stihl 660 seized

Discussion in 'Mechanic and Repair' started by shop22, Jan 18, 2006.

  1. shop22

    shop22 LawnSite Member
    Posts: 134

    question for any of you 2 cycle mechanics. I had a customer bring in a stihl 660 and an older 066. called local stihl dealer, he said 066 and 660 were same jug and piston. original 660 customer brought in had scored cylinder by exhaust port. I took his old saw and swapped out the jug and piston which was not very old. Saw ran for maybe 15 minutes and seized in same spot. Oil mix is echo oil and was properly mixed. i found a slight air leak on the seal behind clutch but would this be enough to seize piston in 15 min. Hope any 2 cycle mechanics may lean me to what to look for next. I don't want to install new jug and piston and seize again. Thanks in advance
     
  2. JHugh

    JHugh LawnSite Member
    Posts: 84

    what are all the steps you took in repair of this saw? replace gaskets, pressure and vacuum test engine, inspect and repair carburetor, check and adjust carburetor settings, check fuel hose and filter, check impulse hose...there are many ways for a 2 cycle to lean seize. the crank seal leaking would cause it to run lean but probably would not the new cylinder in 15 minutes.
     
  3. shop22

    shop22 LawnSite Member
    Posts: 134

    i had checked fuel hose and filter, both looked fine. i checked the intake boot from the carb to the block, found no cracks or leaks. installed new base gasket with the other piston and jug, adjusted carb, test ran at shop. Unit fired right up and ran ok, did not sound like it was running lean, but i guess it was.
     
  4. JHugh

    JHugh LawnSite Member
    Posts: 84

    you might remove the carburetor and check the diaphragms to make sure they are not stiff. check the internal fuel screen to make sure it is clean from varnish or dirt. also check to make sure the inlet needle is not sticking, and make sure the fulcrum arm is set properly. of course you are going to replace the crank seal. do you have a tachometer to check the high RPM setting?
     
  5. shop22

    shop22 LawnSite Member
    Posts: 134

    I'll clean the carb tomorrow and get a rebuild kit for it. I've got a tach that i bought with an echo service kit. What hould the high rpm's be for the 66o magnum?
     
  6. JHugh

    JHugh LawnSite Member
    Posts: 84

    I think the high speed setting is around 12,000 to 13,000 RPM's.
     
  7. davhul

    davhul LawnSite Member
    from Gray,Ga
    Posts: 51

    Also check the crank bearings if they have any movement that would cause seizer very quick, and would cause that seal to leak due to the movement..I see this more on the ts400 and hand held blowers.
     
  8. shop22

    shop22 LawnSite Member
    Posts: 134

    I'll check te bearings, I guess i should clarify when i said seized, the piston didn't set up tight. It scored just to the chain side of the piston on the exhaust port side. that's why i figure I had an air leak that caused it to run lean and scored piston and jug.
     
  9. JHugh

    JHugh LawnSite Member
    Posts: 84

    You are correct that the seal leaking will cause a lean seize. But you should check all the other things mentioned so you know it will not happen again. I have had saws lean seize with an air tight engine. The conclusion why they seized by the OEM and I was from incorrect carburetor adjustments. I always rebuild a carb on a saw or trimmer that seized just as insurance. A 10 dollar carb kit is cheap.
     

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