Stihl BR420 Blower Engine Siezed !

Discussion in 'Mechanic and Repair' started by westernmdlawn, Nov 21, 2006.

  1. westernmdlawn

    westernmdlawn LawnSite Member
    Messages: 98

    I have a Stihl BR420, the engine siezed the other day doing a leaf clean up. I haven't disassembled it yet, but the starter rope won't pull. Also, the engine smelled like it was really hot right before it shut down. Also, it was down on power as well. I was not the one running it, it was one of my employees. We run Stihl 2-cycle oil (50:1) mixed with 87 octane fuel. It is about 2 1/2 years old. It has some use on it, but I think it is definitely a premature failure. I would guess that it has about 250 to 500 hours on it. I would think that this engine should have gone for at least 1500 - 2500 hours. Maybe I'm a little too optimistic on that assumption. Anyway, I'm planning on tearing it down on Thanksgiving day to see whats up. I priced out a new cylinder, piston & ring, and gaskets at around $250. A new unit will cost me about $400. I would like to rebuild it since the rest of it is in good operating condition still, but I am trying to figure out why it siezed (if in fact that is what happened). Perhaps we were not doing maintenance often enough? We do do maintenance but it is possible that it was overdue. We also noticed that recently it has been hard to start (but had good compression according to the starter rope test). Is it possible that the carb is out of adjustment or plugged up (thereby leaning the mix and causing the engine failure). I know the air filter could be choked up, but that should make the mix richer, not leaner - which would cause the opposite kind of problems.

    Any Thoughts?
  2. fortdan

    fortdan LawnSite Member
    Messages: 30

    It sounds to me like your assumption is right; but $250.00 seems a little high to fix the engine. How much would a hole new engine cost? I have a BR-400 with a shot engine. I was thinking of selling it on EBAY, even broken ones go for about $100.00. I'll probably just buy a new engine for it, because new bp blowers cost so much. If you find out how much a new engine costs, let me know.
  3. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,370

    Probably too late but what you should have done when it stopped was immediately take out the plug and put in straight 2 cycle oil. Then take the three screws holding the starter rope assemblyoff. Next force the crank to turn with your hand until the rings free back up. Obviously the cyclinder will be marked but in 2 out of 2 times on a big Echo I got the unit to start and run and it is still in service. I would still try it. You could take out the piston and very lightly lightly buff the marked cyclinder then put in new rings and give it a try.
  4. khouse

    khouse LawnSite Bronze Member
    Messages: 1,465

    gaskets, piston, hone and rings will probably get several more years out of it. the cylinder doesn't have to be perfect. some cylinders won't hold a set of rings, but most do. tear it down run a hone in there and take a look before you go and buy a new engine. nothing to loose but some time.
  5. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,370

    The Echo guys say don't use Hone on their cyclinders since they have a very thin plating??? They said just use fine sand paper to get any ridge out best you can, don't know. I just turned the crank and let the rings do the work but unit was still hot.
  6. westernmdlawn

    westernmdlawn LawnSite Member
    Messages: 98

    Thanks for all the great advice guys! I never even thought about doing that. I will see if the cylinder is in good enough shape to re-use. A new ring and piston might be all I need, depending on the condition of the cylinder. You are right, that is very expensive for a rebuild.

    Does anyone know if these cylinders are Nikasil coated? If they are cast iron sleves they could be honed, but not if they have the coating of Nikasil.

    Thanks again guys. I will get back to you when I get her tore down.
  7. westernmdlawn

    westernmdlawn LawnSite Member
    Messages: 98

    Well, I tore it down on Turkey Day. Piston rings have siezed into the piston on the exhaust side. The exhaust side of the piston and cylinder walls are marked up pretty bad. The piston looks to be totally useless. The cylinder walls look marked up but the marks aren't deep. I'm wondering if I could hone it and throw in a new std bore size piston and rings and get away with that? Probably not. That would be a relatively cheap fix. But I'm afraid that if I do that, the damged cylinder will cause premature wear and failure of the new piston and rings. Then, my next problem is to figure out why the engine siezed in the first place. Like I said, all damage is on the exhaust side, the intake side looks good. Also, the air filter was very dirty and cruddy looking. Does this unit not have the intellicarb (compensating carburator)? Maybe it compensated too much (air filter too restricted, requiring too much compensation)? The only other thing I noticed was that the spark plug center electrode was nearly white (it must have been running very hot). Additionally, the exhaust port had some carbon buildup in it. I would say that it was about a 5% flow restrition (if that even). I can't see that being enough of a restriction to cause overheating, but maybe it was more restricted before it got super hot and blew out? Last thing, I'm not positive, but I think the throttle cable is not hooked up properly. I think it came unhooked on the trigger side. Still that should not make it run lean. It has a half of tank of fuel left in it, so I know it didn't run empty and get lean during the last few seconds. The fins on the outside of the cylinder are not plugged or restricted at all. This brings me to another question - how does this engine get cooling? There are no fans that direct cooling airflow past the cylinder walls.

  8. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,370

    Never had any BR420 apart but Echo has fins in the flywheel that create the air flow. I guess you ruled out your oil mix as probably cause. The ports weren't closed enough to cause any problem, I guess the exhaust was not restricted?
  9. Alta Lawn Care

    Alta Lawn Care LawnSite Member
    Messages: 79

    My Stihl BR 600 mnual calls for 89 octane. I checked with the sales guy who also is a small engine mechanic and he confirmed that you don't want to run anything lower than 89 octane. He said lawn equipment doesn't have O2 sensors and you'll never hear the knocking.
  10. ed2hess

    ed2hess LawnSite Fanatic
    Messages: 14,370

    It is best to run 89 but from a practical standpoint 87 works just fine on 2 stoke stuff w/o valves. There is some buildup in the ports and that can be cleaned out, and sea foam cleans up the cyclinder just fine. The main reason we don't use 89 is the extra time needed at the pump, and some pumps won't allow you to put back to back charges on the same card.

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