Help! Unusual, no compression, 4 cycle trimmer

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Hi everyone, first of all, thanks for taking the time to read this. I hope someone out there can help.

I have a 4 cycle trimmer, Troybilt TB6044XL. It won't start and has low compression (20 psi). When I add oil into the spark plug hole I get a whopping 40 psi. It has spark, it has air, it has fuel.

I have read that there is likely something wrong with my piston rings, because adding the oil has doubled the psi, but I still only get 40. So I've opened-up the engine and examined the piston and rings. They don't seem obviously damaged, rusted, or warped, but I don't really know what I'm looking for other than that. There are some friction marks on the inside of the cylinder, but it feels smooth to the touch.

I'll admit that all my compression tests were done after I opened the thing up then put it back together with the original gasket, but it's an all rubber gasket and the thing was already not running.

The background on the thing is:
It's a year old with probably a good 30 minutes of use on it. I left normal gas from the gas station in it over winter (I have replaced the carb), and a few weeks ago I whipped it out and used it for about 3 minutes before it died. I was able to start it again, after which it smoked for about a minute then died for good. I definitely overfilled the oil tank because it has no fill line.

Anyway, I think I can install a new piston or new rings, but to the novice eye the rings look fine. But can anyone tell me:
1) Did I maybe screw up the cylinder?
2) Can I conclude that it is either the cylinder or the piston rings that are the problem, because of the oil-in-the-spark-plug test?
3) And has anyone ever heard of 40 psi being acceptable in a 4 cycle engine?

Thanks for reading and I hope we can figure this out together.
 
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Guess I'd start with the rings.
They should 'free float' between cylinder wall & piston, if the ring sticks to the piston groove, compression goes way off.
Usually cleaning the grooves with Berryman B-12, and the rings as well, leaves rings free to develop max. cranking pressure.
Last year's gas may be to blame. Does this trimmer feature a de-compression button for easier starting?
 
Despite it low hours, I would cut my losses and get a new one. I wouldn't spend any more time on a low end trimmer. I thought those had a two year warranty which may be worth looking into. Play dumb, don't tell them of your findings and say "it won't start"..No warranty, deep six it.
 
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I've fixed a few with a piston soak with Amsoil Power Foam. B12 works too. I recently let a chainsaw soak for the better part of a week, and it ran very well after. It's worth a try.
 
After reading your post I would buy a higher quality brand.Did you check the valve lash if possible. 4 strokes are not the way to go with trimmers.
 
it's not the rings. 40 psi won't get you started.

check valves - lash, seats, cracks. or fouled gasket/mating surface. it could be a lot of work. I had a 4 cycle ryobi and it was a very poor engine to live with. I now use a 4 stroke husq. with a honda engine and it's the best trimmer I've owned, except for a shaft that's a little too short for me.
 
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Does that model have compression release for easier starting? Possibly something wrong with that if its equipped.
 
I'd check the valves if possible. Does it start then stop? If not, does putting a little gas in the spark plug hole get it to run for a short period of time? I'd consider doing a piston soak like mentioned above, and possibly replace the spark plug (just for good measure). If it still doesn't work, I wouldn't spend any more money on it. What carb did you replace it with, maybe it needs some kind of adjustment?

I'd try contact Troy Built, supposedly it has a 3 year limited warranty: https://www.troybilt.com/equipment/...traight-shaft-string-trimmer-41cdf6pc766

If you do end up trashing it, I'd suggest getting a cordless electric trimmer, it sound like it would be great for your use case.
 
Did you check for spark at the plugs electrode, or on the lead wire? The way it smoked before quitting, maybe the plug is just fouled.
I like to check simple solutions first
smile.gif
 
Had one of these and same thing happened to me. Worked great for about 3 years, then sudden failure, and I took care of it.

It is a throw away, no real parts support.

I'm just a homeowner but I moved on to Stihl products now.

FWIW, I initially went to walmart and bought a "hyper tough" trimmer and I put that power head on the shaft of my old 4 stroke quick shaft change trimmer, that was only 60 bucks to do that.
 
WOW. I was not expecting so many responses so quickly. This must be a very active community! Thank you to all who posted. It has been raining the past few days so I haven't gotten to working on it any more.

vw7674: It was very difficult to pull the piston out of the cylinder, and there was some greyish brown goop in the oil ring, but I assumed that was because it was just oil. I have some seafoam and brake cleaner already - do you think that would work to clean it? I plan to go at the piston grooves with a tooth brush, at this point.

Lubener: I bought the two year warranty.... but only remembered that as I was pulling the piston out of its cylinder. They have a disclaimer that says if I run the thing without the air filter it voids the warranty, so I'm assuming taking it apart will, too, but I'll look into it since I got the deluxe warranty.

Eddie, Ed, Eric, and Meep: Thank you for the valve tips. I haven't looked at them. I'll youtube how to clean them and get back to you this weekend.

DGXR: I ended up replacing the spark plug because the original one was indeed giving me a little brown spark if anything. The new one is sparking fine. I had hoped that would solve it but then I got out the compression tester and almost spilled my beer.

Rand: I actually don't know if it does. I have heard that some small engines have something like that and can start with less compression, but I don't think mine does, at least I don't see anything that could serve that purpose. The manual doesn't say anything about one but honestly the manual doesn't say much past assembly and starting procedure.

I should probably get a better brand but I bought all these attachments (heavy duty brush trimmer, weed whacker, and chainsaw). It is on me for sinking so much money into then leaving gas in it and shoulder-shrugging when I thought "is that the right amount of oil?"

Thanks again for all your posts, help, and interest.
 
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I would put it back together, polish it up take it in for a warranty repair. Tell them nothing but "it stopped running" and I would bet you get it repaired free or get a new one. Been there.
 
I've worked on a few of these small 4 strokes and most of the issues I've found have either been stuck rings or stuck valves. Pop the valve cover off and make sure the valves move freely and return to full closed, I've seen them hang up on a piece of carbon just short of seating.
 
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