What is the BEST/STRONGEST crankshaft FOR 139QMB? By jjoshua20213 (Read 1,905 times)

[jjoshua20213]

So I finally took the time to figured out how to change the crank....

I found that a 50mm piston can run the stock head(higher compression) at high rpm for extended periods of time(8k-10k) without blowing or severely wearing out rings when broken in properly and switching to 15w50 Mobil 1 full synthetic and maintaining oil quality.

With that being said the connecting rod bearing on the stock cranks simply won't last past 6 months (To be expected)

Never had a problem with the crank bearings just the connecting rod bearing.

What is the best most durable crank without having to further modify anything?

Willing to spend a little cash since I will never have to change it again.

Performance is my aim, but durability is my goal.

Also had anyone tried out these performance fans i've been seeing around?

[Alleyoop]

Cranks made in Twain are your best shots:

www.scooterdynasty.com/crankshaftnarakuracingfor50cc4-stroke139qmbscooters.aspx

[jjoshua20213]

Jul 25, 2015 14:50:02 GMT -6 Alleyoop said:

Cranks made in Twain are your best shots:

www.scooterdynasty.com/crankshaftnarakuracingfor50cc4-stroke139qmbscooters.aspx

Thank you. Do you know about stroker cranks. Is it worth it or should I just go with a sturdy stock?

[Alleyoop]

Stroker Cranks give you a little more displacement and more low end torque and power to get the weight moving but nothing on the top end. A stroker will pull the weight easier thereby getting you up to speed a little quicker.

A 2+2 Stroker will add approx 5 more ccs to the motor so being a 49.? it will be a 55cc motor.
Alleyoop

[czmdiver]

Jul 25, 2015 14:31:16 GMT -6 jjoshua20213 said:

So I finally took the time to figured out how to change the crank....

I found that a 50mm piston can run the stock head(higher compression) at high rpm for extended periods of time(8k-10k) without blowing or severely wearing out rings when broken in properly and switching to 15w50 Mobil 1 full synthetic and maintaining oil quality.

With that being said the connecting rod bearing on the stock cranks simply won't last past 6 months (To be expected)

Never had a problem with the crank bearings just the connecting rod bearing.

What is the best most durable crank without having to further modify anything?

Willing to spend a little cash since I will never have to change it again.

Performance is my aim, but durability is my goal.

Also had anyone tried out these performance fans i've been seeing around?

If you truly want something better buy the Taiwan Crank and send to Millennium Tech or Falicon.
They will check for True to .001, and Better yet Weld that Puppy's Pin.
Either one can make whatever Crank you have Better, for a cost$$$ tho.
If somebody haven pin bearing problems that bad they have  something else going on.
I can run some Stupid Cylinder Pressures with smaller bearings.
Your not going to break that Piston Casting and a Forging is only a Novelty in something that small.
We get into Cast Piston Shatter in some HD and Auto above certain RPM's, youl shatter the skirt off it
No so in that lil guy.

[usmcdoc]

Naraku!