576XP Unexplained Seizure

[J D]

Trying to get my head around why this saw seized...
It was run with no issue for half a day on 91 non-ethanol fuel mixed @ 33:1 with Husky LS+ along with half a dozen other 576XP's.
Day 2 (same saws, same fuel) it is started, given a few seconds to warm up, oiler test performed, & then 2 cuts are made on an 18" pine log. Mid second cut the saw dies & on trying to start it the student finds it to be locked up. Instructor (who observed nothing wrong with the students practice) removed starter & plug... At this point saw could be turned over but was obviously catching in the bore around the exhaust port height. Unfortunately we were not able to pull the muffler to confirm anything beyond what I have explained.
Plug looked very (too) lightly chocolate to me (may have been a new plug but was comparable to those in the other saws)
Any input regarding contributing factors would be appreciated... Auto-tune working correctly... Is there a way to know?
It may have been serviced recently so something could have been overlooked there

 

[Fatherwheels]

Could have been a lot of things, how do you know the Autotune was working,
a few seconds is useless to warm a saw up, you need more.
Could have been running lean, that's a big saw for 18 inch bar.
Could have been a mechanical issue, like plating came off cylinder,
dirt came in the intake, ring pin fell out, ring caught in a port.
Without having the ability to investigate further we are only able to guess.

 

[J D]

Bar was 22", chain was sharp, log being cut was 18" softwood.
I agree that there isn't enough information to do anything more than guess, but I would still appreciate educated guesses for consideration... Especially with regards to the Auto-tune side of things. I believe auto-tune has a re-calibration procedure & I doubt any of the saws have ever had this done

 

[Vintage Engine Repairs]

A few seconds isn’t enough to warm it up. With the info you have given - the only assumption we can offer is it’s a cold seizure…

 

[J D]

Sorry, to clarify, by "a few seconds" I was meaning at least 30 seconds & usually longer. While I was not the instructor in this case, usual procedure would be... Start saw, "blip" throttle to bring off high idle, disengage chain brake & give a light rev to confirm chain spins freely (most new operators take 15-20 seconds just to achieve that), then move to a suitable surface & test for oiling at mid rpm, then receive direction on what they are to cut, then start cutting.
While we do tend to have students go "screaming" into their first cut, I don't believe that was the case in this instance

 

[Jasonrkba]

I would think 33:1 the plug should have been black. May have went lean.

 

[Bob Hedgecutter]

You wont know until you pull the cylinder and check the piston and provide photos of the damage- if any- otherwise we can sit here and guess until the cows come home.
Were these NZDF saws? How many hours on the saws previous to this happening? Were these the saws you referred to in earlier posts that had been reworked and revamped?

 

[J D]

I would think 33:1 the plug should have been black. May have went lean.

As would I, at least a reasonable chocolate... Part of my concern & second guessing of the Auto-tune (wish I'd taken pictures of the plugs now)

You wont know until you pull the cylinder and check the piston...

Bob, your assumptions are correct altho the original issues were about 5 years ago & I have no idea if any of these saws we were any of those (it is definitely possible) as equipment can get passed around a fair bit (a whole other issue in itself)
Interestingly this particular saw did not have it's running book which makes me suspicious it has just come back from workshops & something may have been overlooked.
I agree, the only way to really get "closure" on this will be to see the cylinder/piston... unfortunately I'm only likely to see a workshop report (& that could just say "replaced piston" or "uneconomical to repair")

 

[Bob Hedgecutter]

As would I, at least a reasonable chocolate... Part of my concern & second guessing of the Auto-tune (wish I'd taken pictures of the plugs now)


Bob, your assumptions are correct altho the original issues were about 5 years ago & I have no idea if any of these saws we were any of those (it is definitely possible) as equipment can get passed around a fair bit (a whole other issue in itself)
Interestingly this particular saw did not have it's running book which makes me suspicious it has just come back from workshops & something may have been overlooked.
I agree, the only way to really get "closure" on this will be to see the cylinder/piston... unfortunately I'm only likely to see a workshop report (& that could just say "replaced piston" or "uneconomical to repair")

Very possible a bottom rod bearing failure then- but that is only a guess and one of many possibilities.
Don't tell Cindy you are busting her gifts- or you will be issued Masport or Jobmate saws next time around!

 

[J D]

Very possible a bottom rod bearing failure then- but that is only a guess and one of many possibilities.
Don't tell Cindy you are busting her gifts- or you will be issued Masport or Jobmate saws next time around!

To be honest, the way some of the equipment is treated, "expendable" stuff would make sense sometimes (or should I say for some operators).
I did hear a rumor they're now replacing the top ends with non OEM parts... That may be of significance also (thinking about that now I wish I'd looked the cylinders over more closely)

 

[GeorgiaVol]

Have a 570XP on my bench right now that the piston ring locator pin came out and punched through the top of the piston and gouged the cylinder.
1st one I have seen.

 

[frank_]

i had 2 this week where the locating pin had trapped the ring
a makita brick saw (mahle) , and a ts400 brick saw (a/m)

 

[wcorey]

Sounds like it could have hung a ring in the exhaust port, sometimes saws just do it for no apparent reason...

 

[Fatherwheels]

i had 2 this week where the locating pin had trapped the ring
a makita brick saw (mahle) , and a ts400 brick saw (a/m)

View attachment 921752

The location of that pin looks just right to trap a ring, but do very little to stop it rotating, its hardly in the right path at all.

 

[frank_]

The location of that pin looks just right to trap a ring, but do very little to stop it rotating, its hardly in the right path at all.

i think its just ringland wear, loads of slop in the top ring
the bore is very glazed, so i think it did high hours (old hireshop ts400)

 

[Fatherwheels]

i think its just ringland wear, loads of slop in the top ring
the bore is very glazed, so i think it did high hours (old hireshop ts400)

View attachment 921785

So that's what a high hour piston looks like, is this an MT carbed unit.
How does one get such a glaze, that is super smooth looking.

 

[frank_]

So that's what a high hour piston looks like, is this an MT carbed unit.
How does one get such a glaze, that is super smooth looking.

these cutters tend to be hired by paviors, to cut bricks and slabs, so they eat a lot of concrete dust
pre strato old carb, with a sticker ontop saying "use 25:1 only"

 

[Fatherwheels]

these cutters tend to be hired by paviors, to cut bricks and slabs, so they eat a lot of concrete dust
pre strato old carb, with a sticker ontop saying "use 25:1 only"

Any way of knowing what mix was sent out with the saw to the customer, and if they were re supplied
with it for as long as the saw was on hire, some outfits will send out a few gallons of their own mix and
charge for it, other customers just buy their own, or straight gas them, unbelievable how often they put
straight gas in them and come in very angry that the saw stopped.

 

[GeorgiaVol]

Here is that 570XP piston.

 

[Fatherwheels]

That's quite a mess, again the pin looks to me to be located too far up and the ring gets under it
and then you have this.