Nc50 2 speed max rpm, what's safe

Sup everyone, got my 2 speed juiced up and have had it to 53gps so far, which is probably about 13 or 14k rpm based on rough math. I had a working tack with the old kit it did 46 at 12,500. Anyways, it got power at 53 and feels like it would roll over a few more mph but its screaming so hard I'm kinda worried about what's gonna break next.

So what has everyone been gettin away with on stock honda cranks. I know variated bikes are bustin up cranks but that's a f*ck load more heat on a crank then the 2 speed assy imo.(edited)

Re: Nc50 2 speed max rpm, what's safe

Well that's faster than the Cox Brothers

Re: Nc50 2 speed max rpm, what's safe

Back when I use to play with the express's I never had luck with the 2 speed transmissions holding together, had multiple clutch bell failures, but I was running pretty high millage bikes with little to no attention paid to the transmissions before making them fast.

I had a 77 one speed that topped out at 53, those things kinda suck at those speeds.

Re: Nc50 2 speed max rpm, what's safe

53 with a one speed! I bet that rode real easy in traffic lol mine pipes up at about 10k. I got a spare transmission in a box, I'm more worried about the crank. I change the oil often, 20/50 motorcycle oil.

Re: Nc50 2 speed max rpm, what's safe

I'll also post another thread about how to make that 2 speed hold 1st gear to about 35mph, want easy. Not much info out there for the 14" bikes.

Re: Nc50 2 speed max rpm, what's safe

> . . Wrote:

> -------------------------------------------------------

> 53 with a one speed! I bet that rode real easy in traffic lol mine pipes

> up at about 10k. I got a spare transmission in a box, I'm more worried

> about the crank. I change the oil often, 20/50 motorcycle oil.

Both transmissions have the exact same total transmission ratio. The rpm will be the same at top speed.(edited)

Re: Nc50 2 speed max rpm, what's safe

Jack Rutherford /

assuming a tire diameter of 18.75", you're at 13,506. I would guess you are on the edge of no return. Let us know if there's more in it or not.(edited)

Re: Nc50 2 speed max rpm, what's safe

I ordered a cheap inductive tack on prime, will report back in 2 days what max rpm is. Back tire is a 14×2.75 which wasnt easy to fit... it seems reliable I just put over 200 miles on it in key west a few weeks ago.

Re: Nc50 2 speed max rpm, what's safe

Jack Rutherford /

with that tire, rpms will be lower than I calculated. What's your setup?

Re: Nc50 2 speed max rpm, what's safe

Setup doesn't matter, just speed and tire circumference. Oh, and that the speed is not a lie.

Re: Nc50 2 speed max rpm, what's safe

I'm runnin an athena 47.6mm kit ported192/138 with some off brand o ringed head set up 60psi compression 1.5mm quench, dio v block with kx65 boyesen reeds, 26mm round slide mikuni, custom/home made exhaust, lots o transmission mods. Pretty dope setup most dudes dont believe it till they see it. It shreds harder then any 14" bike I've ever seen lol

Re: Nc50 2 speed max rpm, what's safe

Jack Rutherford /

I asked because I figured it was the Athena kit. spacer? What transmission mods? I assume you mean 160 psi compression? custom intake?

Re: Nc50 2 speed max rpm, what's safe

No 60psi. Its been my experience that in general high compression on a 2 stroke is a fools errand, minor low end gained with reliability lost to pay. Plus they always roll over smoother the lower the compression. I run all my jet skis under 120psi, my 250r the highest at 160.

Just a 1mm spacer to get the compression down, like I said 1.5mm deck with an o ringed head. The athena hit came 1mm lower on the transfers then the wizard kit so it took allot of careful porting to get the t ports up where I wanted.

Re: Nc50 2 speed max rpm, what's safe

Wizard kit piston exploded at around 48mph cylinder pictured is the new athena.

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Re: Nc50 2 speed max rpm, what's safe

I'll have to dig around for any pics of the trans

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Re: Nc50 2 speed max rpm, what's safe

I question an engine's ability to run with 60psi compression.

Re: Nc50 2 speed max rpm, what's safe

The dome is like a toilet bowl. Its huge. Most marine engines come about 80-110 psi spankin new in case the moped dudes weren't aware. It's a lot less load on the rotating assy and less heat in the head/exh port. Cold start is obviously compromised. Throttle response under 6k is sh*t. Unridable/impossinle to tune without some clutch work but on such a tiny short stroke extreme rpm engine I see no need for insane cyl pressure. It just turns to heat/pumping loss in the rpm range were using these things at.

Re: Nc50 2 speed max rpm, what's safe

> DPC Ryan Wrote:

> -------------------------------------------------------

> I question an engine's ability to run with 60psi compression.

In the Simplex world , motors can run nicely at 60 pounds compression . They are not the best at climbing hills , but , do run 45 to 50 MPH .

Re: Nc50 2 speed max rpm, what's safe

Overpriced Parts /

I want that hit a dog in the ass with those kind of bikes but hell you did really good job !

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