Author Topic: Engine failure analysis...scrapped generator  (Read 417 times)

Offline machinisttx

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Engine failure analysis...scrapped generator
« on: November 19, 2017, 08:38:01 PM »
A couple of weeks ago I picked up a 6200 watt Troy Bilt generator for $45 or so. It looked pretty good, but had zero compression. I should have done a little more investigating before I bought it, but there's another lesson learned. I was hoping it was nothing more serious than a stuck valve, so that's what I checked first after getting it home. No such luck. My next stop was to pull the spark plug and find out if the piston was moving. It was not. At this point I hoped that the bolts holding the connecting rod cap had come loose and fallen out. Unfortunately this meant I needed to remove the rotor/armature from the crankshaft of the engine in order to remove the "pan" from the engine block. I didn't have any success with the methods I'd used previously and gave up rather than damage anything. Enter youtube and this video https://youtu.be/RsNJLd7j0Yk   :excited:  Mine was the right diameter for 1/2-13 threads, and that method popped it right off. Now I had access to open the thing up and find out exactly what was wrong. Before that I drained most of the nasty black sludged up oil that was in the crankcase. Not much came out, which is a clue in figuring out why this engine failed.

Here's what I saw when I pulled the pan off.  :jaw-drop:



Here are the big chunks laid out.


And now we can get down to analyzing exactly what happened. If you notice in the pics above, the bolts are very clearly still in place holding the destroyed cap and connecting rod pieces together. I'm gonna guess that anyone standing near the generator when this happened probably left with skid marks in their britches....but I digress. Moving on, let's take a look at the bearing surfaces.  :popcorn:





What we see there is not just typical galling, but also outright tearing of the bearing surface in the connecting rod.

Anyone wanna take a stab at what caused the failure? I'm going with insufficient(and appallingly dirty) oil. I also think that the sequence of events was something like this:
1. engine gets excessively hot from low oil level
2. existing oil gets cooked to sludge
3. high heat and lack of oil begin transferring(galling) aluminum from the connecting rod to the journal of the crankshaft
4. conrod seizes on the crankshaft
5. The laws of physics still apply, I.E. an object in motion wants to stay in motion. In this case, the 40-50 pound armature and crankshaft.
6. Conrod breaks, probably at the beam.
7. Crankshaft and armature are still spinning, bearing cap hits the part of the conrod that's still attached to the piston.
8. bearing cap and mating part of the conrod crack and fall into the crankcase.

I still need to finish cleaning the rest of the oil out of the crankcase, along with the small chunks of connecting rod. That said, there appeared to be no damage to anything else in the crankcase....but I found another failure that may or may not be related.

This is the crankshaft bushing in the removable "pan" on the rear of the crankcase. The line that can be seen is a crack.


The good news is that it would probably cost less than $100 if I just wanted to get it running again. I'll end up spending a little more just because I'm already in there, so might as well replace a few other things.
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Offline Stwood

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Re: Engine failure analysis...scrapped generator
« Reply #1 on: November 19, 2017, 10:33:35 PM »
Bad burnt smell in crankcase?

I think you analyas  is spot on.
Low, dirty oil, metal heating.
Seizing, locking and breaking.
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Offline Carl

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Re: Engine failure analysis...scrapped generator
« Reply #2 on: November 20, 2017, 04:40:04 AM »
  I use PTFE (Slick 50 ) oil additive to give a little 'extra' protection ,but you really need to check oil level BEFORE EACH START-UP of portable generators and I find the newer 'synthetic' oils also are worth the extra cost for protection. Thanks for the write-up and excellent photos,very well done..Karma.
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Offline machinisttx

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Re: Engine failure analysis...scrapped generator
« Reply #3 on: November 20, 2017, 06:42:26 PM »
Stwood: The juniper pollen has my allergies all riled up so I really don't know what it smells like. When I was draining it, it seemed more like gear oil in consistency than normal 30 weight.

Carl: If I can find it, I'm going to switch everything over to rotella 10w30 synthetic. I've been putting Rotella 30wt(made for diesels) or 10w30, dino oil, in everything lately since the EPA lowered the permissible level of zinc in engine oils a year or two ago. I'm not 100% sure, but I think there is a warning on the Slick 50 bottle about using it with synthetics. On that subject, some fellow my uncle used to work with filled his  truck's crankcase with slick 50 instead of oil. I guess he thought if a little is good then more would be awesome. The engine lasted three days.  :rofl:

I just looked and if I was really hard pressed, without other options, I could put this back in running order using briggs parts, for $48.81(new connecting rod) plus shipping and another $20 or so for gasket material to make my own replacements. I bet I can find some less expensive, but still high quality, parts.
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Offline Zef_66

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Re: Engine failure analysis...scrapped generator
« Reply #4 on: November 21, 2017, 10:31:39 AM »
Stwood: The juniper pollen has my allergies all riled up so I really don't know what it smells like. When I was draining it, it seemed more like gear oil in consistency than normal 30 weight.

Carl: If I can find it, I'm going to switch everything over to rotella 10w30 synthetic. I've been putting Rotella 30wt(made for diesels) or 10w30, dino oil, in everything lately since the EPA lowered the permissible level of zinc in engine oils a year or two ago. I'm not 100% sure, but I think there is a warning on the Slick 50 bottle about using it with synthetics. On that subject, some fellow my uncle used to work with filled his  truck's crankcase with slick 50 instead of oil. I guess he thought if a little is good then more would be awesome. The engine lasted three days.  :rofl:

I just looked and if I was really hard pressed, without other options, I could put this back in running order using briggs parts, for $48.81(new connecting rod) plus shipping and another $20 or so for gasket material to make my own replacements. I bet I can find some less expensive, but still high quality, parts.

FWIW, 30wt engine oil is close to the same viscosity as 85wt gear oil.

Also, for Rotella oil, you will have to go with 0W40 or 5W40 if you want full synthetic. For semi-synthetics, they do make a 10W30. I use 5W40 Rotella T6 full synthetic in most of my small gas engines; honda ATVs w/ wet clutches, B&S engines, etc. It works well for me.
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Offline machinisttx

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Re: Engine failure analysis...scrapped generator
« Reply #5 on: November 21, 2017, 04:45:00 PM »
It reminded me more of the last time I had to pour some 140wt.

I wasn't sure they made anything other than the 15-40 T6 synthetic. Might have to shop around and see what's available from the others.
The worst form of inequality is to try to make unequal things equal.

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