Crank snapped at pulley

[MalcolmV8]

This, plus how tight was the belt? A lot of guys like to run belts tight enough to put the tensioner against the stop. Not a good thing IMO. I did that with my first centri set up. Then I saw what it did to the front main bearing and never did it again.

That's one of the reasons I like the Thump tensioner. It has no stop so if you need a tighter belt for slip it still has room to flex. If you pop the hood and watch the belt and tensioner as you aggressively nail the gas its amazing how much the tensioner flexes and the belt moves. I can't imagine that been jammed up against the stop with no where to go.

 

[SVTBrandon95]

Picture update


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[SVTBrandon95]

 

[SVTBrandon95]

This, plus how tight was the belt? A lot of guys like to run belts tight enough to put the tensioner against the stop. Not a good thing IMO. I did that with my first centri set up. Then I saw what it did to the front main bearing and never did it again.

I'm not sure how tight the belt was & Idk what kind of tensioner

 

[Black Gold 380R]

In your initial posted photos you could see the stock idler pulley's, so I'm guessing if the pulleys are stock so are the tensioners.

 

[01yellercobra]

That's one of the reasons I like the Thump tensioner. It has no stop so if you need a tighter belt for slip it still has room to flex. If you pop the hood and watch the belt and tensioner as you aggressively nail the gas its amazing how much the tensioner flexes and the belt moves. I can't imagine that been jammed up against the stop with no where to go.

Same here. That's also why I like running the bigger pullies for more belt wrap. I had a 12% overdrive crank pulley with a 3.4" blower pulley on my last set up. With the Thump tensioner I had no belt slip and I was able to put the tensioner about the middle of it's travel.

I will say that until the caged 4lb lower was offered I was going to stick with the stock lower set up.

 

[c6zhombre]

Ive never had any issue with the stock tensioner and 2.6 upper 22psi. I do have the metco tensioner brace plate. Stock caged lower. Everything still performs great after many years now. The tensioner stop is dead center on the grid....but obviously not seen where it goes under boost. Whipple sliding adjustable pulley as the snug idler under the blower pulley.

http://metcomotorsports.com/proddetail.asp?prod=MTP0001

 

[hotford]

anything is bound to break at some point....I have all three of mine with metco lower crank pulley set up with no issue to date(knock on wood)...
sucks that it happen to ya....not a cheap fix either.

 

[ctgreddy]

Can someone school me on what a "caged lower" is...? My 04 drivetrain is stock. I am more familiar with modded GT500's and I haven't heard any discussions about caging a lower pulley there.

the caged lower basically braces the front of the crank/blower drive to the block to take some stress off the crank. The reason you dont see any issues on gt500's is ford moved the blower drive to the inside drive. So the stress isn't nearly as far out. The crank may also have been designed better with a blower drive in mind, but I'm not positive on that.

Distance off the crank isn't always what kills things if the crank is designed good. zl1's come to mind, not sure if you've seen those but their blower drive is further off the crank snout than our engines with zero bracing.

 

[Goose17]

the caged lower basically braces the front of the crank/blower drive to the block to take some stress off the crank. The reason you dont see any issues on gt500's is ford moved the blower drive to the inside drive. So the stress isn't nearly as far out. The crank may also have been designed better with a blower drive in mind, but I'm not positive on that.

Distance off the crank isn't always what kills things if the crank is designed good. zl1's come to mind, not sure if you've seen those but their blower drive is further off the crank snout than our engines with zero bracing.

Thanks for the explanation. That clears it up. I didn't notice the Terminator's supercharger was spun from the outside pulley on the lower. I've had my GT500 apart and even installed a Thump. It all seems pretty stout on the Shelby.

 

[2k2leenin]

Attached is a good upgrade/ mod during repair:
https://www.svtperformance.com/forums/threads/crank-stud-mod-and-stock-lower-pulley-cage.1001076/

 

[modFTW]

the reason this happened is using the 4lB lower. It puts a tremendous amount of perpendicular stress/load on the crank snout. Yes I know there are tons of set-ups exactly like this but you just had the bad luck. By using a larger (in diameter) lower pulley your basically multiplying the force being placed on the snout by using a longer lever (more radius). Giving more leverage. It is more common on bigger blowers because of the rotating inertia of the big heavy rotors have no way of loosing the kinetic energy it has created from high RPM's and then all of a sudden being shut down like at the top of a 4th gear pull. All the energy that is created from the rotors inertia is instantly transferred through the belt to the crank pulley.

 

[MalcolmV8]

It is more common on bigger blowers because of the rotating inertia of the big heavy rotors have no way of loosing the kinetic energy it has created from high RPM's and then all of a sudden being shut down like at the top of a 4th gear pull. All the energy that is created from the rotors inertia is instantly transferred through the belt to the crank pulley.

Be nice if someone made a one way sprocket for the blower pulley so a sudden shutdown of RPMs let the blower free spin and slow down on its own without been yanked down by the crank.

My 911's alternator pulley is that way. So when you rip through the gears at WOT as you shift and the RPMs dip for the next gear the alternator just free spins on the sprocket till the RPMs catch back up or the alternator slows down enough to be spun again. Less stress on everything.

 

[P49Y-CY]

Be nice if someone made a one way sprocket for the blower pulley so a sudden shutdown of RPMs let the blower free spin and slow down on its own without been yanked down by the crank.

My 911's alternator pulley is that way. So when you rip through the gears at WOT as you shift and the RPMs dip for the next gear the alternator just free spins on the sprocket till the RPMs catch back up or the alternator slows down enough to be spun again. Less stress on everything.

i'm pretty sure that's what the chrysler hellcat's have. when they came out i think i read that their blower has some kind of one-way clutch that allows it to disengage exactly like how you describe.

 

[toomanytoys]

It's amazing how this happens. I've had a vortech s trim on my 88LX since 1996. The first 7 years on the stock crank and the last 13 on the nodular iron crank in my stroker. That belt is a helluva lot tighter than the one in my cobra and no problems. Strange how op's crank looks like it snapped off clean. Flaw in the casting?

 

[408Stang]

When you rebuild you should drill the crank snout all the way back to the #1 bearing. Use a 4.75" to 5.25" long 9/16" diameter, ARP stud (length depends on damper), the ARP 1/4" thick damper washer, and the corresponding ARP nut. Torque to 150 to 180 Ft. Lbs. Now all the load is transferred to the significantly more meaty # 1 main bearing area.

The stock bolt is only about 2.5" long, 1/2 the diameter, and just isn't up to the task.

Also if you have the woodruff style key you should have the keyway cut all the way from front to back of the snout and use a 3/16" square tool steel key (tool steel key way stock is cheap and easy to find) ... Not to mention an ATI Superdamper should be used when you rebuild. It's worth the extra cost for the peace of mind and performance.

Mile High Crankshaft in Denver, CO (888 S. Lipan St.) can do the mods above for about $150.

I'll see if I can find the thread that discusses this (with pictures and diagrams) and post the link.



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[408Stang]

Here's the visual comparison of the ARP stud mod, versus the ARP bolt, versus the stock crank bolt.

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[408Stang]

For some reason I can't post the link to the thread(s) . It's over on the Modular Fords Forums. There's a few threads about it, one of them is under "Aluminator Gibtec Build" thread. Ed Schaider and JRGoffin can answer any questions you may have about this.

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[408Stang]

Keyway and stud mod:

Close up:

Finished install:

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[408Stang]

Here's the part numbers for the stud and nut as well as the source for the key stock:

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