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.
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