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

[AUSSIE1]

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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.

Those single transfers do lack a bridge for the ring to ride on.
Is very hard to say if a port with this width would hang a ring unless there is a ring end issue.

Possibility of a broken ring upon assembly?

You can bevel a little more at the centre pettering out toward the ends to give slight curvature.

 

[AUSSIE1]

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


.

Why? No need for a third party. Have at it.

 

[PogoInTheWoods]

Any reason for me to save the fragments?

Do you want em analyzed, or not?

If there is to be a thorough analysis of the situation, dig out the fragments for such analysis. But which fragments are you referring to? The piston, I presume?

Any analysis of the situation worth 2 cents by any independent analyst will also require the cylinder -- which is where I put my bets on the failure of the piston in the first place. Asymmetrical cylinder condition by reason of either extreme modification pushing tolerances beyond acceptable, or general material weakness of the cylinder itself as has been otherwise attributed to the piston, or a combination of both.

The piston was an aftermarket piston. How many others of the same specific type/batch/brand (whatever) from whomever have committed such spectacular suicide in such spectacular fashion in non-modified cylinders? Hell, how about the same question relative to OEM pistons? Seems like a fair question to me.

My guess is the piston disintegration was simply a symptom of a major cylinder problem out of the gate before there was even any gas put in the tank or a spark put to the combustion chamber.

Your independent analysts are gonna wanna see both the piston remains AND the cylinder for any reasonable assessment of whatever it is they are
being expected to evaluate. Some specification and criteria there will also be required to establish what it is the independent expert is even attempting to analyze.

All the above stated, I know a very high-end physics prof at Oberlin College who is very pro-active in many areas of research from cable box power consumption to solar energy stuff to core drilling into landfills for methane recovery to whatever floats his boat and gets him going -- who also has tons of global research connections from NASA to MIT, and is a bit of a chainsaw enthusiast on a backyard level.

Want me to ask him if he'll look into Brad's blown up fragments and Gregg's pistons on an actual scientific level - you know, with material comparisons and facts and stuff?

Didn't think so.

As you were.

opcorn:

Poge

 

[Zombiechopper]

real testing that will generate meaningful results costs money. I would think the manufacturer would be the one to try and figure this out. However, if they are the kind of outfit that uses an unknown mix of scrap metal to cast pistons then how can they possibly know what the problem is? If they don't even care what the alloy was to begin with then how can they diagnose a problem with that alloy?

 

[HARRY BARKER]

real testing that will generate meaningful results costs money.

I thought that was real testing......it failed.

test over.

 

[Grande Dog]

Howdy,
Sounds like the guy knows how to eat with a knife and fork. If he wants to do it for a nominal fee, or for free, I'll send him all he can stand.
Regards
Gregg

 

[wigglesworth]

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

I do...but...

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

I agree with Tzed, it would be better to have a third party do it, get some good analytical facts, not just my word on it.

 

[mowoodchopper]

Gee, those aftermarket BB kits sure are sweet, and cheap too. I think Ill run out and buy one for all my saws, maybe itll make the old German junk run better. LMAO

You can buy them books but you cant make them learn. Ever wonder why your stihl dealer, insist on stihl OEM parts, or why the local Ford dealer insist on motorcraft instead of napa? I dont!!!!! LOL

Did anyone's Grandad tell you, ya get what ya pay for?

 

[edisto]

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 ? ? ?

I didn't say it was too wide, I said there is not enough curvature in the expanded portion for the width. Widening is fine, to a point, but the wider you go the more careful you have to be about easing the rings back into the cylinder.

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

If I couldn't get the shape right, I wouldn't be widening...

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.

Excellent point. It's easier to work on a new cylinder, but in addition to finding out if it's going to crater on you, you can evaluate the improvements you make if you run it stock or blueprinted first.

 

[Tzed250]

Gee, those aftermarket BB kits sure are sweet, and cheap too. I think Ill run out and buy one for all my saws, maybe itll make the old German junk run better. LMAO

You can buy them books but you cant make them learn. Ever wonder why your stihl dealer, insist on stihl OEM parts, or why the local Ford dealer insist on motorcraft instead of napa? I dont!!!!! LOL

Did anyone's Grandad tell you, ya get what ya pay for?

To me the top end is a part of interest, but not the suspect...


.

 

[woodguy105]

Dayummm...That engine is Fubar with a capital F.

 

[Fish]

Seems to me the thread has 2 extra variables.

One variable is: What initiated the failure?

The other is: Did the piston construction initiate it?

OK, more variables: Was the "grenading" exclusive to the aftermarket
cyl/assy?/

Was the failure exclusive?

Would a ring/skirt catching cause that catrostrophic of a failure if it was
Oem?

Woiuld the failure have occurred if it was oem?

My contention from the onset, is that if it was oem, the piston would have
not "grenaded" like that, no matter what initiated the failure.

But that is another "variable".

The modifications the original poster may have done to the assy., that is another very big, complicated variable as well........

Finding an "independant" "objective" party would be hard to find, as the variables are too numerous to even contemplate.

But that is me.

If you found a party to test the metal, and it was found "pourous", what would that say?

Or hard on one side? But the ring clipped a port, the specs were way off,
etc..

Too many variables....

And Brad wants to throw away the gravel!!!!!!

Don't you all watch motorsag csi???????

 

[parrisw]

Gee, those aftermarket BB kits sure are sweet, and cheap too. I think Ill run out and buy one for all my saws, maybe itll make the old German junk run better. LMAO

You can buy them books but you cant make them learn. Ever wonder why your stihl dealer, insist on stihl OEM parts, or why the local Ford dealer insist on motorcraft instead of napa? I dont!!!!! LOL

Did anyone's Grandad tell you, ya get what ya pay for?

Do you work on cars for a living? Probably not. OEM in car market doesn't mean ****!! In domestic anyway. My brother has a 07 ranger with 60,000km on it and it now needs a $700 repair, outa warranty.

 

[parrisw]

Seems to me the thread has 2 extra variables.

One variable is: What initiated the failure?

The other is: Did the piston construction initiate it?

OK, more variables: Was the "grenading" exclusive to the aftermarket
cyl/assy?/

Was the failure exclusive?

Would a ring/skirt catching cause that catrostrophic of a failure if it was
Oem?

Woiuld the failure have occurred if it was oem?

My contention from the onset, is that if it was oem, the piston would have
not "grenaded" like that, no matter what initiated the failure.

But that is another "variable".

The modifications the original poster may have done to the assy., that is another very big, complicated variable as well........

Finding an "independant" "objective" party would be hard to find, as the variables are too numerous to even contemplate.

But that is me.

If you found a party to test the metal, and it was found "pourous", what would that say?

Or hard on one side? But the ring clipped a port, the specs were way off,
etc..

Too many variables....

And Brad wants to throw away the gravel!!!!!!

Don't you all watch motorsag csi???????

I agree, everybody can sit here and take their best guess, cause that's all it is. You'll just never know 100% what caused it, and if you think your 100% sure, then well, you can't be helped.

 

[Arrowhead]

I agree, everybody can sit here and take their best guess, cause that's all it is. You'll just never know 100% what caused it, and if you think your 100% sure, then well, you can't be helped.

:agree2: Even testing pieces won't tell "exactly" why....

 

[Zombiechopper]

Do you work on cars for a living? Probably not. OEM in car market doesn't mean ****!! In domestic anyway. My brother has a 07 ranger with 60,000km on it and it now needs a $700 repair, outa warranty.

this is true. I worked in automotive and industrial cooling systems for years.

Honda oem radiators? Bulletproof. last darn near forever

Chev oem rads?.......always recommend the aftermarket options!

Quality is quality no matter what the name on it. My brother worked as a partsman for years. They used to call the white box brake pads 'family killer specials'

The alloy that these kits are cast from still bugs me. Alluminum alloys vary greatly. There is a huge range of how cast aluminum could perform depending on what the composition is. I ordered a BB kit and I will run it without worry due to Bailey's warranty and top notch customer service but it kind of makes me wonder. I do really appreciate the info from Gregg on this though. It is nice to have the straight poop on the subject.

 

[shawn022]

I remember watching Dirty jobs with Mike Rowe awhile back and he was working in a scrap yard. They were sorting through aluminum and using a hand held "gun" to determine the alloy of the aluminum. Better alloy better money. Maybe call a few recycling yards and see if anyone has a piece of equipment like this.

 

[Justsaws]

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


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I can see that. I think that the piston became the dreaded hot dog in a hallway after five minutes of warm up at idle. The sloppy fit of the piston was compromised by the elongation of the port.

If the P/C were not modified they would still be functional until the piston roof started banging on the cylinder.

That particular piston has some issues but it was the modification that killed the saw.

BS, interesting thread, thanks for putting it out there. If you want it tested you should save as much as possible including the cylinder.

Grande Dog, you are a generous sponsor. Thanks for playing a long.

 

[belgian]

Too many variables....

I agree with Fish. Analyzing that piston requires a lot of sophisticated test equipment. Hardness testing alone will learn you very little, you'll need a Spektrolab to analyse its composition, and several cuts to analyse defects in the casting, porosity, etc.

And you need to compare the results with OEM to be able to make a judgement. Casting technology is not everyone's specialty either.

And one bird does not mean spring...it could be a bad egg in the lot, and that doesn't mean much if a ring hung up...

bad things happen.

 

[willysmn]

Destroyed engine

My two cents is this<
Its always difficult to know what happend first as you guys have said and I do better if I have the parts in my hands, although the photos are real good. Given that, I think the ring caught on the way down and ripped off the part of the piston top above the top groove. Then that piece went thru the engine until it blocked the piston skirt on its way down which broke the skirt and caused the wrist pin to pull out of the piston. Or The piston could have made a few more revolutions after the skirt broke and all those pieces could have blocked the downward motion of the piston and pulled the wrist pin out.

I've seen a 4 cyl airplane engine (old one) where one sleeve got loose and moved down where the top ring popped out at TDC and then ripped half the piston top off above the ring, with the other 3 cyls making power. I've also seen lots of incidents where steel parts go thru a 2 cycle and make nice grooves in the cylinder walls and piston sides. I'm sure you guys have too.

So I don't buy the piston skirt breaking under side load. The load is applied thru the wrist pin and the piston is thicker and stronger in that area than at the thin skirt area, where its feels much less load. The skirts on hi performance Chevy pistons are just a tang and are there to keep the piston centered. the piston rides on the rings and the two skirt tangs. Modern automotive pistons are not round but oval