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valve adjustment TDC?

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Bumblebee

Bumblebee

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Joined
Jan 24, 2010
Messages
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Location
Little River
First Name
Edgar
Last Name
Schlickeisen
TDC on the compression stroke can be found when the camshaft lobes are turned away from each other. My camshaft lobes on cylinder 1 don't turn away from each other; they only have about 90 degrees difference instead of the 180 that would make them face away from each other. Do I have serious problems? Can anybody help? I need my bike tomorrow to get to work. I have all the necessary tools. I can get a six-pack of your favorite beer if you can help. Thank you
 
Your method might work, but usually the spacing between the cam lobes depends on the engine layout, an inline engine might have the cam lobes facing away from each other, but that is NOT the case for a V engine!! The most accurate method is to find the marking on the flywheel. If you have the owners manual it will always tell you how to find TDC as it is always needed to check valve clearances. Only then will you know if you have a problem.. You CANNOT assume that every engine configuration will always have the lobes facing away from each other when at TDC..

Gary
 
"TDC on the compression stroke can be found when the camshaft lobes are turned away from each other." This is taken from the manual.
 
I wouldn't expect 180 degree facing on the lobes. You would have a valve open during the compression or power stroke.

You can turn it to where the where the lobes are pointing outward (90), as opposed to... well opposed (180). This is a convenience if you ask me. It lets you check both valves at the same time. An easier method is to just point a lobe directly away from the head, check it, repeat on the next one.
 
The lobes will not be 180 degrees to each other at TDC. You can also use the method MOKAZI suggested.
 
Spin the engine in the correct direction until the intake valve(s) for the cylinder you are checking open then close. You are now on the compression stroke near TDC. When the intake valves close, continue turning the flywheel slowly until you see the prescribed TDC mark. Check your valve clearance. The lobes won't be 180˚ apart. If it was running when you shut it down, it's ok.
 
If the piston is at the top of its stroke, and the valves are closed, that cylinder is at TDC. There should be a bit of play between the cam lobes and the valves. Cam timing doesn't change significantly on its own, so don't worry about that. What kind of bike are you working on?

One last thing. If you're doing a valve adjustment, don't rush the work. Mistakes can be very expensive to fix.
 
The bike is a 03 Yamaha royal star venture.The cams are definitely out of time the valves have overlap one opening before the other has closed. It has backfired the entire time I have had it. I though it just needed a valve and carb adjusted. Would appreciate any help to get it back on the road. It has to be back on the road by Tuesday or my wife said it goes.
 
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The intake valve will open before the exhaust valve closes. This is called valve overlap and is normal. If you think there's more overlap than normal, the process for checking cam timing usually straightforward. You have already done most of the work since you have the bike apart already. I don't have the details for that bike, so you'll have to look it up.

The most common cause i've seen of extreme backfiring has been adding an after market exhaust and not blocking off the air injection system. A leaky exhaust gasket makes the problem worse.
 
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