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

[blsnelling]

.


Another thing to think about for those wondering about all the crumbled pieces.

Brad stated the the saw was coming back to idle or was at idle when the failure occurred. With a normal saw idle of ~2500RPM if the saw only continued to rotate for another 1/4 of a second that is an additional 10 revolutions. Plenty of time to make crumbles.


.

The saw was idling, probably 2800 RPM, I blipped the throttle, so maybe 3500-4500 RPMs? I guess a few RPMs do happen in a hurry don't they.

 

[Tzed250]

TZed, after reading again, I think we're agreeing, just saying it differently. No? You believe the ring caught as the piston moved up, stripping the skirt off the piston?

The main force was applied when the ring caught in the transfer on the way to BDC. This popped the section off of the crown, and fractured the pin bores. Once the pin bores were cracked the rear section of the piston was shoved into the intake. On the upstroke the rear section of the piston was left behind, then turned into bits on the next revolution.


.

 

[wigglesworth]

I greatly appreciate yours, and everyone's, input.

In the picture below are the 046BB on the left, Wiseco 440 in the middle, and white box aftermarket 460 on the right. The measure left to right respectively, 1.440", 1.555", 1.556".

Why is there such a big difference in the piston height's? Did it free port at TDC? Looks almost like the wrong piston or something???

 

[Tzed250]

The saw was idling, probably 2800 RPM, I blipped the throttle, so maybe 3500-4500 RPMs? I guess a few RPMs do happen in a hurry don't they.

Imagine an 18,000rpm F1 engine...


.

 

[blsnelling]

The main force was applied when the ring caught in the transfer on the way to BDC. This popped the section off of the crown, and fractured the pin bores. Once the pin bores were cracked the rear section of the piston was shoved into the intake. On the upstroke the rear section of the piston was left behind, then turned into bits on the next revolution.


.

I'll entirely buy that. But it still blows my mind that I could have caught a ring in the transfer! Anything's possible though in the world of mods.

 

[blsnelling]

Imagine an 18,000rpm F1 engine...


.

Can you say, "complete disintigration"!!!

 

[blsnelling]

Why is there such a big difference in the piston height's? Did it free port at TDC? Looks almost like the wrong piston or something???

That's typical for the BB kits. They do this for case clearance. It did not freeport at TDC, although it was very close. This was a problem with ealier 066BB kits, but that has been rectified as well.

 

[Andyshine77]

That's where the entire skirt was ripped off as the piston went up, and left the skirt behind.

Correct. Isn't that a bit abnormal? I agree the ring did catch, but what happened first? I'm starting to think there was a hairline fracture that was opening up more and more as the piston was going up and down, this could allow the ring to possibly spin around the pin momentarily. It's just a thought.

 

[Tzed250]

I'll entirely buy that. But it still blows my mind that I could have caught a ring in the transfer! Anything's possible though in the world of mods.

It does not take much Brad. You know how much force it takes to put bearings in a case half. That is a .001 or .0015 interference fit. Now imagine the ring in one of the ports .001 too far.


.

 

[Tzed250]

Correct. Isn't that a bit abnormal? I agree the ring did catch, but what happened first? I'm starting to think there was a hairline fracture that was opening up more and more as the piston was going up and down, this could allow the ring to possibly spin around the pin momentarily. It's just a thought.

Yes, something abnormal happened, as the saw started and ran. It just fell off of the wrong side of the razor.


.

 

[Andyshine77]

Yes, something abnormal happened, as the saw started and ran. It just fell off of the wrong side of the razor.


.

 

[edisto]

I'll entirely buy that. But it still blows my mind that I could have caught a ring in the transfer! Anything's possible though in the world of mods.

You just have to increase the radius of the corners more when you increase the width.

 

[Mastermind]

I've said since post #26 that I believe the lower ring dropped into the intake port. It then caught the top of the port as the piston moved up. There's nothing for the ring to catch on on the way down on the intake port. Also, that would be the opposite force requred to strip the skirt off the piston. The wrist pin was pushing up, the ring stopped at the top of the intake port, and the skirt popped right off, taking the pin bosses with it.

If this were the only damage, that would be the end of the story, IMHO. But there's that big chunk that was broken off the top of the piston. It broke off as the piston was moving down. After carefully lining up the piston in the bore, I believe this happened first, and then allowed the ring to drop into the port.

:agree2:

 

[blsnelling]

I think we may have the smoking gun here. You can't hardly see this stuff by must looking at it normally. It takes a very bright light, and the magnification of a picture to bring it into view. This is a shot I've been wanting to get, and I think it may prove some theories.

 

[Tzed250]

I think we may have the smoking gun here. You can't hardly see this stuff by must looking at it normally. It takes a very bright light, and the magnification of a picture to bring it into view. This is a shot I've been wanting to get, and I think it may prove some theories.

]

That is where it all started. Finding why it started there will show the root cuase of the problem. Once the root cuase is determined then a countermeasure is put into place.

A Failure Mode and Effect Analysis (FMEA) is designed to prevent these things from happening in the first place.

Dealing with the QA section of Toyota Industrial Equipment Manufacturing for quite a while will set you on a path of righteousness...


.

 

[Andyshine77]

Looks like it was scuffing a bit before it finely caught.

 

[blsnelling]

I thought that real bright edge was a ring snag. Upon closer inspection, the other side looks the same way. That's actually the factory bevel that was polished with 600 grit paper. I still believe it started here though. I give up trying to figure this out, lol. No, that wouldn't be any fun. This has been a blast trying to figure this out

 

[Mike PA]

I should have posted this yesterday and after seeing the vid, it really looks like the chunk from the top of the piston happened first (see the compression lines? These happened as the top failed, not after), most likely as a result of the ring catching. So, the piston was on the down stroke when the failure started, popped the chunk off the top and broke the skirt, then the lower ring caught on the way up and broke that portion of the piston. I think you can see where one break is truncated by the other in the earlier pics, which indicates which happened first.

I think in the set of pics, that the ring snag is evident, as there is a v-shaped crevice that formed from a force in the direction of the "v", or on the downstroke. That should be where the ring caught the hardest and had the most force. This occurred on the downstroke, breaking the pin bosses. What I am not sure of with this is the displacement of the metal, as the side away from the "crevice" is lower, which suggested that the failure started on that side. However, the cracks that formed from the original impact may have allowed a lesser force to cause more displacement on the other side on a later stroke.

I think this is the same as what Tzed is saying, I just wish I had said it yesterday when I looked at this, but I wasn't confident enough to say it. I hadn't noticed the compression lines on the top of the piston before the vid, which was a very good quality.

 

[andrethegiant70]

That's one seriously amazing failure. It's really a tribute to the integrity of the saw that it's up and running again. Sounds like you got some knowledge out of it. Great pictures!

 

[Tzed250]

I should have posted this yesterday and after seeing the vid, it really looks like the chunk from the top of the piston happened first (see the compression lines? These happened as the top failed, not after), most likely as a result of the ring catching. So, the piston was on the down stroke when the failure started, popped the chunk off the top and broke the skirt, then the lower ring caught on the way up and broke that portion of the piston. I think you can see where one break is truncated by the other in the earlier pics, which indicates which happened first.

I think in the set of pics, that the ring snag is evident, as there is a v-shaped crevice that formed from a force in the direction of the "v", or on the downstroke. That should be where the ring caught the hardest and had the most force. This occurred on the downstroke, breaking the pin bosses. What I am not sure of with this is the displacement of the metal, as the side away from the "crevice" is lower, which suggested that the failure started on that side. However, the cracks that formed from the original impact may have allowed a lesser force to cause more displacement on the other side on a later stroke.

I think this is the same as what Tzed is saying, I just wish I had said it yesterday when I looked at this, but I wasn't confident enough to say it. I hadn't noticed the compression lines on the top of the piston before the vid, which was a very good quality.

.


Looks to me like it hung a ring on the way down. No matter what that happened, the evidence is the top land blown off. Circlips usually don't cause that much damage.#


.

You might notice I was saying it three days ago...




.