How to set standard cam timing in a Horizontal engine ...
1. Get the piston to TRUE TDC by lining the "T" mark on the flywheel up with the index mark on the crank case ...
2. With the piston held in the TTDC position ... fit the cam sprocket into the timing chain with the dot or "O" mark on it pointing directly to the dead centre of the top of the head (top of the head is the front of a horizontal engine) ... then push the sprocket towards the top of the head to take up all the timing chain slack to make sure that the "O" mark is still dead centred with the "T" and case marks aligned ... IF it isn't , move it over a tooth on the chain until all of the marks are aligned at the same time ... IF you get it wrong , you WILL almost definitely bend one of the valves when you turn the motor over ...
3. Once all the marks are aligned , fit the cam sprocket onto the properly positioned cam shaft with the cam chain still on it ... then RECHECK that all the marks line up BEFORE turning the engine over ... The cam lobes MUST be facing downwards at angles towards the combustion chamber with both valves closed and the rockers must be riding on the cams base circle (heel) They should have clearance when the cam sprocket is fitted onto the cam ...
IF your engine has an IRK with no "T" mark on it , then you'll have to put one on it with a marker pen after working out where true top dead centre is ...
You can find TTDC with the head off by turning the crank with a spanner on the flywheel nut ...
1. With the piston at the top of the stroke ... draw a black texta mark (line) on the backing plate of the IRK ... wherever you can close to the rotor ... That'll be called your new "TDC Index mark" ....
2. Then gently rotate the crank COUNTER CLOCKWISE until you can only JUST feel the piston start to move down ... Holding it there in that position , draw a fine black texta mark (dot) onto the IRK rotor dead in line with your new self made "TDC Index mark" ...
3. Now gently rotate the crank in the the other direction ... CLOCKWISE ... until you can only JUST feel the piston start to move down the bore again and put another texta mark (another dot) onto the rotor dead in line with your new "TDC Index mark" ...
4. True top dead centre is smack bang in the centre of the two black texta marks that you have drawn onto your IRK rotor ... exactly half of the degrees of crank rotation counter clock wise again ... It'd be better to measure the distance between the two dots on the rotor , then draw a texta LINE exactly halfway in between both dots ... That will give you a TRUE TOP DEAD CENTRE ("T" MARK) on your IRK rotor that will be close enough for you to be able to trust for setting up your cam and ignition timing ... Once you've done all this , you could scribe lines or put a small nick or light centre punch mark on the rotor and backing plate to save them for future use ... Don't bother permanently marking the two dots which simply represent the extremes of TDC rockover ...You could also put another mark on the rotor 15 degrees counter clockwise from your new "T" mark ... as an "F" mark where the ignition should fire at when the engine is idling ... (a timing light will show it as lined up dead in line with your TDC Index mark on the backing plate at idle when the timing is set right) ...
I've worded things the way I have in to help any "kids" reading it to understand what I'm saying ...
