I may be getting a lathe=Tru'd cranks for sale
- Thread starter mrfubs
- Start date
mapbike
Well-Known Member
Balanced and trued and proven to offer minimal vibes at cruise speeds, I would be interested, I ask someone else about this same thing and was told they wouldn't do it because every crank was shimmed a bit different in each engine, that doesn't concern me since I'd be willing to bet that not a one of these engines coming out of china has any attention to detail concerning making sure the cranks are shimmed precisely, not meaning to offend anyone here but the person I ask sells his engines for $600+ and it seems to me that the main thing done in the lowers is just a trued and balanced crank along with a little cleaning up and revamping the tranfer port area in the cases which many of us can do ourselves.
You offer a crank that is true and is balanced for upper cruise rpm's and you will probably have several takers including myself.
Hope I don't start an unintended flaming thread with this post, and I'm not disrespecting anyone, just making this staement based on my own opinion and the fact that most will never shell out $600+ for a china girl but some of us who have the tools and the ability would enjoy being able to build up our own better balanced engines and maybe have an option to replace the crank in an old beater that would be a good one if it had a better crank, I have three engines right now that would be really sweet if they had a well balanced crank at 30+mph cruise speeds and it would be great to have the option available.
Map
You offer a crank that is true and is balanced for upper cruise rpm's and you will probably have several takers including myself.
Hope I don't start an unintended flaming thread with this post, and I'm not disrespecting anyone, just making this staement based on my own opinion and the fact that most will never shell out $600+ for a china girl but some of us who have the tools and the ability would enjoy being able to build up our own better balanced engines and maybe have an option to replace the crank in an old beater that would be a good one if it had a better crank, I have three engines right now that would be really sweet if they had a well balanced crank at 30+mph cruise speeds and it would be great to have the option available.
Map
maniac57
Old, Fat, and still faster than you
I would be interested IF it is actually BALANCED. Simply truing on a lathe, while helpful on some of the poorer cranks, will not really do much unless the crank is real bad to begin with.
Truly balancing cranks is a very technical skill requiring experience and precision and is very different from simply removing excess runout on a lathe.
Truly balancing cranks is a very technical skill requiring experience and precision and is very different from simply removing excess runout on a lathe.
mapbike
Well-Known Member
problem is none are balanced good.
Fred shows how he trues the cranks in this vid, no actual balancing being done, but as you can see, just trueing a crank like this can make a huge difference in the way the engine will run at higher rpms especially, just makes sense that this process alone will make that engine run a lot smoother, and if the piston is lightened a few grams it should make the overall balance even better.
http://youtu.be/h0mVFMgFqqE
mapbike
Well-Known Member
I have a lathe and can true my own cranks but i have never dabbled into the truly balancing of the cranks like Fred does, he drills additional holes through the cranks and then make plugs to plug the holes so that crankcase pressure is restored, a truly balanced crank and not just trued is worth $100 but I can true them myself for just the trouble of taking the engine down and reassembly of it.
Map
Map
Dino at 'Screaming Roo'.
Has put a lot of time and money into building a balanced crank.
After much frustration he took one of the better balanced cranks he could find and started from there with balance factor, changing it slightly one way and the other till he found the sweet spot, It sounds as though it took quite a bit of messing about swapping cranks in a test motor before he was happy.
This would be the only way I can see to balance a crank, through experimentation then it would be easiest to reproduce results if you did a run of cranks using the 'same' crank but even then I can imagine that even a box of cranks from the same manufacturer are going to end up with allsorts of variables.
It sounds to me as an ambitious project to offer balanced cranks for sale.
And the time involved in getting them right would likely be prohibitive on a commercial basis unless you had a guaranteed market and volume of turn over.
I'm yet to try one of Dino's 'Roo Print' motors, but very curious.
http://screamingroo.com/online-store/category/engines/
Has put a lot of time and money into building a balanced crank.
After much frustration he took one of the better balanced cranks he could find and started from there with balance factor, changing it slightly one way and the other till he found the sweet spot, It sounds as though it took quite a bit of messing about swapping cranks in a test motor before he was happy.
This would be the only way I can see to balance a crank, through experimentation then it would be easiest to reproduce results if you did a run of cranks using the 'same' crank but even then I can imagine that even a box of cranks from the same manufacturer are going to end up with allsorts of variables.
It sounds to me as an ambitious project to offer balanced cranks for sale.
And the time involved in getting them right would likely be prohibitive on a commercial basis unless you had a guaranteed market and volume of turn over.
I'm yet to try one of Dino's 'Roo Print' motors, but very curious.
http://screamingroo.com/online-store/category/engines/
mapbike
Well-Known Member
Actual trued and balanced cranks, this pic is from a secret club so Im not sure if the link will work or not but if it does you will see what and actual balanced crank looks like, holes are filled to maintain good crankcase pressure which is important for good performance with a 2 stroke engine.
https://m.facebook.com/home.php#!/p...d=1335669155&set=gm.745294465504589&source=48
Map
https://m.facebook.com/home.php#!/p...d=1335669155&set=gm.745294465504589&source=48
Map
maniac57
Old, Fat, and still faster than you
Most balanced cranks fill the holes with Mallory metal, which is substantially heavier than steel (and more expensive!) to compensate for the piston and rod weight. Simply drilling holes does very little. Think about how heavy that piston is at 7k rpm stopping and starting 20 times a second or whatever...
Computerized spin balancing machines don't grow on trees either.
See why balanced cranks are expensive and hard to find?
Computerized spin balancing machines don't grow on trees either.
See why balanced cranks are expensive and hard to find?
mapbike
Well-Known Member
I never offered any threats sub66, and I dont doubt your honesty, also I have nothing personal against you, I have no idea what you mean by "better than average answers" and im not sure anyone here is looking to be set free.....lol!
If you choose not to believe something that is your right, but that doesn't change the facts of the matter and the fact is that Fred has figured out a good balance for the china girl cranks and has been doing it for a while now in his machine shop, he isn't on here much and does most of his commenting on his private/secret club on facebook which I am a approved member of, im not hating on anyone here, and Im not trying to fight a battle for someone, but the truth is that Fred has done his do diligence and he does offer a truly well balance crankshaft in his performance built engines and is actually working on some orher kewl projects including stroker cranks using moped engine con rods and such, I personally have never shelled out $700-900 for a china girl engine, but others who have his engines will qickly testify to them running very smooth and strong.
No offense intended, and I suppose the mods took down my previous post, normally someone would have contacted me first if that was the case but oh well, I trust their judgement and if they thought it was out of line then so be it, I will comply.
Map
