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s40 major failure, balancer hitting case, cause? (Read 653 times)
BlakeEM
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Re: s40 major failure, balancer hitting case, caus
Reply #75 - 07/02/20 at 08:02:33
 
Torque on that nut puts zero pressure on the crankshaft so it's physically impossible for that to be the case.

Again, the clamping force is between the end of the crank and the nut so no amount of torque could have caused this. Even if it was 500 ft-lbs the crankshaft would have the same amount of free play regardless. It's more likely that's caused by the excessive side to side free play in the crankshaft that exists from the factory. He said they old R1s had similar issues when they had too much side to side free play. This was the only time he ever seen marks like that. I trust the guy, he made me feel like an idiot talking to him. He builds race engines daily.
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Re: s40 major failure, balancer hitting case, caus
Reply #76 - 07/02/20 at 08:05:20
 
That nut was still tight when I removed it, I had to use an impact to get it off. If it "lost clamping force" it would have been loose. The flange damage was from the crankshaft banging side to side most likely. This can explain the damage to the case as well.
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Re: s40 major failure, balancer hitting case, caus
Reply #77 - 07/02/20 at 08:14:58
 
The fact that the bearing was out of it's seat makes sense based on what he said and this is what caused the scapes under the main drive gear/case and the broken flange. As the crank went to the side it hammered the bearings moving them out of the seat and hitting the case on both sides.
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justin_o_guy2
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Re: s40 major failure, balancer hitting case, caus
Reply #78 - 07/02/20 at 08:28:52
 
Then do you want to start selling parts?

Because Im gonna have the money in a week,,

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Re: s40 major failure, balancer hitting case, caus
Reply #79 - 07/02/20 at 08:33:59
 
@justin_o_guy2 post everything you want here. No one has claimed the forks yet. I should be able to start disassembling it today and I'll post pictures of individual parts. http://suzukisavage.com/cgi-bin/YaBB.pl?num=1593479677

I want to keep this thread specific to discussion about the engine failure.
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Re: s40 major failure, balancer hitting case, caus
Reply #80 - 07/02/20 at 08:40:23
 
This photo shows the flange was completely broken off:

https://imgur.com/SXPtibU

The diameter of the low point in the cam drive sprocket is 1.105"  (The caliper shows 1.120 as it moved when I set it down to photo).


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camsprocket.jpg

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Re: s40 major failure, balancer hitting case, caus
Reply #81 - 07/02/20 at 08:41:23
 
The diameter of the crankshaft where the right ball bearing slides over is 1.378":
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crank.jpg

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Re: s40 major failure, balancer hitting case, caus
Reply #82 - 07/02/20 at 08:42:48
 
The result is that the crankshaft is more than 1/4" larger than the low point in the cam sprocket:

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Re: s40 major failure, balancer hitting case, caus
Reply #83 - 07/02/20 at 08:47:34
 
So when the "Tech" broke the flange off the sprocket.....the remaining inner portion of the cam sprocket was able to move inward and it tightened up against the crank (rather than the flange tightening up against the inner bearing race) - the flange that is supposed to clamp on the bearing was cracked or broken and was no longer able to push against the inner bearing race.

With the flange being broken off and no longer pushing on the inner bearing race - the clamping force was not being transferred through the bearing race and holding tightly onto the counterbalancer drive gear.



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Re: s40 major failure, balancer hitting case, caus
Reply #84 - 07/02/20 at 09:05:07
 
That flange wasn't broken off, it was perfectly in place when I removed it, I just didn't get a picture. It was likely damaged from the side to side motion that pushed the bearing out of the seat.
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Re: s40 major failure, balancer hitting case, caus
Reply #85 - 07/02/20 at 09:09:48
 
Okey-Dokey

Hope you have better luck with your next bike.......and mechanic.
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Re: s40 major failure, balancer hitting case, caus
Reply #86 - 07/03/20 at 01:42:24
 
"That flange wasn't broken off, it was perfectly in place when I removed it"

I hate to tell ya this Blake, but that flange was broken off (like completely broken off).  Just because the remnants were captured in the fracture doesn't change the fact that it was broken.

I am a bit surprised that centrifugal force didn't throw the chunks out of there, but if you assess the entire design you can see why.  There's a bellville washer in between the nut and primary drive sprocket.  That concave washer continues to apply force even if the sprocket migrates to the left.  That force from the washer kept the chunks of sprocket flange clamped between the nut/washer and the end of the crank.  Unfortunately, there was no longer any force being applied to the bearing inner race, or the balancer drive gear.

Dave's evaluation makes perfect sense, and the photos he provided give almost a perfect visual description of the problem.

This design is a land mine.  Yes, it is probably a very rare failure, but it has the potential to kill someone.  As I see it, there are a number of design problems, and when the planets are in alignment they can all come together to be disastrous.  

First, the nut is LH thread.  Yes, it has to be LH thread but the designer should be taking into consideration that more than likely someone will screw up and try to turn it the wrong way.  That almost always occurs on disassembly and the offending mechanic more than likely will really reef on that bad-boy trying to get the thing loose.  Then there's the potential for rattle-wrench application.  Ruttly has been harping about this sprocket for a long time.  We should all pay attention.   Thanks Ruttly, you definitely have my attention now.  I think cracking that sprocket set the groundwork for your BIG failure.  Whoever designed this should be thinking about maintenance too.  If you must use a LH nut, design the system so the internal threads on the cheap nut will fail before more important stuff (like the sprocket), or make the more important stuff more robust so they can handle the over-torque.  

Second, the flange on the sprocket is thin.  You can see that the designer did a good job on the filet on the flange (it's generous), but the flange bears on the bearing inner race at a point that looks to be beyond, or right at the edge of, the fillet.  Now when you tighten the nut it causes the sprocket flange to bear hard on the inner race at a point beyond the edge of the filet.  It applies a bending moment on the flange and a BIG stress concentration right at the edge of the fillet.  I guess that's fine as long as you don't overtighten the nut.  

Third, the designer is relying solely on friction between the balancer drive gear, the bearing inner race, and the crankshaft.  I know there is a drive pin, but the pin is not an interference fit.  It has a little clearance so that you can assemble and disassemble the gear from the crank.  I guess that's fine as long as the nut doesn't come loose.   But guess what, stuff comes loose sometimes.  Ya gotta be thinkin bout that stuff.

Fourth, the drive pin (the round one) is not captured.  That hole in the crank should be stepped so that in the event that the drive pin starts to creep it can't come all the way out and let all hell break loose.  Your pin clearly came out, and that was the nail in the coffin.

All of that mumbo-jumbo about the crank moving right and left and bustin up the sprocket.  Malarkey.

I previously said we shouldn't be so quick to judge the mechanic.  Now that all the other bits of info are on display (I'm lovin the pics, thanks again), I don't know who's more at fault, the person who designed it, or the person who worked on it last.   Undecided

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Re: s40 major failure, balancer hitting case, caus
Reply #87 - 07/03/20 at 12:46:49
 
Add a post it note to that page in your manual
Reverse/left hand threads,use no impact here,tighten & torque by hand

I hate making the same mistake , again !
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