Homemade crank balancing

no,that is not correct. you will have to weigh the small end and the big end of the rod simultaniously. then use the small end weight in your calculations. you cannot do this with the rod on the crank, it must be disassembled. take all your weights and machine a bob weight, then assemble and true the crank with the bob weight, (not the rod) on your lathe, (you have a lathe, right?) remove weight until the balance point is reached. then you disassemble and reassemble with the rod, true it and run it. take it from someone who has hit a little over 11k with a stock crank.
 
(sorry for necro posting, just alot of confusing jargon, came from Google search) why couldnt you just balance the entire crank assembly (crank, rod, piston) on a flat, level surface (like say two perfectly level levels), and drill until the crank stays in whatever position you set it in? essentially making the whole crank neutrally balanced. Maybe I didnt read the posts clearly enough but not only does it sound like I need equipment I dont have access to, but alot of stuff I didnt quite understand (placing weights in the rod journal??) I suppose what I'm asking is for a translation for noobs.

EDIT: thought about it a bit more and I realized... the piston is heavier the faster it goes, thats why you need to balance for specific RPM's... at 8000 RPM the piston and rod weigh roughly twice as much (I'm not about to go into peak speeds, I just quickly calculated average speed) as normal so that would throw the crank out of balance

EDIT2: So... I suppose I have to ask, seeing as how my noobiness is getting the better of me... how would I balance the crank for an average speed of 50kph (~30mph) on my 66cc? I have a 36T sprocket meaning I'd be running around 6k RPM
 
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Hi, its not done like u ask because thats balancing to 100% reciprocating weight. Singles r balanced to a percentage of total reciprocating weight, usually low 50's for low 2 medium RPM, & higher 50's for higher RPM. U cant actually balance a single, only balance it to a certain RPM range. Cheers
 
Alright... well the crank is already balanced for a 48cc piston right? I plan on shaving off some of the piston skirt to open up the intake port some more, maybe I'll shave it so it matches the weight of the 48cc, anyone happen to know how much the 48cc piston (and probably wrist pin if it's different too) weighs? I think someone mentioned the 66cc piston weighs 55 grams so I imagine the 48 would be around 40 grams
 
Interesting topic. Does it seem like the cranks are out of balance in a consistant location? What I'm getting at is... Can I throw my crankshaft under a drill press and add a couple speed holes near the conn rod area?

I understand that without balancing the thing, you cannot know exactly what to remove and where. But is it possible to make an assumption and make enough gains to be worth while?
 
Probably the only real consistency in Chinagirls is their inconsistency, so I wouldnt put much faith in the cranks having a consistant balance factor. I mean, like, mine came out of the box with a crankcase leak due to an ill placed gasket, which says a lot about quality control. Cheers
 
someone needs to come up with a small harmonic balancer for these making it external and easier for people without a machine shop etc
 
racie35 said:
someone needs to come up with a small harmonic balancer for these making it external and easier for people without a machine shop etc
Click to expand...

I agree with you. But how would you mount it and what side of the engine?

Chris
AKA: BIgBlue
 
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