Where does the timing belt go on a double overhead cam?
Turn the cams until the marks on the drive sprockets (commonly referred to as gears) line up and then fit the timing belt. Timing belts are often directional and will usually be marked as such. The exact configuration of timing marks depends on your engine. The variety of systems devised over the years is vast.
How did double overhead cam timing get its name?
It’s named after its designer and builder, Brian Hart, who worked at the famous Cosworth company in the ’60s. He left Cosworth in 1969 to set up his own company and made engines for various racing classes including F2 and even supplied F1 engines for a number of teams into the ’90s.
How are the clearances of double overhead cams determined?
Different thickness shims are available to adjust clearances and the method is to measure the thickness of the shims with a micrometer before they’re fitted. Then the cams are fitted and torqued down and various thickness feeler gauges inserted to determine clearances.
What kind of camshafts are used in a DOHC engine?
We’ve previously described how to fit and adjust various types of camshafts and associated valvetrain components, so this time we wanted to look at double-overhead camshafts (DOHC). We noticed this classic Hart engine being assembled in Peter Larner’s race engine workshop the other day and figured it was the engine on which to show the procedure.
What happens when you have a camshaft timing error?
When a cam timing error slithers in, it can arrive from either of two directions: A cam drive either wears and becomes loose and jumps a tooth or more, or it completely breaks. In either case, camshaft timing often rattles a death song and the engine quits. Approach a timing problem with caution.
When to set the cams on a crankshaft?
I would suggest at this point in time that you start with the crankshaft at 30° before top dead center and set the cams. At this point, there will be plenty of clearance for valve in every cylinder. When the cams are in position, then rotate the crankshaft to TDC and install the belt.
Can a camshaft be turned without a belt?
However, both camshafts need to be lined up with the timing marks as well as the crankshaft turned to TDC before you install the belt to keep everything lined up correctly. My belt guide also shows this not to be an interference engine, so the cam shafts and crankshafts can be turned independently without causing damage.
Why do I need to check the timing on my engine?
Valves may already be biting into the pistons and you may cause more damage. Should the engine turn freely by hand and you have easy access, position the crank and check the timing marks on the crankshaft and cam.
What’s the best way to set the cam timing?
Rotate crank until the rockers on cylinder one are holding both valves open a little. This is the overlap period and how you are going to set the cam timing. Look at the pointer and pulley. Rotate crank to set them so they are directly opposite each other.
What’s the best way to timing an engine?
Assemble the cylinder head, rocker gear, etc. as you are going to run the engine. Torque it all down, set the valve clearances as suggested by the manufacturer, but do not fit the rocker cover. Rotate crank until the rockers on cylinder one are holding both valves open a little.
What happens if your camshaft timing is not correct?
If you answered “yes” to any of those questions, your camshaft timing may not be what the camshaft manufacturer specified. Improper cam timing can lead to reduced performance, increased fuel consumption and an increased likelihood of detonation.
Rotate crank until the rockers on cylinder one are holding both valves open a little. This is the overlap period and how you are going to set the cam timing. Look at the pointer and pulley. Rotate crank to set them so they are directly opposite each other.
What should the cam timing be on a DOHC engine?
If the cam timing was set to this smaller/narrower 110.5 degree lobe separation angle, the engine would behave much differently than the 113.5 degree lobe separation angle.
Where do you put the timing disc on a camshaft?
It is always recommended to calculate the actual position of TDC rather than rely on the mark on the crank pulley. Fit the timing disc to the front of the crankshaft. A pointer for the timing disc can be made from a piece of bent wire secured under a suitable front cover bolt. Position a dial gauge to measure the travel of No 1 piston (see right).
How do you set up double overhead cams?
The lobe centreline method of setting up cams is as follows: After the engine is together and the cams in place and torqued down with the correct clearances, set the engine to TDC as discussed. Mount a dial indicator on the number one inlet bucket follower with the base circle of the lobe on the bucket.
What happens if your valve timing is not right?
Bad things can happen inside your engine when your valve timing isn’t right! This bent valve would have dented the budget. There are a couple of fundamental ways to match the position of the camshaft to the position of the engine internals during the building of a DOHC engine. The first, and simplest, is to determine lift at top dead centre (TDC).
What happens when you advance camshaft timing?
Not to be confused with ignition timing advance, advancing a camshaft will change the timing of the valve events in relation to where the crankshaft is positioned. Advancing ignition timing causes the spark plug to fire earlier whereas an advanced camshaft will cause the intake and/or exhaust valves to open and close earlier in the engine cycle.
What is a camshaft timing?
Timing belt (camshaft) A timing belt, timing chain, or cambelt is a part of an internal combustion engine that synchronizes the rotation of the crankshaft and the camshaft (s) so that the engine’s valves open and close at the proper times during each cylinder’s intake and exhaust strokes.
What is a camshaft timing gear?
The purpose of timing gears is to allow the camshaft and crankshaft to turn the timing chain. The crankshaft turns to move pistons up and down inside the cylinders. The camshaft turns to allow intake and exhaust valves on the cylinders to open and close. These components are important for proper engine timing.
What does a camshaft sensor control in a vehicle?
The camshaft position sensor gathers information about the vehicle’s camshaft speed and sends it to the vehicle’s engine control module (ECM). The ECM uses this data to determine the timing of the ignition, as well as the timing of the fuel injection that the engine requires.