Wobbly Kingpin. Splined 3/8" kingpin in an M10 bore for American market? M10 everywhere else?

[SternWake]

I know a Wobbly kingpin reduces steering precision, but is the base plate at much higher risk of cracking, or the Kingpin itself snapping?

I have some MBS AS.12 TKP trucks and started hearing a click when rocking over the apex, and then found the splined kingpin quite loose. I keep my truck bushings as loose as possible.

I swapped to my other MBS truck, and am considering removing the Kingpin on previous baseplate and replacing it with a grade 5 or 8 bolt without the splines, but am not sure whether it will be loose from the splined Kingpin factor and whether JB Welding the new bolt in place.

Edit. I changed the title but not the paragraphs above.

[Pecos]

Id think a loose kingpin would start to wear the bore in the baseplate - if it was mine id definitely get a grade 8 bolt as long as it fit and add a little jb weld to lock it in. Wouldn’t think twice about removing the slop - i would start planning on getting a new baseplate incase the jb weld doesn’t hold up

[SternWake]

Yesterday, I swapped to my other baseplate that is slop free, but I expect to behave similarly and develop slop far too soon.

I did not put huge mileage on this truck and venom’s experience with them scares me, where the pivot cracked and broke and sent him streetface.

I really need to get a stronger truck for a flat deck board. I only need one for the front.

[SternWake]

The splined kingpin is grade 8.

Am concerned the hole is too wallowed out and will need to step up bolt diameter

It tapped out quite easily with a little baseplate heating.

Didnt try it cold, just pulled pivot cup and torched it a little bit and 2 light taps with a light hammer

[SternWake]

Closely inspecting my baseplate with the grade8 splined kingpin removed, it appears to my eye, as the receptacle is not perpendicular to the base, like the casting was off or if drilled after casting, the drill press base was off by 1 degree.

The 3/8 / 0.375 inch diameter grade 8 kingpin, above the splines, is also measuring 47/128 or 0.368 inches.

3/8” = 9.48mm. My kingpin above the splines is measuring 9.35mm.

So no matter what my kingpin is loosey goosey in the base plate and the splines are 9.89mm and I can get my calipers to read as wide as 10.07mm measuring side to side where the kingpin was rocking, wallowing out the receptacle.

Grade 8 is equivalent strength to metric 10.8, and if the unthreaded portion is actually 10.00 mm on an M10 bolt, it is also wider, and metric 12.9 is also available and even stronger.

I don’t seem many M10 bolts of the right size with the unthreaded portion that also have a hex head, so I would have to use a socket cap bolt, and to prevent it spinning likely need loc-tite, and if going loc-tite, why not JB weld, and if using JBweld maybe I should just use the grade8 kingpin I already have and stop overthinking each and every aspect of everything.

[SternWake]

Are prebuilt boards that are not intended for the American market, also forced to use 3/8-16 SAE kingpins?

or do they get M10?

Seems all my baseplates that I can get my calipers into are designed for 10mm, and the splines on a supposed 3/8” grade 8 kingpin are just a method to increase the kingpin diameter so that it fits tightly( briefly) in the baseplate designed for M10, more so than keeping the bolt from spinning in the baseplate.

grade 12.9 metric is stronger than grade 8, and M10 is wider than SAE 3/8”

[SternWake]

Got some socket cap M10 partially threaded grade 12.9 coarse thread at Ace Hardware.

The threaded portion reads 9.82 to 9.87mm and the unthreaded portion reads 9.93mm.

I can just start hand threading it into the MBS tkp Baseplate, and almost through black rkp baseplate.

The 3/8” grade 8 splined kingpin is 9.34mm on unsplined unthreaded portion, and threads.

Kind of hoping for a JBWeld/locktite free friction fit on the mbs baseplate.

Was hoping for finer pitch threads too.

[SternWake]

I will not be using the Grade 12.9 M10-1.5 socket cap bolts as Kingpins.

I used some 400 grit wrapped around a ~9.4mm wood dowel in the baseplate receptacle, until I could barely hand thread the bolt into the MBS baseplate.

Can confirm the receptacle is not perpendicular to baseplate. The unthreaded portion of the M10 bolt was going to be a very tight fit, had I proceeded.

Grade 10.9 Metric is more similar to Grade 8 and has higher ductility/less brittleness

Grade 12.9 has higher tensile strength

I have ordered M10-1.15 x 70MM grade 10.9 bolts, and will cut them down to 50MM for my TKP baseplates.

The M10-1.5 grade 12.9s I got today measure 9.86mm on unthreaded portion.

The 3/8” splined kingpin I knocked out of an RKP baseplate measures 9.18mm away from the splines and 9.89mm on the splines.

The 3/8: grade 8 Kingpin I knocked out of the MBS baseplate measures 9.35mm away from the splines and 9.89mm on the splines.

I have a few RKP baseplates with wobbly kingpins and these need 70MM long kingpins

The TKP baseplates need 50mm kingpins, but I can’t find any that are not fully threaded.

The 16 or 17mm Hex heads will have to be reduced in size

So the M10-1.25 grade 10.9 should be 11.7% stronger than grade8 3/8” kingpins, and should eliminate the wobble in my MBS baseplate.

I don’t know the grade of the Kingpin knocked out of my RKP baseplate, but it measures only 9.18mm so the 9.86mm M10 bolt should be 16% stronger, assuming it is grade 8.

Ordered a bunch of M10 nylon locknuts too.

None of my bushings had any issues fitting over the M10 bolt down over the unthreaded portion, but a few cup washers would need a little reaming.