broken outer valve springs

[greggkinney]

my friend has been running the wrong muffler on his gy6 short case (150cc) and with it being the wrong exhaust it wont bolt anywhere in the back to support it. this keep leading to the exhaust studs backing out and/or breaking. i gave him a new head last time because the studs broke off deep. now he's done it again so i was going to put a non egr head on i had but valve covers are different. so i decided to try and remove the broken studs and rethread the 1st head i put on for him. he had also told me it had been running bad and wouldn't hit 50mph anymore. well as i started to clamp the head down to start drilling i noticed one of the valve springs were cracked at the top, so i looked at the other one and its totally broke in two places and spins and collapses and what not. when i changed the head the 1st time i switched cams and rockers too so they were the ones that went with that head. any idea what could cause this? is it a common problem when they sit a while? he also said he rode for 3 days with no exhaust at all.

[greggkinney]

does anyone know if the 150 heads come with different valve lengths? i know the 50s have 64mm and 69mm and the rocker assembly for the two aren't compatible but i dont know about the gy6150. if so maybe to long of rockers destroyed the springs. i searched online and even looked at parts sites to figure it out but no luck.

[90GTVert]

I don't recall hearing about different valve lengths in the 150s. You should notice a problem with the geometry if the rockers and valves are incompatible. They most likely won't meet up flat on the valve tip and rocker.

Over revving is my first thought on the broken spring. Maybe something is off and the spring was binding?

[greggkinney]

i ended up finding a 1p57qmj head in a-1 condition and installed it. the 150 has alot more take off than i expected... i may end up doing a swap into one of my 50 frames 😀 or maybe a small frame/body 150 is in my future