I broke my nut. Er Lug Nut
09-25-2007, 10:23 PM
#1
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I broke my nut. Er Lug Nut
From what I gather and from asking, I've been informed that the 928's alloy lug nuts are pretty sturdy and are not normal wear items that need replacing.
So I was putting on some rear wheel spacers and did not notice that there was not an overabundance of threads showing from the wheel spacer through the wheel. Went to torque down the wheel with my click wrench and one of the lugs did the squirm and kept turning.
Pulled the lug nut back off (glad it wasn't the bolt on spacer's lug yielding) and this is what I found:
The coil is some of the thread I pulled off the stud. Some of the lug threads seem like it was work hardened and flaked off.
I estimate there was roughly 6-7 threads the lug nut had engaged.
The click wrench was working and the lug felt like it yielded in the high 80's ft/lb of torque.
And yes, I believe that someone in the past had decided to use their air tool on the lug nuts.
So I was putting on some rear wheel spacers and did not notice that there was not an overabundance of threads showing from the wheel spacer through the wheel. Went to torque down the wheel with my click wrench and one of the lugs did the squirm and kept turning.
Pulled the lug nut back off (glad it wasn't the bolt on spacer's lug yielding) and this is what I found:
The coil is some of the thread I pulled off the stud. Some of the lug threads seem like it was work hardened and flaked off.
I estimate there was roughly 6-7 threads the lug nut had engaged.
The click wrench was working and the lug felt like it yielded in the high 80's ft/lb of torque.
And yes, I believe that someone in the past had decided to use their air tool on the lug nuts.
09-26-2007, 01:09 AM
#2
Chronic Tool Dropper
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EW--
Just looking at the picture, it appears that the outer part of the log is ever-so-slightly twisted counter-clockwise from the inner cone end. Air tool in the past? I worry more about the air-tools tightening and stripping the bolts.
An old rule of thumb is that you want at least one diameter plus two threads engaged as a minimum. 7 threads at 1.5 pitch 14mm isn't quite enough in my opinion.
Just looking at the picture, it appears that the outer part of the log is ever-so-slightly twisted counter-clockwise from the inner cone end. Air tool in the past? I worry more about the air-tools tightening and stripping the bolts.
An old rule of thumb is that you want at least one diameter plus two threads engaged as a minimum. 7 threads at 1.5 pitch 14mm isn't quite enough in my opinion.
09-26-2007, 02:42 AM
#3
Drifting
09-26-2007, 08:05 AM
#4
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Rule of thumb I found on Rennlist was 9 threads. Wonder if that's enough on lug nuts with a shady past.
And how many cycles of gorilla mechanicing our alloy lug nuts can tolerate before it becomes an issue.
Anyone original owners stayed at the dealership to make sure the US mechanics do not air wrench or Tork Stick (those colored extensions) the wheels back on.
Do other cars use alloy lug nuts?
"Professional" mechanics are so spoiled by what they can get away with on them steel lug nuts/bolts.
And how many cycles of gorilla mechanicing our alloy lug nuts can tolerate before it becomes an issue.
Anyone original owners stayed at the dealership to make sure the US mechanics do not air wrench or Tork Stick (those colored extensions) the wheels back on.
Do other cars use alloy lug nuts?
"Professional" mechanics are so spoiled by what they can get away with on them steel lug nuts/bolts.
09-26-2007, 09:04 AM
#5
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IIRC the alloy lug nuts have 9 threads engaged.
Normal rule of thumb for us structural engineers is at least one dia which normally works out around 6 or 7 threads - but but but that is for a steel nut which is the same grade nominally as the bolt (actually the nut is usually a bit stronger) and for a normal thread.
Wheel nuts on a 928 are a fine thread hence more threads per one diameter.
Your failure is due to previous abuse. the alloy wheel nuts are way strong enough to do the job they have to do if they are not overtightened.
Normal rule of thumb for us structural engineers is at least one dia which normally works out around 6 or 7 threads - but but but that is for a steel nut which is the same grade nominally as the bolt (actually the nut is usually a bit stronger) and for a normal thread.
Wheel nuts on a 928 are a fine thread hence more threads per one diameter.
Your failure is due to previous abuse. the alloy wheel nuts are way strong enough to do the job they have to do if they are not overtightened.
09-26-2007, 09:53 AM
#7
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You've already received some very good advice, but I switched over to steel lug nuts on my heavily abused 928. I like seeing the threads extend beyond the stud as noted above.
Ken
Ken
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09-26-2007, 12:37 PM
#8
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the rule in PCA racing is the diameter of the stud. that works out to be around 5 threads (5 turns)
I used this before i was able to get longer studs to work with the spacers i was using.
the aluminum lugs are find for street applications. (if they are installed correctly) something caused these threads to strip out in my opinion. (dirty threads, or most likely, cross threading)
mk
I used this before i was able to get longer studs to work with the spacers i was using.
the aluminum lugs are find for street applications. (if they are installed correctly) something caused these threads to strip out in my opinion. (dirty threads, or most likely, cross threading)
mk
09-26-2007, 01:14 PM
#9
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the rule in PCA racing is the diameter of the stud. that works out to be around 5 threads (5 turns)
I used this before i was able to get longer studs to work with the spacers i was using.
the aluminum lugs are find for street applications. (if they are installed correctly) something caused these threads to strip out in my opinion. (dirty threads, or most likely, cross threading)
mk
I used this before i was able to get longer studs to work with the spacers i was using.
the aluminum lugs are find for street applications. (if they are installed correctly) something caused these threads to strip out in my opinion. (dirty threads, or most likely, cross threading)
mk
14mm nominal stud diameter, divide by 1.5 threads per mm. Needs 9.3 threads on my calculator. With open nuts, you need to have at least two threads exposed above the nut if 9 threads are not engaged by the nut. Mark, check to be sure that your calculator is set for 'degrees'. 
09-26-2007, 04:40 PM
#10
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I didnt calculate at the time. I took the diameter of the stud and just counted the threads that equaled that distance. turned out to be 6 turns (i wouldthink that is 6 threads) Ill have to go back and measure, as was a long time ago before i was able to get the proper studs in my hubs .
mk
mk
I'm math-challenged again. 14mm nominal stud diameter, divide by 1.5 threads per mm. Needs 9.3 threads on my calculator. With open nuts, you need to have at least two threads exposed above the nut if 9 threads are not engaged by the nut. Mark, check to be sure that your calculator is set for 'degrees'.
14mm nominal stud diameter, divide by 1.5 threads per mm. Needs 9.3 threads on my calculator. With open nuts, you need to have at least two threads exposed above the nut if 9 threads are not engaged by the nut. Mark, check to be sure that your calculator is set for 'degrees'.
09-26-2007, 08:10 PM
#11
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When I first got the shark I made the mistake of going to PEPBOYS for a couple tires. The snapped off 7 of the front 10 lugs. Bolts were fine, the lugs themselves twisted and split in half. Half on the lug still holding the wheel and half in the impact wrench...
Even after I had told them not to use air tools. What's worse is after the first one split, they kept going... The had to use an impact chisel to get the nuts off, tearing up my rims. Only they didn't get them all off. They called me, gave me the keys and said, "Have a nice day, we don't work on Porsches anymore". I had to have it towed to a local Porsche guy to get the wheels the rest of the way off.
About 2 weeks later, and a personal call from the CEO, PEPBOYS not only gave me the tires free and paid for the Porsche guys labor and the tow, they gave me $400 for each of my ruined 15" phone dials! That was enough to get a set of 17" TT rims! In the long run I guess I made out. Oh and I just sold the phone dials for $125. They were still functional , just butt ugly.
Even after I had told them not to use air tools. What's worse is after the first one split, they kept going... The had to use an impact chisel to get the nuts off, tearing up my rims. Only they didn't get them all off. They called me, gave me the keys and said, "Have a nice day, we don't work on Porsches anymore". I had to have it towed to a local Porsche guy to get the wheels the rest of the way off.
About 2 weeks later, and a personal call from the CEO, PEPBOYS not only gave me the tires free and paid for the Porsche guys labor and the tow, they gave me $400 for each of my ruined 15" phone dials! That was enough to get a set of 17" TT rims! In the long run I guess I made out. Oh and I just sold the phone dials for $125. They were still functional , just butt ugly.
