Safe max rpm for 155cc GY6?

[CrankingWithCG]

Finally got my baby back about a month ago and got her running good. Swapped out my old shitty ported head for one where the spark plug hole didnt piss compression, 114 jet in the carb, freer flowing pipe, an actual foam pod filter, 11.5g weight mix, and swapping the vacuum petcock for a manual one cause it would suck the bowl dry after about 10 seconds of WOT.

Shes an absolute monster now. Basically just a 155 with an a9 cam. 24mm cv carb. She was so choked up before, now it rips. Faster than my old Zuma 125. I thought it was just a low rpm motor, but I figured out she likes to rev a bit. Hit 60-61 mph between 7300 to 7500 rpms in a tuck. I really like how it makes power. Sometimes in a 40+mph cruise you peg it and itll shoot to 6900-7100 and walk down fast traffic.

Just wondering, whats the safe limit on a kinda old stock crank GY6? Ive heard around 7500, but just wondering if any tuners here have any input. Im happy with it as is, uses most if not all of the cvt gearing (stock cvt). Now if this motor gets tired before i put a 171 on it, ill throw lighter weights and send her off in a blaze of glory 😂😂

[90GTVert]

I recall hearing 8,000-9,000RPM discussed as max RPM if you want the engine to last long. Some say lower or say only get it to 9,000RPM or above for short bursts periodically. I don't really know. My 155 with an A9 would regularly run over 9,000RPM without issue, but I didn't put tons of miles on it to tell you for sure if it holds up for a long time. I did do multiple long stretches where I'd be WOT the whole time and put a few thousand miles on it like that.

The other RPM limit is either valve float or where the engine wants to make power. I see valve springs sold that claim to be OK up to 14,000RPM. At that RPM, most setups are not making good power anyway and I would expect them to fail pretty rapidly due to stress and possibly oiling issues.

[CrankingWithCG]

Jan 1, 2022 11:33:41 GMT -5 90GTVert said:

I recall hearing 8,000-9,000RPM discussed as max RPM if you want the engine to last long. Some say lower or say only get it to 9,000RPM or above for short bursts periodically. I don't really know. My 155 with an A9 would regularly run over 9,000RPM without issue, but I didn't put tons of miles on it to tell you for sure if it holds up for a long time. I did do multiple long stretches where I'd be WOT the whole time and put a few thousand miles on it like that.

The other RPM limit is either valve float or where the engine wants to make power. I see valve springs sold that claim to be OK up to 14,000RPM. At that RPM, most setups are not making good power anyway and I would expect them to fail pretty rapidly due to stress and possibly oiling issues.

Ooh.....8000, i dont think this motors ever seen the likes of that 😂.

My only worry is that the bottom end probably has 7 or 8 thousand miles on it. The crank was good when i installed the big bore kit so i think she could handle it. This thing loves to rev out what she doea though, i think the bad head just made it run like crap. May try 11g weights and see how she does