Valve Clearances

[akamor]

Hello All,

I have a general question about valve clearances.

On a four cylinder engine you must rotate the crankshaft 360 degrees between measuring 'partner valves'. When I say 'partner valves' I mean something like Intake on Cyliner 1 and Intake on Cylinder 4. Or the exhaust on cylinder 2 and the intake on cylinder 3.

My understanding is that the camshaft lobes are 180 degrees apart on these 'partner valves', does this mean that a 360 degree turn of the crankshaft corresponds to a 180 degree turn on the camshaft? This is a 4-stroke engine, btw.

Also, how do you verify that you are at TDC of cylinder 1? Is it when the cylinder is at its highest position. I was checking by sticking a screw driver down the spark plug hole and moving the back wheel in 5th geer. When the screw driver was sticking out the most (i.e. the cylinder was at its highest) I assumed it was TDC.

Also, if cylinder 1 is at TDC does this mean cylinder 4 is at TDC?

Thanks as always,

Adam

[HoughMade]

OK- here is the surest way (I know of) to find TDC on the power stroke. Since you are adjusting valves anyway, take the cover off the intake valve on the cylinder you are working on (works on any cylinder, just make sure you are looking at the right valve). Rotate the engine until the intake valve goes down, then back up (opens, then closes) and the next time the piston reaches the top, you are at TDC compression/power stroke.

I'm no expert on 4 cyls., so I'll leave that for someone else...2 is enough for me.

[akamor]

OK- here is the surest way (I know of) to find TDC on the power stroke. Since you are adjusting valves anyway, take the cover off the intake valve on the cylinder you are working on (works on any cylinder, just make sure you are looking at the right valve). Rotate the engine until the intake valve goes down, then back up (opens, then closes) and the next time the piston reaches the top, you are at TDC compression/power stroke.

I'm no expert on 4 cyls., so I'll leave that for someone else...2 is enough for me.

That sounds good. I did that tonight but I am still having problems with the bike. The darn thing wont idle without a choke. I think I am going to move on and reclean the carburetor and recheck for vacuum leaks.

Thanks,

Adam

[HoughMade]

Probably a good idea. Unless the valve clearance are way, way off, they won't really affect idle.

I'm guessing some bits of crud in the idle circuit. Took me something like 5 cleanings to get it right. In the end, i disassembled everything and boiled the carb bodies in vinegar water and that finally worked. the skim of crud on the water was amazing from carbs i thought were perfectly clean.