Valve seems to bottom out

[alphabetica]

Have had my bike to one side for awhile. It is running a Lifan 150 motor. Took off the cam cover to check the timing since it was getting a bit hard to start when I was riding it last. I saw that the cam timing circle was off by one tooth when the stator is on TDC. I figured this would be due to it just wearing in.

So I rotated the cam sprocket back one notch so that its circle mark lines up perfectly with the notch in the head while keeping the stator at TDC.

*But* I found after I did this when I gently turned the stator around by hand I could feel the valve bottoming out against the piston through the stroke. Not so bad that I could not overcome it by continuing through the stroke but I could still feel it.

So I think next I should check the valve clearance yeah? Just want to know if I am on the right track

 

[bulldog93]

Sure am mate. 0.003 inlet 0.004 exhaust/outlet (thou):
- http://www.miniriders.com.au/motor-tutorials/24965-how-set-valve-clearances-horizontal-engines.html

 

[krazed0451]

I would not be kicking that engine over until you are certain there is no valve interference on the piston... You'll have to wait for some of the more technical guys to tell you how to correct this if it continues, but I'd start by pulling the spark plug and seeing if you can see or hear the interference

 

[Cactus Jack]

Maybe you should have left things the way they were ? ... It'd be pretty rare for the timing chain to jump teeth on the timing sprockets in a new stock motor ...

I've held a Lifan ORK rotor up to the screen to check and it appears that you've got it all set in the right places ... BUT ... some rotors have been reported to have the keyway out of whack with the "T" mark ... In cases like that the piston wouldn't be at true TDC with the stock rotor and cam sprocket index marks aligned ...

The only way to know for dead sure would be to check for true TDC of the piston to see if the stock "T" mark is stamped in the right place on the rotor ...

As part of blue printing any engine ... they're the first thing that engine builders check ... You should never assume that the stock mass produced timing marks are accurate or even "close" enough ...

The fact that you had to move the timing chain over a tooth (and the engine had been previously running as it was ) indicates that the factory may have set the timing marks where they were to avoid a known problem ...

To find true TDC you rotate the crank anti-clockwise until the piston only JUST reaches the top of the bore ... At that point , draw a texta mark on the flywheel in line with the case mark ... then rotate the crank clockwise until the piston only JUST reaches the top of the bore again and draw another mark inline with the case mark ... TRUE TDC will be dead in the centre between those two texta marks and that's where the "T" mark should be ...

IF your stock flywheel has been made correctly ... the stock "T" mark will have a texta mark evenly spaced either side of it after you've performed that procedure ...

Some people use a piston stop bolt in the spark plug hole ... but true TDC is more accurately checked with the head off and using a degree wheel and dial indicator ...

Another scenario could be that the cam sprocket timing mark is out of whack with the cam lobe centrelines ... That's more likely to occur on cams that have a pressed on sprocket flange ...

Once again ... engine builders set cam to crank timing up using a dial indicator and degree wheel to ensure that the timing marks are accurate ...

 

[Cactus Jack]

I would not be kicking that engine over until you are certain there is no valve interference on the piston... You'll have to wait for some of the more technical guys to tell you how to correct this if it continues, but I'd start by pulling the spark plug and seeing if you can see or hear the interference

Man !!! His pics are sooo big that it's hard to post ... LOL ... The above info is excellent advice ... Whenever you move the timing chain over on the cam sprocket it's a wise move to do a piston to valve clearance check using plasticine or "clay" as some people call it ... (for the reasons that I've stated in my previous post) ...

 

[sean01]

yep chances are the tdc mark on the magneto is wrong..

unscrew the spark plug and get the piston to the top feeling with a small screw driver. then sus out where the marks are on the magneto..

also if you were to remove the magneto (or even just the nut)you should find that the keyway on the crank will be @ 9 o'clock @ TDC (pointing at the chrome barrel bolt)

half a tooth out on the cam is pretty normal but not 1 tooth..
set your valve clearances after your happy with the cam timing

also a word of warning... valves only need a slight nudge and they'll bend.. definitely dont go tryin to start it in this condition

can we get a resize on the pics too pls.. they'll actually look better too..

 

[topguntravis]

Is the timing on these engines like most where the timing is set like a few degrees forward so that for example on the induction stroke, the inlet valve opens just prior to TDC (valve lead), and the exhaust valve closes just after TDC (valve lag), so you get valve overlap for better efficiency. (I think it's called "volumetric efficiency" to be technical lol). Because I'm pretty sure the valves aren't meant to open/close at exactly TDC... If you get what I'm on about?

Just curious you engine nerds?

 

[sean01]

most magneto's have a couple of marks @ and before TDC

 

[alphabetica]

Kill - Eat - Destroy

When I set the stator to TDC I took the plug out and pushed something in to the hole to check the piston was at TDC. Just like I would do for a car.

Also when I said TDC I meant the straight line next to the T on the stator 'T |' which I assume takes in to account some overlap so the inlet is open.

If it was perfect TDC the motor would be very hard to start I think.

I was thinking myself that maybe it was set 1 tooth off so that the inlet is a bit advanced but a tooth just seemed so far. That is enough room to march an army of ants through in valve terms so I think it is something else.

I wasn't going to kick it over until I have everything nice and happy since I don't want to bend anything.

I *did* turn the stator over by hand and felt it the valves pushing against the piston.

Not by much. Just a tiny bit more hand pressure than normal to turn it around. So I think the inlet is bottoming out the smallest bit. Can't hear them pinking though. So it must be a really small amount.

I do think next up I will take the head off to look. I am quite comfortable with this stuff so no probs.

Just hard to figure Chinga stuff out since I can't find a manual for it !

Going to pop the head off now and check that piston comes up to the top when the mark is to TDC and check that the valves are seating and not bent or damaged. I wondered if maybe something was stuck in the seat.

What torque settings for the head bolts on the Lifan 150's ... ?

It is only a China motor I can probably just guess :grinning-smiley-003

 

[sean01]

no real need to go pulling the head off.
with the screw driver down the spark plug hole resting on top of the piston just rock the magneto and youll feel where the piston is..

 

[alphabetica]

Yeah. I did that already. Seems like the piston is at TDC. But something isn't right. Now is my chance to destroy something expensive!!!!

 

[sean01]

if the piston is @ TDC then theres not much you can do by pulling the head off..
andl you know it ran before you moved the cam timing but was hard to start, so replace the cam timing to where it was and set your valves..
i bet it starts..

and as for the cam timing problem/illusion, im guessing its a factory stuff up of some sort..

 

[alphabetica]

Yeah. I thought the same. I set it back to where it was before and it turns fine. I did mark where the cam was set before I took it off the first time. I also want to check the state of the valves anyway because at one point ( don't ask ) the sump bolt fell out and it ran with all its oil peeing out down the Edithvale highway for about 5-10 minutes .... just thought I would mention that *now .. heh ...

 

[alphabetica]

Actually I will do the valve clearance first and then take the head off. Fix first. Destroy later.

 

[sean01]

valves would be the least of your problems if it ran low on oil..

 

[alphabetica]

Yeah. I was amazed it kept working. Lucky I was passing bunnings having just turned off the highway when I noticed. Poured in some oil. Jammed in a hardware store bolt. Ran fine on the way home. That was last year. Has been sitting since. Turn it over about once a month.