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February 21st, 2014, 04:35 PM   #31
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Re: Balancing an 80mm 650 crank

the old "fat" cranks of weeds and mine,

no problems with the welded weights about 200 hrs on mine .. weed even more I think.

so if you don't have a spare $800 to spend on Mallory or have fancy carbide drills a little preheat and some stainless weights work very well.





various lightened KTM RFS cranks, GWR DJH and others





























and mine again, not quite as radical but not much work either and no expensive mallory

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February 23rd, 2014, 03:40 PM   #32
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Re: Balancing an 80mm 650 crank

lighter conrod ?



http://flashbackfab.com/how-to-build-a-racer/

lots of old school machining
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February 24th, 2014, 12:17 AM   #33
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Re: Balancing an 80mm 650 crank

I wish I had a lathe. I do have access to one but since the owner is a sub contractor to Íhlins I'm not so sure they'd let me use it!
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February 24th, 2014, 07:37 PM   #34
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Re: Balancing an 80mm 650 crank

lathes are amazing machines, It always spins me out how people where making reasonably accurate lathes and mills in the 1700s by hand, and with those machines they produced better ones... and so it went on until today when you can buy a computer controlled "mill" robot with less than 0.001mm resolution for less than the typical operators yearly salary

drive side pressed in and welded (more on how to weld later)



press the other side on 10mm or so and get both halves parallel by measuring in 3 spots and pressing more as needed







if you need to open it up somewhere use wedges



when its parallel check for twist between centres, mark the high spot on either side







take the crank out hold it by your rod and hit the un-welded (free) flywheel to twist it into the right place

recheck parallel and look for high spots again

when it not twisted your high spots will line up



happy with the twist, press it together. use a feeler gauge to help stop at 0.1mm bigger rod axial play than you want to have at the end. im going for 0.7mm so i set it at 0.8mm here

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February 24th, 2014, 07:46 PM   #35
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welding the pin

the ignition side weld needs to be flush to clear the bearing and the bearing mount in the case

so grind a fillet out



make sure the crank is as true as possible at this point then put 4 tacks in

make sure the crank isn't twisted before you tack it. after tacking you can't correct the twist



preheat to 150C then use the weld shrinkage to keep the crank true as you weld, fill in a bit at a time and check how its going between centres

after the welding starts is is pointless to use force (press or wedges) to true the crank, you have to use the weld shrinkage only.

before checking the crank each time take a hammer and tap the crank around a bit to let it settle

I use a TIG welder with a foot pedal ER7OS2 filler rod and pulsed DC



welds on this one pulled the flywheel up.. sometimes they go down ..need to be aware

so if one side needs to come up (or down depending on its mood) just go over it again, nice big fillet with good penetration .. doesn't look very pretty



I keep a bucket of diesel ready and if I reckon its getting too hot i drop it in there for a while, you want to minimize the blueing if possible

ground down to clear the bearing and case



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February 25th, 2014, 07:52 AM   #36
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Re: Balancing an 80mm 650 crank

THANKS! I'm learning a ton of stuff here!
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February 25th, 2014, 04:03 PM   #37
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Re: Balancing an 80mm 650 crank

me too

everytime i do this something new comes up, this crank wanted to open up with the weld shrinkage usually they close up.

maybe something to do with the different type of timing marks i drew.. opposite behavior of the rockets
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February 25th, 2014, 05:59 PM   #38
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Re: Balancing an 80mm 650 crank

Originally Posted by bushmechanic
maybe something to do with the different type of timing marks i drew.. opposite behavior of the rockets
There's ya problem right there.
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February 26th, 2014, 03:40 PM   #39
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Re: Balancing an 80mm 650 crank

So one thing that I've been mulling over - what if adjustment is needed later? Or if the conrod needs replacement?

Re. adjustment/change afterwards: Someone posted a picture of a cracked weld on a crank here - do you just grind out the weld and start over?

And if you need a new conrod? The same, or could the conrod be sawed or ground off without damaging the crankshaft? and then replaced with a conrod with a bolted big end? (correct term?) Or are the welds ground out like when you're preparing for the weld job on the ignition side?
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February 26th, 2014, 04:38 PM   #40
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Re: Balancing an 80mm 650 crank

Hi tourist

yes you are on the right track

I grind the welds out of the ignition side then press the flyweel inwards so the rod axial play is zero

the end of the pin now protrudes a bit more so I grind the sharp edge off and then press it out as normal

same the other side if the pin needs replacing

or yes if the rod and pin are toast just cut the pin through the rod, much easier

my other crank in the 700 is on its 3rd pin

Cheers
Bushie
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