String Trimmer Overheating

drajJune 10, 2013

I have been using this Troy Bilt 4-cycle straight shaft trimmer from about 2 years, changed oil twice a season. It worked very till recently - now its overheating like crazy. I checked spark plug, carb, muffler everything looks good. It still runs well, just that it gets super hot in 3 minutes of use.

Which part is the most likely culprit ?
Will it be permanently damaged if I continue use it ?

Thanks in advance - DR.

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Did you check the muffler and spark arrestor good for carbon blockage? Pull the muffler and you should see in the cyl and if it's damaged/scored.

    Bookmark   June 10, 2013 at 11:37PM
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I would check the valves and make sure they are adjusted properly. BTW, removing the muffler will not allow you to see inside the cylinder since this is a 4-cycle engine.
I'm not sure what would be causing the extreme heat, but I wouldn't continue to run it until you find out what is going on.

    Bookmark   June 11, 2013 at 3:30PM
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rosemallow(z7 Md)

Hopefully, you are storing it in the horizontal position.
If the attachment is removable remove it and see if it still overheats.
Is the oil correct.
Older 4 cycles use 30wt Hd. newer ones use 10w30.
And I am using 20w 50 synthetic.
After it overheats remove the plug ad see if it pulls easy. If it does not pull easy I think you have problems.
So, before you pull out your hair try that first.
I am also glad to see someone adjusts the valves on 4 cycle trimmers.

    Bookmark   June 11, 2013 at 7:48PM
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Problem Persists..

I changed spark plug, rebuilt carburetor, cleaned muffler, changed oil but trimmer continues to overheat within few minutes of using it. I have always used full synthetic oil, storing it horizontally all the time.

I am guessing increased friction b/n cylinder & piston/rings. I guess it is close to it's end of life - will post if it dies soon.

Thanks for all replies.

    Bookmark   July 7, 2013 at 1:18PM
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Will the cylinder pull fairly easy for inspection? If so this could end some speculations. I tried to find a youtube that should show this. If you know of a youtub on rebuilding please share. It could show an easy inspection or not. Pulling 100 pieces w/n be easy to see a scored cyl.

    Bookmark   July 7, 2013 at 4:03PM
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I am confused by you term overheating?? does it just stop and you can't pull the rope? or does it die and won't start? Is the lower shaft still spinning during the lost of RPM or when it died?

"I am guessing increased friction b/n cylinder & piston/rings" I take it you remove the shaft to iltimate any problems down the road??????

First I would make sure there is no grass around the cylinder head cooling fins (you may have to take the plastic housing off to ensure this)

Next the problem could be in the clutch, upper drive shaft cable, lower drive shaft cable, or the gearbox down at the business end. All of this can be troubleshot by remove first the lower end shaft. run the string timmer and see if you notice any binding or lower of RPM or sound like it's bogging down. It should sing like sewing machine with the lower shaft assy. off.

If it don't them you have to take the upper shaft off do the same. next would be the clutch assy. Compression check, VALVE adjustment and another compression Compression check?

"about 2 years" New or second hand??? Mine 12 years old and still runs like new, starts on second pull. I had to replace the fuel lines, upper drive shaft, adjust the valves, and regrease the lower gearbox. Course if I had never done any of that it would not be working.

    Bookmark   July 7, 2013 at 4:50PM
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Overheating - the rear of trimmer (cylinder area) gets super hot after 1min of running at nominal speed. I can smell oil vapors - not gas, not burnt oil.

It continues to run, but I take breaks - scared it may die. It never got his hot till recently, it ran cooler & never radiated heat like it does now - even after hours of use. I bought it new 2yrs ago.

I opened it up - fan, clutch, cylinder cooling are all clean. When engine of off, I can spin the string head effortlessly with one finger & can see clutch spinning too.

Valve adjustment is one last thing I haven't done - how can that lead to excessive heating after just 1minute of use?

thanks for your time & ideas.

    Bookmark   July 9, 2013 at 10:29PM
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An exhaust valve gap out of spec would possibly do it as well as burn the valve. Remember someone suggested to not run it w/o finding the cause and that could be a major reason.

    Bookmark   July 9, 2013 at 11:03PM
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Are adjusting the overhead valves something that is needed yearly? Sounds like my 1968 and 70 VW every 6,000 mi or Etc and the specs were changed (larger) and they needed it. TX Heat is hard on air cooled equipment IMO. I saw a youtub that recommended once a year overhead valve adjustment on Briggs Engines in the video (at the address below). That is a lot of stretching but I have seen it on some air cooled engines resulting to burnt valves (exhaust mainly).

Adjusting Briggs Overhead Valve Engine.

Here is a link that might be useful: Adjusting Briggs Overhead Valve Engine

    Bookmark   July 16, 2013 at 11:10PM
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I just checked the warranty on my Cub Cadet 4 cycle which I purchased a little over a year ago. It is covered for 3 years from date of purchase. I would check my warranty and if in is within or a couple of months older I would take it back to the place where you purchased it, or to a dealer with proof of purchase.

It does not seem that a 4 cycle should die within two years.

This post was edited by knuttle on Wed, Jul 17, 13 at 19:24

    Bookmark   July 17, 2013 at 7:19PM
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Properly adjusted and gapped intake and exhaust valves transfer heat much more readily when in spec. This is especially true of the exhaust valve.
Heat WILL build up in the engine until some type of failure occurs if the valve lash is incorrect even on these smaller engines.

    Bookmark   July 22, 2013 at 7:09PM
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