If I remember correctly 10/9 has more fatigue resistance. Here is another idea, how about using a slightly larger diameter kingpin?
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2 of my My 3/8” kingpins measure 9.18 and 9.34 mm thick.
The 12.9 M10 bolts I got today are coming in at 9.86mm
Dont Trip has made LDP trucks with 1/2" kingpins, as LDP makes 3/8" kingpins fail from fatigue way too often. Especially since they run spherical bearings. I don’t recall seeing even just a single one of those 1/2" ones failing. I think its called Poppy XL.
For my swingarms I want to use M12 kingpin as the failure mode of a kingpin would be pretty much guaranteed crash, and I really don’t want to find that out firsthand.
Only issue with upsized kingpins is lack of bushing availability for them. Drilling out the bushings with a hand drill sucks. Even a drill press is hard to find repeatability with. A lathe is the only way I can get them repeatedly concentric, and most people don’t have access to a lathe. I’m considering buying a small lathe primarily for this, at least if I can figure out where to put it in my small shop/ room
AI agrees that 10.8 is a better call than 12.9 for fatigue resistance, as you mentioned.
I have wrapped a wood dowel with some 320 grit sandpaper and got the M10 to thread in upto the unthreaded portion. The column is definitely not perpendicular to the baseplate.
I am not going to seat this 12.9. M10 socket cap I’d really prefer finer pitch threads.
I did put my calipers on some 10.8 M10’s in the hardware store, and they were ~ 0.1mm less diameter
I really wish we could move away from standard and go entirely metric. M12 is petty close to 1/2”. One option is to ask a company like @RipTideSports to make custom bushings for a M12 kingpin.
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The two 3/8” kingpins I have removed from my baseplates measure 9.18, and 9.35mm on the unthreaded portion.
The Kingpins in the posts above broke right at the end of the splines, whether due to it being the flex/fatigue point, or the splines themselves weaken the shaft, or both.
The M10 grade 12.9 metric cap screws I got yesterday measured 9.86mm
If the M10 bolt was grade 10.9 it would be 11.7% and 16% stronger than my 2 kingpins, if both were unsplined and grade 8, just because of the extra diameter.
I have ordered M10 partially threaded 10.9 bolts and will make them fit my baseplates. I have some other RKP baseplates with wobbly splined 3/8” kingpins
I had no issues sliding my bushings over the grade12.9 M10 bolt, but some of the cup washers will need a little bit of reaming.
I will have to carry some different tools.
Seems the Splines are a half ass way to lock the kingpin in, which also weakens the kingpin.
I’ll be seeking a friction fit in the baseplate, and hope the M10 grade 10.9 bolts I ordered come in a bit thicker than 9.86mm on the unthreaded portion.
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Every 3/8 bolt has different measurements? I wonder if this is why my 3/8 bolt has some play on my cnc baseplate..
Riptide bushings for m12 kingpin sounds awesome , I have also asked https://riot-mfg.com/ and he can machine bushings for m12 kingpin
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I had my digital calipers in the hardware store and the grade 10.9 M10 bolt was 0.1mm lesser diameter than the grade 12.9. I suspect there is some sort of acceptable range of diameter and looseness of threading which is deemed acceptable across manufacturers.
I have only put my calipers on two 3/8 kingpins so far and they had a much greater disparity in diameter.
The Splines seem to be the preferred way to not just prevent the kingpin from spinning in the baseplate, but make it fit tightly within. I assume the diameter of the receptacle can also vary whether the baseplate is CNC’d or cast or cast and drilled.
One thing I am trying to wrap my brain around is what skating actions produce the most stress on the Kingpins.
The reports of Long distance pumping KP failures points to lateral loading from side to side fatigue, and a wobbly kingpin, in my case, would seem to oval out the receptacle.
Does this mean my wobbly kingpins point towards me stressing the KP more as I weigh 200Lbs/90 KG and like to carve rail to rail near the limits of traction?
Is is because I keep my trucks so loose that the dang cup washer rattles against the nut?
Is it because my truck baseplates are largely cast aluminum?
I would much rather not have to use JBweld and return a 3/8” splined kingpin into the immediate baseplate of concern. The M10 bolt will be a pretty tight fit, and the extra diameter, and lack of splines should equate to greater strength/ lesser likelyhood of failure and subsequent streetface.
I am trying to remind myself I am old, and to slow down and take less risks (but love the sound and feeling of warm urethane hissing under load, and going slow is boring) , but my biggest fear is what if I hit that expansion joint and My hanger pivot breaks or the Kingpin snaps, or baseplate cracks?
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10 new Taiwanese made, 70mm long M10-1.25 grade 10.9 hex head bolts arrived yesterday.
I don’t know how long this link will last for U.S. based members, so I will include the product description too so one can copy and paste and easily search.
.M10-1.25 x 70mm Grade 10.9 Hex Cap Screw Bolts Metric Zinc Hardened FINE THREAD.
They measure 9.86mm on the shank/ unthreaded portion.
I pulled out an old RKP baseplate that I think is Paris, or a clone there of. It came with a set of Puaida hub motors and trucks.
Its splined 3/8 kingpin had become wobbly as F, and was retired in the bottom of my box of skate parts.
The unknown grade 3/8” splined wobbly AF kingpin tapped out with the lightest of blows from a lightweight hammer.
It measures 9.51mm on the shank.
I had to grind down the M10’s 17mm hex head to fit inside the baseplate. I went slow as to not overheat, and the water quench never sizzled, so it would seem the hardness and temper is preserved.
The threads would not fit into the receptacle from the bottom, but they would from the top, so I hand threaded it from the top until it got stuck, and then used a 17mm wrench to screw it all the way through. This did not require much force at all.
Then backed it out and was able to thread it in from the bottom till the shank bottomed out on the baseplate receptacle.
I then pulled it into the baseplate using its own threads and some spacers under a new M10-1.25 flange base locknut. This was very cathartic, and seemingly the only thing I did today which went right without fighting.
The bolt was pulled into the baseplate, not requiring too much force on 15mm socket, nor too little. It seated perfectly, and even if it were not prevented from spinning by the ground down sides of hex head, the Nut on top would be unlikely to to so when compressing bushings. It’s tight, but not so tight that the aluminum baseplate could have cracked.
The Flange base M10 -1.25 lockNuts I got are tall and burly.
I did not notice in the product description that they also had some Scotch grip 204 thread locker applied threads. This was the source of much cursing as I has handthreaded a nut on the bolt upto the nylon for grinding, and when I went to remove it was absolutely not going anywhere. Vice grips on ground bolt head and a regular ratchet had no chance. I had to use 1/4 inch impact driver to get it off.
The flanged base of this M10 nut is the same diameter as a tall cone bushing. Since I always flip my roadside cup washers upside down for that extra lean, and because the nut is so thick, and I keep my trucks so loose, I just skipped the cup washer entirely, as I was not able to engage the nylock portion of the nut with the cup washer unless I tightened the trucks far more than I like.
I had removed the Scotch grip 204 thread locker from the M10-1.25 nuts interior threads as that was some serious stuff.
This 3/8 to M10 kingpin swap was easy enough, that I will be swapping all my Kingpins to M10-1.25 Grade 10.9. No Splines to weaken the bolt, no more Wobbly kingpin , and some extra bolt diameter for extra strength and fatigue resistance is win x 3 in my opinion.
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I removed a caliber 2 front truck from my mini kicktail.
Its unsplined Grade 8 king pin was all wobbly, and could be slid out of the baseplate with no tools.
It measures 9.36mm on the unthreaded shank.
I will have to grind the 17mm hex of the M10-1.25 down to fit the Caliber baseplate, And the new M10 kingpin also does not want to hand thread into the caliber baseplate from the top or bottom. so some 400 grit on a 9mm wood dowel will have to get the diameter just wide enough to accept the M10 threads.
I’d like to thank this thread for igniting my fear of broken kingpins and forcing me to do what i could to lessen my personal risk
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It is very easy to drill out the ID of a bushing to 12mm
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What’s your recommended method for this? I tired it in a drill press and the holes never turned out perfect. Fresh from the freezer helped but still wasn’t 100% success rate. I think I was drilling to 14mm though, definitely more than 12.
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Sharp drill bit, highest speed rotation. Place the bushing on a piece of wood and a layer of sand paper to prevent the bushing from spinning. Peck away at it a couple of mm at a time and drill from both sides. The urethane should be powdering, not stringing. Be patient and cut a little at a time due to heat buildup.
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This is the baseplate on my high mileage Daily driver with its new M10 kingpin.
Its former 3/8” splined kingpin was still nice and tight, and difficult to remove. I was heating the baseplate to 185F and holding a quickly melting ice cube on the kingpin, and with baseplate screwed down, Was just about to consider a heavier hammer or swinging harder, when it moved.
The Unknown grade splined kingpin in this baseplate measured 9.36mm on the shank, the unthreaded portion above the splines.
A new M10-1.25 would not thread in from the top or bottom easily, but I got it started, and it then started cutting its own threads from the bottom. The M10 with the ground head fought being pulled past the hard stop of the threaded shank, by the M10 nut and spacer, So I unthreaded it and tried the 400 grit on a 9mm dowel thing, 2 more times, without success.
I then used a new M10 bolt that still had the full 17mm hex, threaded it in until it stopped, and then kept turning it, and the threads pulled the shank into the base about 5 or 6mm and then it stripped. I unthreaded it, vaccummed and cleaned the interior with a Qtip and rubbing alcohol of all the powdered aluminum, and then hand threaded in tthe ground head kingpin until it stopped and then used vicegrips to twist it further, and it too pulled its unthreaded shank into the baseplate deeper.
I then was able to use the M10 nut and spacers to pull the Kingpin in. I rotated tge ground head to it would not bind, and then used ratchet to pull kingpin in to full depth.
It was not quite as tight of a fit as yesterday’s kingpin swap in the same design Baseplate. It took less pressure on the rachet to pull it in, but the Kingpin is tight. Certainly No wobble, and I doubt that loosening the m10 lock nut could twist the kingpin in the baseplate.
I did the same thing as yesterday, using a taller red cone washer that has the same diameter as the flange on my M10 Nylock locknuts, cleaned of their red threadlocker, and skipped the flipped cup washer. So the narrow part of conewasher is directly on the Flanged underside of the locknut.
A test roll with a newer less worn Pivot cup revealed all was well, and The new tall cone bushing is allowing me the extra lean I desire.
It feels good to have a slightly thicker, non splined, and New, non fatigued M10 grade 10.9 Kingpin locked in place, No JBweld or Loctite required.
I did overgrind the 17mm hex head, but it cannot spin.
I have two more of this same baseplate that I will swap M10 grade 10.9 kingpins into, even though they are not wobbly. Several other baseplates will also get the same treatment even if they are not in immediate use.
Sliding the bushings down over the slightly thicker kingpin certainly takes more effort than they do over the standard 3/8”, but I would not say it is difficult. I did have to very slightly ream out the boardside cup washer that rests on the baseplate.
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