I'm in the process of removing the top end cover of the engine on my 1984 XT 600.

I began to hear a knocking sound with 500 miles left on my cross country trip. The motorcycle had been performing with less than peak power for the better part of a trip lasting several thousand miles. I checked and cleaned and rechecked and cleaned the carb a few times, never to much gain. I finally took notice of the shape of the 30 year old boots. They were showing cracks, potentially letting unfiltered air into the fuel/air mix.

Now that I am getting into the engine, I can see that the right-side intake valve is caked in crud. Now is where I do not know how to proceed: to take off the top end cover, my Clymer's manual says to find top dead center. Well, every time I kickstart the motor I'm nearly positive I'm finding top dead center; this is one of the basics of starting a kickstart motorcycle, I believe. According to the manual, the top dead center is found by aligning the inscribed " lT " on the rotor assembly in the center of the quarter-size window at the top of the left-side crankcase cover. When this is aligned, the rocker arms will have "free play" allowing them to be wiggled, it says. I am unable to align the marking and as far as I can tell, at no point is there "free play". As I approach the inscribed " lT " when turning the rotor by hand, the rotor rotates freely, or slightly falls, just past this mark. This position is what I would say is the top dead center by feel alone. I'm confused and I hope that my description of the problem is not confusing to you, the reader. Thanks in advance to those who read.

Get a manual (download from this site) and read the part aboaut setting the valve clearences.

You can't find TDC... (Top dead centre).

The |T mark will indicate top dead centre AND bottom dead centre.

So, if by rotating the Alternator 180 there is no free play, rotate another 180 and try again.

The sure way to know if you have TDC is to remove the spark plug and slide a long, thin probe (screw driver will do). As you turn the engine the piston will go up and down. As will your probe.

When the piston is at it HIGHTEST point in the barrel and the mark |T is showing, you will be at top dead centre.

__________________
Did some trips.
Rode some bikes.
Fix them for a living.
Can't say anymore.

The piston goes up and down in the barrel and every time it's as high as it will go that's tdc. But the rocker arms can only be free play wiggled every second time the piston comes to tdc. You'll need to work out which of the two tdc's is which.

Ted route is the way to go. Take the plug out and poke something thin down the plug hole. Turn the engine over slowly - otherwise the screwdriver or whatever you're using can get jammed in place, and feel the piston come up. When it gets to the top (you don't need to be exact - near enough is good enough) check for wiggle. If the valves are held down or moving you need to turn the engine over once to the next tdc and check again.

A quick way of doing it is to take the plug out and put your finger loosely over the plug hole. Turn the engine over and you'll feel air escaping past it on the compression stroke. That's the correct tdc.

Take the spark plug out, and use a pencil to put it in the spark plug hole. Spin the stator rotor counter-clockwise, and stop when the pencil starts to go back down again, then find the highest point the pencil goes to. The valve clearances arent much on these bikes, it may be hard at first. If there is no wiggle, rotate the engine 180 degrees (piston goes back down, then back up). Im betting your knocking noise is a bad piston/bore, but check the easy stuff first.