Wednesday, November 23, 2016

Why Won't My Saw Start?

 This is a story about a guy that thought he was doing everything right until I rained on his parade.

 So this guy shows up at my workbench with a chainsaw that wouldn't start. He was an elderly gentleman with just enough mechanical knowledge to get by but not enough to figure it out. He told me he pulled the spark plug for inspection and to check for spark. I'm told it was clean and grey and he did have a nice blue spark. His next move was to squirt starting fluid in the carb but still nothing. Not even a burp. He then decided to pull the spark arrestor from the muffler to see if it was blocked with carbon. I guess it was nice and clean with a grey tint to it. "I just don't understand why it won't start", he stated.
 At this point I had a pretty good idea what was wrong but I didn't yet know why. I told him he had a scored piston and a stuck ring, and this was resulting in low compression. Engines need a certain amount of compression to run. The unit was junk as repair costs would exceed the value of the saw. I pointed to the scrap metal dumpster but he didn't think that was too funny.
 I was getting that look. It's the look you get when the customer thinks you're just trying to sell new saws. I told him this failure was possibly from, among other things, a lack of lubrication. Now I was getting the look and attitude. He said he didn't believe it and proclaimed he only uses premium ethanol free gasoline and the best outboard motor oil money can buy.
 I believed every word of his story but now I knew the rest of the puzzle. As he ranted about the price and quality of his oil, I pulled the muffler off his saw. Sure enough, the piston was roached. The wannabe mechanic just couldn't believe his eyes. He used quality oil and mixed it with the precision of a pharmacist. I pulled the recoil slowly to allow viewing of the intake side of the cylinder and that wall was scored too. I wondered to myself how many buddies he bragged to about his use of that "quality" marine oil.

Just a generic image of a scored cylinder wall taken with a small inspection camera that connects to my phone.

 I don't like having to tell people they ruined their equipment. I don't get pleasure from this but come on, this stuff is right there in the owners manual. The sad part is most people think a chainsaw owners manual is really just meant to lay in the bottom of their saw case and soak up bar oil. The techies reading this saw the clues. For the rest of you I"ll point out that the grey color on the spark plug and spark arrestor screen was actually aluminum transfer from the cylinder/piston scoring. If you think the scoring was from the starting fluid that doesn't contain lubricating oil, you'd be wrong. The engine never ran on that stuff. The oil he did use was for marine use. That oil is not formulated to work on air cooled engines and will fail under the high temps and loads these chainsaw engines develop.
 Despite the fact that this guy snuck in the back door and I didn't have a work order to justify the time I spent with him, I took another minute or two to educate him on oil. I didn't sell him a new saw that day but as he left he shook my hand and I knew that even though I was the dick head that gave him the bad news, he'd be back and I had earned a new customer.



  1. Thank you. I just went out to check what I was using for 2-cycle oil. I never paid attention to what it was for. (It was Stihl branded, whew!)

  2. The current highest JASO(japanese oil standards rating) rating is FD. Search for oils with this rating. Your Stihl oil bottle probably has this printed on it. Every major manufacturer tech school I've been to preaches this stuff. I figure if they are the ones honoring the warranty and this is what they want in their engines, then why run anything else.

  3. Learned something new today. Thanks. Will be sure to check what I'm using (although I know it's not marine formulation.)