KymcoForum.com

General => Technical | How To => Topic started by: Stellagod on August 03, 2014, 01:50:05 PM

Title: Big bore kits
Post by: Stellagod on August 03, 2014, 01:50:05 PM

Hi, can anyone please let me know what sort of performance increase an 80cc or 100cc big bore kit will provide to a derestricted Agility RS 50? The scooter is stock apart from smooth roller and derestricted ecu. It does 36-37 mph at the mo'
Cheers

Title: Re: Big bore kits
Post by: tortoise on August 03, 2014, 04:04:21 PM

Potential downside is heavier piston = unbalanced crankshaft assembly = enhanced odds of bearing failure.

39mm,47mm, and 50mm compairson (http://www.youtube.com/watch?v=zRv0hwToFCY#)

CRANK SHAFT BALANCING BY: MAYKEE RACING WORKS (http://www.youtube.com/watch?v=EQmj9Nw8mtU#)

139QMB GY6 Crankshaft Rod Bearing Fail (http://www.youtube.com/watch?v=dslp5nkdGAQ#ws)

Title: Re: Big bore kits
Post by: blue on August 05, 2014, 03:12:12 AM

Better off with bigger scoot.bbkkare a wast of money .I have seen to many scoots blow up or bend cranks.

Title: Re: Big bore kits
Post by: Chris0381 on August 05, 2014, 02:51:32 PM

I second the bigger bike, if you a good bike mechanic and have the shop to balance everything then a BBK may be good but for us tinkerers, we could do more harm than good. I have read people seizing their motors at 200 miles with a BBK not to mention wear and tear on other crucial components like reed valves and needing carb and exhaust tuning also.


Im no expert but I do a lot of searching other forums etc.

Title: Re: Big bore kits
Post by: Stellagod on August 06, 2014, 08:29:16 PM

Hi again, Thanks for the feedback. I take it there is no good reason to fit a big bore kit then? Does anyone on the forum have anything positive to say about them?
Cheers

Title: Re: Big bore kits
Post by: Chris0381 on August 07, 2014, 11:10:17 AM

Quote from: Stellagod on August 06, 2014, 08:29:16 PM

Hi again, Thanks for the feedback. I take it there is no good reason to fit a big bore kit then? Does anyone on the forum have anything positive to say about them?
Cheers

Yes, they add HP and enhance the performance but need to be done right.

Title: Re: Big bore kits
Post by: JJJoseph on September 04, 2014, 12:30:52 AM

Quote from: Stellagod on August 03, 2014, 01:50:05 PM

Hi, can anyone please let me know what sort of performance increase an 80cc or 100cc big bore kit will provide to a derestricted Agility RS 50?

No need to change the crankshaft, it's the same crank used in 50cc and 100cc models.  Any GY6 cylinder & piston kit works fine.  There's not that much difference from one brand to another. With the stock head, the compression is on the high side and it's stiff to start.  A new head matched to the BBK might be a better choice.  I use the stock head and hog it out with a Dremel to lower the compression slightly, plus carb rejetting.  All the above just gets you faster acceleration (a LOT faster), but no extra speed.  Adding a performance cam and gears in the rear-end will give you more speed. 

Suggestion: when you order your BBK, ask if replacement oversize head gaskets are available. They're specially-formed steel gaskets.  If the supplier doesn't offer them, don't buy the kit.  You'll need a gasket sooner or later, and you don't want to have to buy a complete BBK just to get a head gasket.