139qmb big bore

[vg]

hello to all in 49ccscoot! recently got myself a scooter and have been looking into big bore kits. 72cc, 80cc, and 90cc kits but I've been wanting the 90cc for rhe most gains. I do realize the downside of hurting my reliability when installing the bigger kits, but I really want the most out of my little engine before I eventually swap it out. the engine has about 4200 miles on it, so should go through the bottom end and replace those components as well for maximizing my reliability?

[GrumpyUnk]

To replace the 'bottom end' parts requires splitting the engine case, disassembling the crankshaft, installing a new rod and pressing the crankshaft back together(using a PRESS!!!) and THEN you get to balance the crankshaft.
I would not do it unless no other option.
OPINION is that a 72cc/47mm BBK will give decent increase. Set the new piston/cylinder next to the original once you have the cylinder head off. There is a good difference.
There is a thread on site about reliability of the different BBKs available, indicating how long they last, etc.
tom

[vg]

May 21, 2024 10:57:25 GMT -5 GrumpyUnk said:

To replace the 'bottom end' parts requires splitting the engine case, disassembling the crankshaft, installing a new rod and pressing the crankshaft back together(using a PRESS!!!) and THEN you get to balance the crankshaft.
I would not do it unless no other option.

yeah as I thought, I just wasnt sure because my engine has some miles on it, and wanted to be sure it lasts the longest it can. I mainly ride mine for pleasure so its not a daily commuter. I also like to go fast, so thats why i was thinking the 80/90cc would be good

[FrankenMech]

Trade the scoot off and buy a 125/150cc or larger scoot.

[averagehillenjoyer]

Go for a 90cc, bigger valves and a A9 cam! if the bottom end breaks just get another used one, theyre cheap