What is everyone's thoughts on AIP pistons?

[spacemule]

Sometimes it takes alot of input for a good output.

Fred

Ex Lax will cure that. :hmm3grin2orange:

 

[Freakingstang]

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.

Ok Dean, answer me this...

If the squish was set at .018, how was it hitting?

How was it that i took the jug off the weekend before after it had some heavy use on it and eveything was fine?

That damage you say came from the piston smacking the cylinder is just not the case. I took the topend off to inpsect it for abnormal wear, as this was a former scored cylinder that I honed and reused.

There was no damage upon the first disassembly. There was some wear marks in the cylinder that showed the edge of the piston, meaning the definite lines where the piston travels, like any other jug in ok shape will have after some use.

After the piston broke, and i tried to turn the motor over, it would not. I had to put a socket on the clutch to get the motor to spin over. I am guessing this caused some of the edge marks and cracks that you are referring to.

I will get better pics up in the next couple of days before I leave town for a month. I will also get a pic of the spark plug for the world to investigate.

You can see in the photo where the rope got caught.

Can you please show me this? I'm serious.


I guess i need more pictures of the damage. The squish was very safe at .018. I have a 372 that has been running much longer at only .012..... I would venture to say that the rope caused the "shiny spots" as you call them. It simply removed some of the fresh carbon where the rope made contact from the otherwise almost new piston. It might look shiny in the pics, but there is no shiny spots on the top of the piston. The motor was placed Before TDC, opposite rotation, so the rope was above the ports, it could only come up, not down, as the clutch was preloaded before removal-no chance for the rope to get caught.

The rope did not fall into the transfers, the way it was postitioned, it couldn't. I do this because on my first trial of the rope method, I had the piston too low and as it rotated to come up to ATDC, the rope got caught in the exhaust port of a smaller saw. There was no damage to that piston, but it sheared the rope off and I had a mess cleaning up the rope strands from inside the case.

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.

I know who at least one of them is..

All i can say is that this isn't my first saw, and most of you seem to think this is some high reving hotsaw...It was a stock saw with the exhaust raised about 1mm and the lower transfers opened to the case. It was never above 13.5K, as it was to be a reliable work saw. I had it set at 13K for my cutting needs.

I have used other aftermarket pistons in other saws of roughly the same cc and rpm from differant manufactures and never had such a problem.


I appreciate your thoughts, but I don't think I was the cause. I am not afraid to admit when I am wrong, but I honestly do not think that is the case here. I have learned enough over the past saw projects to inform myself of the potential hazzards that can happen.

If the cracks were there before the clutch removal, how were they cause? (assuming the saw was tuned correctly).

Like I said earlier, I am not here to bash AIP, but more of trying to find out why it happened. I am also trying to keep an open mind, and relize that I do not know all there is to know. I just feel strongly confident in this situation that It was not my fault.

-Steve

 

[belgian]

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.

Bingo, if you ask me.
Good post for a starter. Welcome to AS
take care.
roland

 

[paulkx5]

If you don't mind, how much side clearance was there between the piston and the bore after the hone job?

 

[klickitatsacket]

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.

First you story is full it. The piece of rope you show is the piece that was pinched off. If you look at the left end of the rope you can clearly see where it was piched ahead of the cut. It is pinched and there is carbon rubbed off on the pinch mark. If that end was outside of the cylinder how did that happen? Also the chunk of rope won't even stop the piston. I have 3 pictures showing this. The rope I cut was even longer than what you show and it will not work. What happened is; you got the rope stuck and broke the piston. You most likely were trying to find the tinging noise; assuming it was the clutch and not realizing it was the piston hitting the top of the cylinder. If you look at the edge of the piston on the exhaust side you can see it is deformedand the corner is shiney from hitting. You might want to check your bearings. If what you said was true about the squish clearance then I would say your bearings are loose and were allowing the piston to slap the top.
Here is 3 pictures showing your description and it does not fly.
http://i5.photobucket.com/albums/y186/klickitat/freakingstainpiston_3837.jpg
http://i5.photobucket.com/albums/y186/klickitat/freakingstainpiston_3835.jpg
http://i5.photobucket.com/albums/y186/klickitat/freakingstainpiston_3838.jpg

 

[Freakingstang]

For the record, the clutch was being removed to get to the oiler. It quit oiling. There was no noise, no other problems other than the worm gear was worn, and caused my oiling problem...

As for my BS story..That's the way it happened. I actually took these pics this afternoon before coming home and seeing the pics of your "example" I wonder if you could have found a smaller diameter of rope..


Ok, here goes...A bunch more pics..

After installing the rope the way it was, I think I might have found the problem was to why the piston exploded. Note the size of the rope....If you look closely at the pics, the rope is somewhat up in the air. With the piston in there to push down on the rope, it would end up on the squish band on one side of the cylinder, but not at the other side. This preloaded the exhasut side of the piston and caused much stress to that side of the piston. I'm speculating this is what caused the failure, acutally after witnessing it from the "inside" I really thing this is what cause it. I still have yet to have any problems with this method in other saws. This being the first sign of a problem, I will change my methods, by packing more rope into the combustion chamber, so the load is spread over the entire piston surface, instead on just in one spot.

You should be able to see the ends of the rope ok. There is no pinching here..Any black marks you see on the end is from a lighter to keep the rope from freying. This rope has been used to remove 15-20 other clutches or flywheel nuts.

Here is a closeup of the top of the piston. I still don't see a "shiny" mark. I do see a smudge in the carbon about where the rope would have ended up. It is right where the arrow is on the exhaust side. The light glare towards the top of the picture is from my workbench light.

Here is the bottom of the piston. one Crack is very visable on the left side. Notice the big chunk missing from the bottom of the pic. Just above that chunk, on the topside of the piston is where the smudge of carbon came from the mark. This must have been the first point of breakage

Dean, I may have fooked up and only had the rope on one side of the piston, but can you still see the shiny spots on the piston? I cannot, in plain view without a camera or flash to make shiny spots. The piston was not hitting the jug. The rope never was in the transfers or exhaust. I might have caused this, but like I said before, using the same method, I have never broken a piston. I must have been lucky, or this one was just on a lot tighter than the rest.

BTW, the saw is back together and running just fine. Same squish, same everything, except piston.

Everything was fine before I took it off. Like I said, I don't know it all or claim to. Last night I honestly didn't think I was at fault, but after doing my own further investigation (prompted by you, lol) I found that the user ---->=ME was the cause and the problem.

I'll talk to the mods and see if I can get the title changed so as not to bad mouth AIP.

I'm sorry for jumping to conclusions.

Dean, I was really hot last night, thought that what you were saying was BS and trying to make me out to be the bad guy.

After i thought about it, I cooled down and tried to see a differant perspective. That is when I put the rope back in the cylinder and took the pics.

Thanks you for making me think from the other side.

People are human and they do make mistakes. Some just don't do it on the internet forums. lol

Sorry folks, show is over, Steve needs to learn to use the rope method a little better next time.

 

[Lakeside53]

Good summary Freaken, but I doubt it was your rope... I have done a biszillion (ok.... many hundreds plus) clutch removes with rope and never had an issue on any saw. All I take care with is that the piston is above the exhaust and "going the right way". Then just stuff in the rope...

 

[klickitatsacket]

Stang, Now I feel like a complete ARS. The Pictures you just took look completely differant than the first set. (same piston but differant lighting). Looking at what I thought i was seeing (especially the way the rope looked) I was sure you got it stuck in the transfer. Even the wrist pin hole looks completely differant. Let me know what you drink. I will send some out to you and we can have a drink over the phone. BTW you are big man. Let me follow in your foot steps and offer an appology for being a jackass and going off.

 

[Canyon Angler]

Sorry if this is a dumb question (and I haven't read the entire thread), but

Why are you folks changing out the pistons on these motors?

I mean, I can see changing the rings, but why change the pistons? Are the skirts wiped out? I don't get it.

Thanks,

CA

 

[Lakeside53]

Sorry if this is a dumb question (and I haven't read the entire thread), but

Why are you folks changing out the pistons on these motors?

I mean, I can see changing the rings, but why change the pistons? Are the skirts wiped out? I don't get it.

Thanks,

CA

The piston in a 2 stroke is a valve. Skirt wear of just a few thou makes for poor idle and other problems. Usually by the time rings are needed, the piston is bad.

 

[TopJimmy]

Glad you guys are all happy again. Now that the cause may have been the rope used to remove the clutch, I have a question. What about the piston stops that Bailey's sells? I can see the advantage of the soft rope vs the metal stop, but it appears that the rope can have it's own complications. My 346 does not have a nut for a wrench or socket. It has a couple of recessed areas for a screwdriver to hit the clutch. I have been able to remove the clutch with a sharp quick blow without using any type of piston stop. I gather from the other posts that the clutch's on the larger saws are much tighter. (I have never had to remove a clutch from my larger saws).

It seems that the impact wrench may be the safest method, but if it does not work, then what is the best piston stop?

Thanks.

Jim

 

[PetrolHead]

"It has a couple of recessed areas for a screwdriver to hit the clutch. I have been able to remove the clutch with a sharp quick blow without using any type of piston stop."

Yep, My husky has the same recesses and I have used them to remove the clutch a few times. Be gentle old son, the last time I tried, I cracked the counter weight casting and had to buy another clutch. There is a proper tool from Husqvarna that fits into the clutch centre to remove it using the dreaded piston stop. Next time I would like to try the rope trick.

 

[Lakeside53]

Glad you guys are all happy again. Now that the cause may have been the rope used to remove the clutch, I have a question. What about the piston stops that Bailey's sells? I can see the advantage of the soft rope vs the metal stop, but it appears that the rope can have it's own complications. My 346 does not have a nut for a wrench or socket. It has a couple of recessed areas for a screwdriver to hit the clutch. I have been able to remove the clutch with a sharp quick blow without using any type of piston stop. I gather from the other posts that the clutch's on the larger saws are much tighter. (I have never had to remove a clutch from my larger saws).

It seems that the impact wrench may be the safest method, but if it does not work, then what is the best piston stop?

Thanks.

Jim

Screw-in piston stops are supposed to only be used on cylinders that have a vertical plug in the top center of the cylinder. The offset angled plug (most saws today) needs a different approach. Stihl sell a flat plastic device that fits inside the plug hole and is then rotated until it's flat. Doesn't work well on big cylinders and occasionally snaps of! I use rope on all the larger saws.


Impact wrenches have their own problems. It's really easy to shear the key of the flywheel (cast type, not the tool-steel metal woodruff keys) when taking off the clutch. I use them, but if it clutch doesn't come off easily, I use rope and reach for a long bar. Constant and even pressure is better... and you know how much you are applying.

For putting the clutch and flywheel back on, you still need to stop the piston while torguing... Even if you can get away with not torquing the clutch (bad idea, but it's done), your flywheel definitely needs torquing to the correct spec.

 

[Freakingstang]

Dean, thanks for the E-beer. sorry for thinking I wasn't at fault. It took your comments to make me see from the other point of view.

Now, what are your thoughts on that flame pattern?

I ws gung ho on getting pics of the plug, but after I found the rope in the cylinder dilema, I kinda bypassed that. I will try to get a pic of the plug later tonight.

 

[Freakingstang]

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?

I missed this the first time around.

No the jug was not damaged. That Nikasil from Mahale is pretty tough. More so in the Stihls than the huskies from my little experience.

 

[klickitatsacket]

freak, what is you gap set at on your plug and for the coil?

 

[klickitatsacket]

btw. PM me what you drink and your address.

 

[Freakingstang]

Plug is 20 thou and the coil is about 8 thou if my memory serves me right.

 

[klickitatsacket]

how much did you take off the base? Advance your ignition timing about 1.5 degrees for every .010 you take off the base. Also what was done to the transfers if anything?

 

[Cut4fun]

Ok, this got me to try a different method of clutch removal. I was trying to get the clutch off of my 5000 plus to switch to 3/8. Well I always do the rope trick too and seeing how it was setting at a angle in there too and after not being able to budge the clutch, even after using a hammer and remembering steves piston here, OUCH! I got scared, dont know if i could find a 5000 plus piston for the saw. So I used someones idea of, pull the plug, 100psi and pull the trigger for a quick burst, on the 3rd try she came loose. Well I am switching methods for now. Phew.