RE: Need Help with Saito 120 !!!
Gary:
Forget what was said about switching the inlet and exhaust push rods and guides, only a total klutz could do it, the tappet guides point to the correct rockers, it would be too obvious an error. See the first picture.
I'll assume yours is a FA-120S version, you can't use the timing pin on the S engine because the tappets have to go in the housing before the cam, you can't put them in from the top. This makes the S engines real bears to time the cam. What makes it hard is that it's almost impossible not to hit the gear on something as you set the assembly in place.
You said "...The exhaust valve opes just after compression..." This in itself says the cam is 90 degrees out of time.
Pull both rocker covers and the glow plug. Turn the engine in forward rotation, watch the rockers. You'll see the exhaust open, then start to close. As it's closing you will see the inlet start opening. When the exhaust is 1/2 closed and the inlet 1/2 open you are at the point of maximum "Overlap," stop there and use a toothpick or similar probe to feel the piston position. If the piston is not all the way at the top of its stroke the cam is out of time. Holding your probe on the piston rock the crank back and forth to double check the piston position, the timing gear teeth are coarse enough that even one tooth off will show up in this test.
If it's out of time lift the cam assembly out again, set the piston to TDC using the probe as you did in checking it, set the cam mark straight down, very carefully set the assembly back in place. DO NOT ASSEMBLE IT WITHOUT THE GASKET. The gasket sets the clearance in the timing gears.
Don't tighten the screws, just snug them and check to be sure the timing is right. You don't have to reassemble the valve gear, just set the push rods in place, with a finger on each one you can feel their position as you watched the rockers before. When you're sure it's right tighten the screws, and put the engine back together.
Bill.