I appreciate your get to the point no nonsense approach, I have been a mechanic for a really long time and small engines are a specialty. I love the super quick high revving response of a 2 stroke, but clearly they have their issues especially the really small ones, and Chinese doesn't help either lol. The comments that claim or assert that 4 strokes are not as reliable isn't even close to true. However build quality plays a huge role! This machine could easily have just been a lemon, BUT looking at the oil tells you a lot about the owner and the working life. Maintenance, especially of your lubrication is essential and especially in a very small engine such as this. The oils viscosity has a life span under normal conditions and unlike a full size engine these smaller engines destroy oil sooner, so checking and changing oil as often as needed should be job one. There is no way to definitively determine exactly what happened here but one thing is a fact, that oil sure didn't help! It running lean (way to much air) will definitely cause over heating, but I would expect to see a hole in that piston not so much the edge, but no way to know that! The spark plug gap being closed is a dead giveaway!

Great video. I wish you would have shown the hoses to the carb in a little more detail, but it was enough. I took my trimmer (same exact model) to a shop and they wanted $147 to fix it. I could buy a new one for that, so I paid the diagnostic fee and brought it home. They reassembled it incompletely and incorrectly connected the hoses between the fuel tank, primer bulb and carb. Watching your videos gave me all the information I needed so that I was able to fix the machine for the cost of replacing a missing o-ring they lost and the metering diaphragm, which was probably the original defect. I had it up and running in about half an hour with $10 in parts. Thank you for sharing these details.

"The oil's a little bit dirty." Looks like it came out of my old '94 turbo diesel Chevy truck! As for 4-cycle trimmers. I like them. They are quieter and don't require expensive and pita to mix gas/oil mix fuel. But then I didn't buy a Troy-Bilt. I bought a Honda 4-stroke trimmer back around the 2003 era. It still runs perfect to this day. I'm watching this video as I'm trying to diagnose an old 4-stroke 2007 Troy-Bilt that I found while cleaning out my Dad's garage. It's been sitting for at least a decade, hanging upside down. I put some ethanol free gas in it, changed the oil, got all the oil out of the air filter, and in about 20 pulls got the thing running but it's smoking like a chimney. My guess is the exhaust is full of oil.

I have the same trimmer, except older with no power start thing. I think I bought in in 2008. It sat in the barn about 7 years when I was hiring a guy to do the lawn. Had to learn how to clean the carb to get it running again. Then the gas tubes and primer failed. Just put new gas lines and a new carb on it. The new carb lets you adjust the idle and run mixture settings. Changed the oil for the first time this year. Runs great now. Need to slow down the idle. You mean you change the oil more than once every 12 years? wow. :) (Yes, I will try to change it more often.)

I appreciate your knowledge, you have a new subscriber. Thanks again. Best Regards

That was not a rivet that you drilled out it was a small hex screw. Thanks for sharing this as I am having an issue with the same one.

Good information! I love mine, I've used it a ton without any problems. I rev the hell out of mine and it's actually good for it. It keeps it from overheating.

I agree with the too lean theory. A lot of people adjust the carb for top rpm’s and don’t realize they are ruining their engine. Thanks as always for your videos. I’m now in your archives watching

I just got a new 4 cycle trimmer. I bench ran it for 1 hour at various speeds at the 30 minute mark I changed oil and added SAE 30 with zinc additives, it runs cool and strong and dose not use oil.

My 525 appears to have been built some years before this one. She’s a little stubborn to get started. Sometimes even after just shutting it off and letting it sit, but it’s proven itself to be more capable than the cordless black and decker my old man bought.

I think you have exactly diagnosed the problem because my 4 cycle troy built of the same model is doing the same exact thing. It happened while I was using it.

I have two of these weed eaters. Both have no compression. One has the same wall scarring as yours but without a broken piston. The other has perfect cylinder walls and piston skirts. My conclusion is overheating caused the loss of compression. The engine is apparently not cooled very well.

To the final question posed at 7:40 - I would say they went cheap on the metal used in the piston. Metals are complicated, they can be extremely durable, extremely exotic or on the opposite end, made of chinesium, a special "metal" blend from China that saves a lot of money but is brittle and unreliable. Manufacturers see the chinese price of production and get big smiles on their face at all the savings, but they don't calculate they'll end up with a bullshit product that enrages customers within the first year of purchase. All they focus on is the short term profits and don't anticipate having to yank troy-bilt off their shelves entirely like Lowes just did across the country after selling this crap for a few years and dealing with insane rates of angry calls and returns.

I have the same model with the same problem. Thank you so much for this informative video. I guess I'm going to buy a new one. This was my first 4 stroke trimmer, and I'm guessing I should have changed out the oil more frequently. Lesson learned. Going back to 2 stroke for now though. Who knows, I may just buy a battery operated one.

I think you pretty well nailed it. Also could have been a defective piston from the factory. And held on till it finally broke.

My dad has that trimmer and I also have a craftsman 4 Cycle 30cc and that Troy Bilt trimmer will be my backup if I need to service my craftsman trimmer

As oil gets old it can loose some of its lubercating properties I suspect the oil was never changed and simply lost its properties essentially running it without oil

If you don't teach you should the level of explanation is awesome I learned alot from just this one video. Thanks!

On my first one, 5 minutes out of the box, it started massively burning oil. Sprayed my leg with hot oil. One of the piston rod bolts worked it’s way out and punched a hole in the cast aluminum block. Lowe’s took it back. The person that sold it to me was still working on the floor! You could see daylight straight thru the oil sight glass. The second one I’ve had for two years. But at some point the palls/pauls on the fan became dislodged. Wouldn’t start except via ez start fixture and a drill. The unit aluminum shaft seems to be too thin of a gauge aluminum. Bought the parts to fix the starter.

This is the issue I have with mine. It will be interesting to see if it is the same cause. Glad I didn’t try the jump start option yet.

MTD happened to that engine. LOL

Odd failure. My 4-stroke Craftsman trimmer (B&S engine, I think) still functions just fine after 8 seasons, but it gets fresh oil twice per season. Only takes about 6 ounces. It's in semi-retirement (backup status) because it's just too heavy, even with a shoulder strap. So I bought a new Echo GT225 2-stroke for primary use.

Thanks for the detailed view of the plate at the back of the crankshaft about minute 4:00 that is part of the starting unit. My Craftsman E Z Pul vintage 2017 is the same trimmer. My problem was it partly locked up due to some trimmer string that got into the cooling air vent in the front, wrapped itself around the front crankshaft and got snagged into the magneto (I know - HOW did that happen?). Vigorous pull starting on my part eventually BENT the plate starter mechanisms (the little springy things) and cracked the plate, which is unobtanium. It had been a good runner for 5 years. PS - anyone reading this that wants to send me a spare plate, let me know.

I have a TB6040 XP that I bought new in 2012. The only issue I have had is the lower drive cable broke. The only way to replace the cable was to buy the lower tube and cable. Other than that, the trimmer has worked well. I did have to replace the fuel lines and clean the carburetor. But sense switching to non-ethanol fuel, I have had no fuel related issues. These little 4 cycle engines use such small amounts of oil, I replace my oil twice every season. If I was a lawn maintenance guy, I would change it once a week. I also use 4 cycle small engine oil in all my outdoor power equipment. Air cooled engines need specific additives that liquid cooled automobile engine oil lacks.

That model I believe was made by Murray. The one I had was sold as a Craftsman. They were complete and utter crap. I went through 3 of them in less than 15 month. Had the cooling fan break into pieces, the pull start free-spool and the string heads were junk. See ears replaced the first 2 and then refused any further customer service on the last one. I'll buy Husqvarna next time since all the attachments I have will mate up the same. I do like the 4 cycle though. Hate mixing fuel and oil and only have to carry one gas can for all .

How do the pawls look like when you remove them from the flywheel because my troybuilt has like some pegs in it and I’m not sure what goes there

Like how you get to the point,no bull.

As oil get old and dirty it looses its ability to cope with the engine temperature. If you need any engine to last ch age the oil regularly before it go’s as dark as this one .

I wonder if it got tilted to such a degree that the oil was dislocated and got into the piston or in such a position to where it could not oil properly and caused the rod and piston to heat up too much. I have a Troy Bilt weed eater/ edger. I have no experience with the edger attachment and am concerned about adjusting the edger attachment so as not to tilt the engine too much.

I don't know if mine is older than that one or not. The pull start is towards the front of the unit, not at the back like that one. It really would have been interesting to see what the valves looked like. I enjoy watching the small engine tear-downs and repairs. Subbing to your channel. I've got a couple of old 2 cycle weed eaters that I am going to go back and see if I can get them going now too.

I’d say the piston got too hot, welded itself inside the cylinder yet broke itself free. In the process, it began destroying the piston and cylinder and all else in its way. I have a Troy Bilt that the clutch broke on recently. Which tore off pieces of the flywheel. Ultimately, the service shop says that MTD makes cheaper products and I believe it. My trimmer wasn’t ran through the mud, and it was only 5 months old at the time it broke. It’s still under warranty. I’m assuming a broken clutch would be covered.

Mine seems like it has too much compression. The cord will pull great without the spark plug but is too hard with spark plug in. What should I check. It was given to me so ...

I'd say you're correct. Fuel got leaned out by main jet getting partially blocked at full throttle. then got hot and kaboom.

Thank You.

I have a Troy bilt tb415cs 4 stroke weed eater. Same as you, I was pulling on the starter cord because it was not starting. I noticed it starting to lose compression as I was pulling on it. I said screw it because I was going to go get a new one anyway because of this ones hard starting issue. Before I knew it, it had 0 compression. I still have it and haven’t tested into it yet. I think I’ll tear into it on Monday and I’ll update you guys on what I find🥴🥴

I'm not certain if it is an interference engine or not but I am fairly confident that if the sparkplug came in contact with the piston it would come to a immediate hault. if the crankshaft was able to rotate after the piston came into contact with the sparkplug it wouldn't be able to run because the sparkplug would no longer have any gap for the spark to jump across.it wasn't going to run after the crankshaft made just one revolution. Your engine failure is from piston ring. They expanded and became mechanically welded the the piston. Either from to much carbon in the ring groves, lack of lubrication, gasket failure allowed fuel to become to lean overheating piston causing it to expand faster than the cylinder could expand in unison of it was held wide open throttle.

i have a Cub Cadet ss470 i think is the Same engine as this one 25cc Emission Compliant for 150 HRS better than the Previous troy Bilt 29cc - only 50 Hrs Emission Compliance

I have a young Troy-Bilt 685 that's slightly out of warranty, but lots of hours on it. Yesterday it started great and did 15 minutes of lake edge weeds, then just quit dead. Very little compression (50 psu), Spark plug lots good. I assume it's a valve or cam, so junked it.

That trimmer looks like it is still pretty new as the gas tank looks great and clear, that looks to be in great condition externally but horrible internally. I wonder how long the customer had it before it stopped working, I would guess less than 2 years. It is sad that trimmer had a failure like that, I have never seen that happen before. These Troybilt 4-cycle trimmers seem like they have some of the most damaging reasons for failing. Now I have seen one that has had a broken camshaft and one that has had a broken piston! Seriously how does the piston break if it is metal? My guess is that Troybilt is just not using good quality materials and they are using more and more aluminum in their engines because it is cheaper to manufacture, but it is much weaker than metal would be. Maybe they are trying to make it as light as a 2-cycle trimmer would be and that could be the reason for more aluminum?

I have a TB685EC (41CDZ68C766). My fan blade broke and I have been searching the net ALL day looking for JUST the blade. It can have the pawls attached. The best I could find was an oil pan assembly for $45 on Amazon. I do not need the oil pan. All the parts diagrams I found did not single out the fan, it wasn't even mentioned as a part. Would you happen to know where I could find JUST the fan assembly?

Ciao ma una bella pulita al cilindro è una lucidata con le spazzole che hai pistone nuovo.. dici che ne varrebbe la pena?

I own a TBC625EC it's 5 years old now and it runs fine. Just needed a primer replacement. But I change the oil every 4 runs. Oil is cheap compared to a new trimmer

That’s damaged very badly. My question to you is could the black oil have anything to do with the engine failure? It looks pretty baf

I would've pulled the valve cover off first to check the valve adjustment. It's just like a car engine with rocker arms and pushrods. Just me though....could've had a broken valvespring or a valve dropped into the cylinder.....then you'd know without disassembling the bottom end first.

1. Not giving the engine a long warm up time before running at full throttle is very damaging to those engines (AND almost everyone does it) It can and will cause cylinder wall scarring on it's own and loss of compression. 2. That oil is not just "a little dirty" is completely trashed and likely helped usher that engine to an early demise. Oil is cheap and SO easy to tip it out...there's no excuse.

This video is a eight minute explanation on why you always buy the extended warranty on a string trimmer .

I have two of these, bought with known recoil starter issues. The jump starter accessory for a driver suffered a clutch (one-way bearing) failure. The next three starter accessories did the same. The clutch on the AC powered jump started suffered the same failure. I bought two replacement "oil pan assemblies" to repair the recoil starter failures. After changing the first one, the recoil starter would not function. Life is short, I gave up on both. This was discussed in detail with personnel at MTD. They were not particularly remorseful regarding the poor design. I would say never again, but find myself repairing a "free" TroyBilt riding mower for Dad. The "automatic transmission" is an entertaining design exercise.

Smart dude

What happen to it is Troy built it.....cause mines just stop working on me. It was running well then just stopped, cut off and now has no compression...

I bought a 4 cycle yard works trimmer. I used it a couple of times and I left it in working condition last week. This week when I tried to start it white smoke comes out from the carburetor when I pull the string. I didn’t start it fearing that it might damage it more. What would be causing this?

Either that or a foreign object such as dirt got sucked into the combustion chamber,it could've also been caused by a chunk of carbon on top of the piston crown which gouged the cylinder walls,it is a very common problem in the 2 stroke trimmers as well. The design in the video is a similar design to the Honda overhead camshaft 4 stroke lawn mower engines,it's a silly design because the cylinder head & cylinder are 1 whole assembly so it makes if difficult to decoke the piston crown & the cylinder heads combustion chamber because the cylinder head cannot simply be unbolted !

Over revs probably did it in! It got to hot! Are you going sell any parts,I could use that cooling fan! Good video!! Thanks very helpful

Will you be fixing it? Or are you just going to buy a new trimmer? If you do plan on fixing it, I'd love to see a how too video. Great video as always, keep up the awesome work

I still prefer the mixed oil and gas (non ethanol) usually a little strong on oil.

Man, that's some black oil !

what causes oil to run thru the breather tube on a 4 cycle troy built weedeater

I was surprised to see a fan for the engine. I guess they used a pore quality piston. I’ve never seen that happen to a engine. Do you know how expensive the trimmer is new?

Sad to me to say;a new Piston and rings,not to mention the cylinder would be more costly than the trimmer itself...

Nice video. Good info. Going Electric. Done.

Hi, Outstanding video. Let me guess on what happened...remember this is only a guess. I noticed when you drained the oil it was really dirty. On a scale of one to ten, I would give it at least a nine on how dirty it was. Again thanks for the video Vinny aka Chief Bauer

How do you call that black fan we’re the pull start is

These trimmers need frequent oil changes whereas they only hold a couple of ounces of oil. And because they run so hot it breaks down the oil. They’ve come out with some pretty good battery units you’re better off.

I would think that a poor quality piston casting was to blame or the piston had a hairline fracture when cast causing a break from usage. The oil being black as tar does not help. I never heard or seen a piston do that in a truck or car. Nice job on the video. VF

Oil was burned, the whole system went cherry red, valve seats moved/melted, that rod looked bent, etc. In short...nuked.

i could be wrong but that locked like one of those expensive $50-90 walbro carbs better hold on to that.

Cant you just change the piston and head to brand new and be using it again ?.

I'm going on about 10 years on my MTD 4 cycle trimmer and It runs great and my oil never looks like that. I only use Mobil 1 in everything i own. My MTD Tractor is 1998 and the MTD snow blower is from 1980. I want to get a new zero turn, Ariens snow blower and a powerful battery trimmer but I won't until they break and I can't fix them

where does the three lines going to the bubble go to

I wish I knew half of what he's talking about 🤣🤣🤣 I guess I'll just start taking it apart. Wish me luck

I wish someone would explain how the oiling system on these engines works, oil pump, splash, or what, and how can they oil when turned upside down? I can't find anything online about these oiling systems, I guess it's a secret

If you are lazy to mix oil and gas for 2 stroke engines, you can buy bottles of pre-mix oil and gas at the store. I also use premix oil and gas on this 4-stroke engine without any problem. The oil leaked in my 4 -stroke engine. I believe it is due to the plastic attached to the reservoir with only one screw. Two screws can fix the problem. I used jump start with an electric drill and adapter. After several uses, the pull string starter and the fan inside broke apart. I removed the starter string pull start and now is using jump-start only. The only advantage of this engine is that it is easier to start the engine with jump start. Pull start can take many pulls on cold engine.

So now you need a piston a rings and can you fix the scored block?

the rope is not start in the engine when i pull it why?

Just would be great to see you work on one something different maybe a snow blower to but you probably live where there's no snow

I’m about to do an oil change on a Briggs lawn mower should I use the bottom drain plug or tip it over

I spotted the problem before you took it apart. It's a trybilt. Lol

I wouldn't buy a four-cycle anyway personally but aside from the oil looking awfully black and thin, (the white cup made it look worse I'm sure) running full throttle for to long is rough on aluminum and I've seen that inside of weed eater brand machines on the flywheel being distorted from overheating. That would be my guess but it takes more than one time to doing that usually.. I Lent a Murray to my stepdaughter who brought it back with oil coming out of the spark plug hole. Mind you this is a brand new weed wacker that I had only run once but she ran it for 2 hours without stopping full throttle and it was done! They fried the darn thing..

Did you run it out of gas or low on gas at wide open throttle?

Didn’t change the oil. But to be fair the construction of the weedeater is one of the cheapest I’ve seen yet

Thanks for the teardown I will never buy a 4-stroke after watching this video stick with a two stroke.

It was running hot and and the pistonring expanded too much and broke of pistontop. With a larger ring-gap and a richer air/fuelmix this would never happened.

For the question on what I think happened to the engine , I think it was a little bit of what you said and lack of maintenance with how black the oil was it may not have been changed in a while, old oil with dirt and contaminates in it doesn't protect the engine as good as clean oil that's why there's oil change intervals for engines , so I'm thinking it went a little lean or someone set it a little lean and the oil loss some of its cooling and wear protection and then a bang piston broke , could be the cheapness of material but alot of engines and their components are made in China so I'm on the fence with that one

you never changed the oil , thats what wrecked the engine DAHHH

I honestly believe it's the oil. That was some thick and nasty stuff and depending on when this trimmer was used if it was in cooler weather that would even make it harder to pump the oil around the engine. As you're now the consumer who's buying lawn equipment do not think like you and I. They just fill it with gas and when something happens they curse the brand out and in most cases they go by a new piece of equipment. Which for people like you and I that's great that means we are getting ready to get something free lol. Most of these people could have a lawn mower for 10 years or more and not once ever think about changing the oil. Just look at the air filters you see them as I do completely clogged up and the consumer has no idea how to go about changing that. God forbid if they could figure out how to get the spark plug out that looks like it would be in its own adventure. I had a very good friend of mine bring me over the riding mower talking about how it was given to him and that he had no idea how to get it running. He said he looked at the spark plugs and they were fine. That night when I came back home I wasn't tired so I went out and checked the machine. I don't know how he got the spark plugs out he screwed them in not even halfway. When I was trying to start it I kept on hearing a weird noise that I have never experienced while working on lawn equipment. It was just a fluke that I said to myself look at this plugs yourself. Of course after fixing his blunder I had it running within the hour typical carburetor clogged up drum roll please nobody bothered to change the air filter and he definitely never changed the oil. I really do enjoy watching your videos. I have a four cycle weed trimmer that's practically brand new that was given to me from my neighbor when he sold his house. He gave me that and a brand new lawn mower since he wasn't going to need it again. That I'm really interested in taking that apart just to see what it's all about. When I get curious I come out and take things apart on purpose to see how they work and if whatever motor it is would have a problem I would be able to figure it out more quickly. As always I'm sorry for leaving you such a long response I just love watching these sort of videos and leaving comments and have people writing back. Like I always say also there is more than one way to approach an engine problem and that's one of the biggest reasons that I watch all these videos. Who knows one day I might stop doing all my work for free and have a side hustle going on since I had to retire early and I enjoy fixing things I always have. Of course I hit the like button and I do look forward to your next video.

I agree with you

hey how to fix the rope to start the weedwarker

i have the same model but ithink its the start rope something inside it

Low oil -gas spark friction time bomb

2:32 a little bit dirty. Haha. :D

That failure looks similar to some 4 stroke dirt bike engines I’ve seen. Too many hours. When a 2 stroke fails you slap a new piston in and it’s good. When a 4 stroke fails it fails HARD. You have to rebuild them *before* they blow.

Well I’m watching it after

I've had too high of a throttle break off clutch and burn off coil.

Too much RPM's when Engine is cold. Let it warm up!

Can you even use them sideways?

I've seen this on turbo charged cars. the engine definitely prematurely detonated and caused a crack in the piston. which then splintered off. eek.

Got the same issue with piston broken on sides. I bought the same trimmer again for cheap due to all attachments that I have already so most likely will happen in the future. O well really poor material design.

Agreed. This is why I hate 4-cycle weedeaters or blowers. I have owned one of these and it just broke after a year, now Would not start. They are so difficult to maintain. The problem is that the weedeater was made in China, which is why they were meant to break in no time anyways. Troy bilt thinks they never let people down, which is absolutely not true. I have used a vintage Montgomery ward tiller (40 years old) without an issue, and STIHL equipment with no issues whatsoever. Ethanol is another thing that kills weed eaters whether 2-stroke or 4-stroke. Not only that, these new engines (even the MTD-clone engines, including craftsman, etc) nowadays are pure China junk, whether 2-cycle or 4-cycle. My mom had a MTD riding mower from 1991 and it works after years of use. Research WeedEater GTI15T running in 2018, these old engines were the best back in the old days, made in USA. So much for Built for life.

The designer of this unit came from the auto industry. These guys design to build without thinking about repairing them. That's one reason everything is throwaway. I hate that. Thank goodness for small engine repair private guys that don't charge an arm and a leg to fix something.

I’ll stick with my 2 cycle equipment as long as possible. Only 3 moving parts and a continuous supply of fresh oil. They usually last between 12-15 years if I buy a good quality unit. I cheaped out and bought one of these a few years ago. NEVER AGAIN!

That broken cylinder makes me think that if you plan to run this one for a while you might want to add oil to the gas anyway as that is the place where you'd expect an overheat to break. Of course it could be cheap metal too but that's the Chinese model -- make it real good for the first couple of year models until you get good word of mouth, then cheapen everything and let the market run its course. That's their profitability model and it has worked in the past. Of course, there's no real future in it but they don't care about that -- make as much money as you can for a few years and then get out while the gettings good.