Crankshaft truing & balance part dux

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biknut

Well-Known Member
Sep 28, 2010
6,631
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Dallas
Last time I tried to true a crankshaft I had good results balancing, but I didn't have a real good way to measure the runout accurately.

I'm in need of a couple more cranks, so I'm having another go at it. This time around I've got better tools, and more experience to help me.

I'm unlizing this small wood lathe as a truing stand. I was able to buy a live center on eBay, that allows me to chuck a crankshaft up in order to get accurate measurements. I just turn the crank by hand, and check the runout with my harbor slave dial indicator.

Last time around, all I did was measure the runout, and keep buying new cranks till I finally got one that wasn't to far off. This time I'm going to try to make the crank true by adjusting it myself. Actually I've already been working on one for 3 days. I've finally got it to less than 0.001 runout

 

maintenancenazi

New Member
Oct 22, 2011
157
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0
Asheville
Excellent work! Truing the crank certainly looks to be a much better option than trying to order one and hoping to find a good one. Who knows, you may be the man we all end up ordering trued cranks from!

Peace, James
 

tooljunkie

Member
Apr 4, 2012
663
5
16
Manitoba,Canada
i plan on chucking it in my lathe to check for runout,do you have any details for the actual truing?
i doubt i have the skills to balance,but truing i think i could manage.
 

biknut

Well-Known Member
Sep 28, 2010
6,631
409
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Dallas
i plan on chucking it in my lathe to check for runout,do you have any details for the actual truing?
So far what I know is when you get one shaft good, it messes up the other shaft. I think I'm going to need 2 dial indicators.
 

tooljunkie

Member
Apr 4, 2012
663
5
16
Manitoba,Canada
i came across some instruction for truing years ago,but its in one of my many repair manuals,i will start searching.
i recall specific places to strike in order to align crank.it was not very important to me at the time so i only skimmed over it.will be getting another dial guage too,as well as making a set of vee blocks and a couple jig blocks for my press.
 
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tooljunkie

Member
Apr 4, 2012
663
5
16
Manitoba,Canada
looks like you got that crank pretty close.should improve performance,no?
i would like to think it helps rpm's,vibrations and lessens bearing and seal wear.
good video,i see a couple other bb videos too.
 

biknut

Well-Known Member
Sep 28, 2010
6,631
409
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Dallas
I'm done with one crank, and working on another now. I can understand why the stock crankshafts aren't better. It takes a lot of time to get them better than 0.006". If the factory trues the crank, just that part alone would cost as much as the whole motor.
 

biknut

Well-Known Member
Sep 28, 2010
6,631
409
83
Dallas
I'm done with one crank, and working on another now. I can understand why the stock crankshafts aren't better. It takes a lot of time to get them better than 0.006". If the factory trues the crank, just that part alone would cost as much as the whole motor.
The ball bearings probably have 0.003- 0.005" play, so the factories probably feel it's not that important to get them better than that.
 

multipaul

New Member
Mar 31, 2012
74
0
0
Germany
Biknut, you've made an excellent work. Respect!

At the moment I have reached 0.0055". I had started with 0.015..". It was a horror. The crankshaft is new. I built it out of a new engine. I want to finish my work with 0.0012", but probably my result will be worse.

Multipaul

PS: C3 means min 11µm and max. 25µm for a 6202 bearing (according to my old SKF catalog). That are maximal 0.001".