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My 660 again - yep ?

Started by Dalden, February 23, 2010, 07:48:48 PM

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Dalden

 :P

OK we put in a new jug and piston and rings,  reassembled.  Ran fine again for a few days - then quit.  I went through the normal checks: fuel =yes  spark = yes so in a little further we went.  New rings are ground down to the piston edge on the exhast side -exactly like the condition that caused it to sieze, and me to scare Al with my original post in Oct.  I have been just sitting because of the weather (too snowy/cold to mill).  I went to fell a large maple on Sat.  Made two cuts with a 36" bar and freshly sharpened skip tooth chain -litterally two cuts to make my hinge gap and that was all she wrote.

I know the new parts were never run on straight gas - unless the small engine guy that re-assembled it did it. (I had some other parts that were messed up and no time to finish it up.  I put the jug and pistion in myself.

I know I did not mill with it - never got the chance.....

What might be causing this -could the needle bearing be at fault - bad muffler? 

I'm lost - I'll take pics if you need them
1 Landscape trailer w/ home built cutting platform
MS660
EFCO MT8200
Smaller saws and some other stuff.

Rocky_J

Lean seize. Too lean equals way too hot and not enough lubrication, which equals seized motor. Find the air leak.

Dalden

OK, where do I look - I've never had a problem before I got this saw. (not new - evilbay)
1 Landscape trailer w/ home built cutting platform
MS660
EFCO MT8200
Smaller saws and some other stuff.

tlandrum

you need to check your seals and check anything that could pull air in and lean it out. if you dont figure out what got the jug and piston the first time you will keep frying them
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Dalden

OK,  I'll start pulling it apart more tomorrow - OK if I post pics if I get lost?
1 Landscape trailer w/ home built cutting platform
MS660
EFCO MT8200
Smaller saws and some other stuff.

chevytaHOE5674

Find somebody who can vacuum test the saw. That will tell you right away if there's a leak, and if so where it is.

Al_Smith

The son of a gun is sucking air bad to hang that fast .Whomever that "small engine " guy was evidently didn't do something correctly . Any experianced engine builder knows a lean runner . Although without naming names I've seen them ran at GTG 's so lean I ducked for cover figuring any second they would come apart like a dollar watch . :o

windthrown

Well, its easy to lean out the carb too much. First place to look. Pull the limiters in the carb jet screws and trim the tabs and re-seat them, and richen that sucker up. O/w as said its an air leak. Crank seals? Carb not bolted down tight? Holes in the air filter? Carb boot not tight, or an air leak in it? Not much else can leak, unless its something weird like a case seam leak or crack in the case. Or a break in the cylinder gasket.

Seems odd. The 660 is a pretty bullet proof saw.
Stihls: 440R, 361, 360, 310, 260, 211, 020T. Husky: 372xt.
I ship Stihl saws down under: message me for details.

cjchainsawman

Just wanted to weigh in as I am a Stihl Dealer/Repair Shop and have just had such an issue.Had a new 660 returned twice for same kind of problem.Second time started looking close for owner misuse or something missed in the saw.Turns out it was all in the carb from the factory.After rebuild saw ran up 1400-1500 rpm!Removed limiters and screws,reinstalled and adjusted to tach and saw is now the beast that wont quit.Stihl Tech and I can only surmise there was some metal left in carb at production.As it was set correctly just ran up way too high and seized from high temps of running too lean.So I suggest you put it on a tach and see where its running.Should be close to 1300.

Rocky_J

Isn't that what ALL Stihl dealers/service shops are supposed to do anyway? Are you saying you normally send out saws after simply adjusting them "where they are supposed to be" without firing them up and putting a tach on them?
??? ??? ???

Al_Smith

I'm not disputing using a tachometer .My only point is that anyone with any experiance with two cycles should know by sound if the thing is running lean or not .

However since the comment about I carb now I wonder .Is it possible that like the MS 200T's with funky Zamas from China a new menace is on the horizon for MS 660 owners ? Geeze first Toyota now Stihl .

windthrown

You are off by an order of magnitude on the revs. Should be 14,000 -15,000 RPM WOT, and the 066/660 should be set to 13,500 WOT unloaded with bar and chain on it (plus or minus 500 RPM) according to the factory specs.

Saw should burple or 4-stroke at unloaded WOT:

      If it sounds clean, its lean.

Stihls: 440R, 361, 360, 310, 260, 211, 020T. Husky: 372xt.
I ship Stihl saws down under: message me for details.

windthrown

Quote from: Al_Smith on February 24, 2010, 04:18:45 PM
However since the comment about I carb now I wonder .Is it possible that like the MS 200T's with funky Zamas from China a new menace is on the horizon for MS 660 owners ? Geeze first Toyota now Stihl .

Better make sure that the carpet does not get up and under the saw's throttle linkage. ;)
Stihls: 440R, 361, 360, 310, 260, 211, 020T. Husky: 372xt.
I ship Stihl saws down under: message me for details.

jteneyck

This is interesting.  I had a Husky 55 do the same thing.  I had a scored piston after 3 years of pretty good use.  The cylinder looked and measured fine, so I put in only a new after market piston, cylinder and carb. gasket and pulser tube on it, and adjusted the carb so that it was as rich as possible while still being able to cut.  Did not check it on a tach or for air leaks.  It cut fine for 1 hour then wouldn't even run.  Pulled the muffler and the ring was worn right down to the piston and the piston was scored. 

If I set up the carb. so that it was running rich wouldn't that make up for any air leaks if there were any?  Isn't it the air/fuel mixture in the cylinder, no matter how it gets there, that's important?  Or could the cylinder be the problem even thought I couldn't see or measure it?  You guys have a lot more experience in this area than I, so any ideas are appreciated.  At this point, the saw is sitting as I'm wondering whether or not to throw even one more $ at it.  Thanks.


Al_Smith

I unknowingly tore a carb boot on an 038 Mag I had ported .It ran just fine except it had "run on " after I let off the throttle . I retuned the carb ,fiddled  with it ,cut more wood .I knew something was amiss so I investigated and found a bad top shock mount which caused the boot failure .

Since repairing that saw with new mount boot  etc I once again did more port work on it and found nary a thing wrong with piston or cylinder . However during the time of the bad boot I had the saw set rich as I was breaking it in with new rings on a used cylinder . Now weather it was that or the 32 to one mix that saved it I can't be certain .

Dalden

Aint found the leak yet.  But I did notice somethin weird.  While it was runnin - It looked like it sucked a chip into the muffler - I would not think there should be vacume in the muffler?
1 Landscape trailer w/ home built cutting platform
MS660
EFCO MT8200
Smaller saws and some other stuff.

mtngun

Quote from: Dalden on February 26, 2010, 10:43:05 PM
Aint found the leak yet.  But I did notice somethin weird.  While it was runnin - It looked like it sucked a chip into the muffler - I would not think there should be vacume in the muffler?
Plus the factory muffler has a spark screen, unless someone removed the screen.

My two cents:

As others have said,  test for air leak before making another move.   

Check all fuel lines and impulse lines for decay or breaks or anything that might leak.   If there is a leak in a fuel line, it will suck air.

Clean or replace the fuel filter that is inside the fuel tank.   Unless you are more careful than I am, some sawdust gets into the fuel tank when you open the cap to refuel.   The sawdust ends up in the fuel filter, which eventually becomes restricted and changes the carb tuning.

As others have said, the carb needs to be tuned correctly and retuned every so often.   Chainsaw carbs do not stay in tune for years at a time like cars.     

A trained ear can tune a carb very well but those of us with tin ears do better with a tach.   Factory spec is 13,000 rpm wide open throttle, not 13,500 or 14,000.    Milling saws should be tuned richer because milling is very hard on a saw.   I tune my milling 066 to 12,000 - 12,500.   

Carb tuning may temporarily compensate for an air leak, but eventually the air leak will get bigger and bite you in the butt.    You gotta fix any air leaks, they are poison to chain saws.


windthrown

From a Stihl design engineer I was told (and corroberated by several Gold trained Stihl technicians):

All Stihl saw specs are +/- 500 RPM. So a Stihl factory 13,000 spec max RPM really means 13,500 RPM. That's from the horse's mouth. I run all my Stihls 500 RPM over spec. No problems.

Stihls: 440R, 361, 360, 310, 260, 211, 020T. Husky: 372xt.
I ship Stihl saws down under: message me for details.

captain_crunch

Take Some mixed saw gas in squirt type oil can with saw idleing squirt gas carefully around seals and carb mounting block if there is an air leak it will kill the saw instantly. Squirting around muffler not recomended ;D ;D
M-14 Belsaw circle mill,HD-11 Log Loader,TD-14 Crawler,TD-9 Crawler and Ford 2910 Loader Tractor

Al_Smith

A tach is a good tool to have around .However if per chance you happened to have the inclination plus the knowledge to rework the engine for enhancement those specifications are no longer valid  regarding RPM .

Even a stocker is going to run where it runs . It does little good to set a saw at 13,000 in free air if it bogs to 8,500 in the cut .

I've seen people nearly wear out a tach trying to get the saw just so so where a good ear could have got it in 30 seconds flat .

Cut4fun

Quote from: Al_Smith on February 23, 2010, 09:09:03 PM
Any experienced engine builder knows a lean runner . Although without naming names I've seen them ran at GTG 's so lean I ducked for cover figuring any second they would come apart like a dollar watch . :o

It's scary to watch him tune a saw isn't it Al :o :D :o

I've tried them so lean for those 2-3 cut races I scared myself before.  Not anymore.  8)

windthrown

Quote from: Al_Smith on March 03, 2010, 04:23:02 PM

I've seen people nearly wear out a tach trying to get the saw just so so where a good ear could have got it in 30 seconds flat .

Depends on the saw. Some of the newer ones, like the 361, are really hard to tune by ear. They are really choked up. I start at the factory setting and then tach it, then tune by ear and then tune by a few cuts, and then tach to verify. And after that I do a cut and kill, and check the plug. I like chocolate color brown plugs.

Once the saws are tuned and dialed in, it takes me a few seconds and one cut to tune them by ear in the woods if needed. Also it depends on the saw. A tight high compression good running saw with the right carb is fast to tune, both the L & H sides. An old tired lower conpression saw with leaks can take forever to tune, and the tune usually does not hold for very long.
Stihls: 440R, 361, 360, 310, 260, 211, 020T. Husky: 372xt.
I ship Stihl saws down under: message me for details.

Dalden

Well - having trouble diagnosing the leak -saw won't start.  I suspect that with the rings eaten it has nearly no compression.  This thing is I think just beat -

I have decided to break down and pay the dealer to rebuild it- if it screws up again it's on him.  ($500) but hey you can't hardly by a used one for that....
1 Landscape trailer w/ home built cutting platform
MS660
EFCO MT8200
Smaller saws and some other stuff.

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