What is everyone's thoughts on AIP pistons?

[Freakingstang]

= 1/2" Impact wrench

Or make yourself a Virginia Wife Beater (AKA custom long handled clutch removal tool)

http://www.arboristsite.com/showthread.php?t=31654&highlight=makita+clutch+removal

How does the viginia wife beater help me here? The 066 has a 19mm hex on it, no need for fancy backyard fabrication....

I did try my dewalt 18V impact and it didn't budge....

 

[Justsaws]

F.S., it is hard to tell but it looks as though the wrist pin spun in the piston holes. As L.S. was talking about wrist pin fit that might be the issue. I have come across a few used saws with after-market pistons in them and they have suffered the same fate. I do not know what brand piston. The holes suffered stress fractures and cracked. A couple were in Huskys, 288s I think. Been a while. I have also seen the same thing in OEM pistons if the saw has been spun way to lean. Had a 066 with that and a spun crank bearing.

As to removing hard clutches, air wrench with spark-plug removed. Set wrench at 100 and fan trigger once. If that does not work in two tries step up a notch. If it still does not come off install spark-plug, start over. Have not had any problems. Piston stops and the rope "method" can be as well.

Hope it is up and running soon. Good luck.

 

[Freakingstang]

The ISO9001 doesn't mean they are as good as OEM - it just means that the factory has QC and QA in place such that everything coming off the line is built to the standards they put in place. Question is : what are those standards?

I haven't seen any pistons from Stihl that are forged. They are all "cast". The question for the aftermarket pistons is "what are they cast from" .... recycled aluminum or virgin 2021 (or whatever Mahle uses) alloy, and what heat treatment was done after casting and then (sometimes) after machining.

I'm sure the manf. would give you a new piston, but would you feel comfortable in using it?

Mahle is one of the the world's largest piston manufacturers. The 066 has pushed them to the limit - even their pistons have had problems with heat and have been revised a couple of times. The 084/088 have an iron heat disk cast in to the piston to alleviate this issue, and that engine isn't a huge leap in HP over the 066 Dual port Magnum (7.7 to 8.7), roughly. I'd be suspicious of any aftermarket piston in large saw.

Freaken: How tight was your wrist pin fit? I've noticed many of the aftermarket piston pins are really loose. The Stihl/Mahle fit is an extremely very tight specification: Bore +0.002mm to +0.006mm -> figure that in 10,000ths of an inch!. It's a narrow range tight interference fit often requiring heating of the piston in hot water for easy insertion. If your pin was loose, even up to 1 thousandth of an inch, it could have fractured the piston from vibration. As the piston gets hotter, the fit gets looser as the piston alloy expands faster than the steel pin. I see you used the AIP pin. The Stihl pin has a ground taper bore to reduce weight and possibly thermal considerations. The AIP is a straight bore weighing considerably more.

Sorry about the forged thought I injected in there. I have never seen a mahale piston break in a saw. I was thinking from my automotive experience when this one crumbled like it did. I just assumed the mahale were forged from the abuse I've seen them take.

I'm not so much worried about the replacement piston, as to warn others about the possible cause. This was a parts saw that i bought and put together quick. I served my needs at the time. The jug was a formerly scored piston one, and i cleaned it up and used this piston to try to save a buck.

I have a good used jug (non scored), but need a real mahale piston....too bad they are about a buck thirty new-> my cost at local dealer.

As for the wrist pin fit. Honestly I don't remember. I did, however go out and check a AIP 046 piston I have still in the box. I'm afraid to use it now...
The pin fits snug, but not like the super tight pita factory pins. Leads me to think you might be on to something with the wrist pin tolerances...


honestly i never thought about the pin differences, just used the one that came with the new piston. I can tell you from comparing them after your post, they are considerably differant, with the AIP being almost twice the weight. My performance brain should have recognized that up front...Less rotating weight= thumbs up!

I did measure the OD of both pins, and they are dead nuts the same, reading from my cheapo digital calipers.

 

[Lakeside53]

I did measure the OD of both pins, and they are dead nuts the same, reading from my cheapo digital calipers.

Pins are easy to make are are usually exact - reaming the hole the piston to the required tolerance is where the problem occurs,

 

[ShoerFast]

Just my .02 cents worth, but is there a chance that the rope was in the ex-port, or extremely favoring one side?

As the wrist-pin boss is cracked toward one side as if the piston were cocked to one side, (fist pix, red arrow) and carbon is missing at the point of the second pix's yellow arrow?

To me, it just looks like the side thrust on the wrist-pin boss (red arrow) may have been the start of the brake? And the possible area that the rope crowded and induced the side thrust?

What I think is interesting is the flame front track as the carbon is swirling against the flow (lite-blue arrows) and perhaps could use a little more ing. timing as it may be starting from the plug (late timing) as opposed to starting from the dome in the combustion chamber causing a slightly more incompasing flame front?

Kevin

 

[belgian]

Freakingstang,

Looking at the top pictures : could it be that the piston had already some cracks before you started to work on it. I mean, look at the color of some cracks, some look to be black or not "fresh". It's not very clear in the picture, so difficult to tell.

PS. I have used the rope technique too a few times, no problem.

 

[ShoerFast]

Freakingstang,



PS. I have used the rope technique too a few times, no problem.

Most everybody has used the rope trick, but with seeing this, makes me think how lucky we get.

There is a chance that using a lot more rope and stoping the piston a ways before TDC (as this one may have been stoped very close to TDC) That way the piston would have a huge presantage less load on it as it would have more athority over the crank via the leverage.

 

[bump_r]

...I'm wondering if the key would be to pack the chamber with grease or heavy oil and put the plug back in to ensure even loading and eliminate stress points of the piston's top... Messy, but less so than a 'sploaded piston... Mid-stroke would be ideal, (correct?) as the crank would be at 3 o'clock and 9 o'clock - biggest resistance (available by crankshaft) with least load (applied to piston)

Just thinkin' out loud, take it easy...

 

[ShoerFast]

...

Just thinkin' out loud, take it easy...

Thinking is what it is all about!

The grease idea is very cool, as there would be zero side or area specific stress. Yes, the ideal place to stop the piston would be just after the closing of the ex-port.

As we all know that Steve is a very good Mechanic and a valuable contributer to this site, anything could have happened, even that he may have had that one a year reject piston that any company could have?

As for me, I will not run my MS-660 till I put install an AIP piston, (it's ordered and on it's way) I take it on good integrity that there are just way too many AIP pistons out there getting the job done.

Steve, my thoughts / .02 cents , or $50 - 60 bucks here is with AIP, I will run them. Did you lose the jug during this brakage?

 

[slipknot]

Yikes!!!

I do believe the company in question makes oem pistons for efco products!
Who else do they make pistons for?

 

[Freakingstang]

Just my .02 cents worth, but is there a chance that the rope was in the ex-port, or extremely favoring one side?

I highly doubt the rope was in the exhaust port. i learned that mistake of cleaning out the many strands or rope on my first attempt at the rope long ago on a 55 Rancher. I had the rope in a "U" shape, with the ends out in plain view, outside of the spark plug hole. If it would have been caught in the exhaust port, the middle of the rope would be pinched, or freyed, right? It is not. If anything, it would have preloaded the piston in the center, where most of its meat is.

What I think is interesting is the flame front track as the carbon is swirling against the flow (lite-blue arrows) and perhaps could use a little more ing. timing as it may be starting from the plug (late timing) as opposed to starting from the dome in the combustion chamber causing a slightly more incompasing flame front?

Kevin

I noticed this too, Could very well be from my porting, and I have yet to touch or even check the timing. This was an experimental jug, so it was a learning process.

 

[Freakingstang]

Freakingstang,

Looking at the top pictures : could it be that the piston had already some cracks before you started to work on it. I mean, look at the color of some cracks, some look to be black or not "fresh". It's not very clear in the picture, so difficult to tell.

Might be my monitor, but they all look the same to me. If you are talking about the top view looking down, there are not any cracks on the top of the piston, that is carbon.

There are more cracks that are not visable, all around the wrist pin support. I had it running a big bar right before the oiler quit. Literally, had it running and 10 minutes later tore it apart, erh well broke it apart.

 

[ShoerFast]

I noticed this too, Could very well be from my porting, and I have yet to touch or even check the timing. This was an experimental jug, so it was a learning process.

Steve, understand that for all I know, the swirl pattern may be exactly what you do want or just what your going to get, I just think it looks cool, very defined flame activity there!

 

[Mr.]

Steve,

This is a tough one. You have made a few assumptions that were incorrect and asked Dean to hold off. Why?

I would make an assertion, but seeing the spark plug will make any statements for me. Was it a new plug? Let's see it.

I popped two Golf pistons in the 2100 and 1 Stihl in the 066 before it was right.

Poo happens with these saws.

Fred

 

[Freakingstang]

Steve,

This is a tough one. You have made a few assumptions that were incorrect and asked Dean to hold off. Why?

I would make an assertion, but seeing the spark plug will make any statements for me. Was it a new plug? Let's see it.

I popped two Golf pistons in the 2100 and 1 Stihl in the 066 before it was right.

Poo happens with these saws.

Fred

It was a fairly new plug, meaning it had about a tank run through it. I will post up a pic tomorrw of it. The piston had approximately 10 tanks run through it, so if there was a problem with it, I would surely think that it would have shown up before i tried to take the clutch off. Am I wrong in thinking this way?

I didn't tell Dean not to respond, I just wanted other feedback. Dean is a dealer for them and thought maybe his thoughts would be biased, do you know what I am saying?

Dean, you are more than welcome to respond. Have at it.

Fred, what incorrect assumptions are you reffering to? wether they are cast/forged...doesn't really apply does it? i'll reread the thread and see where else I fooked up.

-Steve

 

[Mr.]

Didn't say you F----ed up anything. Look at the carbon on your piston.

The break happened before the clutch removal. IMO

Good the plug should give us an accurate read since it is fairly fresh. Not trying to be accusatory, just trying to get to the bottom with you.

If there is a problem and you put another slug in there it MIGHT happen again.

I pointed out my own folly to try to show I am not trying to sound like an authority, just an enthusiast that blows saws up. LOL

Fred

 

[Lakeside53]

I'm also in the boat that thinks the break or at least a crack was there before you tried to take it off..

Maybe you were lucky you did break it fully, instead of it coming unglued at 15k or where ever you run that thing.

 

[klickitatsacket]

Freakingstang. I have been waiting like you asked. The rope trick is a good way of pulling clutches, if done right . I have used it 1000's of times with never a problem. This however was not the initial cause of the problem. This is because the squish was not set right and you were smacking the top of the cylinder. #1 In the first picture you can see the shiney spots where it was hitting. #2 on the second picture you can see where the edge is smashed on the exhaust side (corner of top and edge) You beat the crap out of the piston. By the way the hit pattern looks on top; it also looks as though the base of the cylinder was not quite flat. When you tried to pull the clutch it finally gave way.
Oh yeah and #3 the rope fell into the transfer and the piston was broke by a pulling force because you did not have the piston set BTDC but ATDC before you tried to pull the clutch. As the rope fell in the transfer and hung up the rod pulled the piston apart. You can see in the photo where the rope got caught.

This was not a ploblem with the piston, but the installation and the attempt to take the clutch off.

I have had 3 differant people look at this besides myself with out telling them the story and all 4 of us feel the same way.

 

[Camping57]

I have been lurking for quite a while and decided to post since this is an area where I have a little experience. I have been analizing fractures for a fair number of years, so when I saw those photos of the broken piston I wanted to see what I could tell from looking at them.

The photo showing the bottom view is the one that I think gives us some information. The pin boss on the left side shows pretty strong evidence of being 'cracked' prior to final failure. Someone else noticed the discoloration on the fracture surface closest to the pin bore and you can also see evidence of a fatigue crack ('beach marks' like wave marks in the sand) radiating from the pin clip groove. That is right where I would expect to see cracks originating (clip grooves are where I have seen most pistons cracking; it's a major stress riser).
The right side boss also seems to show discoloration that is evidence of cracking prior to final failure. The cracks created enough reduction in cross sectional area that when the added high stress of the rope trick was placced on the piston it suffered a catastrophic failure.

If the engine had continued to run it would have broken the piston in a pretty short period of time in pretty much the same place. At high loads (read "speed") the fatugue cracks would have continued to grow until the remaining cross section of the bosses broke. How long is open to guessing.

What caused the initial cracking I don't know, but since it seems to be on both bosses, I think it is likely not a defect in the piston, in that case we would see failure starting in one spot (where the defect in the casting is). Since the cracking appears to originate from the retainer groove, my guess is that there was a repeated high stress that started the crack growing from the spot.

I think that most OEM pistons that I have seen have been cast (high pressure die casting) not forged. There may be forged pistons out there, I just havent seen them.

 

[Mr.]

Welcome Camping.

Contrary to popular belief (LOL) this place values informed opinions, as yours most definately is.

Sometimes it takes alot of input for a good output.

Fred