Some bad 50mm BBKs going around?

[scootnewb]

Hello,

Not exactly sure where to post but thought this would be a good place. I was hoping to get additional confirmation about the releifs and put out a warning.

Reference original thread where it kind of started.

49ccscoot.proboards.com/thread/21242/gy6-wrist-pin-sizes





I ordered a BBK for my scoot. It's a TaoTao.



After reading some forums, I guess there are some bad kits going around which contain a piston without any reliefs for the valves. Some may or may not contain a wristpin that is too large.



Well, I got a kit where the wrist pin was too large. It fits the piston in the kit but not the stock connecting rod.







The seller sent out a replacement piston that has and accepts the correct diameter wrist pin. But there aren't any reliefs.











The stock piston has them







People are saying the pistons with no reliefs are not even for a scooter but for dirt/pit bikes and I was shown what happens if you install them in your scoot.







Update on bad BBK 


I prolly posted this else where but...

Even though the seller of this kit sent out a 2nd jug with a 2nd piston (that was still the wrong piston - no reliefs) he then sent out a 3rd piston (correct one - dished). I no longer trust any of these parts and got a different kit.


Before the seller sent out the 3rd piston (dished) ,when i questioned him about the flat-top piston he sent, he said they were okay because, "They are designed with a shorter compression height than stock or dished BBK pistons." He was completely full of it. The flat-top piston he sent has a TALLER compression height!


Flat-top on left dished on right with a 13mm wrist pin connecting them.





Who knows all the damage installing the kit would have caused.





Update on the head that came with the BBK


I decided to try the head that came with the BBK because it doesn't have a pathway for the already removed PAIR system.

Got everything in place at TDC and spun the flywheel a few times. I set it back to TDC then went to adjust the valve clearance.

When i tried to adjust the clearance I realized there was a problem.



The head had a stuck valve or something. Maybe a bent valve or a bad spring on the exhaust side



There wasn't any sign of contact on the piston with the valve.




I removed the 'BBK head' and put back the stock one. Just in time. The new exhaust and block off plate arrived.

I adjusted valve clearance slapped on the block-off plate, valve cover and the exhaust.

All good





Thanks

[90GTVert]

You can check piston to valve clearance and even cut your own valve reliefs as long as the piston has enough meat on the crown. For the average user, it would probably make more sense to replace the piston or return the whole kit though. It's more work to check all clearances and crown thickness and cut reliefs than to do the standard BBK install. I don't think it's a bad idea to check p2v clearance anyway, but most have 0 interest in that.

49ccscoot.proboards.com/thread/15714/piston-valve-clearance-info-checks


Thanks for posting the info. Sounds like someone rushed a sourcing job, just finding cheap available pistons without regard to much more than bore diameter.

[scootnewb]

Apr 28, 2018 8:02:22 GMT -5 90GTVert said:

You can check piston to valve clearance and even cut your own valve reliefs as long as the piston has enough meat on the crown. For the average user, it would probably make more sense to replace the piston or return the whole kit though. It's more work to check all clearances and crown thickness and cut reliefs than to do the standard BBK install. I don't think it's a bad idea to check p2v clearance anyway, but most have 0 interest in that.

49ccscoot.proboards.com/thread/15714/piston-valve-clearance-info-checks


Thanks for posting the info. Sounds like someone rushed a sourcing job, just finding cheap available pistons without regard to much more than bore diameter.

Thanks.


I have indeed ordered a new kit and it arrived today. A Glixal 50mm one (it doesn't come with a head though). I might mess with that flat top piston and try creating valve reliefs for it after I get more experience under my belt. I guess it is possible the flat top may work without causing damage if I used the replacement head contained in the kit.    

[scootnewb]

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