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

[Justsaws]

I think that RD is correct.

It looks similar to some well worn piston skirt and cylinder bombs, perhaps on occasion encouraged by a grinder.

I would have said hung ring but as previously mentioned usually there is more damage where the ring was feeling around for grip before the actual failure.

The images of the breaks in the casting are interesting. There seems to be a wide variety density present. Heat/duration during casting process was not correct for alloy. Could just be the images, but I would think that the modifications may have pushed that particular piston's quality past the safe zone.

 

[parrisw]

i've seen enough of brad's "improvements."


bent connecting rods, broken fins, slower than stock runs, etc. Etc.

pos

 

[vincem77]

Sorry about the blowup.

Sounds like you might have gotten a California emission reduction piston. They shut down after 5 minutes of idling to save all the trees.

 

[spacemule]

pos

asbl

 

[belgian]

One could say "improve" but nobody will ever learn anything if we don't fail a few times. Many of the greatest improvements have been made with trial and error.

+1 ! and kudo's to Brad for posting the "error" with the public.

Modding in general, which includes widening ports, piston windows, etc. involves also removing material and weakening the construction. I've seen pics here before from pistons that were really beefed down to the bone, so to speak. Combined with increased power/rpm, that also means that you may balance at the edge of construction limits sometimes.

The risk also becomes higher if you work with aftermarket materials, whose specifications are unknown and untested under those circumstances.

Looking at the debries of this blow up, the piston casting doesn't shine really, but it's speculation really on my part.

I am somewhat glad for Brad this blow up occurred on his personal saw and not on one of his customers. Customers have very little understanding for "errors" of such kind. That's why manufacterers spent millions in research and development and bring products to the market that are safe and lasting. It is also a reminder for sawnuts like us that we should be carefull with critique on sawmakers why things are done the way they are

 

[nmurph]

Brad, what do you make of the dings in the top of the piston? something made those and it wasn't done in a single stroke or two. that took a bit of running to make that many and what happened with the bottom of the piston put an immediate stop to everything. i think you have a two part event.

 

[MCW]

That's what happens when you try to "fix" a perfectly good saw. Shame.

Maybe a cooling fin found it's way in there?

I've seen enough of Brad's "improvements."


bent connecting rods, broken fins, slower than stock runs, etc. etc.

If you're studying "law" Space you should probably learn to open your mouth when you know it's absolutely necessary. I'd love to know how many of your 14,000+ posts actually contributed anything constructive to this forum...


Brad,
Are you sure your little throttle "blip" wasn't to 19,000rpm?

 

[AUSSIE1]

I used the clips from the kit. I really don't think it was a failure of the clip. Right now I'm thinking skirt failure or ring caught on the transfer. I'm still surprised to think a ring would catch in one of these transfers. They're not near as wide as an intake or exhaust. Plus I've ported too many cylinders like this and never had a problem. I guess there's always a first though. Fortunately, this was my saw, reguardless of the cause.

No not the clip, just noticed the shape, but that could have happened during the explosion and the pin is central.
The transfer doesn't look that wide with a second look. The grinding marks can be twice as wide as what's been removed.
Oh well if you reckon the ring end was well away it wouldn't have been here.
You don't normally go wider than 70%. Was this an exception or are you still at 70%?
If the lower ring drops into the inlet it seems to be pointing here or the skirt.
Damn lucky though in one respect as it could have been alot worse.

 

[porky616]

graphic images! im gonna need counselling after looking at these pics.

 

[Arrowhead]

The damage had to happen in several strokes. So who knows for sure what pieces were where at the time. It's possible a ring caught a port. I think this would be more likely at lower speeds though. I'm thinking it's a casting flaw. By the looks of the piston.... I say it was too hard/brittle. There could have been a tiny crack somewhere undetectable to the eye. The company's that make these BB kits are trying to do it as cheaply as possible. The cosmetics may have improved over the years, but who's to say they are using quality alloy to produce them. It makes sense to me that if there was a factory defect with the piston it sustained itself at idle. Once it warmed up and the heat expanded the problem area and the increased rpm..... she blew. Just my .02

 

[john inglis]

bad luck

sometimes thing go wrong but you will never learn anything unless you have a go , thanks for the post brad , was just thinking about a big bore for one of my 460's but might wait a while . do enjoy all the modifications you do , keep it up .

 

[blsnelling]

I am somewhat glad for Brad this blow up occurred on his personal saw and not on one of his customers.

I couldn't agree more!!! I made the same comment to my wife, and earlier in the thread.

Brad, what do you make of the dings in the top of the piston? something made those and it wasn't done in a single stroke or two. that took a bit of running to make that many and what happened with the bottom of the piston put an immediate stop to everything. i think you have a two part event.

I really don't know. But I now do not believe the clip failed though. Something else instigated this.

Brad, Are you sure your little throttle "blip" wasn't to 19,000rpm?

Not even close. I hadn't even tried to tune the H at all. This was the first of a couple heat cycles I was going to put it through first.

No not the clip, just noticed the shape, but that could have happened during the explosion and the pin is central.
The transfer doesn't look that wide with a second look. The grinding marks can be twice as wide as what's been removed.
Oh well if you reckon the ring end was well away it wouldn't have been here.
You don't normally go wider than 70%. Was this an exception or are you still at 70%?
If the lower ring drops into the inlet it seems to be pointing here or the skirt.
Damn lucky though in one respect as it could have been alot worse.

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.

By the looks of the piston.... I say it was too hard/brittle.

There's no question that this piston was extremelty hard, much harder than normal.

 

[mtngun]

I went back and looked at the pics again, and still don't see a smoking gun.

It's probably not going to happen, since the government is not funding this project, but I'd love to see the piston remains checked out by a metallurgical lab.

Any major universities in your area, that would have an engineering lab, to test hardness, and ideally run a SEM on the piston, and compare the results to an OEM piston -- for free ?

If it is true, as you say, that the piston metal was unusually hard, then that's your answer.

Other than the piston alloy theory, there's no smoking gun. Yes, it was an aggressive port job, maybe a little too aggressive for my taste, but nevertheless, racers run aggressive port jobs and get them to last at least a few minutes.

 

[parrisw]

asbl

fjoeilsdfghde

 

[cat-face timber]

sometimes thing go wrong but you will never learn anything unless you have a go , thanks for the post brad , was just thinking about a big bore for one of my 460's but might wait a while . do enjoy all the modifications you do , keep it up .

:agree2:

 

[blsnelling]

I've always been one to share the good, the bad, and now...the ugly. I figure we can all learn something from it.

 

[Tzed250]

I couldn't agree more!!! I made the same comment to my wife, and earlier in the thread.


I really don't know. But I now do not believe the clip failed though. Something else instigated this.


Not even close. I hadn't even tried to tune the H at all. This was the first of a couple heat cycles I was going to put it through first.


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.


There's no question that this piston was extremelty hard, much harder than normal.

How many catastrophic failures have you diagnosed Brad?

I promise you hung a ring. I have seen plenty of skirt failures and they don't turn out like that. The pin boss broke out from the bottom because the piston was stopped on the downstroke.

If you are going to claim a problem with the metal then please start a new thread about how the quality of the Chi-com big bore kits is going downhill.




.

 

[blsnelling]

How many catastrophic failures have you diagnosed Brad?

I promise you hung a ring. I have seen plenty of skirt failures and they don't turn out like that. The pin boss broke out from the bottom because the piston was stopped on the downstroke.

If you are going to claim a problem with the metal then please start a new thread about how the quality of the Chi-com big bore kits is going downhill.




.

TZed, you don't always have to go on the offensive like that. Fortunately, this is the first catastrophic failure I have seen. Your opinion is only one of many. I'm not saying yours is wrong. But your implying that I should buy what your saying over everyone else. You might also do good to remember that a poorly cast piston was not my idea. Many others keep mentioning it, so I'm not throwing that out. There is evidence that the piston is far harder than a typical piston. Try to keep this a discussion, rather than a fight, if you can.

 

[mtngun]

I promise you hung a ring. I have seen plenty of skirt failures and they don't turn out like that. The pin boss broke out from the bottom because the piston was stopped on the downstroke.

Tzed, let's say your theory is right, what exactly was done wrong that caused the ring to hang in the transfer port ? What should have been done different ? How are Brad's port mods more radical than what is routinely done on race saws ?

I'm just trying to learn.........

 

[Dan_IN_MN]

I went back and looked at the pics again, and still don't see a smoking gun.

It's probably not going to happen, since the government is not funding this project, but I'd love to see the piston remains checked out by a metallurgical lab.

Any major universities in your area, that would have an engineering lab, to test hardness, and ideally run a SEM on the piston, and compare the results to an OEM piston -- for free ?

If it is true, as you say, that the piston metal was unusually hard, then that's your answer.

Other than the piston alloy theory, there's no smoking gun. Yes, it was an aggressive port job, maybe a little too aggressive for my taste, but nevertheless, racers run aggressive port jobs and get them to last at least a few minutes.

:agree2:

Here's a site on metal hardness FWIW: Metal hardness

As always, Brad posted his pics to his photo album. Here's a link to more/larger pics: Brad's pics