timing issues By seanstr (Read 52,320 times)

[seanstr]

nown the scooter doesn't wanna start even with a new battery. I have electricity but I'm wondering if the timing is still off . how do I find out?

[sprocket]

You replaced the head, was the piston top dead center when you put the cam chain back in place? You can't use the flywheel 'T' mark they aren't accurate...the cam must be positioned correctly also..

If you are out one cam link it probably won't run very well if at all...

Do you have spark to the plug?

Batteries don't run the engine...the stator runs the engine...

[seanstr]

It was tdc, spark is good, been sitting, so I'll check the fuel supply

[sprocket]

Clean the carb..run wires through the carb body and jets

[imnts2]

There are 2 very different timing needs in a 4t engine.

Ignition timeing which is typically aseveral digrees befor TOC ( top dead center) on the compression stoke. A GY6 engine typically has marks on the flywheel and the crankase indicating Ignition timing position That is not TDC but several degrees before TDC.



Valve timing is totally different. Each valve ( intake and exhaust) is designed to be opened and closed at 4 different and specifiy points during the 4 stroke cycle. I is controlled by the shape of the camshaft and the linking of the the camshaft sproket to the crankshaft by the timing chain An a GY6 there are marks on the cameshaft sproket that must be liked up with the surface of the valve cover to head joint WHEN THE CRANKSAFT IS AT TDC. There are no factory markes to idicate TDC.

Thats the rub. Using the ignition timing marks to time the camshaft sprocket will screw you up. YOu need to find TDC.

NOt that is not as tough as it sounds. Partly because the cam and sprocket teeth are farely course so are either OK or a long way off. Rmember the Ignition timing is several degrees befor TDC. So set the crankshaft a bout 1/2" after the Ign timing mark and then try to align the camshaft timing mark as you put the chain on. At least that is how I have done it a few times.

[sprocket]

Using the flywheel 'T' mark or any mark on the flywheel on the GY6 opens you to problems. (parallax) As imnts2 mentioned people think the 'T' stands for top deal center.. it dosen't it is the spark plug firing point, sort of.

The ONLY way to correctly set true TDC is to pull the head, set the piston, lock the flywheel with something like a wedge, retorque the head nuts, set the cam sprocket and put the chain on.

Then re-tension the cam chain and guides and unlock the flywheel..done.

This way you will absolutely be guaranteed of TDC and the correct cam chain link.

[Alleyoop]

Yes the firing point is anywhere before the T and F markings. Some align the Leading Edge of the Pickup Coil on the T and then set the cam sprocket correctly.
Alleyoop

[bcgreatness]

i guess i got very lucky when i used a feeler for mine...

[Alleyoop]

BC,
No if you were just adjusting your valves and you lined up the Cam Sprocket Holes like in this picture that is what you us a Feeler Gauge to set the Valve Gaps, so you did just fine. When the piston is on TDC BOTH valves are closed the Rocker is OFF the high lobes on the Cam and when they are in that position you should be able to grab the rockers with your fingers and wiggle them. That is because they are off the Valve Stem and there is a little gap between the Valve stem and the Rocker. If one of the valves is to tight it will not wiggle so easly.

Tight valves cause loss of compression because the valve is not completely closed and allows gas and air to escape when the piston is coming up compressing the fuel and air before the spark plug fires to ignite the mixer. That causes loss of power and hard starting and usually when hot will want to die at low rpms like when coming to a stop.

If taking out the Cam mark the chain and one of the teeth on the Cam Sprocket so when putting it back on it is not off a tooth.
Alleyoop

[bcgreatness]

no i have not done the valve adjustment yet, i follow the motto, if it aint broke, dont fix it. my scoot runs way too good for the valves to need adjustment, although im supprised i didnt blow this little interference motor up. when i learned about the time chain tension screw, it started as an oil leak. didnt know where it was coming from. would clean engine, and it would get oiled up again. finally found a little piece of gasket and traced it to the tension screw housing. like i said i was learning, and i wanted to see if thats where the oil was coming from, so i took the whole housing off, and started the motor, the chain jumped time almost immediately. i had my hand on the kill switch so i didnt make an oily mess but good thing i had my hand on it to kill it fast. when i was setting the chain, i remembered that the piston has to go through 4 strokes before it starts a new cycle ( 4 stroke engine ) so i turned the piston untill i heard the exhaust stroke, and then put a piece of wire down in the spark plug hole and felt for the piston to go all the way up, and then i turned it just a little bit more to where i could feel it were about to go down, then i set my chain and let her rip. then i used black rtv hi temp silicon gasket maker to fix the tension housing. never had a problem. she starts up almost every time on first button press. like i said, maybe i just got lucky.

[seanstr]

I'm trying the fuel first, it turns very easily, but not starting

[Alleyoop]

First check if it is getting spark holding the SPark plug on the motor before you go messing with the fuel. If it is getting spark, then you want to find out if it is a fuel delivery problem. Squirt some gas down the INTAKE MANIFOLD take the Vacuum hose off and squirt some gas down through the nipple. just get a piece of hose same size as on there 3/16 ID and dunk it in some gas fill the hose with gas holding the bottom of the hose put it on the nipple and it will drain right in. put the hose back on and see if it attempts to fire it may even start. If it does then you know it is a fuel delivery problem.

Next check if fuel is flowing to the CARB from the petcock or fuel pump. Get a little container and Take the fuel hose off the carb put it in the container and crank it. Fuel should stream out if it does your ok there and you know the carb needs cleaning.

If it doesn't then check if the problem is the filter or Petcock by doneing the same test, take the filter off crank it if fuel comes out then replace the filter if no fuel comes out then VERIFY that the VACUUM HOSE coming from the intake to the PETCOCK is ok if ok the replace the petcock or you could take it off and try to clear it if not replace the pectock.
Alleyoop

[sprocket]

>>>if it ain't broke, dont fix it.

That's is what they all say and the valves tighten, sometimes in a day or two, and you will be stalling... check the gaps...

[bcgreatness]

Guess your right, wouldn't hurt to check, when i buy a new clutch i will get a set of feelers

[sprocket]

Use a strip of aluminum from a coke can it is .0034" thick, it is fine to use to gap the valves...