changed head now won' stay running By capncrunch (Read 541 times)

[capncrunch]

Hey there peeps! I haven't been posting on the board for quite sometime, but a need has arisen.

Somewhat recently as a result of changing exhaust on my 150cc gy6 the exhaust bolt stripped the threading on the head...I took this as an opportunity to bump up to a performance cylinder head and a14 camshaft.

Everything went extremely well until it came time to crank it up...it basically laughed at me initially and then i realized i hadn't tightened the nuts on the rocker arm assembly to specified torque...all good. Valves adjusted to .004 and .005. She started up with a hedonistic raucous sound! Beautiful!

But, she wouldn't stay running...Now its been extremely difficult to keep her running without giving her some juice...I adjusted the a/f ratio and saw some improvements...but getting her to crank on the first go round and keeping her running has been a chore...

My thoughts are that it may be that I simply need to upjet the main and slow jet on the carb...any thoughts or ideas?

[sprocket]

Well it is likely fuel flow...or electrical

Are you certain the cam chain is on correctly...did use use top dead center? If you used the 'T' mark on the flywheel you probably a link out on the chain...the 'T' is the fire point of the pick-up coil.. it is NOT top dead center

[capncrunch]

i believe the cam chain is on correctly...after reading your response i have my doubts...i did use the t mark and not the f...if im understanding you correctly, i should reassemble using the f mark?i used tdc to the best of my understanding....but im def not even close to perfect.

so based upon your response to this i will reassemble this way that i am understanding...i am also planning on ordering new jets regardless...

[sprocket]

NO Flywheel MARKS.. you MUST set the piston at Top Dead Center (TDC) at the top of the cylinder, physically.

This is critical.

I know there is stuff on the internet talking about T marks or F marks but they are WRONG.

You take the head off... then rotate the engine on the fan/flywheel side clockwise and watch the piston move up and down in the cylinder. Look at the flywheel for the T mark.. this will put you on the compression stroke... when the T comes close to the marker point slowly turn the engine over until the piston comes UP and then just begins to fall back DOWN.. then move the engine back a bit until the piston is EXACTLY at the top of the cylinder.. this is top dead center. I usually jam the flywheel with a door stop etc so I don't move things by accident.

Put the head on, align the cam sprocket to the edge of the head EXACTLY and then making sure the cam chain is fully on the lower crank sprocket, put it on the cam sprocket. Tighten the head bolts down and tension the cam chain.. . then torque the head bolts to spec about 13 ft/lbs on a 150cc in a criss-cross pattern... you should be good...

this work best for me...

There are methods that use a straw in the spark plug hole to 'feel' TDC.. but I have never had much luck doing it this way...If you do a search here I'm sure there are descriptions of this method.. might be worth a try rather than pulling the head again...

[capncrunch]

Nope, don't mind pulling the head again. Not much to it really. I will most definitely do this your way. I feel very strongly that this will cure my ills. This explains why when long before when I first adjusted the valves with the original head the t and f marks weren't very good markers in relation to the cam shaft.

Thanks for the advice, Sprocket. I will definitely do exactly as you outlined...Im sure that you agree that the upjetting is also a necessity(not the root cause)?

[bcgreatness]

i would upjet for sure, also check your diaphram needle in your carb to see if its adjustable, you might be able to notch it once or twice, that should help allot with adding more fuel. you also never mentioned if you upgraded your airbox. if you have not i would recommend doing so because with your new cam shaft upgrade and your free flow exhaust upgrade, you wont notice much different in overall power until you increase the amount of air flowing into the motor. happy scooting!

[capncrunch]

Yeah, I actually have been riding with a free flow intake that i manufactured using a mandrel bent aluminum tube with a k&n filter at the end. Thanks for the shout out.

[capncrunch]

Sooooo, I confirmed that I was indeed at TDC the whole time. So that was not the problem. I didn't get to find out one way or another as to what the problem was though.
When I originally put everything back together a corner of the rocker arm assembly broke/crushed. I didn't know at the time it was this extensive. I did get a new one just because. When I put everything back together then new rocker arm assembly did the same thing as well as one of the cylinder studs appear as though they may have stripped out the engine casing. Not too sure what to do now....

[capncrunch]

Two things....I discovered that the cylinder head stud did not strip out of the casing but, rather, the nut stripped off the stud....crazy. Ive never seen that happen before. But, Im still not running. Im thinking that its something really simple at this point like compression because I know I have fuel and spark and that I am at TDC. So, Im guessing that I need a new gasket, rocker arm assembly(which really sucks), and cylinder head nut.

The head had a dry seal originally. So, Im guessing thats ok to stay the same...Do any of you ever put any type of gasket sealer between the cylinder and head?