How hard is it to change the crank rod
- Thread starter mac2mac
- Start date
Blaner
Your Friendly South African Ambassador
yes you need to have the run out to spec you see in the manual, also the two lobes need to be aligned, if they are not, it will be out of balance and mess everything up. for that i guess you would need a set of V blocks and a dial gauge
I need a little more DIY info . What other tools might I need. Is there any kind of way to align them both up before I put the pin in..I really want to try it myself just in case I need to do the one on a blaster ..Right now I'm trying it out on a kx 125
The reason crankshaft rebuilding is difficult is because it has to be aligned and pressed at the same time.
A 12 ton press may or may not be enough to get the tolerances necessary. As the crank nears it's complete size and shape, the pressing action becomes exponentially harder (takes more force).
The crank needs to be tested on a set of V blocks to gauge runout against a runout tester (a specific type of dial caliper). The tolerances for runout are really small.
Take some really good pictures of your experiences, good or bad. I'd be interested in how well this works out for you.
A 12 ton press may or may not be enough to get the tolerances necessary. As the crank nears it's complete size and shape, the pressing action becomes exponentially harder (takes more force).
The crank needs to be tested on a set of V blocks to gauge runout against a runout tester (a specific type of dial caliper). The tolerances for runout are really small.
Take some really good pictures of your experiences, good or bad. I'd be interested in how well this works out for you.
Yea I just found this video , I do not have a jig like that one. But I'm going to try and make one before I take it apart ... YouTube - koconnor07's Channel
That jig is a custom manufactured unit to exacting tolerances which would probably cost 5 times more to make (or have made) than it would cost to simple purchase a new crankshaft. It would only make sense to make a jig like that if you are going to be doing a lot of crankshaft rebuilding of a particular type of crankshaft.
I know a guy a work who used to race YZ250's (flat track I believe) and he did all his own machine work. He pressed cranks himself using a set of v blocks and a small press (in all probability smaller than what you've got) but I'm not sure what sort of tolerances he was able to achieve. The fact he was pulling his engines apart every 5 hours or so anyway probably means he wasn't hitting the tolerances all that close but it didn't matter as much anyway because they were coming out a race or two from now anyway....
I know a guy a work who used to race YZ250's (flat track I believe) and he did all his own machine work. He pressed cranks himself using a set of v blocks and a small press (in all probability smaller than what you've got) but I'm not sure what sort of tolerances he was able to achieve. The fact he was pulling his engines apart every 5 hours or so anyway probably means he wasn't hitting the tolerances all that close but it didn't matter as much anyway because they were coming out a race or two from now anyway....
We modified the jig to accept bushings so we can do anything in it now. We make the bushings as we need them. I'm up to 6 different sets and they seem like they cover almost everything. I'm sure we'll be making more.
Good idea. I was wondering why it was specific to a blaster crank...
Even if you have it to fit every crankshaft in the world, it only makes sense to have a jig like that for someone in your situation. You will profit from having a jig that will accurately press crankshafts quickly. Someone at their house will spend like 50 hours building a jig (which will probably not have the accuracy your jig has) which they might use a few times.... not really worth that sort of work.
To the original poster; document your work well. I'm interested to see how well it turns out. It can be done at home with a LOT of patience
Even if you have it to fit every crankshaft in the world, it only makes sense to have a jig like that for someone in your situation. You will profit from having a jig that will accurately press crankshafts quickly. Someone at their house will spend like 50 hours building a jig (which will probably not have the accuracy your jig has) which they might use a few times.... not really worth that sort of work.
To the original poster; document your work well. I'm interested to see how well it turns out. It can be done at home with a LOT of patience
My local guy told me he always measures the exact space between the crank throws before pressing them apart. That way he knows how far to press them back together. He uses a vernier caliper. Afterwards it needs to be checked for true (v-blocks and dial indicator).
a harbor freight press is not going to cut it. them things flex and creak more then my old mans knees. it really needs to be done with the right equipment. as you can see in kens video he is not pumping away on his press its all hydrological and done in a smooth motion. the man has about 10+ grand in tooling to do the job RIGHT. his labor price is money well spent.
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