LawnBoy engine - no compression

Discussion in 'Mechanic and Repair' started by Roger, Aug 15, 2005.

  1. Roger

    Roger LawnSite Fanatic
    Messages: 5,941

    I posted a question a few days ago about a LB DuraForce carb screen problem. After that was resolved, it has worked great -- until mid-morning today!

    It fired this morning, like usual, sounding and working fine. We used it for a couple of lawns, and was using it on the next one. It started to loose power, and within a few minutes, stopped running.

    I discovered it has no compression. I took out the plug, and see nothing unusual (I concede not much can be seen). The piston does move as expected when cranking. Also, when cranking, I hear a sucking sound, presumably from the carb area.

    The fact that it spins quite freely tells me there is a major problem, internally. The blade isn't loose, either the nut holding the blade to the adapter plate, or the lower engine bearing. When cranking, I hear a sound that is not usual -- I'm hard pressed to say it is a knocking sound, but can't describe it another way. It isn't as "solid" as I believe a knocking sound might be, but I believe something is loose someplace.

    I have not yet had a chance to take anything apart. I returned to pick up a backup machine, and finished out the day's mowing schedule.

    My only thought is that a ring is broken.

    If somebody is quite sure the problem is a major internal one, I wil get a short-block on order ASAP. If not, I'll take time to disassemble, and go from there. I would like to get it back in service quickly -- my backup is another LB, pre-DuraForce, but has seen many, many hours of service.

  2. lawnmaniac883

    lawnmaniac883 LawnSite Silver Member
    Messages: 2,613

    Take it apart first. Dont get a shortblock until disassembly confirms that is the problem. My guess is a bad ring.
  3. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    If in deed it is a broken ring it had to do other damage (Piston, Cylinder, Ect.) before stopping. So if time is money you mite be better off to get that shortblock coming.
  4. Lawn Masters

    Lawn Masters LawnSite Senior Member
    Messages: 850

    may have been too lean, which can result in piston damage especialy if its a 2 cycle engine. possibly a broken ring, but the lean engine scenario seems more likely from what you describe.
  5. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    That is probably the case, Due to a clogged fuel screen in a earlier thread and talk of it happening previously.
  6. Roger

    Roger LawnSite Fanatic
    Messages: 5,941

    Thanks for the replies -- I wish I had the experience to diagnosis these matters better, and the technical knowledge to make the repairs more easily.

    restrorob - your observations may well be correct regarding the clogged filter. BTW, I did put a fuel filter in the fuel line between the tank and carb, just as I had asked about in the previous thread. But, my actions may have been too late.

    I may have some time today to tear it apart. I'll let you know what I find.
  7. Roger

    Roger LawnSite Fanatic
    Messages: 5,941

    Problem solved today -- I'm in a hurry to get back to mowing, so will post the findings and resolution later this evening. But, now I have even bigger questions to answer.

    ... later.
  8. Roger

    Roger LawnSite Fanatic
    Messages: 5,941

    OK, there is good news to the story, and bad news, and perhaps even worse news.

    The good news is that the mower is up and running well.

    The bad news is the engine lost the needle bearings in the crankshaft bearing. When I pulled off the head, a couple of the needles were visible beside the piston. Obviously, they had jammed when the engine was running, scoring the cylinder wall. This was the reason the engine had no compressing -- easy bypass where the needles had jammed between the piston and the wall.

    I made some phone calls and found a dealer who had a new short block. I was surprised because in the past, I learned that a short block is a rare inventory item. However, they had one and I picked it up.

    I'm no professional mechanic, just an amateur with three tool boxes crammed with simple tools. However, in about four hours I had the old one out, and the new one installed, and the mower running. I fired on the first pull of the rope. The top end speed was a bit low and I had to make an adjustment with the "clicker" knob over the throttle post. I did have foresight enough to buy a new throttle spring with the short block. Those springs are so delicate and I've learned in the heat of battle, the carb and air box come separated and the poor little spring gets bent out of shape.

    I'm sure I didn't take the most effective path in doing the operation. The sequence of putting things back in the right order eluded me a time or two. The most difficult thing for me is getting the carb and air box back in the right place, with great care not to damage the throttle spring. Also, I had some difficulty getting the muffler gasket positioned right, while getting the bolts up from the bottom. And, I don't know any good way of getting the U-tube on the exhaust port positioned right while putting in the bottom plate. That is a terrible design!

    I did not split the block, but I can feel the slop in the crank/piston movements. Also, a little shaking and I can hear the needles rattling inside the crankcase.

    Perhaps the worst news: This is the same failure I had on the original engine. See this thread.... page down until you get to some August dates, then October dates.

    The point of failure seems to be the same. However, the events leading to the failure are different. As you can read from the previous thread, the original engine never ran well from day of delivery. And, it was especially difficult in the last two weeks before failure.

    In this case, the engine gave no warning signs. I used it for some work yesterday morning, and then turned it over to my wife (she works with me a good part of the time, and generates about 60% of the service time). When I used it (about an hour before hand), it ran great. And, she said it ran fine for her, until a few minutes before failure. Her only assessment, "... it didn't seem to have quite as much power." Hmmmm. However, there had to be more to the final minutes. With the needles gone/going, there had to be some pounding. I was running my Exmark, with muffs, and didn't hear anything. The death was when she was emptying a bag of clippings. It just stopped.

    Of course, this is very distressing to me. I'm basically solo, and I don't have a fleet of equipment. The mower does get used heavily, sometimes going through more than a tank of mixed fuel every day. It was put into service last September, but we ran it sparingly last Fall after I installed the new short block. I feared another failure. However, this Spring, I made a conscioius decision that we would use to fully to the extent we needed. I also have a Toro ProLine with a Sizuki, still in great condition. However, it is not the mower of choice (weight, bagging capability, and quality of result).

    The fuel mix this entire season has been Opti-2, about 75:1 (9 oz/5 gal gasoline). That decision was made based upon so much talk here. Since the first engine primarily had LB oil, 32:1, and it failed, I decided to try Stihl oil last Fall after the rebuild (32:1). However, I learned Stihl oil is not ashless, and I had heavy carbon build up. I had good success with Amsoil in my 2 cycle Stihl hand tools, but since Opti-2 was given such high marks by so many people, I decided to "use the best and proven." The performance of the engine this season has been great! I have commented often how much better it runs this season, and how pleased I've been with the Opt-2. Now this revelation!

    So, now my dilema -- what oil to use? I have to believe, however, from my experience with the original engine, the oil did not have anything to do with the failure. I think something else was wrong - perhaps the reeds (just grasping at straws because these engines are so simple). And, maybe the oil had nothing to do with this failure.

    I made a new mix of 5 gallons of fuel late last week, so it has been running on a new mix, about 2.5 gallons are gone by now. Maybe I put in 4.5 oz of Opti-2, not 9 oz. I have a gallon supply bottle of Opti-2 and measure each mix ("senior moment" as we old folks say). I'm tempted to discard the last part of this container and mix a new one, continuing to use Opti-2.

    Any thoughts on this matter of oil?

    One last question for you folks in the repair field. Do you make such repairs as I made? Or is the mower junked? I paid $177, plus tax, for the new short block. Even if somebody was skilled at making a replacement, I doubt such a replacement can be done in less than two hours. Or am I wrong? How much time would you allocate for such a repair. If the parts are $180 (round numbers), and two hours of shop time (at $45-50), a repair would be $270-280. Would many customers pay this? This morning was a rainy morning here, as well as the early part of the afternoon. I would have lost mowing time anyway, but did sacrifice a couple hours of work time to complete the job. Any insights into what a repair shop would have done with this mower?

    Sorry for the length of post. I'm sure only a few interested people would read anyway. Maybe my experiences can be of help to somebody else.

  9. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    Ok, First of all I still believe it's possible the plugged fuel screen caused the engine to lean out which is oil starvation also. I believe the oil your using is just fine, If the mix is in question I would mix another can to be safe. You can add a little at a time of the old mix to your larger unit instead of dumping it out, Gas is too expensive anymore.
    As for this type repair, I won't recommend it to a customer unless it's a near new unit. If a customer request this type job on a small walk behind the parts are pre-paid before work is started.
    For your repair where I work, It would have been in the $300.00 range so Glad you were able to perform the task at hand yourself and save some bucks !
    Btw; Keep an eye on that fuel filter, And it mite not be a bad idea to do a carb. clean in the off season just to be safe.
    Good Luck
  10. Roger

    Roger LawnSite Fanatic
    Messages: 5,941

    Apparently all is well. We ran the new engine about 3 1/2 hour this morning, and another 4 1/2 hours this afternoon. Four of those hours this afternoon were non-stop (we have several connected lawns). It seems smooth and starts fine. So ... perhaps we are on the right road with this one!

Share This Page