the advice alone was worth that much.

What is the deal on the octane ? I can't recall what I have run in my 390, piston and cylinder wall checked out to be fine, its an '02, and has cut a fair amount, I've always run Stihl oil 50:1, what the book calls for, and I make sure to rinse the little jug with gasoline to get the last bit out and mixed. I know people have their preferences and all, but if there is something too this, I'd sure like to know. Only trouble I've had is one fuel line with several cracks.

Not that hard, I've done one. Make sure its not running to lean (probably caused the problem in the first place) or the repair will be short lived.