Grenade!!!!!!!!!!!!!!!!! Warning, GRAPHIC content!!!

[Paul001]

my personal opinion: lower ring dropped in intake at bdc and broke skirt off on its way up. then on its decent the skirt was laying under piston keeping it from traveling back to bdc thus breaking the bottom of the pin boss and then the c-clip came out doing the damage shown in the transfer on its next round before everything got piled up in the bottom. i've never saw a just a c-clip coming out do that kind of damage unless the wristpin catches the transfer port.

+1

Either that or it had a broken cylinder fin!



I've posted pictures of some pretty good kaboomies, nothing this far gone. Even most interesting is the fact it happened just off idle. Causes me concern as to the material used in the piston/cylinder. As others have said, circlips coming loose normally do not produce any where near this kind of damage. But add in the fact you are dealing with an unknown, the material this piston is made out of, and we can not rule it out.

Still the above quote most accurately presents my thoughts.

 

[Tzed250]

I can buy that. That's basically a combination of my theory, and TZeds. I still believe it started at the transfer side, and then progressed to the intake. This theory supports that.

The more I think about it, I'm just not buying that a ring caught in the transfer. They just aren't that wide, and they were beveled. I've done too many just like this.



Like I said earlier in the post, I value everyone's input. That means I value the input of those that don't agree with you. I'm using those two ear to listen to both your and everyone else. And just for the record, I won't install a BB kit on a paying customers saw. But that's beside the point.

Yes, I did make a mistake, one way or the other. I'm fine with that, but want to learn from it. I'm also big enough to post it here for everyone else to see. I figure everyone has room to learn something. I guess you're done learning, ehh? You're still asserting your opinion over everyone else's.

I do want to hear what you, and everyone else has to say. But I'm not going to have one person's opinion shoved down my throat.

If your intentions here are what you say they are, you'll drop this and let the thread continue.

Looks like you were the first to state that you were done..ehh?


Best thing about this whole deal is that I don't have a blown top end.
What I do have is 3 decades of experience with two-stroke engines to help form my opinions.

BTW, just thought I would let you know that I'm impressed that you brought this into the light, even said something to that effect to my girl this morning.

Awaiting your diagnosis and countermeasure...


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[Paul001]

Howdy Brad,
As long as a lot of people are speculating, I think it was that German junk you hung under our fine top end.
Based on the pictures I would most have to agree with Tzed250's scenario. This doesn't rule out what many have said that they thought it was poor, or improper casting. If you want to find a place that will test the damaged piston compared to OEM, I'll pay for it. As far as the disposition of what you have now, whether it was the chicken or the egg is to hard to tell with the photos. I know this came out of your pocket, so I don't have any problem replacing it, or refunding you.
Regards
Grenade Dog

Class act at all times.

 

[Tzed250]

Tzed250, are you thinking that after idling for five minutes it hung the ring on the down stroke, clipped the top off the piston with other small damage, tipped the piston, partial skirt shattering, stroked through once more, completed the shattering and and locked up?

Pretty close. I believe it fractured the botoms of the pin bosses at the same time.


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[Tzed250]

Class act at all times.

:agree2:

 

[Grande Dog]

Howdy All
It would be interesting to get the material inspected by an independent tester. I don't have anyone in the little black book that does this. Anybody out there interested or, know of a qualified tester?
Regards
Gregg

 

[striperswaper]

piston analysis

there has to be at least one person with work or university connections on this site but will they read all the way thru to here?
start a new thread to ask for help? do you have the specs on what the alloy of the piston should be to compare?

 

[Grande Dog]

Howdy,
Hopefully someone will see this and help out. I wouldn't have any specs for the OEM but, I could come up with a OEM piston for comparison. When I went to our piston manufacturers, It was pretty low tech. They buy there ingots from the middle east ( cheap electricity for processing). The just made it in batches. They had two different kinds of ingots that had different compositions. All they did was take like 5 of one kind, and 1 of the other kind and melt them til it's ready to cast.
Regards
Gregg

 

[porky616]

i would be looking into the piston myself. i have minimal 2 stroke experience but a lot of diesel experience and in the last 5 years ive seen 4 piston failures in earthmoving equipment. one such failure made court as one of the worlds number 1 heavy equipment builders would not have it that the piston failed. my boss won the case after the piston was inspected in a lab and found to have several casting flaws. quality and name brands dont always mean they are perfect. just my 2 cents worth

 

[Zombiechopper]

Howdy,
Hopefully someone will see this and help out. I wouldn't have any specs for the OEM but, I could come up with a OEM piston for comparison. When I went to our piston manufacturers, It was pretty low tech. They buy there ingots from the middle east ( cheap electricity for processing). The just made it in batches. They had two different kinds of ingots that had different compositions. All they did was take like 5 of one kind, and 1 of the other kind and melt them til it's ready to cast.
Regards
Gregg

I just ordered a kit yesterday and I gotta say this scares the crap out of me. I can't beleive they don't know what the alloy is. Wow. I guess I just found out why OEM pistons cost so much

 

[mtngun]

Hopefully someone will see this and help out. I wouldn't have any specs for the OEM but, I could come up with a OEM piston for comparison.

I don't have a Rockwell hardness tester (yet), otherwise I'd love to help.

But as I suggested earlier, most engineering colleges will have a materials lab, and if you ask them nicely, and are willing to wait (because they may do it as a student project) they may be willing to help you for little or nothing.

Brad claims the piston was unusually hard to grind. If that's true, a hardness test should show it, compared to OEM or another BB piston. Only thing I can think of that would cause that is unusual silicon content ? ? ? Porosity wouldn't cause it to be hard to grind, would it ?

Years ago, I had a local college test the hardness on a gun barrel. A student I knew did the testing, and it didn't cost me anything. Unfortunately for this thread, I no longer live near a college.

There are fancier tests, but they take fancier equipment, and much more time. A hardness test would be quick and easy.

I don't have any dog in this fight, I just want to learn. I'm sure Brad does, too.

 

[blsnelling]

Would a simple hardness test be helpfull? Wouldn't a larger machine shop have one of those tools that puts a little dent in the metal to test the hardness?

 

[blsnelling]

Any reason for me to save the fragments? I've already thrown them in the garbage, but could dig them out. I have the main part of the piston saved though.

 

[Zombiechopper]

Any reason for me to save the fragments? I've already thrown them in the garbage, but could dig them out. I have the main part of the piston saved though.

you need a flat smooth peice for a hardness test.

Lee (the reloading tool company) makes a cheap brinell hardness (lower scale of measurement suitable for soft metals) tester. It works on the same principle; make a dimple and measure it under magnification. It is designed for lead alloys so not sure if it would translate to aluminum

 

[Tzed250]

I just ordered a kit yesterday and I gotta say this scares the crap out of me. I can't beleive they don't know what the alloy is. Wow. I guess I just found out why OEM pistons cost so much

I doubt you have anything to worry about.


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[Tzed250]

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Hardness is only a small slice of the pie...


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[mtngun]

So what caused the ring to hang? I would say the widened portion of the port was much too square.

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So you think the upper transfer port was too wide and too square, and it snagged a ring on the downstroke ?

Fair enough.

The most severe piston damage does appear to be near the flywheel side transfer. That does make the transfer port look suspicious.

However, it doesn't explain why many, many people have widened transfers without incident ? ? ?

If we buy the snagged-ring-in-transfer theory, then how should porters handle the upper transfer to avoid this problem ?

It is easy to say the port should be less square, but...... few of us have an angle grinder to sculpt transfers.

Personally, I would not have widened the ports that much on a work saw, but I understand Brad wants to have the fastest saw on the block.

The only other preventative suggestion I can offer, is to run a new top end in stock form for a few tanks of gas before porting. I don't always have the patience to do that, but, if it had been done in this case, it would have made troubleshooting so much easier.

 

[mtngun]

Would a simple hardness test be helpfull? Wouldn't a larger machine shop have one of those tools that puts a little dent in the metal to test the hardness?

True, a larger machine shop might have a Rockwell hardness tester. Any shop that does a lot of heat treating should have one. Maybe Nick knows of one in the area ?

The test point is tiny, so you don't need a big piece. It does need to be a shape that will sit still while it is being tested -- that may be a challenge with your shattered piston. A round piece is OK as long as it will sit still (the gun barrel that I had tested was round).

Thanks for posting this, Brad. It would have been easy to pretend it never happened, but then we wouldn't learn anything.

Personally, I just like to have a definitive answer so I can either 1) rethink how to mod transfer ports or 2) rethink aftermarket pistons.

 

[MCW]

I made an announcement in off topic a month or so back that I'm no longer in law school and do not plan on finishing it.

I don't read off topic very often unless a thread from the chainsaw section is moved there and I follow it

That aside, I have just about as many posts "contributing" something as you have complaining about my lack of contributing.

That'd be two or three contributing posts then

Truth is, people just get annoyed and attack me instead of what I'm saying because I say the glaring truth. You can't attack the truth, so throw mud and ignore.

Seriously though you pop up in the middle of a thread where people are talking about what may have gone wrong with this setup just to have what I would call a cheap crack at Brad? How many hundreds of builds has Brad done with no problems? There is some truth to what you're saying as in the risk of a failure will increase when modifying but if properly done shouldn't cause a reliability issue. I'm no modding guru but believe that what has happened here is a casting flaw. Of course I could be wrong


I can see why some people think that by modifying a perfectly good saw you are wrecking it and to be honest I would have agreed until I got one (which to me was a very tough decision - just so happens I had a bit of money to waste at the time!). If I can take a 79cc Dolmar out tree felling that will perform the same as a heavier 395XP then count me in anyday...

By the way though, I do like your avatar

 

[Tzed250]

True, a larger machine shop might have a Rockwell hardness tester. Any shop that does a lot of heat treating should have one. Maybe Nick knows of one in the area ?

The test point is tiny, so you don't need a big piece. It does need to be a shape that will sit still while it is being tested -- that may be a challenge with your shattered piston. A round piece is OK as long as it will sit still (the gun barrel that I had tested was round).

Thanks for posting this, Brad. It would have been easy to pretend it never happened, but then we wouldn't learn anything.

Personally, I just like to have a definitive answer so I can either 1) rethink how to mod transfer ports or 2) rethink aftermarket pistons.

There is a hardness tester 10ft. from where I eat my lunch. Better to have a third party do it.


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