Thread: Crank Truing Basics 101
09-08-2007, 07:46 PM #1
Crank Truing Basics 101
To check the truing only takes a set of v blocks and a dial indicator. You might be surprised to see how much run-out your high dollar crank job returns with.
Or how much run-out on a brand new Yamaha crank, out of the crate.
09-08-2007, 07:51 PM #2
The following will only make sense if you watch the video.
To clarify in my video when I say 'pop it with a hammer and chisel'
...I don't mean start to hammer on the bearings or rods, nope.
Depending on which way the dial indicator goes, either – or + will determine if you need to open the web or close it to decrease run-out . When spinning the crank and watching the dial indicator you can see the hi and low points then it is obvious if the web needs to be closed or opened ….slightly.
To open the web Get a chisel that is bigger than the space between the crank webs. Grind the chisel so it forms a slight wedge shape on its sides and just fits in between the crank webs. This will let you open the webs (slightly) to true the crank.
Place the chisel between the webs; it should not go way down between the webs, just sit right at the top of the webs. Now pop it lightly with the hammer, now re-check the crank run-out on the dial indicator.
To close the web or if you went too far opening it, squeeze the webs with a vise grip and then tap the outer web when the vise grip is applying pressure.
Going back and forth between these 2 procedures should allow you to get the run out down to under the .006" Yamaha run-out limits... easy
If you want to be anal you can get it to <.001" or under...just takes a lot of time going back and forth... unless you get lucky and get it on the first pop.
After you weld it you must recheck the run-out since the heat from welding will change it slightly.
You can and should re-adjust the run-out AFTER welding. It is a little bit harder to move the webs, but no problem at all. Only run two, 1/2" beads of stainless filler rod on each pin 180 degrees apart if possible, use a Tig welder.
Just remember to be gentle, you don't need to use a 10lb sledge hammer, we are just moving things thousands of an inch it does not take much, go slow and re check the run-out after each adjustment.
After you’re done, be careful with your crank. Do not toss it around or bang it around on the bench.
This procedure was taught to me by one of the top 2-stroke crank shops. I simplified it a little.
Their shop does build some sweet atv stroker cranks and have been doing 2-stroke crank rebuilds/truing for lots of dealers for years and years. They also make some nice 2-stroke atv/pwc heads.
I have seen trued and welded cranks come shipped from reputable tuners and have the run-out lots more than I like it to be.
All it takes is for the shipper to toss around or drop the crank. Even if it is packaged well, rough handling a crank can put it out of true.
09-08-2007, 10:43 PM #3
- Join Date
- Aug 2006
My brand new Hot Rods crank checked out better than speced it was almost perfect!
09-09-2007, 08:40 AM #4
Crank Welding 101
Very good informative thread allcool thanks for sharing.
You make a very good point about differentiating between phasing & trueing. It defines it well.
*Some people do confuse truing as phasing.
When I had my second crank welded back in 2003, I had talked to 3 crank shops for information to dig on. They were all so nice to supply me with pics, email information and even talk on the phone to discuss the process.
If I may add, here is a piece of information emailed to me from one of the crank companies. >
Crank welding 101
I talked to 3 crankservice shops.
All use Stainless 308L. some use Chrome-moly if the proffessional racers ask for it, more expensive, but just as equal to 308L.
The letter L in 308L refers to the control of carbon concentration to a specified lower level... while still complying with the chemistry of 308 stainless.Were there an H instead,it would mean that the electrode has a higher carbon level, possibly not consistent with the chemistry of the parent 308 class.
308L is Low carbon content
308H is High carbon content
The TIG process is the best process used for this application. It ensures the best bind of the two metals with minimal heat intrusion. the gas atmosphere TIG provides is the best for crank welding application becaus it ensures a a clean contaminant free environment for the welding of the two metals to adhere to each other.
* My crank was welded by a master welder work with at the refinery. Excellent job. Impeccable work.
09-09-2007, 09:51 AM #5
just a little about tig welding
( tungsten inert gas )tig welding is the best weld to use on your crank . it dose have a high heat intrusion because of the high penetration . get a hood and watch a code welder , the tungsten actualy looks like a sewing needle as it breaks the metal down . the argon shields the weld from oxigen and cools the tungston .( pinch the hose while some one is welding, it will arch like a 5P+ rod ) tig is the best weld quality it's a slow weld .
stick welding medium penetration . looks like a puddle of metal you don't spend a lot of time in one spot so there is less penetration . open air weld , so it's eazy to contaminate .
mig ( metal inert gas ) low penetration serface weld , very fast . most of the production you buy are put together with a mig . mig welds are pron to have cold fusion , this weld will look good , it just wont have any penetration . i can't count the times that i have cut a mig weld apart and found over an inch of wire pushed through .
most of us own reese hitchs . just for kicks cut you hitch apart at the weld this is a good example of a mig weld that will have cold fusion and low penetration .
hope this info helps out ,
no more cry baby welders
09-09-2007, 01:34 PM #6
hmmmm...I have some 308 ,309 and some er80-s which is what I use on chrome molly(4130n)..I think ill use the 308L ....are these cranks cast steel, cast iron, or forged steel if they are cast iron I have a specil high nickel rod made just for cast iron ( very expensive)...Im going to make v-blocks with a place for a magnetic base dial indicator to check this new crank before and after I weld it......It will make a good anchor for my malibu if I screw it up...lol
09-12-2007, 09:51 AM #7
Allcool Great informative post!!! I made this one a sticky.
09-22-2007, 02:29 PM #8
You guys that don't weld but can use a pair of v blocks and dial indicator try this....
Next trued and welded crank any of you guys get from a shop, ask,
"how many thousands run-out did you true it too"...
and then watch their facial expression when they reply.
Then check it yourself on the v blocks. This could give you a good indication of exactly how good the shop is you are dealing with.
09-25-2007, 06:20 AM #9
I did it..followed the allcool video.... motor runs real smooth. does not shake as much as it did stock.....the metal in these yamaha cranks welds very nice...seems to be a very pure metal. dosnt weld like regular cast iron.
11-28-2007, 05:36 PM #10
Just a ? I found 308L wire for a mig, can this be used in lu of rod ??
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