Broke a grade 8 today :(

LDPanda · Broke a grade 8 today :(

After hearing so much about bennett kingpins breaking, i never imagined it would be my grade 8 in my tracker rts that would break frist. Fortunately i was just hanging out in a garage and had another baseplate with me, but still, kinda bammer. Makes me want to replace the kp in the bennett now too.

pavedwave

LDPanda

lol wut? well, your post USED to say: pix or it didnt happen, so here ya go:

Btw, i had put around 300ish miles on this tracker and i do tend to weight heavily on the rear when going over rough terrain like cattleguards and bridges.

pavedwave

haha, well the first time I posted I was just talkin trash, but then I just decided on "I bow to you" cuz man, that took some serious crankin off the rear truck to bust it this fast. it was pretty funny we could all hear the "POP" and then watched your board going three different directions. most of all i'm just glad you weren't hauling ass at the time!

we should head over to Tacoma Screw in Ballard and see if they can order some grade8 bolts at just the right lengths, with as few threads as possible.

LDPanda

Sounds like an awesome idea, if we all got together and put in on an order (even if it was just us local guys) we could get a sweet deal. I like the idea of steel over titanium as steel tends to have just a touch of flex to it while titanium is strong but a bit brittle.

bluebugbuster

So, there is a collaborated effort to find the "perfect" kingpin? I'm in. When someone finds one and needs a few more bucks to order, I'm down.

Just let me know the specs, and give me a paypal addy, and I'll contribute.

Ian the Groove Worshipper

Glad to hear you weren't hurt

pavedwave

I believe we'll be making that trip to Tacoma Screw this week perhaps Panda?

The man just busted his Bennett front pin this morning as well... Shocked

bluebugbuster

no way! broke both front and back pins? Damn, I wish I had time to ride the hell outta my board like that right now!

LDPanda

2 kps in 2 weeks, not bad. They both lasted in the 300 mile'ish range, which considering im a heavier rider and i hit some nasty trail areas, isnt too bad overall. Im really thankful that both of these breaks happened in the garage and not out on the trail (and that i wasnt hurt beyond a bit of a swellbow). Id love to change out our KPs before the ultra, hit me up anytime, my schedule is really flexible.

northcoast

i wonder if a spherical bearing in the hanger would relieve some of the stress on the kingpins.

my thinking is (correct me if i'm wrong) that kingpin wear comes from the hangers knocking on the kingpin when you turn...putting a spherical bearing in the hanger would eliminate the "knocking" by fixing the pivot point into one spot, and eliminating the side-to-side play that causes kingpin wear

LDPanda

I dont believe kp wear comes from the hangar knocking agaisnt the KP, althought that would certianly cause wear if it were to happen. If that was the case though, the break point would be higher up. You would also see signs of that damage on the threads of the kingpin where the hangar rests and i havent. Also, im positive the hangar isnt knocking into the KP in the rear, i have it locked up tight. I think the wear comes from constant vibration and the KP itself turing back and forth with the hangar. Especially with harder bushings, some of the force applied to the truck moves the KP itself (i think). Thats not to say that spherical bearings wouldnt help the situation, i simply dont know. But im pretty positive that the wear to the KP does not come from the hangar, its more just vibrations.

pavedwave

I'm pretty sure that the looseness of the pivot won't have an immediate effect on the kingpin, only because I've been riding two of my Bennetts with horribly mangled and sloppy pivot pins for a couple years now. I wore them down on accident by letting the rubber pivot bushings turn to mush, then kept riding them until the pivot pin was rubbing directly against the pivot cup for ####?? miles until I finally noticed it. Doh! But they still feel awesome so I just watch the pivot cup wear more closely and ride them 'compromised' -- oddly, still no kingpin breaks, but I'm not taking my chances too much longer on that.

petary791

Titanium kingpins actually seem reasonable in the LDP arena. Anybody try it?

egret

something about titanium doesnt seem right for a kingpin. Same reason titanium wouldnt be used for a sword blade. Iron has a certain amount of flex depending on how hard it is tempered and I dont think titanium flexes as much. It may be harder but may also be more brittle like very hard steel. I wonder where kingpins fall on the Rockwell hardness scale and if maybe a bit softer would make them less prone to breaking. I'm surprised with all the engineering but into baseplates and hangars that kingpins appear to be off the shelf.

LDPanda

Broke ANOTHER grade 8 today >< This time it was the stock KP from my orion baseplate (made by tracker i believe). No falls or anything, just a long walk home.

blake

Maybe some one needs a diet haha Wink

Ian the Groove Worshipper

How many miles did you have on that KP?

LDPanda

Hmm, im not sure but id prolly say around 450 mi.

Unfortunately, the KP is pressed into place pretty good, i couldnt hammer it out so for now im using an RT-S baseplate. Its not quite as good a fit for the airflow but its not terrible.

stocago

Two @300 miles and one @450 miles? I guess you need to replace your kingpins every 250 miles!

angelo_pb

Titanium

I hear people saying titanium is brittle. But there must at something that aeropace engineers know that longboarders don't about its fatigue properties. I suppose the only way to emperically state they are too "brittle" would be for somebody to a) buy one b) use one c) break one. I'm certainly no engineer. But differnt metals will have different fatigue thresholds.

At $30 or so, i can see why nobody is jumpting on it. I know Radickal sells one but my plates came with a std. Its really a piece of cake to replace them. The rear truck KP would be difficult but those don't seem to be the problem. The front KP can be easily replaced since the agnle is so high(55#). No JP weld or anything. So its a tough sell to me to buy a titanium.

LDPanda

Titanium is good for areospace applications for two reasons. One, its very light for the strength it provides and two, it doesnt change properties much with temperature changes. Neither of these two properties are particularly important to longboarding (unless your REALLY want to cut down on weight). I still have confidence in grade 8 pins. So far ive NEVER broken a grade 8 FRONT kingpin, only rear ones. The custom pins that james and i had made have not broken so far. I suspect it has more to do with the shape of the KP (splines or no splines, how much threading) than the quality of the material. I agree with blake and stacato, i prolly should shed some pounds and reduce the wear on my gear and also should be more mindful of replacing kingpins BEFORE they break.

egret

I want a kingpin made of Busse Combat's infi steel. Those knives take some a use and I am not aware of any that have snapped. I think Jerry Busse charges 100 dollars an inch for a custom knife. 300 for a kingpin would be an expensive experiment.

LDPanda

When they come out with adamantium kingpins, then ill drop $30 on one. Laughing

angelo_pb

i thought it was the front that breaks. The rear breaking seems like it would be more easy to recover from.

My Rads are supposedly Ti but don't seem very light weight to me for some reason. I am sure the Ti is lighter than the grade 8, however.
But why would Randal and Rad bother casting them? Just to save a few grams? It seems that strength would be important to both.

Again, somebody has to test one and break one before i believe it is more brittle. Air frames and the fan blades of a jet turbine can't be too brittle, can they?

LDPanda

Yeah, rear KP breaks are a lot better than front KP breaks, believe me ><

When a rear breaks, you hear a POP and then a little jingling as your washer and pin hit the ground. Then your rear truck becomes uncontrollably unstable and you jump off and pick up the scattered bushings and hardware.

When a front breaks, you hit the ground, fast.

Ive broken a stock Bennett KP but they are weakly designed and I suspect they are not grade 8 (they dont bear the grade 8 markings). Trust me, its 0 fun.

As to why truck manufacurers produce TI kingpins, i think the answer is that people will buy them for $30. I do agree with your testing argument tho, no one that i know of has actually tried to break one and seen how long they last. If you want to buy me one ill beat the hell out of it and report back tho! Wink

egret

I'm no engineer but I don't think titanium has much give. It is rigid. The jet engine parts you mentioned would not be absorbing a lot of shock. Are the bolts and rivets used titanium or steel?

I'm with panda. 30 bucks is not outrageous fir a kingpin if it won't break. I bit the bullet and bought virages primarily for the clearance and stability. My Bennetts have hooked up and sent me flying enough that 300 dollars is worth the peace of mind. I hope, haw haw. Falling sucks. LDP stance is not the easiest to land on your feet from when the board suddenly stops. I've never broken a kingpin but it is always on my mind. My heart goes out to camel.

stocago

egret

I'd chip in. In the name of science.

model.citizen

yeah titanium is infinitely stronger than steel, but it depends on how it's being used.

for aerospace use titanium fastenings are exactly that - fastenings torqued up to hold components together, with no give allowed or desired.

on a skateboard, the very nature of tac'ing puts lateral stress on the kingpin, and as it's not secured hard-and-fast in the baseplate, there is room to move and to break. at least grade 8's bend a little before snapping.

stainless steel is similar in brittleness to titanium, too much flex or vibrations cause it to crack before bending.

now from all this, i was looking at some old-skool boards the other day and some old ACS trucks caught my eye.
mainly 'cause the kingpin was secured into the baseplate with a nut BEFORE the bottom barrel is installed. which got me wondering, something like this could alleviate the requirement for an additional cone/barrel at the bottom, plus hold the kingpin in place securely with no chance of sideways movement in the baseplate. obviously the kingpin would need to be threaded almost the whole length (which might negatively offset any benefits).

whaddayareckon?

angelo_pb

Grind King says they KPs are stronger than grade 8. I am not sure how the 300 year warranty works. Perhaps they will repair or replace a broken KP so long as you are the original purchaser, have your receipt, and did not abuse or misuse the product and don't die or otherwise quit skating 300 years henceforth.

I will try to find out if they have any mutant 3" KPs laying around or if they do custom orders. Any takers?

Ian the Groove Worshipper

Better idea is to go to your local bolt supplier and buy 10 Grade 8 3/8 inch 24TPI bolts in the length of your choice.

I buy 3.25 inch, cut them with a dremel, bevel the edge on my bench grinder, clean the threads with the wire brush, and I have the perfect 2.5 inch kingpin with about 3/8" of threading.

The kingpins cost 60 cents each at my local supplier.

So it costs less than a buck a month to change a kingpin and have the peace of mind of knowing its way less likely to snap and cause at best a walk home, and at worse a severe joint or head injury. As a added benefit, I get major upgrade with regards to bushing wear, and the threaded part, which seems to be where they most often snap, is not on the fulcrum point of the hanger and is now quite a bit higher.

If you are not handy, you can just buy 2.5" kingpins and deal with the threading. If you change them frequently you'll have way less likelihood of a kingpin snap/bail/carnage/head injury/broken clavical/broken teeth/torn ACL/torn labrum or anything else that can happen when you are completely surprised by wheelbite that comes so quickly your reflexes are not quick enough to save you.

I also don't have to be as concerned about fatiguing my kingpin when riding over sidewalk cracks or cattle guards, if that happens in my path. I often find myself happy about that, I used to worry about that quite a bit. I know it's a fresh kingpin and will be changed before it gets old - peace of mind.

The common denominator in all of the broken kingpin threads seems to be that they have a few hundred miles on them. Also, heavier dudes seem to be usually involved. I weigh 198 right now, so I'm gonna change them frequently.

There is no guarantee that I will not snap a kingpin one of these days, but it is probably way less likely.

LDPanda

Classic 70's Bennett pro's were also made with a nut on bottom before the bottom bushing. Im not sure what purpose this served or why no modern manufacurers are doing it this way. I can only assume that since 0 truck designers are using this that it was shown to be faulty in some way, but who knows. I do know that cutting threads onto a rod reduces its strength by a minimum of 18% and that may be a reason not to have threading near the baseplate.

Grindking KPs (if im not mistaken, and im not a street skater so i might be) are mounted with the nut inside the baseplate. We already know that setup is VERY weak for the kind of riding we do and it is not suggested. Plus, the head of the grindking bolt is non-standard so i dont know if it would work to reverse it and mount it the way we normally do (nut on the 'top side')

I agree 100% with Ian, custom bolts and replacing them often is the best way to go. Theres info on this in another KP thread but James and i made several custom KPs from 3" grade 8 chopped down to bennett size (actually a lil shorter than the current bennet KP). This means they have very little threading at the top and no splines near the head. Its a cheap and easy item to replace and at least in the front can save you from some nasty falls.

model.citizen

fair 'nuff about the GK KP having the weak side down.

but reversing them is sooooooo easy...since they have a rather wide head, simply grind down the sides a little so that it slots into the Bennett baseplate.

a little loctite wouldn't hurt, as from what i can see you only have to remove 1-2mm of material from each side, which won't give a terribly wide face (although perfectly sufficient since there isn't much torque used when tightening up the truck).

Ian the Groove Worshipper

I think that the Grind King KPs are shorter than 2.5

egret

At Milehigh they sell 3.5 inch kp.

On the far left is the Bennett stock. Far 2 on the right are the 3.5 inch minus an inch.

I lied earlier. I have snapped a kingpin on a rear Carver CX (rear is actually C2).