044 broken piston skirt

[lledwod]

Hi there. I just joined this site. I am spending some time this winter getting all my saws in good shape. I dug out my Stihl 044 that broke a skirt on me a few years ago. I had put a new piston in this saw about a year before the skirt broke, but had few hours on it, probably 10 or less. The reason I replaced the piston was scoring due to a cracked intake rubber/boot. The cylinder still seems fine. My question here is, is it possible this is a defective piston? I don't recall in the past seeing a skirt quite so thin, or thinner on one side than the other? If this is just the way these pistons are built, I wonder what else the cause may have been .... I hate to rebuild it and have this happen again!

Thanks for any help.

Jonathan


 

[sablatnic]

Seen this before. Check air filter, intake boot, pulse line, cylinder and crankshaft seals.

[ZeroJunk]

My bet would be defective. What brand was it, or was it OEM ?

[lledwod]

This is an oem,Stihl piston. The intake boot was new when the piston was replaced. I am not sure what trouble my air filter would have caused, I am pretty 'up' on all my maintenance. Like I said, the cylinder seems to be fine, there is no scoring to speak of. I will take a closer look at everything, and maybe see if my Stihl dealer can check out the piston for me.

[deerslayer]

I have seen broken piston skirts in the past and usually it is on the thin side of a badly worn piston. The thinning of the skirt is the result of wear but if yours was low time, not sure what could have caused that. Was the saw used a lot? Calender time is really no indication of use. If the saw was running 6 hours a day, it could wear out in a couple years. I suppose if the cylinder was "rough" or oversized, then that could cause abnormal wear as well.

Make sure you don't have any cylinder issues before redoing this saw again or you may be revisiting the same issue down the road...

I see in your original post you were estimating the saw was used only 10 hours after the rebuild. Was the piston used? I can't imagine any way the piston could get that thin in that few hours. Something doesn't make sense...

[ehp]

Check your base gasket , on the 044's there were a small amount of saws that the factory sent out with a metal base gasket that was the wrong size in bore , the gasket didnot have any wiggle room for when the piston got up to temperature , The piston grew a couple thousands from heat but the gasket did not and the result was the gasket torn the skirts off the piston and did it in a very short amount of hours . Stihl made the dealers change the gasket but I'm not saying all the dealers did change the gasket , If thye gasket is metal check it , if its not them check the intake port on the cylinder for something buggered up in it

[Al_Smith]

--either what Ed said or it ate something that didn't  agree with it and gave  it a terrible case of indigestion .

It doesn't take much,tramp metal orbiting around the crankcase ,ingested trash,a wire broken out of a flocked filter ,snag on the intake port .

The good thing is most OEM Stihl cylinders are pretty tough .I own an 038 Mag that literally grenaded a piston .I mean like a bomb went off .JJ from Oregon sent me an OEM piston ,back together and ran fine for 7-8 years until the owner retired it and gave it me .Never as much as put a dimple in that cylinder .

[ZeroJunk]

You could tell more if the broken pieces were intact . Still looks like it broke along a flaw in the casting to me. If there was damage from a gasket or piece of foreign material enough to break the skirt there would be damage on the bottom edge.

[lledwod]

OK thanks for the replies. I had a brainwave, duh, and measured the piston. The thin skirt seems to be due to wear. I will go through the saw more thoroughly in the next day or two, and try to track down the problem. So far the crank and bearings seem to be fine, I did split the crankcase and will clean everything up. I'll look the cylinder over very carefully as well though it seems fine. And I'll check out the carburetor, intake boot and filter for signs of a problem or debris. I suppose the damage could be due to me not cleaning out the crankcase properly last time I rebuilt it? I can't recall what I did at the time.

[ZeroJunk]

Ten hours or less must have been off a little.

[sablatnic]

Ten hours or less must have been off a little.

You didn't discard the new one and put in the old one? Don't start guessing why I ask!  :-[

Normally the skirt will break, when it is worn so thin, that the piston will start rocking, hammering the piston skirt into the cylinder wall. Normally caused by excessive wear.

[ktowne030311]

was just about to say, just because the cylinder looks good, doesnt mean its not ovaled out a bit, resulting in "piston slap". which would result in a broken skirt. measure the bore , see if its still factory spec.

[lledwod]

Yes I will measure the cylinder. I am kind of assuming it is nikasil plated, and assume this wouldn't wear egg shaped without wearing through the nikasil?

[AdkStihl]

The intake skirt looks worn extremely thin as compared to the exhaust skirt.
That's usually a sign of poor air filtration and/or beyond service life.

[ktowne030311]

Yes the nikasil can wear. The inside of the cylinder has to be exactly round ( with-in specs)
to perform properly. This can only be accurately checked with a dial bore gauge, it can measure to with-in
one ten thousandths of an inch. The Nikasil plating that's on the walls of your cylinder is only a  few
thousandths of an inch thick but it is very hard. It wears extremely well as long as everything is tight and
sanitary. If you maintain your engine as the factory recommends it will last for years.

[ehp]

problem is the bore is not in nicasil its in chrome which is alot softer , if the chrome is that bad you should be able to see with your eyes around the intake port cause if there is a problem that is where it will be . You better check your crankcase over very close , if any larger pieces got into the case with the motor still turning the crank can shove those pieces into the oil tank part of the case or straight down into the bottom part , either way check the casr out very well for any kind of cracks , to wear a piston skirt that bad something major is wrong , if you can see the shape of the intake port in the intake skirt on the piston then you got major clearance problem but kind of from the looks at the skirt I would say some bad stuff has been going by the air filter into the saw when its running , give us a shot of the intake side of the piston

[lledwod]

I took more photos, will post them when I get a chance. I measured the cylinder, I don't have the # in my head but I can detect no out of round. My method is telescoping gauge and micrometer. To 1/10 000". I'll test my memory, was it 1.9681" ......

I did split the crankcase, with the intention of careful inspection and cleaning. No real physical damage, though the paint is browning and flaking.



  

  

  

  

  

 

[Al_Smith]

Pistonoligy 101. Contrary to popular belief a piston skirt as a rule is not round nor perfectly square in relationship to the sides ,crown to skirt being parellel .Although I've shared this  with many saw builders we cannot agree .

Here it goes having installed two complete piston manufacturing lines .One  for Ford ,one for Honda and having done on going line maintance on 4 for Ford .

The crown or head if you prefer is perfectly round .The skirt is slightly larger than the face and has as slight ovality and a slight taper from bottom skirt to just below the piston rings .

The reason for this is as a piston is moving first it acts like a liniar sleeve bearing .However because of the forces involved it rocks slightly .With this rocking action because of the ovality the skirt presents a more perfect alignment with the cylinder than a perfectly round one .The ovality is measured at a right angle to the piston pin but because of the fact most modern saws use a reduced piston skirt it's not always easy to detect .

[Al_Smith]

More on this which involves my favorite subject with the amsoil crowd .Because in essence the piston skirt acts like a liniar bearing -plus a liniar valve it would make sense it requires lubrication

Now a 2 cycle engine doesn't have the luxury of being drowned with lube oil like a 4 cycle .Whatever lube it gets is only a microscopic film of the oil in the fuel .Heading right back to the ever popular oil wars .--see how I turned that one around  8)

[jwilly3879]

Pretty slick Al!

[lledwod]

 

  

  Thanks again everybody, for the info and ideas. I added photos to my post above. My measurement of the cylinder was 1.9681". There are two cracks in the rear housing where it is possible some debris could bypass the filter. Also, I did do some milling with this saw, with this piston. Personally I think I could re-use the cylinder, but I see chainsawr has a used piston/cylinder for sale, which is tempting. I will have to clean and inspect the crank bearings ....

[ehp]

that cylinder needs to be cleaned bad before even thinking about reusing it and you cannot measure the bore with it like that , to much build up on the bore , where is the second ring on the piston ? , A saw doesnot eat a piston like that unless something is wrong big time . I am quite surprised that the intake port part of the cylinder is not torn all to crap with a piston looking like that , I would of thought the cylinder would of had some pretty bad damage after that skirt dropped like that

[weimedog]

Just finished putting together a saw that had a skirt broken like that... and a chunk got down in the crank case and the crank punched it hard enough to make a hole in that case. Didn't notice it at first... just dumb luck as was using the parts cleaner to flush out the cases and noticed leaking where I didn't expect.... closer inspection. Ruined cases.

[Al_Smith]

On a grenaded piston it's good advice to completely field strip the saw clear down to the bones .

That black stuff inside the crankcase is most likely very fine wood dust which combined with the oil from the fuel has became pyrolited .In essence turning it to petrolium coke .The oil didn't do it ,the dust did .

You can go less expensive with say piston rings but a good filtration system is a must .

[HolmenTree]

lledwod, I see your up in the Yukon and probably run your 044 in snow and freezing cold conditions.
Snow ingestion which will wash away the lubricant off the piston intake skirt causes damage  called water or snow score .
Adding alcohol de-icer to the fuel mix to prevent the icing up condition in the carb's venturi, will further add to washing away the piston skirts lubricant film.
Under these conditions  with no lubrication film the piston's intake skirt will wear thin very quickly as your photo shows. Plus on top of that if the saw is icing up it will be running lean furthering the problem. Piston rocks severely slapping the cylinder breaking apart the piston skirt.

My other question is was the saw run without a lower piston ring to gain extra r.p.m.? If it was that could be another reason for the piston rocking causing excessive wear.

[lledwod]

I feel like I am making progress with my saw. I think that the saw was worked hard; I spent about 3 hours cleaning parts yesterday, esp. the crankcase. As I worked I thought about all the work I have done with the saw, lots and lots of ripping/milling and fine sawdust. (Mostly on the 1st piston) I had thought that the cracks in the intake housing area were there when I bought the saw (used) but now I recall one good fall that the saw and I had together near the end, (of building my house) and it is quite possible that this is what caused the cracks, and that these cracks allowed the induction of fine saw-dust and so wear and abuse to the intake side of the piston? Does this make sense?

I now have a bandsaw mill and will not likely subject this saw to the same long full throttle runs anymore. I will fix the cracks, and rebuild the saw. I built my house with this saw, so some sentimental value. Otherwise I've done the vast majority of my sawing with Husqvarna. I am currently tuning up/rebuilding a 353, 51, 162SE, 024 and this 044.

PS I do run the saws a lot in the winter, and find all kinds of related challenges (sometimes down to -45) My 1st 044 piston went in relation to snow ingestion I think.

[HolmenTree]

Ok so possible snow scoring damage. Were you using de-icer in the fuel?
What happened to the bottom piston ring? ???

[Al_Smith]

45 below zero,good heavens .

After those pictures were added you could tell it was rocking bad .The exhaust side piston face above the ring is rounded off .Took a long time to do that .

Not the mention the fact it used in milling service which is about the most demanding task a chainsaw could ever get .I'd say more than anything it's just plum tuckered out .

[lledwod]

Oh yes the bottom piston ring .... both rings were in place and intact. I just decided to remove the bottom one for some reason the other day. And the top one but it is 'peened' in. I used to use de-icer in my chainsaw fuel sometimes, I've always used a tiny amount. I've used enough in my snowmobiles to see how effective a very small amount is, and understand the dangers of using too much. As for my 044, I am hoping to get a used piston and cylinder from chainsawr.

[HolmenTree]

It's common knowledge to a few by removing the lower ring gives a fair bit more rpm at WOT. Not recommended for a todays work saws. Just something a few cookie cutters did back in the day on old relics like Jonsereds 80's or such, at the local fair chainsaw speed cutting contest.

The 044 were notorious for sucking in snow and cold through that split top cover.
There's a winter kit available for the 044 but all you get is a plastic rewind cover block off plate to reduce the intake of cold freezing air and snow.
The 038, 034, 064 had a 2 piece kit with the plate plus a rubber flanged air filter cover that actually sealed that gap between the 2 top covers. Icing up prevention on these saws was very favorable.
The 044 had a poor design with only an extension on the air filter to help fill in the gap of the top covers, but still allowed lots of snow and cold air ingestion.

A cheap and easy artic weather fix is tape up the lower half of your 044's  rewind housing's air intake grille and the gap of your top covers with duct tape . At -45 below you will need about 3/4 of the rewind housing covered up :D
Make sure the top cover partition window is open to allow heat back to the carb. Also plug that square hole on the left hand side of the lower part of the air filter housing cover.

[lledwod]

I guess about a years gone by ..... but I have got the 044 back together, new meteor piston, seals and gaskets. She's running great! Smooth and strong and lots of power. I also bought and installed a 'heat shield', the piece between the cylinder and muffler. My saw never had this piece, (since I bought it used) and missing this surely did the saw no good.

[joe_indi]

Looking at that picture of the Exhaust side of the piston, I would check the piston needle cage and the crank bearings. The damage as seen from the inlet side points to that or something left over from the last repair. Though you have not post one, a picture of the piston top would show damage along the perimeter, maybe with the edge(of the piston top) curled up.
Joe