# Assembled crankshaft ???



## kadora (Mar 31, 2019)

Hello  friends
I would like to ask you on your opinion or what do you think about machining crankshaft from parts.
I have tried to build crank for my new 4 cyl. engine by this "method" but unfortunately crank is slightly 
bent so I did something in wrong way.
All parts are hard soldered together then unneeded rods cut off . 
IS POSSIBLE TO MAKE CRANKSHAFT IN THIS WAY ?
Thank you for your comment.
Pictures shows more.


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## kuhncw (Apr 1, 2019)

I feel it is possible to build a crankshaft this way.  I know several builders who have built twin cylinder crankshafts using hard solder and had good results.

I've built single cylinder cranks from pieces like this, but I used Loctite 609 in the joints.  Once the Loctite was cured, I drilled  and reamed the crank throws and journals for tapered dowels.  I did not use hard solder. I've also built up a twin cylinder crank with Loctite and dowels, but I've not run it yet in the engine.  

Can you straighten your crank with a small press.

Chuck


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## kadora (Apr 2, 2019)

Hello Chuck
Thank you for your answer .
I use Loctite quite often but for 4 cyl. crank shaft I do not know ???
I have to learn TAPERED DOWEL technique maybe this is way how to build more complicated crank.
I will probably try to hard solder all parts at the same time in oven not journal by journal with torch.


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## kuhncw (Apr 2, 2019)

Using the oven should be a good way to solder your crank. 

 Please let us know your result.

Chuck


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## minh-thanh (Apr 4, 2019)

Hi !
Have you tried making a crankshaft with a steel bar ??
I asked because I will try it. My crankshaft just fits perfectly with everything when I put it into the crankcase, so I have a spare part of the steel bar and am planning to make the crankshaft for V4


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## kadora (Apr 4, 2019)

I have not  tried to build new crank because now I am working on different project.
Please inform us about machining  your V4 crankshaft + do not forget to take PICTURES.


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## minh-thanh (Apr 4, 2019)

kadora said:


> + do not forget to take PICTURES.


 
I do not promise, but I will try to take pictures  if this time there is a difference in how to do it
I'm still thinking more about how to do it.


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## davidyat (Apr 5, 2019)

This is interesting reading. Can you point me to a reference blog on how to make a crankshaft with tapered dowels? Next, kuhncw, I do have some Loctite 609 with 609 primer also. Have you run your crank in an engine yet? When you're talking about "hard solder" in an oven, what kind of solder is that and what percentage of silver is in the solder and how hot do you run the oven up to? Thanks,
Grasshopper


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## Longboy (Apr 5, 2019)

I make multi piece crankshafts for my engines. They are a pain to get straight in assembly and you have to have patiences. The more inline cylinders, the more time needed.
 This 3 bearing, 2 cyl crankshaft starts as round stock that is thru drilled for the center crank pins to the length of all web segments in the lath. The throw pins are drilled upright in the mill. Laid down in the vise under the mill the set screw holes are all drilled in line in the singular web piece for continuity then returned to the lath after marking for web length, segment sequence, and order direction (front/ back engine bearing plates). Then they are parted off and there is no turning the assembled crank backwards in engine or any web segments installed 180 degs from the other webs.  The .250 in. throw pins are matched for machined flats in the vise the same way for 10-32 set screws then cut to length as needed.. The flats have to be wider than the thread size set screw used. If the taper in the set screws between the cup and the edge of the flat milled across the round stock contacts, it will cock the web segment. If you don't get it right, the cup indentation in the flat will have to be milled out again and that re-mile has to be on the same level. Sometimes, I have to make a couple of bars of throw pins to get it right.  From bearing to bearing, lay the webs in and check rotation and take apart, 640 Loctite on shaft and be quick to put together and crank down the set screws using blue Loctite on them. The center pins on the crankshaft ends the pass though the end plate bearings are knurled and pressed into their webs with some 640. The webs are  placed in the lath after, hand rotated and the shaft can be tap malleted to parallel its web in rotation.  They have to be good as the flywheel is hanging off its' end!
Find my build logs for  better pic by pic explanations.


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## ignator (Apr 6, 2019)

kadora said:


> Hello  friends
> I would like to ask you on your opinion or what do you think about machining crankshaft from parts.
> I have tried to build crank for my new 4 cyl. engine by this "method" but unfortunately crank is slightly
> bent so I did something in wrong way.
> ...


Kadora, I had a similar experience, and tried twice to 'stick' build a crankshaft, with just 2 connecting rods, and 3 mains. I'm curious about how tight the fit was in your assembly? I see grub screws on initial assembly before solder. Did it run true at that point?
My attempt was with press fit, and was too tight causing distortions to the squareness of the shafts to throw arms. It's possible my machining of the bored holes in the crank arms were not as perfect as my attempts to make so.


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## kadora (Apr 6, 2019)

I reamed all holes in throw arms then pushed shafts trough these holes then secured shafts with screws and trough small holes drilled over each joint  I applied silver solder //650 Celsius melting point// then cut off unneeded shaft pieces.
Unfortunately i did not check assembled crankshaft before heating it up //my big mistake//
I am not able to machine crank shaft from bar on my little lathe /not solid enough / so I am forced to find some
another way.
Thank you


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## minh-thanh (Apr 6, 2019)

Hi kadora .
Maybe I will try with this way
https://www.homemodelenginemachinist.com/threads/opposed-4-cylinder-4-stroke.14558/


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## Mechanicboy (Apr 6, 2019)

I used the locktite 648 on all the joints.  Then drilled 2.5 mm hole and mounted the 2.5 mm pins of pianowire + Locktite 648 into the 2.5 mm hole. Never knock the pin into the hole due the shaft will be out of true. It was the Stuart Triple expansion steam engine.


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## kadora (Apr 7, 2019)

Mechanicboy thank you for your crank shaft machining description but for 120 ccm straight  four cylinder it probably 
will not be solid enough .
Minh Thanh Thank you for this  post . This GEOFF-H machining way //squeezing shafts in throw arms //
seems to be solid way + I can use Loctite and D pins.


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## Mechanicboy (Apr 7, 2019)

kadora said:


> Mechanicboy thank you for your crank shaft machining description but for 120 ccm straight  four cylinder it probably
> will not be solid enough .



With Locktite 648 + steel pin is very difficult to dismantle if correct work is done. I tried to dismantle, then i gave up, really strong.. The clearance must be little then Locktite 648 will bind the parts togheter very well.  120 ccm engine with 30 ccm cylinder for each crankpin is not big load.


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## Wizard69 (Apr 8, 2019)

Even if you machine the crank from bar stock some distortion is likely to happen.   Bar stock that is stress free can really help here.    So part of the skill comes in straightening the crank.    Remember the cranks can easily be bent due to their size, you cna do it with a 2x4 if you really wanted too.


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## kadora (Apr 8, 2019)

Mechanic boy I was not able to release loctite glued joint with heavy hammer in spite of this fact crankshaft can be hot
mainly during cutting unneeded parts..
Wizard excuse me I do not understand - what you mean // you can do it with a 2x4 if you really wanted too.//
Thank you


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## Wizard69 (Apr 8, 2019)

kadora said:


> Wizard excuse me I do not understand - what you mean // you can do it with a 2x4 if you really wanted too.//
> Thank you


Bad communications on my part, sorry.

I'm not sure where you are form but a 2x4 is a long stick of lumber commonly used in the USA for studs.   The lumber is relatively strong but soft, thus you can use it bend or spring shafts and such back into straightness.   Basically you find a pivot point that is solidly mounted and then lay your shaft or item to be straightened between two supports.    Use the 2x4 to apply downwards force on the shaft at the place where the bend is (back side).    Push downwards carefully until the desired results are achieved.

Basically you end up with a simple human powered press.


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## Tim1974 (Apr 9, 2019)

Hmm ok it bent ! So straten it not hard


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## kadora (Apr 9, 2019)

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 .


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## Wizard69 (Apr 15, 2019)

kadora said:


> 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.


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## kadora (Apr 16, 2019)

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.


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## kadora (Jun 28, 2019)

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 .


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## Mechanicboy (Jul 1, 2019)

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..


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## kadora (Jul 1, 2019)

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.


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## bluejets (Jul 2, 2019)

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


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## Mechanicboy (Jul 3, 2019)




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## kadora (Jul 4, 2019)

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


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## Neil Lickfold (Jul 4, 2019)

kadora said:


> _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.


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## Mechanicboy (Jul 4, 2019)

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


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## Andy Munns (Jul 4, 2019)

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...)


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## TonyM (Jul 5, 2019)

I thought rocking couple was more a flat four phenomenon.


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## kadora (Jul 5, 2019)

Neil Lickfold said:


> 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.


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## kadora (Jul 5, 2019)

Mechanicboy said:


> 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.


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## minh-thanh (Jul 5, 2019)

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


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## kadora (Jul 5, 2019)

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


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