125cc gy6 motor with 150cc head? By willemjjbotha (Read 493 times)

[willemjjbotha]

Hi all, so here is a question I hope someone can clarify for me. If I have a 125cc gy6 motor, with piston and sleeve, will it work if I put a 150cc cylinder head on there?
I have the head for 125cc but the case is shorter then the case of the 150cc so at the end when I install my cam and rockerbox my Cain is to long. The 150cc head fits 100% and chain length is also 100%, the problem is when I start it up it does not run right, keeps back firing and missing, won't reg up as well.

Can it be because it a 150cc head?
Do I need to check some thing els?

Timing is 100% on its marks, has a new stator, cdi and coil.

[cyborg]

You may find the chain is indexed wrong,,, double check the cam tower height and if everything checks ok then you're off a tooth or two

[willemjjbotha]

May 3, 2017 19:23:02 GMT -6 cyborg said:

You may find the chain is indexed wrong,,, double check the cam tower height and if everything checks ok then you're off a tooth or two

So meaning I can use the 150cc head on a 125cc piston and sleeve?

[cyborg]

Measure them all ways,,, if they match go for it

[willemjjbotha]

May 4, 2017 13:27:26 GMT -6 cyborg said:

Measure them all ways,,, if they match go for it

Thanks, will do, I'll post the results as soon as I am done.

[willemjjbotha]

May 4, 2017 13:27:26 GMT -6 cyborg said:

Measure them all ways,,, if they match go for it

So I measured the head and its exactly the same as the shorter GY6 125cc head accept its longer and were the valves open and close, sead.... Its not as deep as the shorter one. If everything is installed the motor starts but it sounds out of time. I have the piston at top dead centre and the cam is rocking" big hole on top and two small holes are aligned with the case. I even advanced and retarded timing with a tooth or two with the same results. When I took the head off again I can clearly see marks on the brand new piston were the valves hit the piston.

No my question here is will a new piston work, the one I have in is a flat surface piston, I'm thinking maybe if I install a piston with the groves cut in that makes way for the valves?

Or should I just use the short head and install a shorter timing chain?

Any advice here will be greatly appreciated as I'm lost.

[cyborg]

Or a thicker head gasket,,,

[willemjjbotha]

May 16, 2017 16:29:13 GMT -6 cyborg said:

Or a thicker head gasket,,,

Thanks that sound like a good option where would I find a head gasket that thick?

[cyborg]

Contact scrappy dog,,,they should be able to help you out

[2stroked]

Or a sheet of anealed copper??