Camshaft basis

 

What is the spread on a camshaft?

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Exhaust spread is defined as: The angular distance, against the direction of rotation of the crankshaft upper piston dead centre to the max. exhaust valve lift.

Intake spread is defined as: The angular distance, against the direction of rotation of the crankshaft upper piston dead centre to the max. intake valve lift.

What is the valve overlap?

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In motor rotation direction, the intake valve just opens and is already open to the overlap lift.

In motor rotation direction, the exhaust valve just closes and is already open to the overlap lift.

What is the valve drop?

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The valve drop is the distance of the valves from the closed valve in the seat to the contact of the valve with the piston when the piston is at TDC.

The drop height must be a min. of 1.5 mm larger than the measured overlap lift of the camshaft.

It must further be ensured that at a max. overlap lift, the intake and exhaust valve retainer cannot touch each other; a min. of 1.5 mm distance.

Valve spring installation lengths

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right spring installed length

at max. valve lift, the spring has a min.1mm distance to go

wrong spring installation length

at max. valve lift, the spring does not have any possible distance to go

The valve spring must have a min. of 1.0 mm distance to go available at max. valve lift.

The installation length of Schrick valve springs must match the information in the Schrick catalogue and must be set to the correct overall installation length. For example, by placing washers underneath or twisting off the lower valve spring retainer.

What is the timing of a camshaft?

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Timing is when the intake and exhaust valves open and close again with respect to the crankshaft angle and the test stroke. An example of a test stroke of 0.5 mm:

Intake opening angle 238° EM (intake centre) 114°

EÖvOT= (238/2)-114 ESnUT=238-(180+5)
EÖvOT=5° ESnUT=53

Exhaust opening angle 238° AM (exhaust centre) 106°

ASnOT=(238/2)-106 AövUT=238-(180+13)
ASnOT=13 AövUT=58

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