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isedawishy
GTPPTT6REIGHTY
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It's pretty likely you'll need a longblock :(
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Crankshaft snout snapped
- Thread starter isedawishy
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olaosunt
Well-Known Member
Lol
WIll at RPG tuning is almost done with the replacement 5.2 short block .
Gen 2 5.2 block with Manley H tuff rods / 11 :1 pistons .
I had another set of GT 350 heads I thought I could save but cams are scored beyond repair .
So will be assembling long block with new GT heads / stock cams and PAC springs .
Hopeful the longer 12 mm head studs will help with lifting and springs should take care of float .
Going it be using the the GT 350 spec phasers / Boss tensioners and new chains .
WIll at RPG tuning is almost done with the replacement 5.2 short block .
Gen 2 5.2 block with Manley H tuff rods / 11 :1 pistons .
I had another set of GT 350 heads I thought I could save but cams are scored beyond repair .
So will be assembling long block with new GT heads / stock cams and PAC springs .
Hopeful the longer 12 mm head studs will help with lifting and springs should take care of float .
Going it be using the the GT 350 spec phasers / Boss tensioners and new chains .
DAVECS1
Well-Known Member
Here is to knocking on wood. I made a tool to out my balancer on. I wanted to use a conventional installation tool but did not have anything long enough. I used a small brake hone on my balancer. Also installed it and removed it with once, with some putty on the backside to make sure I was seating against the timing gear. To boot I have the balancer everyone is scared of. I have had several track days with the blower installed and an off track excursion. So far fingers crossed. I am in the process right now of adding a new oil pan and windage tray to keep the oil in check better at the track.
Oscifer
Member
Plan on a long block or a lot of head machining. The valves will most likely still be intact but in my case none of them would seal properly. The majority of the rockers broke and the one hero rocker that held out resulted in a broken cam cap. Also, all that debris in the heads left scoring and gouges inside the heads and on some of the cam lobes.
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Jay-rod427
Well-Known Member
N/A, turbo, pd, centri. All have had this problem on rare instances.
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No reason to waste the money on shipping. That crack leading from the keyway is all that pretty much needs to be said.
Twisting one off is one thing, cracking it in half is a totally different issue. The key/keyway was obviously upset about something.
Either to tight, or two loose, or something.
dguzzi
Well-Known Member
"OR something" And guessing is what I'm getting at. A lot mentioning the possibility of hardening issues. That nose piece is no big deal to send, after all the money spent getting the HP, why not spend a hundred or so to really know what happened?
sigintel
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Dunno...
Cracked keyway might just mean very heavy parts with significant inertia on opposite sides of the keyway wanted to be turning at different rates and the torque attempted to be transferred across the keyway grossly exceeded the designed capability.
Would like to see some well focused end on pics of both sides of the broken surfaces. Had a broken crank myself and asked a metallurgist in the family. Sucked cause he thought it was funny and then laughed harder when I told him I didnt appreciate it cause it was my motor. Its fantastic but can still suck to have a world class engineer as a father. He usually doesn't work on piddly things below 100MW (~130,000 hp). He did not do a professional technical analysis or suggest I send it off for the simple reason that if you lose timing on these engines, the chances of breaking the crank are very high and it is very difficult to know which happens first especially at high RPM.
If you do want detailed analysis: Structural Integrity Associates and M&M both have offices here in Austin and I have a beer drinkn buddy that runs SEM. Just send the small end if you want (or cut last 1" off crank from the break).
I 100% broke my crank from slipping timing at 8400rpm. Motor had been beat to shit on road courses with a Whipple and was losing 7&8 rings (<160psi) so I was being rather abusive thinkn I was going to swap a short block anyway. ECU rev limiter was off. Rev limiter was purely accomplished by the shift points on the 6R80. I purposely did not lift as much as I should have trying to maximize on throttle time during a 2/3 shift on the street (hmmmm.. wonder why... lol) and trans not only slipped on attempting 2/3 but tripped fault and depressurized 3rd pack (basically going to neutral at 7900RPM while throttle was pegged WOT). I lifted instantly on the missed shift but the RPMs were already passing 8300 and I already tapped upshift to try and get one (mistake). Trans did shift at 8400 w lift throttle and pulled in 3rd gear and I lost timing with the rapid crank/valve train decel and blower and valve train trying to stay at 8400 with crank trying for ~5600. Stock chain guides with the FRPP upgraded tensioners on 2nd set of main OEM stock chains and 1st set of secondaries (yes Im lazy not changing both).
Comments I got on my crank:
Multiple scallops appear from cracks propagated from valve impacts binding the valve train. Each "self clearancing" event imparts force above the yield strength of the case hardened surface at the snout trying to turn the bound valve train. If you have multiple concentric rings in each scallop then you had multiple impact events at each angle. You can measure the angle of the scallops and work backward to see the same angle/timing on the cams. I had massive chain stretch/lash in the timing chain and evidence the chain was overloaded. Expect chips from the teeth of the timing gear. These are not clearance engines so if the timing chain rides up the timing gear teeth and then slips timing, you will bind the valve train and break the crank snout.
Now, I did get some advice about the wear patterns on the crank, timing gear, and damper: there was some localized strain hardening and compression damage on the case hardened surface of my crank snout. Evidently, the forged timing gear I was using is perfectly straight center bore with very sharp chamfer internal edges. As the crank had been flexing over time, these edges dug into and left long term surface compression strain hardening marks. The cracks look like they go from that surface damage immediately inboard thru the case hardening to the step in the crank diameter (stress riser).
I was advised it would be wise to substantially round the inside edges of the timing gear to increase the compression edge interface during overload to 10x as much area if possible. That would be a couple mm softer radius instead of a hard sharp chamfer inside edge.
Also, my damper was bottomed on the timing gear. ie the timing gear was sandwiched firmly between the crank shoulder and the inboard face of the ATI damper. This is very important. It means that IF the crank tries to flex to absorb shock, the TG/damper have a substantial longitudinal bending moment advantage - meaning all bending in such a stack up can only occur by lengthening the crank (guess how?) at the far side enough to allow the interface of the shoulder/TG and TG/damper to open. Basically, the sandwich makes for a freakn stiff ass crank snout that might be stiffer than even stock.
In the future, I would definitely make sure my TG longitudinal compression is exactly same as stock and that the TG can 'float' some on the crank (on the keyway) and that the snout can bend slightly without the TG/damper stackup binding. I will also ONLY use the FRPP forged TG going forward.
Did Vanilla break the crank at high rpm? on a shift?
Are there circumferential compression marks on the snout near the inboard shoulder?
Any evidence any valve train damage / interference/ binding?
Any marks indicating damper was compressed hard against or bottomed on the TG?
Cracked keyway might just mean very heavy parts with significant inertia on opposite sides of the keyway wanted to be turning at different rates and the torque attempted to be transferred across the keyway grossly exceeded the designed capability.
Would like to see some well focused end on pics of both sides of the broken surfaces. Had a broken crank myself and asked a metallurgist in the family. Sucked cause he thought it was funny and then laughed harder when I told him I didnt appreciate it cause it was my motor. Its fantastic but can still suck to have a world class engineer as a father. He usually doesn't work on piddly things below 100MW (~130,000 hp). He did not do a professional technical analysis or suggest I send it off for the simple reason that if you lose timing on these engines, the chances of breaking the crank are very high and it is very difficult to know which happens first especially at high RPM.
If you do want detailed analysis: Structural Integrity Associates and M&M both have offices here in Austin and I have a beer drinkn buddy that runs SEM. Just send the small end if you want (or cut last 1" off crank from the break).
I 100% broke my crank from slipping timing at 8400rpm. Motor had been beat to shit on road courses with a Whipple and was losing 7&8 rings (<160psi) so I was being rather abusive thinkn I was going to swap a short block anyway. ECU rev limiter was off. Rev limiter was purely accomplished by the shift points on the 6R80. I purposely did not lift as much as I should have trying to maximize on throttle time during a 2/3 shift on the street (hmmmm.. wonder why... lol) and trans not only slipped on attempting 2/3 but tripped fault and depressurized 3rd pack (basically going to neutral at 7900RPM while throttle was pegged WOT). I lifted instantly on the missed shift but the RPMs were already passing 8300 and I already tapped upshift to try and get one (mistake). Trans did shift at 8400 w lift throttle and pulled in 3rd gear and I lost timing with the rapid crank/valve train decel and blower and valve train trying to stay at 8400 with crank trying for ~5600. Stock chain guides with the FRPP upgraded tensioners on 2nd set of main OEM stock chains and 1st set of secondaries (yes Im lazy not changing both).
Comments I got on my crank:
Multiple scallops appear from cracks propagated from valve impacts binding the valve train. Each "self clearancing" event imparts force above the yield strength of the case hardened surface at the snout trying to turn the bound valve train. If you have multiple concentric rings in each scallop then you had multiple impact events at each angle. You can measure the angle of the scallops and work backward to see the same angle/timing on the cams. I had massive chain stretch/lash in the timing chain and evidence the chain was overloaded. Expect chips from the teeth of the timing gear. These are not clearance engines so if the timing chain rides up the timing gear teeth and then slips timing, you will bind the valve train and break the crank snout.
Now, I did get some advice about the wear patterns on the crank, timing gear, and damper: there was some localized strain hardening and compression damage on the case hardened surface of my crank snout. Evidently, the forged timing gear I was using is perfectly straight center bore with very sharp chamfer internal edges. As the crank had been flexing over time, these edges dug into and left long term surface compression strain hardening marks. The cracks look like they go from that surface damage immediately inboard thru the case hardening to the step in the crank diameter (stress riser).
I was advised it would be wise to substantially round the inside edges of the timing gear to increase the compression edge interface during overload to 10x as much area if possible. That would be a couple mm softer radius instead of a hard sharp chamfer inside edge.
Also, my damper was bottomed on the timing gear. ie the timing gear was sandwiched firmly between the crank shoulder and the inboard face of the ATI damper. This is very important. It means that IF the crank tries to flex to absorb shock, the TG/damper have a substantial longitudinal bending moment advantage - meaning all bending in such a stack up can only occur by lengthening the crank (guess how?) at the far side enough to allow the interface of the shoulder/TG and TG/damper to open. Basically, the sandwich makes for a freakn stiff ass crank snout that might be stiffer than even stock.
In the future, I would definitely make sure my TG longitudinal compression is exactly same as stock and that the TG can 'float' some on the crank (on the keyway) and that the snout can bend slightly without the TG/damper stackup binding. I will also ONLY use the FRPP forged TG going forward.
Did Vanilla break the crank at high rpm? on a shift?
Are there circumferential compression marks on the snout near the inboard shoulder?
Any evidence any valve train damage / interference/ binding?
Any marks indicating damper was compressed hard against or bottomed on the TG?
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dguzzi
Well-Known Member
See, you can read that like a rap tune....very nice!!
(just kidding) Its like sending failed ball bearings in...yes they failed for a reason...yes there was damage after they failed...but analysis can read through that. I was amazed at what we were told about bearings from centrifuges which run a long time after a failure, turning the balls and races into shrapnel.
(just kidding) Its like sending failed ball bearings in...yes they failed for a reason...yes there was damage after they failed...but analysis can read through that. I was amazed at what we were told about bearings from centrifuges which run a long time after a failure, turning the balls and races into shrapnel.
grabber_17
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Has anyone actually confirmed bottoming the install bolt caused their failure? I actually made this mistake and pushed over the first couple threads on the install bolt. I was able to chase the threads and start over and install the balancer. I was super worried about it and called MMR and they said I just ran it in to far and would be fine that they have never seen that cause a crank failure. Not much I could do now but I am just curious. I did it with a socket wrench not an impact I hope that is my saving grace.
Jay-rod427
Well-Known Member
Without hammering it with an impact or large breaker bar trying to force it on you should be just fine.
Jay-rod427
Well-Known Member
I'd have to disagree. The bottom of the bolt hole, and the end of the bolt are basically wedges. Forcing the bolt into the bottom will stress the crank trying to wedge it open from the inside out. But also like you said stressing the threads tensile pull, and thread galling. Bolt loosens and balancer loosens losing it's absorption purpose. 99.9% of people will never know. Just assumptions. Most I've seen had an obvious crack develop. Longitudinal crack doesn't come from belt tension or load or anything like that.
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