Most common causes of engine failure

old2stroke · December 03, 2015, 04:14:12 PM

Here's my list of things I've seen in no particular order of importance. Do any of you have more favorite ways to destroy a chainsaw?
1. Running too lean an air-fuel mix on the main jet.
2. Over heating issues. Consistently lugging the engine down under full power. Low engine speed means the flywheel fan pushes less air through the cylinder fins. Keeping the rpm up maximizes the air flow for best cooling. Wouldn't hurt to take the covers off and blow the crud out of the fins now and again.
3. Oil and oil-gas mixing. Use of low quality oil and too much guesstimating (or bad math) about the amount of oil to add to a container of gas and the amount of gas in the container not known accurately. IMHO a mix ratio of 50:1 is a little scary. Yeah, I know, less oil - more power, a myth fully endorsed by your local repair shop.
4. Excessive carbon build up in the cylinder head and on the top of the piston. Causes higher compression and hot spots leading to destructive detonation.

rasawing · December 03, 2015, 04:59:01 PM

QuoteOil and oil-gas mixing. Use of low quality oil and too much guesstimating (or bad math) about the amount of oil to add to a container of gas and the amount of gas in the container not known accurately. IMHO a mix ratio of 50:1 is a little scary.

What do you think is the best ratio (at the risk of going off-topic)?

thecfarm · December 03, 2015, 05:40:51 PM

I'll get this going. ;D I've been using 40:1 in 2 saws for years now. But I also buy high grade too for all my small engines.

ladylake · December 03, 2015, 06:05:11 PM

I'll go with number 1 in 80% of the burn downs, carbs set lean with people thinking they are going to cut faster when a saw revs a zillion RPM when if fact they cut faster when they are set to 4 stroke out of the cut. Steve

sawguy21 · December 03, 2015, 07:15:44 PM

The big problem with #1 is Nader and the EPA. Minimum emission settings lead to more equipment in the scrap pile. Paul_H and I looked at a hand held blower today that did not seem to be developing full power, we could not see how we could easily reach the mixture screws.
IMHO mixing heavy leads to number 4 but I don't want to get into that, it has been discussed to death.

Texas-Jim · December 03, 2015, 09:30:21 PM

I'll also go with #1 but theres a lot of things that can cause leaning out beside carb adjustments. And theres nothing wrong with 50:1 mix if tool was designed to use it.

One thing we often over look is RPM, if a tool runs to slow under full power its not a matter of if it fails but when. A good example is, if you bring a Stihl string trimmer in with a bad engine and theres no guard on it, you have no warranty. Every inch that string gets longer than the cutter on the guard it slows the engine down. Like driving your car around in high gear all the time, it will fail.

Spike60 · December 04, 2015, 10:59:23 AM

Most common cause is operator error. By a large margin.

You guys should see the stuff that comes in here. Most of you know how to take care of a saw. But the typical saw owner.............

snowshoveler · December 04, 2015, 11:31:46 AM

Operator error.
That is by far the biggest problem with anything.
Very difficult to tell people they are the cause of their trouble.
Regards Chris

49er · December 04, 2015, 03:02:57 PM

Quote from: Spike60 on December 04, 2015, 10:59:23 AM
Most common cause is operator error. By a large margin.

You guys should see the stuff that comes in here. Most of you know how to take care of a saw. But the typical saw owner.............

I am going to a charity cut a week from Saturday my buddy says it is very entertaining what some people bring to cut with. Also, some of the operators are scary to watch.

old2stroke · December 04, 2015, 04:05:14 PM

I personally do not go any leaner on the oil mix than 35:1 and I use the best synthetic 2-stroke oils meant for race dirt bikes and snowmobiles and I mix the volumes VERY accurately.

CR888 · December 04, 2015, 05:29:58 PM

Usually when my OPE wears out to the point a a freshen up ain't worth it, the motor is usually in the best condition. Feed them fresh mix and run them the way they like, service life is long. My guess is poorly mixed gas, gas with no oil, ethanol, and poor operator basic tuning skills are responsible for 95+% of engine failures.

Dixiebonsai · December 04, 2015, 08:55:59 PM

Quote from: old2stroke on December 04, 2015, 04:05:14 PM
I personally do not go any leaner on the oil mix than 35:1 and I use the best synthetic 2-stroke oils meant for race dirt bikes and snowmobiles and I mix the volumes VERY accurately.

I am curious, do you foul a lot of spark plugs mixing that rich?
I had an old Suzuki RM400 dirt bike that called for 40:1 and it was constantly fouling plugs.
I have two Stihl saws an 028 Super and a MS361. The 028 requires 40:1 mix , the Ms361 requires 50:1 .I have been compromising and mixing 45:1 . If the MS361 would run at 40:1 I would rather be there.

thecfarm · December 04, 2015, 09:15:23 PM

Dixiebonsai,have no idea the age of the Stihls you have,but I run my 372 Husky at 40:1. I think I bought it around 2005??? It's tuned to that mix.

sawguy21 · December 04, 2015, 10:15:46 PM

The MS361 will run fine at 40:1 if that is your preference as long as the carb is set accordingly. Five points either way won't amount to a hill of beans. How were you running that RM400? Hard charging on a moto cross course which is what it was designed for or chugging around a bush trail? If the latter your plug was likely to cold. I rode one once, it was more than I could hang on to. ;D

JohnG28 · December 05, 2015, 11:37:27 AM

All my saws get 40:1 with no issues, including my 361. I have ano old thread on muffler modding thst saw here, you can see some shots through the exhaust port of the p/c running that mix if you look it up. No fouling or other issues at all.

coxy · December 05, 2015, 03:37:24 PM

50:1 never have any trouble till I get my paws in it ;D and I always put the guards and other stuff back on before it goes back ;)

sharkey · December 05, 2015, 07:58:13 PM

Quote from: old2stroke on December 04, 2015, 04:05:14 PM
I personally do not go any leaner on the oil mix than 35:1 and I use the best synthetic 2-stroke oils meant for race dirt bikes and snowmobiles and I mix the volumes VERY accurately.

I agree!. Too many are scuffed or scored at 50:1. Never had a fouling problem with the newer oils even at 20:1.

Texas-Jim · December 05, 2015, 09:21:30 PM

Its not the mix that scores or scratches piston. 50:1 is more than enough oil. More oil does not mean longer life. Probably 95% of the time damage can be traced to a cause other than oil, most times its from a person who thinks hes a mechanic. Over oiling a machine designed to run on 50:1 costs money, pollutes the air and gives poorer performance. More is not always better.

man of stihl · December 06, 2015, 05:58:05 AM

Some things I've seen.
Using old fuel. When I get a saw in to fix, I'll dump the fuel and put fresh in.

Working the saw too hard because of a dull chain. I've seen this multiple times. The piston was smoked and the chain wouldn't cut butter.

Running the saw with an air leak,(bad crank seals, hole in fuel line, torn or cracked intake boot or block) which means its running too lean.

Loose muffler bolts which changes the tune.

snowshoveler · December 06, 2015, 07:39:37 AM

You know I have never seen a saw hurt its self while it was sitting on the shelf.
If you don't use it or lend it...yea lending is very bad, then it will always be good to go.
Having that fancy canned fuel might not hurt any either if the saw is going to sit for a while.
Chris

cbla · December 07, 2015, 05:42:33 AM

been running 50:1 in my Husqvarna saws for 20 years with no problems. I run 32:1 for the 390 xp when milling with the Alaskan.

CTYank · December 21, 2015, 11:35:33 PM

Quote from: old2stroke on December 03, 2015, 04:14:12 PM

1. Running too lean an air-fuel mix on the main jet.
Sustained operation hyper-lean will melt piston.

2. Over heating issues. Consistently lugging the engine down under full power. Low engine speed means the flywheel fan pushes less air through the cylinder fins. Keeping the rpm up maximizes the air flow for best cooling. Wouldn't hurt to take the covers off and blow the crud out of the fins now and again.
Big thing here is regularly cleaning crud blocking airflow, and cleaning fins. Oil and sawdust=bad juju.

3. Oil and oil-gas mixing. Use of low quality oil and too much guesstimating (or bad math) about the amount of oil to add to a container of gas and the amount of gas in the container not known accurately. IMHO a mix ratio of 50:1 is a little scary. Yeah, I know, less oil - more power, a myth fully endorsed by your local repair shop.
Straight-gassing leads to sudden-death, the rest can take much longer.

4. Excessive carbon build up in the cylinder head and on the top of the piston. Causes higher compression and hot spots leading to destructive detonation.
Won't happen if you exercise the engine regularly, and avoid excess fuel/oil. Main prob: starting fires. If engine gets normal (ab)use, those deposits won't last long, nor will they accumulate. Excessive oil reduces overall octane rating.

CR888 · December 22, 2015, 06:26:46 AM

Plug fouling is more of a tuning issue than mix ratio issue. Not many can ride a RM400 hard enough to keep plugs looking good. It takes kahoonas and good skill to ride them the way they are intended to run. A RM250 might have been a better choice but l get we don't always get what we want or need. I reckon failing to read and comprehend a saw's manual kills most saws. It's the basics that usually get over looked.

weimedog · December 22, 2015, 10:18:29 AM

Quote from: CR888 on December 22, 2015, 06:26:46 AM
Plug fouling is more of a tuning issue than mix ratio issue. Not many can ride a RM400 hard enough to keep plugs looking good. It takes kahoonas and good skill to ride them the way they are intended to run. A RM250 might have been a better choice but l get we don't always get what we want or need. I reckon failing to read and comprehend a saw's manual kills most saws. It's the basics that usually get over looked.

Lets be a little more specific..

NO one could ride that orange first gen TM400 hard enough to clean off a plug! (There was this guy Stanley Calhoon in District 34 who could...it was quite the show watching that thing sliding, skipping, and swapping all over the tracks...scrambles typically..as he just wasted the competition) Then when the RM370 came out, that was a sweet handling bike for its time and the subsequent RM400 derivative of that bike was pretty good too.

Saw failures? WOW hard to generalize as it seems to be model dependent...late model Husqvarna 350's melted their bar oil tanks when the muffler's rattled loose, early model ones went lean when the plastic intake boot clamp relaxed, The first couple of years with 562's ... well...you know.. Old saws? Air leaks or bad rubber parts. Bet the MS391 and saws with similar throttle linkage designs slowly but surely start loosing power as the steel throttle wire/actuator eats into the plastic and you no longer can get to full throttle! So like I said, generalizations are tough. Oh Yea...certain loggers will have CRUSHED their saws way before any mechanical issues turn up! (You KNOW who u r, lurker!)

BrokenStihl · December 26, 2015, 09:20:44 AM

I also say that using the terrible Ethanol gas is harmful. I have a station that sells the good old-fashioned Non-ethanol blends, and thats all I use in my saws, mowers, motorcycle, and old vehicles. Otherwise, the ethanol eats away at the fuel lines, and most plastic lines and gaskets.

I say, keep the corn on the cob, and boil or roast it on the grill. No corn should be allowed in our fuel tanks.