Changed Crank gy6 125, Connecting rod too big for wrist pin.

Kevin265 · Post by **Kevin265** » Sat Mar 05, 2016 5:31 am

I screwed up the splines for the Variator on my Crankshaft. So, I ordered a new crank, split the cases installed new crank and got down to installing the piston and found out the connecting rod on the new crank is too big for my pistons wrist pin! What are my options? Can I change the rod? Any advice would be very much appreciated.

sc00ter · Post by **sc00ter** » Sat Mar 05, 2016 5:06 pm

If the new crank end is to large for the piston pin, meaning it and the bearing flop around, then you need a step down bearing. Step down bearings are thicker to take up the slack. We use them on 2t motors. Example: The crank end is a 12mm but the piston pin is a 10mm-the step down bearing solves this problem. Usually we just order the correct piston/pin assembly but the step down solution works just fine. Such a thing may be tricky to find for a Buddy 125 motor but I know its out there. SPmoto has a good selection. They have the Stage 6 brand needle bearing 12 to 10mm 10x17x13 in stock (maybe other sizes also), just measure twice and order once as I dont know the 125cc sizes myself, only 50cc stuff.

az_slynch · Post by **az_slynch** » Sat Mar 05, 2016 5:24 pm

I believe that the Buddy 125s have a 13mm wrist pin. Discovered that when I was looking for big bore components for Elite 80s ( which only have 12mm wrist pins). The Buddy 150s have a 15mm wrist pin; maybe you wound up with one of those cranks?

In thinking about this, I remembered a related thread for reference:Buddy 150/GY6 parts interchangeability?

lovemysan · Post by **lovemysan** » Sun Mar 06, 2016 2:54 am

Ive never heard of anyone installing a 150 crank into a 125 because the 150 crank is shorter stroke. To make the 150 crank work you need a 150 camshaft because it has a different number of teeth. Any gy6 camshaft will work in a 150. An a12 is a good non stock camshaft. You may have to install high performance valve springs. You will have to find a 52mm piston with a 15mm pin or have a wrist pin sleeve adaptor milled for your stock piston. A much easier solution is to get a stock 150cc cylinder kit(57mm). Or a 59,60, or 61 mm big bore kit. Some 61mm kits require the cases be milled. I believe ncy and a few others make a no boring need 61mm kit. Lastly if putting a larger cylinder in I would get the matching head. The 125 head is restrictive but will give high compression. I've run 125 with ported stock head, 161cc standard 150cc head and 161cc ported 150cc head. The bigger the better. Get a head to match the bore. You've definitely got a can of worms there.

Kevin265 · Post by **Kevin265** » Sun Mar 06, 2016 4:09 am

Thanks guys, thats what I was afraid of. I purchased the crank on ebay, the ad said 125 and 150. I assumed they were interchangeable. You know what they say about assuming....... I will send it back and get the 125 crank. I will say the job of removing the crank was a lot easier than I thought it would be! Once again thanks for the info.

sc00ter · Post by **sc00ter** » Sun Mar 06, 2016 3:51 pm

How much cheaper was the Flea Bay crank then ordering it from a know Genuine product selling vendor? Also, will the Flea vendor take the crank back after it was installed? Keep a eye on the main bearings condition. If you even remotely damage one during the assembly/re-assembly/assembly then you will quickly be doing another rebuild very soon. We have done the same thing here so you are not the only one, we just did it worse. Put the super speed crank in stock engine cases-not the ported/polished/stuffed cases that were put aside for the super speed crank. That was fun. Purely our fault.

Kevin265 · Post by **Kevin265** » Sun Mar 06, 2016 5:47 pm

I paid $50 for the crank. So, I will probably just order another crank and chock it up to another lesson learned. As far as damaging the crank during installation, I think that would have defeated the purpose of changing it in the first place. It will slip right out out. Waiting for the new crank will give me time to find the wrist pin clip that shot across the room while removing it.

lovemysan · Post by **lovemysan** » Sun Mar 06, 2016 8:22 pm

Does the eBay crank have long splines for the kick start?

sc00ter · Post by **sc00ter** » Sun Mar 06, 2016 9:41 pm

Be warned my friend, reuse c-clips at your own risk. Due to the fact that they are cheap we replace them with new no matter how good the old one looks!

Kevin265 · Post by **Kevin265** » Mon Mar 07, 2016 1:59 am

Sc00ter- Good lookin out , I will get new clips. The crank looks identical except for the rod.

Kevin265 · Post by **Kevin265** » Mon Mar 07, 2016 2:07 am

Whoops, just noticed the splines. OK you guys have convinced me, going cheap was a mistake. Where should I get a new crank?

babblefish · Post by **babblefish** » Mon Mar 07, 2016 3:00 am

You can still use a crank with the shorter splines. You'll just lose the use of the kickstarter. Most modern scooters with FI such as the Buddy 170i, Hooligan, and modern Vespas' don't have a kickstarter at all. For my Blur, the stroker crank I bought had the short splines, but being old school, I modified my variator to accept the kickstarter mechanism. So though I still have it, I've never used my kickstarter except just to try it out to see if it works.

Kevin265 · Post by **Kevin265** » Thu Mar 10, 2016 8:09 am

Purchased a new crank from my local dealer for $180. Going to install this weekend, Thanks everyone for your input. Can't wait to get back on the road. My commute is so boring in the car!