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Replacing a cylinder gasket on a Stihl br 420?

Discussion in 'Mechanic and Repair' started by HenryB, Feb 16, 2008.

  1. HenryB

    HenryB LawnSite Bronze Member
    Posts: 1,828

    Blower is leaking oil at the base of the cylinder (gasket area). Any tips on replacing this gasket. Will the cylinder just lift off after removing the 4 screws?
    Thanks in advance.
  2. lwcmattlifter

    lwcmattlifter LawnSite Senior Member
    from NC
    Posts: 859

    It lifts off. Be careful with the piston rings they are really fragile.
  3. MowerMedic77

    MowerMedic77 LawnSite Bronze Member
    Posts: 1,164

    Pull off your carb and muffler, it will make handling the cylinder easier. Drop the piston to the lowest point of travel and remove the screws from the cylinder. Pull off the cylinder from the lower case and clean both surfaces making sure to clean anything that drops into the cylinder or the lower case. Install your new gasket and lube the cylinder walls with a little raw 2stoke oil. Make sure that both rings are floating free and the end gap is in-line with the anti-rotation pins. Take you time and slowly reinstall the cylinder down onto the piston one ring at a time being careful not to force it as they will break very easy. Once both rings are inside the cylinder tighten it back down to the lower case. Reinstall muffler and carb, run and test.
  4. HenryB

    HenryB LawnSite Bronze Member
    Posts: 1,828

    Thank you ! Any other last minute tips.:waving:
  5. Landrus2

    Landrus2 LawnSite Platinum Member
    Posts: 4,812

    It would be a good idea to replace your piston and rings at this time.:drinkup:
  6. ed2hess

    ed2hess LawnSite Fanatic
    Posts: 13,200

    Not a tip but a warning those cylinders didn't use to have bevel on them so they are a living hell to get back over the piston/rings. A helper person can be beneficial on helping get it over. The echo is very easy compared to these, unless they changed recently.
  7. heybruck34

    heybruck34 LawnSite Senior Member
    Posts: 300

    Take it to a shop. I tried to do it myself and failed, enlisted my father who used to rebuild engines for extra cash on the side and we failed. I broke 2 rings and almost a 3rd before I gave up. 2 days later and a relatively small amount of money, my blower runs like a top.

    I like doing my own maintenance and repairs, but this job was a b---h and I felt better left up to the pros.
  8. topsites

    topsites LawnSite Fanatic
    Posts: 21,653

    Yeah once we get into that TDC compression bit the only way I'll DIY is if I got nothing left to lose.
    The dealer can probably do it for a lot less than the headache is worth.
  9. Stillwater

    Stillwater LawnSite Platinum Member
    Posts: 4,834

    when they say those rings are easy to break they mean the rings are very very brittle if they get flexed more than a 1/8 of a inch in any direction and in any way they will snap. but it is a easy job....
  10. Mowinforaliving

    Mowinforaliving LawnSite Bronze Member
    Posts: 1,258

    What's the "end gap" and "anti-rotation pins"????

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