Vernier pulleys fine tune the power band which can be raised or lowered and may also have widened or shortened. Make a small adjustment, test it out thoroughly and use this as a baseline for further adjustment. Some engines are more forgiving than others. Please avoid making large changes, you can do some serious damage to an engine by getting this wrong. Again this depends on the cam profile chosen and engine type. Having spoken to many people it would seem that most people run up to 3 degrees difference. Alternatively turn it anti clockwise to Advance the cam timing and moves the power band down the rev range. NB: If you turn the pulley clockwise you will Retard the cam timing which you would do to improve top end power. Loosen off the bolts and turn it in your chosen direction just 0.5 to 1 mm at a time. Now you can start to make those tiny adjustments on the vernier pulley. Rotate the engine a couple of times and stop at the TDC mark (reading off the degree wheel on the crank).Fit and tension the belt and recheck the crank and cam are both at TDC, if they are then you can tighten the vernier bolts.Fit the cam and lock this in the TDC position but leave the vernier adjustment bolts loose with the bolts in the middle of the gap, which is usually the zero degree point!.Reverse the crank again until you hit a dead stop and note the marker position.Rotate the crank until it stops on the Piston Top Center Tool.You'll also need a degree wheel bolted to the crank and a pointer to read the degree wheel. To start determine the TDC position of the engine with a piston top center tool.With the cams removed from the head you'll need the TDC position.This varies from engine to engine, pulley size and other factors so we can't make a rule of thumb here. Ignition timing is down to the ECU and the cam profile sets the duration of lift. You are only controlling the time the inlet and exhaust ports open and close by doing this (you can't change the duration, just the start point). Generally each 1mm mark you move the pulley you change the cam timing by 2 degrees. Pulleys designed for tuning are generally fitted with marks to allow you to see the fine adjustment you are making. (Duration is still controlled by the cam profile.) A vernier pulley allows fine control over cam timing. Your fast road cam may be introducing an annoying flat spot or raising the power band too high. With the fine tuning on offer from vernier pulleys the power band can be raised, lowered and depending on where you move it to it may also have widened or shortened. Why would you want to do this? Very small adjustments in the cam timing can alter the power band in your engine quite dramatically. On standard cams and engines there is little need for adjustment or fine tuning.Ī vernier pulley has a set of bolts around it that allow you to turn the pulley slightly so it is in line with a fraction of a tooth on the belt. It is essential to ensure that you line up the cam pulleys correctly with the cambelt. How to adjust the cam timing easily with vernier pulleys and setting them up.
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