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Lighter Crank

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I did a little research on Wiseco's website regarding using a 92-01 crank(lighter) in my 03 as I have heard a few suggest.The crank bearings are the same and the stroke is also but center to center of the rod is 4.7mm shorter on the older part.Also the lower bore diameter of the rod is 1mm smaller and lower width is 3.25mm narrower.It seems like to much work so I'm wondering if the 05 and up crank is lighter and will it fit? Anyone know? Thanks.

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I'd like it to rev quicker and by that maybe get through the laggardly low end quicker.But for me it'd also add to the fun factor

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Sounds like you should start with jetting, it's a lot easier and cheaper than changing a crank. Plus, it might have actual benefits.

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Jetting is not an issue.I have a JD kit installed.Plug is a nice tan brown.She runs as clean as I can imagine.I've had PC redo the squish and its alot more consistent temp and altitude wise.

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A JD jet kit doesn't mean you have the right jetting for "your" bike. JD's kits are a safe but better alternative to stock. You can still dial it in from there. You will be supprised at the throttle respone you get whwn you hit it right. The tan color of a plug has more to do with the temperature range of the spark plug than the jetting. You need to jet with a fresh plug and read the mixture band at the base of the insulator. Wider is richer.

This bike is still a hair rich, but safe for all conditions:

DSC_00020001.jpg

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Well I can also hear and feel when my bike is lean and I realize your trying to help but I'm asking about the crank.It's not like I've been riding this bike for years with blubbery rich jetting.

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A JD jet kit doesn't mean you have the right jetting for "your" bike. JD's kits are a safe but better alternative to stock. You can still dial it in from there. You will be supprised at the throttle respone you get whwn you hit it right. The tan color of a plug has more to do with the temperature range of the spark plug than the jetting. You need to jet with a fresh plug and read the mixture band at the base of the insulator. Wider is richer.

This bike is still a hair rich, but safe for all conditions:

DSC_00020001.jpg

'The ixture band at the base of the plug' - I've not heard of this before but i'm intrigued....what am I looking at?

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The black carbron ring at the base of the insulator. Narrow is lean, wide is rich. Jetting has to be done on a new plug. This only shows WOT mixture. With a new plug, warm the bike up, run it WOT through 5th gear, shut it down, and pull the plug.

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I think I would just add a couple teeth on the rear sprocket before I changed out the crank.

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I have several sprockets(48,49,50).Eventually the crank will need to be replaced so I would like to know my options.

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I have several sprockets(48,49,50).Eventually the crank will need to be replaced so I would like to know my options.

Have you thought about a light flywheel, we use to shave off some weight from the pit bike flywheels, worked fine for them.

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If you've seen the flywheel on an 03 CR 250, there isn't much there.

I really hate to give any suggestions on this because I really think it's a waste of time, but... When talking rotational inertia you need to talk a combination of two things, the mass and the distance of the mass from the centerline of rotation. You can reduce mass all you want but if you do it towards the centerline of the crank it will make no difference whatsoever. The easiest and greatest reduction in crankshaft rotational inertia would be to bore out the crank pin. This will put the crank out of balance, you may be able to live with this. If the extra vibration is an issue, you would then have to remove the sheet metal covers on the crank and have the flywheel weights drilled in order to bring the crank back into balance which would also make the crank lighter. Pendulum cutting the counterweights and adding heavy metal such as mallory into the counterweights is another way to further lighten cranks. But remember, you need to keep enough weight to properly balance out the reciprocating mass of the engine and provide enough inertia to drive the crank through the non-powered portions of the cycle. This all may work, I don't know, you are the first person I have ever heard complain about the sluggish response of a properly tuned 2-stroke.

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Check with wiseco but I think H101 is the lite crank they make for these bike I do believe its a bolt in. I have never done it yet but heard about it.

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If you've seen the flywheel on an 03 CR 250, there isn't much there.

I really hate to give any suggestions on this because I really think it's a waste of time, but... When talking rotational inertia you need to talk a combination of two things, the mass and the distance of the mass from the centerline of rotation. You can reduce mass all you want but if you do it towards the centerline of the crank it will make no difference whatsoever. The easiest and greatest reduction in crankshaft rotational inertia would be to bore out the crank pin. This will put the crank out of balance, you may be able to live with this. If the extra vibration is an issue, you would then have to remove the sheet metal covers on the crank and have the flywheel weights drilled in order to bring the crank back into balance which would also make the crank lighter. Pendulum cutting the counterweights and adding heavy metal such as mallory into the counterweights is another way to further lighten cranks. But remember, you need to keep enough weight to properly balance out the reciprocating mass of the engine and provide enough inertia to drive the crank through the non-powered portions of the cycle. This all may work, I don't know, you are the first person I have ever heard complain about the sluggish response of a properly tuned 2-stroke.

I'd rather not shave the flywheel.I've heard several mention this mod on this forum,skipn8r,faded and kuritaro9 if I remember right,so it's not like I'm making this up out of my head.Regarding the lack of bottom end (on case reed motors)it seems to be the most talked about topic on this forum.

4stroker,the H101 is the crank rick from RPM's recommended to give the case reed a snappier delivery(Dirtrider mag,older issue) but I noticed the different dimensions of the rod on wiseco's site.Honda went to a heavier crank in 02 amongst all the other changes. Thanks all for your interest.

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Most people add weight to the flywheel to improve the bottom end of their CR 250's.

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Yes but all that does is increase tractability,it doesn't add low end.The lighter crank won't increase low end either but it will rev quicker.I don't know if you've ridden a case-reed CR but I've ridden an 87cr250 a while back and I'd say it even has quite a bit better lowend than my 03.

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How about an 02 cylinder and pipe, I love the power from the 02. Those things will pop the front wheel in any gear at any speed. Anyways, changing the crank wont change the power output of the engine. It may affect the power delivery but if you really want more low end, have the motor ported to produce more low en.

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