Assembled crankshaft ???

[Wizard69]

Wizard thank you for 2x4 explanation , here in Europe we use mainly oak wood for such purposes.
To straight crankshaft properly is ART I have tried to do it without success .

Most of my use for wood has been to straighten lead screws at work. It really doens't take a lot of force and the wood prevents damage. It is real easy to over do it in a mechanical or hydraulic press.

The biggest problem with a crank is figuring out where the distortion is coming from. Once that is determined then you need to find a way to get a purchase on the parts to adjust them.

 

[kadora]

Thank you Wizard
You are completely right main problem is - as you said - figuring out where the distortion is coming from.
Maybe building a crankshaft fixture with gauges to find the points of distortion would help.

 

[kadora]

I have built "assembled " crank shaft again .
This is not as easy way to machine crank shaft as it looks on first sight .
First is needed to drill precise holes to the throw arms , not easy to solder all parts together
and finally machining holder for shaft straightening plus to cast lead counter weight to the throw arms.
Ten days of work but I am happy with crank now .

 

[Mechanicboy]

Eeehh?? Why not crankpin 1 and 4 would be up and 2 and 3 would be down then the firing order will be 1-3-4-2 or 1-2-4-3. How will it be the firing order with crankpin 1 and 3 up and 2 and 4 down??? And the engine is not balanced so well with this crankshaft..

 

[kadora]

I agree engine is not balanced so well so I have two lead counterweight opposite each crank pin.
Important is two crank pin up two crank pin down.

 

[bluejets]

There are also other "balance" issues to consider.
See Wiki for more details.
https://en.wikipedia.org/wiki/Engine_balance#Rocking

 

[Mechanicboy]

 

[kadora]

Why is first crank balanced and second one rocking ?
I think there are different torsional stresses - in small engines negligible .

 

[Neil Lickfold]

Why is first crank balanced and second one rocking ?
I think there are different torsional stresses - in small engines negligible .

This is because the centre of mass is not in the centre of the crankshaft as it goes up and down. The second as the arrows show is turning to the right as TDC has a higher inertia than BDC. So on the next 1/2 rev the RH side will be TDC and encouraging a counter clockwise moment. It is when you have the con rods and pistons in place that it will show more.

 

[Mechanicboy]

Probably best in the platevibrator for asphalt when the engine is rocking and out of balance..

 

[Andy Munns]

I think it's called a 'rocking couple' in relation to the out of balance unbalanced forces. Vertical twin motorcycle engines avoid this by running both pistons up and down together - gains even firing pulse and avoids rocking couple. Some twins (Kelvin J2 and K2 diesels) kept the rocking couple but have uneven firing pulses (sound like a Harley...)

 

[TonyM]

I thought rocking couple was more a flat four phenomenon.

 

[kadora]

This is because the centre of mass is not in the centre of the crankshaft as it goes up and down.

Neil I think that centre of mass is the same on both cranks. Difference between these two cranks is in firing order.
"Balanced" crank has less torsional stress due to firing order 1-3-4-2.
In my case "rocking crank" has more torsional stress but I can use simplified firing order /wasted spark/
1,3-2,4.
Anyway thank you guys for your effort to help me.

 

[kadora]

Probably best in the platevibrator for asphalt when the engine is rocking and out of balance..

I hope it will not be so terrible unbalanced.

 

[minh-thanh]

Hi kadora !
I don't understand the part in the picture, can you explain why it's like that?

And do you have pictures or sketches .. of the engine ?? I'm curious about it

 

[kadora]

Hello Minh
The part is engine holder .Pic .says more.