Crankshaft conundrum

Tim_B_172

Tim_B_172

New Member
So I was going to replace my crankshaft and I don't know which one to get.

This one from piston bikes is cheaper, but it doesn't look like my crankshaft. I don't see any holes or screws for the counter weights. I wanted to order it from them because they have a few other things that I need.

This one from Bike Berry looks more like my crankshaft, except for those two holes on either side of the center shaft. I have the counter weights off of the old shaft so bolting them on to the new one is fine with me.

I'm replacing it because I had a serious out-of-balance condition. INSANE vibration at high end and whatnot. I found that the cut-out parts of the counter weights were full of casting sand! And also a portion of the center shaft is not concentric. It's hard to explain, but I'll try. Right where the center shaft is pressed into the crank cheek there is a little groove machined around the shaft. That groove is deeper on one side than the other. If it were just the sand, I would use the old crank but it's not.

Also, it might help to know what the engine is. Redbat 66cc, and according to the sticker it was made in 2010. I don't have the sticker any more so I couldn't narrow down when in '10 it was made.

Sorry for the long-@$$ post, I just wanted anyone who reads to have as much info as possible before answering.
 
I had a motor that vibrated badly above 15mph, so I balanced it myself with info I got online and local auto machine shops. Search my thread titles "no more vibrations". Let me know what you think.
 
That sounds great and I think I will give it a try. If I screw up I can always order a new crank while the engine is apart anyway. I love how cheap the parts are for these engines.
 
Sure, and you never know when you're going to get an out of balance motor in the future, so it's a big plus knowing how to make them right.
 
Well, I got it balanced. I had to remove a lot of weight, but it worked as far as I can tell. I'm waiting on a few other parts to arrive before I reassemble the engine. I won't be 100% satisfied until I can run it and see if the vibrations are better or not.
 
That's great. I removed over 100 grams from my motor. Also check the bearings. They come very low quality. Sometimes you can't feel the roughness so I put just a little tension on them in my vise jaws and spin the inner race with my finger. I have several bearing houses locally, so quality bearings and seals are fairly easy to get at a reasonable prices. I learned years ago that a head gasket can be reused by painting several coats of metalic paint (copper, aluminum, gold, silver or brass) on both sides and adding just a couple more foot pounds of torque to the specified number. Good luck and let us know how it runs.
 
As a matter of fact, the parts that I'm waiting for are clutch bearings. One was a little rough, but I'm replacing both with higher quality bearings. I work in an aviation shop, so I have access to an arbor press to install them with.

Also, I discovered a way to check and see if my balancing actually worked. Maybe not the best idea in the world, but I chucked the crankshaft in a drill and spun it with the extra weight still attached. The connecting rod moved like it normally would, up and down and it spun very smooth at whatever the top RPM of my drill is. I'm 90% satisfied now. ;)
 
Well, I got the engine all reassembled yesterday and it runs better and smoother than ever. I still have some vibration, but now it's in the lower RPM range and I don't even notice it when riding, just when sitting still and revving to that RPM. All in all, I'm happy with it. Thanks again msrfan! :)
 
Good job, Tim. Most of the stuff we do is only as good as our workmanship. I glad the formula saved your motor as it did mine. Maybe some others can benifit.
 
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