There have been some other posts mentioning this, one with a roll pin shearing on the dyno and a few others, but I thought I would get the information out that this does not look to be a question of if it will happen, but when.

I will be on the dyno Friday and beforehand I decided to check my pin. I had installed a Perrin lightened crank pulley a few months ago and was curious to see how it was holding up. Pictures will be posted shortly, but the result is as follows:

Primary failure mode - roll pin bent in the pulley side of the hole (pin now shaped like a J), causing the crank pulley to shift. Given more time, the pin would have sheared, leaving the pulley to free spin on the crank, causing timing irregularities and possible engine failure.

Secondary failure mode- roll pin caused an elongation of the pulley hole as it bent, damaging the aluminum crank pulley. As it bent, pin also recessed in the pulley hole, causing greater strain and additional pulley damage.

With a new, 1/8" cobalt steel pin installed, the pulley now has a wobble so it will be swapped with the stock steel pulley for greater durability. The new pin was fashioned from a 1/8" cobalt steel drill bit from the smooth end, not the cutting end.

Please take this under advisement, the replacement takes about an hour on the Greddy supercharger and is doable with one person. You will need a 10, 12, 14 and 19mm socket for all of the bolts, and a breaker bar or impact wrench is recommended for the pulley itself.

 

My car is at Ptuning getting dyno tuned today and tomorrow as well, so will both will be hitting up the track Friday night on fresh tunes!!

 

Got the pictures in, the bent roll pin and chewed up pin hole in the crank pulley are pretty clear. I'm running the steel pulley for now and will be drilling a new 1/8" pin hole on the opposite side for a new install.

 

HOW DOES THE NEW PIN HOLD UP?

 

OR DRILL BIT

 

Not sure, I haven't pulled the pin back out. I'm in the process of putting a new pin hole on the aluminum pulley on the opposite side of the original, once it's swapped I can see how well the bit holds up.

 

are those aluminum pully's even designed to take that kind of strain? from what I have learned those can't even take the strain put on the motor from a large audio system. Don't you think it would be a better idea to just leave the stock one on?
mabey the weakness of the aluminum is what cause the pin to bend in the first place by putting all of the strain in a single location.

 

That thought had crossed my mind, not sure how the audio system would cause additional stress, aren't alternators fixed output? I did notice the stock roll pin was recessed in the hole a bit resulting on less area on the pin to distribute the torque. I would like to give the aluminum one another go with a fresh hole drilled, and then check it after running for a few weeks to see if the pin swap makes a difference or if failure is a result of the softer aluminum.

If the failure is caused by aluminum, I'll just run stock steel and post a notification. Worst case if the pin does shear is a loss of alternator and water pump (assuming free spin of the pulley, failures I've heard of result in slipping but not total free spin), neither of which would result in immediate engine failure, only after over temp. I will probably run an engine temp sensor to check, just need to upgrade my two pod to a three.

 

sounds like a good plan. yes, alts are fixed output, put when you try to suck more juice out of it than it's able to handle, it can cause some strain on the pully. (you can see this on some cars when they have a big system and every time the bass hits, their lights dim)

anyway, good luck and hope it goes well.

 

performance dcars use billet pulleys all the time.

it's strong enough.

I used a hardened nail when i replaced my pulley and not a problem since.



oh and a freewheeling crankshaft pulley will not cause timing irregularities.

 

i did the drill bit pin swap over a year and a half ago and i have had no problems with it ever. even swapped the pulley once from an underdrive to the perrin and the drill bit, i mean pully dowel pin it still perfectly straight.

 

That "shear" pin is designed to shear for a reason...