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Hi, i'm slowly putting my motor back together and ran into a little issue with valve timing. The motor has been completely rebuilt. The manual is a little confusing regarding the timing procedure:

"Turn crank until TDC...Turn cam CW(from left side) until all inlet clearance has been taken up. Turn the crank in its normal direction of rotation until the timing disc reading agrees with the specified value (INLET valve opening point. See technical spec=12d BTDC)"

So I took the cranks "normal direction" as clockwise from the left side. That is the same way the cam is turning. However, this would have the intake valve opening 12 after TDC, which seems logical to me. The piston is traveling down and drawing in a charge. But looking at the manuals spec it says the intake valve opens 12d before TDC. So either i'm turning the crank the wrong way or the manual should say 12d after TDC.

Can anyone help me out with this?

What the instructions are having you do when you rotate it backwards a bit, is to prepare the valvetrain to become preloaded. When you go around to the right side and turn it clockwise in its normal rotation, all of the slack is taken out of the belt, valve clearance, etc.

Opening BTC would be correct. Intake, as well as exhaust timing, must start its movement before the piston begins a particular stage of its four cycles. This is because cam lobes have gradual ramps, rather than immediate drop offs, thereby taking a while to reach max valve lift.

Additionally, the "intake opening while exhaust closing" event is necessary for volumetric efficiency of a cylinder and is called valve overlap.

The manual is wrong.
Turn the crank back 12deg btdc.

Tobymv

Here's how I did it:

I first brought the front piston to TDC and also set valve clearance to 1.0mm. I then turned the camshaft pulley clockwise until the 1.0mm clearance on the inlet valve was taken up (I could not twist the inlet pushrod anymore). With the inlet cam/rocker now just about to open the inlet valve, I turned the crank clockwise (not to the left as incorrectly translated in the manual) until the inlet open mark I had scribed on the rotor (28deg for my Sport or approx. 8mm to the left of the ANT1 mark) aligned with the notch. Now, the camshaft is about to open the inlet valve and the crankshaft is 28deg BTDC just finishing the exhaust stroke. When I then turn the crank the 28deg needed to get the crank/piston to TDC, the mark on the bottom crankshaft pulley and the punch mark on the bearing boss and the keyway on the mainshaft all align at 2 o'clock. The dot on the camshaft pulley now also aligns on top with the notch on the case. The camshaft pulley keyway is now at the bottom 180deg opposite the notch. This is TDC on the intake stroke and all the the dots/keyways align as shown in the various videos and in the manual.

The manual is incorrect when it states that it should be at TDC of the compression stroke - the only time the cam pulley and case notch align and the crank pulley, crankshaft keyway and punch mark on the bottom bearing boss ALL align is when the piston is at TDC on the intake and NOT compression stroke.

Hi,the valve clearence should be 0.1 mm the manual is wrong,at 1.0mm you'll have a highly rattlely engine!
Dave.

morini500dave wrote:Hi,the valve clearence should be 0.1 mm the manual is wrong,at 1.0mm you'll have a highly rattlely engine!
Dave.

No, the manual is not wrong.

The valve clearance is 0.1mm for running and 1mm for setting the cam timing.

j2maria wrote:Tobymv

Here's how I did it:

I first brought the front piston to TDC and also set valve clearance to 1.0mm. I then turned the camshaft pulley clockwise until the 1.0mm clearance on the inlet valve was taken up (I could not twist the inlet pushrod anymore). With the inlet cam/rocker now just about to open the inlet valve, I turned the crank clockwise (not to the left as incorrectly translated in the manual) until the inlet open mark I had scribed on the rotor (28deg for my Sport or approx. 8mm to the left of the ANT1 mark) aligned with the notch. Now, the camshaft is about to open the inlet valve and the crankshaft is 28deg BTDC just finishing the exhaust stroke. When I then turn the crank the 28deg needed to get the crank/piston to TDC, the mark on the bottom crankshaft pulley and the punch mark on the bearing boss and the keyway on the mainshaft all align at 2 o'clock. The dot on the camshaft pulley now also aligns on top with the notch on the case. The camshaft pulley keyway is now at the bottom 180deg opposite the notch. This is TDC on the intake stroke and all the the dots/keyways align as shown in the various videos and in the manual.

The manual is incorrect when it states that it should be at TDC of the compression stroke - the only time the cam pulley and case notch align and the crank pulley, crankshaft keyway and punch mark on the bottom bearing boss ALL align is when the piston is at TDC on the intake and NOT compression stroke.

I worked from the right side of the motor. Or the magneto side since it has a clockwise arrow on it. After seeing the rotation indicator I knew which way the motor turns from what side. So I took the F piston to TDC and marked the crank pulley with a sharpie pen. Then turned the cam CW to where the front intake valve starts to open. Its about 5d away from the timing mark alignment with case mark. Then I turned the crank from the oil pump side with my trusty NLM tool until 12d before TDC. Then installed the belt. You could also install the belt half way and rotate the cam CCW by using 2 screwdrivers in the pulley holes. Or maybe two lockunts on the crank might do it.

I agree with you on the timing marks aligning at TDC of intake stroke only.