What Went Wrong with my Bolens BL110?

[mh9162013]

I was using my Bolens BL 110 the other day, when I started smelling this faint burning smell. It smelled almost pleasant, like toast, a fireplace or wood burning. It was faint, and I assume it was just some dust or dirt on the muffler or w/e that was burning from the heat. This was the first time I was using the Bolens this season.

Well, I noticed a drop in power...like a big drop in power. I turned off the engine to adjust the head that wasn't feeding line properly, but when I tried to start it back up, it wouldn't start. I wasn't surprised.

I figured the issue was a clogged spark arrester, thinking the low power was due to insufficient "breathing" of the engine. I removed the black plastic "cover" over side of the engine and it turns out this plastic cover is also the side of the crankcase of the engine. I noticed that part of the plastic cover had been scored/melted and there were many bits of black plastic in the crankcase area. I removed these pieces, but the string trimmer still won't start.

I know I need to test for spark, air flow and fuel flow. I already have tested for compression and it's about 110 PSI or so. And I doubt it's the spark plug, because it was running (albeit it poorly) before it refused to start. I also don't think it's the muffler as the engine still won't start with the muffler removed (is that an effective way to test for a clogged muffler?)
But are the melted bits of plastic related to the CAUSE of my engine start troubles? Or are they the CONSEQUENCE of my engine troubles?

Any advice would be appreciated.

 

[Manic84]

Honestly, I'd say the melty bits are a sign of a coming failure in the engine itself. These style of trimmers have a design flaw that allows the crankshaft pin to worm out when hot, and eat away at the inside of the back cover.

From experience, sometimes there is an o-ring on the back cover that acts like a seal for the crankcase. It can deteriorate over time, and when in use, the machine will lose power, refuse to restart or run poorly (if you can get it running).

Both things can make the machine lose power, hard/impossible to start, and difficult to adjust the carburetor. (unless an absurd setting is used)

I'm not going to give you false hope, I see this kind of problem a lot (it's the market here) and it's almost never worth repairing.
If you're lucky it's the o-ring, and you might be able to replace it, and get more use out of it. (Although I strongly suggest looking for a replacement trimmer)
A good way to check early on if the o-ring has failed, is to check for any oil residue on the seams of the back cover.
But more than likely, it's the pin starting to come out.

Questions:
How long have you had the trimmer? (If I had to guess maybe about 2-4 seasons?)
And if you can, put up some pics of the crankcase and back cover. (Just out of morbid curiosity)

 

[mh9162013]

Hmmm, those are some great points and great advice, thanks!

I purchased this string trimmer in the summer of 2017. Each season, I probably ran about 3-4 tanks per month in the trimmer.

I'll try to get some pics up later, but I won't do any yard work for another week or so, but when I do, I'll take some pics and post it here.

As for the o-ring, it looked ok, but I'm guessing it can look just fine and still cause trouble. Although, I didn't notice any residue leaking from the crank case.

Is it possible for the o-ring to cause trouble so suddenly? This is what makes me think it's the crankshaft pin. This would explain the sudden burning smell, loss of power and plastic shavings. I'll try to get the pics to confirm this diagnosis.

Is it possible it's still the o-ring even if I'm getting "ok" compression?

Assuming a replacement is necessary, I already have an old electric Black & Decker trimmer I can use with 2 spare battery packs. I also have the Echo PAS-225, so for $80, I will have a solid replacement. But given the economy and my finances (and the ready-to-go replacement), I'll probably wait until next year/season to make that purchase.

 

[mh9162013]

Ok, I got some pics:



I definitely noticed the pin being pushed out and it seems to coincide with the donut ring in the plastic crank case cover.

And despite multiple attempts to start it, I see no fuel in the piston or crank case. My guess is that some plastic shavings clogged up the carb. What do you think?

Thanks again for you help, Manic84.

 

[Manic84]

Oh yeah... it's done for, that back cover should be flush and smooth.
Now...
If there's no oil residue, the o-ring is probably good. It doesn't really affect the compression, but does affect the performance of the machine itself. Much like a leaking oil seal... just worse because of it's position.

When it fails, it leaks out any residual oil in the crankcase, which loses lubrication, and damages the crankcase (it grinds/shreds itself to death). And it begins running lean, scoring the piston and cylinder, reducing the compression needed to properly run. Sadly, these machines have a very short lifespan, and are meant to be affordable, so they don't really have a high compression reading to begin with. (which is why they "die" so quickly)

If there are bits of plastic in the crankcase, and the inside of the back cover has the distinct circular wear marks, no doubt it's the pin.
When the pin is beginning to, or does give out; it's immediately noticeable, and the damage can be catastrophic. There is almost nothing you can do after it starts to give. You can adjust the carb, and look at everything else to no avail.

Once the pin starts worming out, it's game over. Everything else in the machine fails. I've tried to revive these types of trimmers, once the pin goes, nothing works, and if it does; it doesn't work for long. And they're not really meant to be repaired, it's always too expensive. (and pointless because it will fail in the same way) They're good while they last, but at this point, it's better to just retire it, and use it for parts: carb, fuel tank, ignition coil, P+C (if they're not scored) etc.

I don't want to seem unsympathetic or arrogant. I've seen and dealt with the frustration these machines bring, and don't want you to waste your time on a machine that is already doomed. It's good that you have a back-up trimmer, and I am glad you are saving up for another trimmer in the future (just get a different style). I'm sorry that this isn't what you wanted to hear, but it's the sad truth for these style trimmers.

P.S: If it would interest you, there was a thread awhile back called * "Engine Damage Autopsy" it's an extreme, but it shows what does happen to the engine when the pin lets go. And the inherent design flaw of these trimmers. Other members (myself included) gave a rundown of what the cause of failure was.
*link

 

[mh9162013]

Thanks for your advice, Manic84. Just a few questions, for my curiosity.

1. I understand how these machines are basically "disposable" and I'm not surprised at all. They're cheap for a reason. But you said even if I fixed the pin, the fix would be temporary. Is that because there's no cost effective way to keep the pin from sliding out again?

2. Ok, so it's the pin. But how does that explain the apparent lack of fuel and oil getting into the piston/crankcase? Do you think the plastic shavings caused some clog somewhere? I'm just curious as to why this machine won't even start anymore.


You don't seem unsympathetic or arrogant at all, no worries! You've been really helpful, so thank you. I purchased this machine knowing it had a limited life span and that we'd need a higher quality machine in the future. Unfortunately, now's just a bad time for it to fail and me to buy the add-on for my Echo PAS-225. But luckily, we have the electric trimmer. I just ask these questions because I'm genuinely curious about the "why," whether it's a small engine or some news headline about what's going on in Washington. I also want to make sure I didn't do anything wrong. Unlike the Bolens, I expect the Echo to last a very long time.

 

[Manic84]

To answer your questions:

1: Yes, the pin will never seat properly again due it heating up and shrinking with use, and with nothing to keep it in place; (why it came out to start with) it will always come back out again. I've heard of people trying to change the properties of the pin by cooling and heating it, to make it stay put. And other things that are never a permanent fix. And with a new short block rivaling the cost of a new trimmer, it isn't worth it. (in time it'll likely fail in the same way )

This will be a long one
2: The area where the pin eats through, and the cover itself is a surprisingly thin plastic. As the pin rubs, it gets thinner and thinner, like one of the pics you posted. If you look closely at the cover, or shine a light through it and look, there is a crack in the cover.
Here, I've highlighted the fault in one of the pictures you posted.


The pin has wore clean through the cover. This is why you aren't getting any fuel to the engine. It's a fault with the primary compression, an air leak. Each time the pin goes while running, it eats more and more of that cover, changing the fuel/air ratio as it runs. Making it like an open window, and impossible to properly adjust the carb, or get it to run. (if at all) I've even seen where the pin makes a perfect hole right through the cover.

*over simplified*
Primary compression is crankcase pressure, it's what feeds the engine fuel. As the engine cycles, (starting or running) it's sends a pulse to the carb through the insulator block, and actuates all the diaphragms needed to get fuel to the engine. If there is an air leak, it throws it off; and it runs poorly. If there is a massive air leak (like this one) it won't get any fuel at all. Because that pulse isn't being channeled correctly, instead it's escaping though the cover; resulting in no fuel.

What you feel when you pull the rope is called secondary compression, it's responsible for compressing the fuel/air mixture at the top of the cylinder for combustion.

If there's a leak, it'll run erratically/poorly. If left alone, damage to the cylinder and piston will happen. But if it's a massive leak, It doesn't matter how good the compression is when the rope is pulled, if that pulse isn't channeled right, it'll never run good, if at all.
***
It seems unlikely that any plastic shavings are to blame here. And as you may have guessed, there is no use repairing or replacing the cover either, especially if the pin worms itself out again. Which is why once the pin comes out, there is nothing to be done.

And I do agree that the echo will probably last longer. Except for those zama RB carbs, they really don't, but the machines overall do last.

I hope I've answered your questions.

M

 

[mh9162013]

Wow, great eye! Yeah, I hadn't noticed that crack and that definitely explains everything (along with the pin issue).
Thank you so much for your insight and advice, Manic84!