Testing Crank Balance

[Deleted member 12676]

If you both ar referring to the crank wheels having additional weight due to manufacturing irregularities then you are right, unless the location of the additional weight is near the crank pin or on the opposite side.
It best to have it pressed apart and checked on a lathe that it is perfectly round.
But really that is nit picking.
I'm sure my old crank was as out of round as any of them but by drilling two 9mm holes it became almost as good as any two stroke I've ever ridden.
Worry about the big stuff before worrying about the little stuff.

 

[HeadSmess]

I'll try that, after I finish my cigarette. Does it have to be a spoke or would a coat hanger wire work? ROTFL!

shhhh, dont tell him you smoke or he really WILL have a freak out at you!


does it have to be the spoke off of a 26" wheel or can i use one from a 27" cus i got a whole stack lying around?

how do i get the spoke out from behind the freewheel, dangnammit?

answers! i DEMAND EFFING ANSWERS!

 

[FurryOnTheInside]

[QUOTE
If my crank is out of true in another plane this could be an impossible task though as I don't think I can get it trued. I wonder if it can be partially remedied by another hole...

If the crank is out of true then putting more holes in it is not fixing the problem. If you lived near me I would check and true it for nothing.[/QUOTE]
Out of balance or eccentric with a heavy side that isn't in line with or opposite the big end bearing, is what I meant.. Now I'm not sure what out if true means, wobbly like a bent wheel rim? Thanks for the kind offer, if I lived near you I would take up that offer!

 

[Deleted member 12676]

check out my video about crank balance:

 

[Deleted member 12676]

I just used a laser light to substitute for the spoke and the direction of movement was the same although very small. So I think the spoke is an excellent way to demonstrate the direction of engine movement/vibration because it amplifies the movement.

 

[Wolfshoes]

Perhaps stick a small curved mirror, like the ones used as a auto rear view mirror add on, to the side of the motor, point the lazer at the mirror and view the reflection.

 

[Deleted member 12676]

that would work but you'd have to move the mirror around till its plane of amplification is at the same axis as the laser movement.

It's so cheap and easy to use a bicycle spoke.
I'm really disappointed that no one has done the test yet.

 

[FurryOnTheInside]

If my engine was rebuilt and running yet I would as I'm interested in any and all comparative tests.
To make it a standardised test so that we can compare bikes it needs something we all have, and we don't all have a bmx spoke, and those vary in length for flange width and spoke lacing pattern anyway..
So I wonder if the (measured and possibly cut) inside part of a Biro pen will work? It is shorter but has a bit more flex, still some mass to give it enertia so it should wiggle I think... What do you think?

 

[Wolfshoes]

In doing the spoke test to a bike, I did run into what is believed to be harmonic frame vibration at throttle midrange. The engine may be in better than average balance out of luck. I'll run the test again.

 

[FurryOnTheInside]

We're you sitting on the bike or just holding the handlebar? brakes on fully/not? I'm sure the mass added to the bike matters to the test and to the experience..