Cam sprocket align By pretendentas22 (Read 6,294 times)

[petrol42]

Another thing you can try is pop the valve cover on and start it up the way you have it now. The engine should start even if the timing chain is off a tooth.

The first thing to look for at this point is to see if your engine starts up right away or not.

After start-up, get your engine hot while its on its center stand and after its hot, rev your engine high.

If there aren't any backfires or hesitation, then your timing is ok. If there is backfiring at full throttle or close to full throttle, turn the engine off and go have a beer at this point so you could let the engine cool down. Then pop off the valve cover, chain tensioner and camshaft holder and move the gear up or down.

Then do the above steps again.

This happened to me recently where I was off 1 tooth on the Cam and my engine would backfire at the intake during full throttle.

[Alleyoop]

This is what I would TRY because I think it is OFF by 1 LINK:
1. Line up the CAM SPROCKET HOLES evenly, that will actually rotate the Flywheel further from the "T".
2. Then Move the CHAIN 1 LINK BACK, that will rotate the Flywheel Clockwise bringing the "T" closer to the Caseing Pointer.
Alleyoop

[sprocket]

As many know...I'm not a fan of using the T mark... I have seen too many mis-stamped flywheels and it is easy to get it off due to parallax..best to set the piston to TDC, then there is no room for error...

[pretendentas22]

Hi again,
At the end I assembled the engine and still have problem. In the mornings it started ok but i constantly was hearing noise. It sounded like a light blow. These blows come repeatedly in couple seconds intervals. When it blows rpm gauge is jumping as well. Plus when the engine still is cold after couple blows it just stops, unless I keep it on high rev. Does anyone had similar problem? it is a bit difficult to explain but I hope you will get me.
I am thinking may be because alignment isn't proper the valves and timing just doesn't operate properly.
Valve clearance is done.

[Moat]

I'm not sure just what the "light blow" noise would be, but as to the cam timing - no one yet mentioned the reason the marks don't align perfectly, and how to approach that issue.

It's common and normal for the cam chain to "stretch", increasing in length as it wears during normal service. This lengthening of the chain's overall length - given the location of the tensioner and it's taking up this slack on the backside (top) of the chain's run - results in the cam following the crankshaft later and later (retarded) as miles go by, and the chain wears itself longer in length.

So if there is a question as to which tooth on either side of TDC to set a sprocket that falls somewhere in between... the safe, proper method is to set the cam to lag behind the crankshaft (retarded timing), as this is the way it wears - and is designed to wear - normally, in service.

Of course, this is all assuming that the cam chain hasn't worn beyond it's service spec length, and is still useable.

Is the knocking "blow" noise a sharp, metallic noise? Or more of a cold misfire/backfire?

Bob

[pretendentas22]

I would say it is cold misfire/backfire.
I will sound a bit stupid now but I am just trying to understand misfire/backfire and their link to cam sprocket. I always thought misfire/backfire is caused by spark which comes out before piston reaches TDC or after it passed TDC. And for it is responsible CDI, trigger pick up coil and flywheel. Where cam sprocket only operates valves opening time and makes sure they are closed or opened at certain time.

[Moat]

No, no - sorry if my question was confusing... I was only trying to determine if the "blow" noise you mention was a mechanical problem (broken engine part) or an ignition/carb/fuel/air problem (misfire). It sounds like it's more the latter (ignition/carb/fuel/air).

That said - it is possible that a cam that is way, way out of time can allow burning combustion gasses into either the exhaust pipe (cam opening the exhaust valve too early) or out through the carburetor (cam opening/closing the intake valve too early/late), causing an audible "pop" or misfiring sound. Bent and leaking valves, from a badly mis-timed cam, can do the same also.

Does the scooter run OK otherwise, once it's warmed up?

I think it would probably be best to first double-check cam timing and make sure compression is good... and then go on to ignition/carb/fuel/air from there, if need be.

Bob

[pretendentas22]

Thanks for explaining it. I didn¡¦t have scooter before and it is difficult to judge does it goes ok. I can do 50 mph quite easy but this is top speed. Once I did 55 from the hillƒº. The blow is harder on top speed, in the beginning I thought something is loose and just bangs into bottom.
On the idle it just ¡§blows¡¨, ¡§blows¡¨, ¡§blows¡¨ and stalls, unless I increase idle to 2500 rpm. If I let to stall, it is difficult to start engine again.

[pretendentas22]

Hi again, well I moved one tooth over as was advised and unfortunately no change. Then I decided to check electric side and found my spark is very weak. Does anyone knows how to check CDI unit and other electric parts? I check alternator charging volts and it is 14.1, which is correct.