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99 Crank Pulley Bolts - shearing

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#1
RazerX

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I thought there was a thread on this but the search revealed nothing.

 

3 of the 4 bolts sheared off my crank pulley on the last weekend.  

 

This happened previously two years ago,that time i didn't catch it before the pulley flew off in the engine bay.  To fix it two years ago, i got a new button on the end of the crank, and put in 4 new OEM bolts torqued to specification.  (I actually bought a 1/4" drive torque wrench for this exact job)  I have the reinforcement ring between the bolt heads and the pulley.  Everything "looks" fine.  I am using a Mazdaspeed timing disk.

 

Yes, I can replace these bolts every season, but why is this happening?  Anyone else having this issue?  

 

 


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#2
Steve Scheifler

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Do you use locktite? If not, perhaps they are backing out a bit then getting beat on by a slightly loose pulley before snapping.
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#3
MPR22

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OEM bolts seem to fail in the 99s, they stretch and loose clamp power.   Put grade 10.9 bolts in, think they are a hex head.  Engine builders please correct me if i am wrong about the hex head. 


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#4
Mark

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We fought this issue for a while. Ultimately we cured the issue by using M8 hardware (approved in GCR) but that was not the cause although it did stop the motor from throwing the pulley. The fix didn't stop it from killing oil pumps and main bearings though. Ultimately we found that the crank snout was bent. Point is - there is a reason that the pulley keeps getting thrown off. Best to find it if you can. Also - Make sure that the bolts you are using to fasten the pulley are the correct length and are not too long. As Michael just pointed out - 10.9 bolts only.

 

Mark


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#5
BNaumann

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It was recommended to me to upgrade to M8, but I use M6 ARP bolts torqued to ARP spec with blue loctite for crank and waterpump pulleys and have had no issues for a year with stock timing wheel and 3 weekends with Mazdaspeed timing wheel.  Davew sells the right bolts in the right quantities.



#6
FTodaro

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I will throw my useless opinion in here, I think the fact that we are opening the holes on the timing plate may be a factor that we are in there changing things. I think the Locktite, and up graded bolts with higher Tq is a common fix.


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#7
BNaumann

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I will throw my useless opinion in here, I think the fact that we are opening the holes on the timing plate may be a factor that we are in there changing things. I think the Locktite, and up graded bolts with higher Tq is a common fix.


From an engineering standpoint the elongated holes should not have an effect. It's all about maintaining clamp load. The shape or coating thickness of the optional part may have an effect, or overstretching the stock bolts whether through reuse or overtorquing.

#8
38bfast

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Drill and tap to m8 SHCS and problem solved.

I have seen the ARP m6 fail as well
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#9
davew

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Multiple things to watch for:

old oem bolts need to be replaced

make sure the timing wheel is flat with no burrs from grinding the slots

make sure whatever bolt you use is not too long. When everything is tight the bolt must not bottom out

This is especially important if you use oversize bolts as the proper length is not available. You must grind the bolts to length.

I have seen many oversize bolts break. One prominent engine builder has been doing this for years, and his have broken also.

 

I have not seen an ARP bolt break. I have them in all 46 cars for 2 years. But Ralph can break anything.

 

I also have ARP replacement bolts for caliper bracket mounts and drive shaft bolts

 

I don't think there is a cure for this. Just several versions of band-aids. Use quality bolts as you see fit, replace at every engine build, check often, use locktite.

 

IMHO

Dave


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#10
Rob Burgoon

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Some way to move the sensor rather than moving the wheel would probably help.


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#11
ChrisA

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Some way to move the sensor rather than moving the wheel would probably help.


Would have no effect. The sensor only detects the nibs on the wheel. The wheel is what is keyed to the crank position.

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#12
Rob Burgoon

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Would have no effect. The sensor only detects the nibs on the wheel. The wheel is what is keyed to the crank position.

 

Why wouldn't that work?  By rotating the wheel you make the sensor see the nibs sooner which advances the timing.  Moving the sensor to see the nibs sooner should have the same effect, no?


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#13
ChrisA

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No, the nibs essentially tell the ECU where the pistons are so it can sequence the coil firing. Since the relationship between the wheel nibs > crank > pistons would not change the timing would remain the same. The slotted wheel allows us to change the of the relationship of the nibs to the crank > pistons, thus fooling the ECU to fire the coil earlier in the compression cycle.

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#14
BNaumann

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:no:


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#15
Tom Sager

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Make sure your plastic belly pan is tightly fastened.  That way when the bolts break your pulley, wheel and belt will be waiting for you on the pan when you open the hood. 


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#16
Jim Drago

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Make sure your plastic belly pan is tightly fastened.  That way when the bolts break your pulley, wheel and belt will be waiting for you on the pan when you open the hood. 

 

I found mine there once at Road America heading into turn 5 :)


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#17
RazerX

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Make sure your plastic belly pan is tightly fastened.  That way when the bolts break your pulley, wheel and belt will be waiting for you on the pan when you open the hood. 

That is how i found one.  They are snapping right near the head of the bolt.  

 

I am an engineering by education, So I always "want" to know why stuff happens.  To reiterate these were NEW OEM bolts order from Mazda by the part number for this job.  I am usually not that anal, but given this happened before, and the parts are cheap...  

 

My only hypothesis, given the bolts are the right length for the job and torqued correctly.  Is one of these two things (or both) are causing this, vibrations (harmonic) from the higher RPMs.  Or  The replacement timing disc from Mazdaspeed is flat while the OEM timing disk has a concave section that fits into the pulley recess.  Thus perhaps red time disk is 'flexing' with the RPMs/vibrations.  If you think about it, wihth the OEM setup the compression of the bolts is directly against the crank button, but with the Red mazdaspeed disk which is flat it is creating tension on the gap between the concave of the pulley and disk/button.   


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#18
EMatoy

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My only hypothesis, given the bolts are the right length for the job and torqued correctly. Is one of these two things (or both) are causing this, vibrations (harmonic) from the higher RPMs. Or The replacement timing disc from Mazdaspeed is flat while the OEM timing disk has a concave section that fits into the pulley recess. Thus perhaps red time disk is 'flexing' with the RPMs/vibrations. If you think about it, wihth the OEM setup the compression of the bolts is directly against the crank button, but with the Red mazdaspeed disk which is flat it is creating tension on the gap between the concave of the pulley and disk/button.

I agree and that's why the red one I bought is on the work bench and not in the car.
I also used bigger diameter bolts.

#19
Danny Steyn

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In some highly stressed engineering environments, we only use bolts for a single use. Once they are tightened to the specified torque, they elongate and are not viable as a re-use item. Does this apply in this environment?


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#20
RazerX

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Well these bolts were new and not removed yet, so in this case they failed in their single use. 


 - Speed

 

 

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