Estimating timing chain wear
From Crankshaft Coalition Wiki
(Text; interim save) |
(→Resources) |
||
| Line 12: | Line 12: | ||
The wear in degrees can be estimated by comparing the distance between the lines to the timing scale, similar to how distance is measured using a map mileage legend. If the timing scale shows that 10 degrees = about 0.7" (which is what it will be if the damper is 8" in diameter), use that to calculate how many degrees of wear there is in the timing set. | The wear in degrees can be estimated by comparing the distance between the lines to the timing scale, similar to how distance is measured using a map mileage legend. If the timing scale shows that 10 degrees = about 0.7" (which is what it will be if the damper is 8" in diameter), use that to calculate how many degrees of wear there is in the timing set. | ||
| − | If the damper diameter is something other than 8", you | + | If the damper diameter is something other than 8", you can do this: |
*Measure the damper diameter, multiply diameter by 3.14 to get the circumference. | *Measure the damper diameter, multiply diameter by 3.14 to get the circumference. | ||
| Line 26: | Line 26: | ||
As mentioned earlier, wear to the timing set retards the cam and ignition timing. The ignition timing can be corrected by adjusting the distributor using a timing light, but the cam timing error cannot be corrected without disassembly. At that point it would be much better to simply replace the timing set instead of correcting for the wear by using bushings or different keyways, etc. | As mentioned earlier, wear to the timing set retards the cam and ignition timing. The ignition timing can be corrected by adjusting the distributor using a timing light, but the cam timing error cannot be corrected without disassembly. At that point it would be much better to simply replace the timing set instead of correcting for the wear by using bushings or different keyways, etc. | ||
| − | ==Timing | + | ==Checking for "jumped timing"== |
| + | To check for jumped timing: | ||
| + | *If the distributor was moved, put it back to where it was when the engine was running correctly. | ||
| + | *Take the plugs out so the engine is easy to turn over by using a socket on the damper bolt. | ||
| + | *Bring the line on the damper to TDC on the timing tab. | ||
| + | *Remove the distributor cap and note where the rotor is pointing- on a V8 it should be close to either #1 or #6. If it isn't, the timing has jumped, providing the timing marks are correct. | ||
| + | |||
| + | In cases where the timing has been disturbed or the engine has not run yet and it's suspected the cam phasing to be wrong, the cam can be degreed using the "intake centerline method" (linked instructions from Comp Cams). This will show if there's any error in the way the cam was ground, or a problem with the timing set: | ||
| + | |||
| + | ===Camshaft degreeing instructions=== | ||
| + | The reason for degreeing a camshaft is to check that it is phased correctly to the crank. Some things that may cause the cam to be out of phase are: | ||
| + | * Cam or crank gear marked incorrectly | ||
| + | * Incorrectly machined keyways. | ||
| + | * Misaligned cam gear dowel pin/bolt holes. | ||
| + | * Improper machining of camshaft. | ||
| + | * Accumulation of machining tolerances | ||
| + | |||
| + | ====Equipment needed:==== | ||
| + | * Degree wheel, or at least a [http://www.crankshaftcoalition.com/wiki/How_to_make_a_timing_tape '''timing tape'''] on the damper | ||
| + | * A stiff wire pointer attached to the block. A coat hangar or welding/brazing rod will work. | ||
| + | * Dial indicator with enough range to measure full cam lift | ||
| + | * Magnetic or attachable base to affix the dial indicator | ||
| + | * [http://www.crankshaftcoalition.com/wiki/Determining_top_dead_center Top Dead Center] (TDC) stop. | ||
| + | * Solid lifter to fit the engine, or a hydraulic lifter made solid by stacking washers in it or filling with grease. | ||
| + | |||
| + | ====Intake centerline method==== | ||
| + | This method of cam degreeing is not he only way to degree a cam, nor is it considered to be the most accurate. But in this case and for this application it is plenty accurate enough and is quicker, too. | ||
| + | |||
| + | All that is required is finding TDC, then turning the crank in the normal direction of rotation until reaching the point where #1 intake valve is at its maximum lift. | ||
| + | |||
| + | [[Media:Degreeing instructions.pdf|'''Degreeing instructions here''']], about 2/3 down the page. | ||
| + | |||
| + | ==Timing set types== | ||
| + | ===Gear drive=== | ||
Gear drives have become cheap to buy- in some cases less than a timing set with a chain. This entices some into using them, thinking they are superior to a chain. But what has been found is that a gear drive can transmit harmonics from the crank to the cam. In some cases this can lead to unexpected failures of valve train components. The noise a timing gear set makes may be desired by some and disliked by others. There are "quiet" gear drives, but this is done w/helical cut gears that can cause the cam to "walk". This in turn can wear the thrust surface of the block or cause the gear to move out towards the timing cover, necessitating a cam button to position the cam correctly. | Gear drives have become cheap to buy- in some cases less than a timing set with a chain. This entices some into using them, thinking they are superior to a chain. But what has been found is that a gear drive can transmit harmonics from the crank to the cam. In some cases this can lead to unexpected failures of valve train components. The noise a timing gear set makes may be desired by some and disliked by others. There are "quiet" gear drives, but this is done w/helical cut gears that can cause the cam to "walk". This in turn can wear the thrust surface of the block or cause the gear to move out towards the timing cover, necessitating a cam button to position the cam correctly. | ||
| − | Unless a belt drive is used, or (like in the case of some reverse drive and inline engines) a gear drive is standard equipment, the best choice for the majority of engines/applications is to use a true roller chain and gears. | + | ===Chain drive=== |
| + | Unless a belt drive is used, or (like in the case of some reverse drive and inline engines) a gear drive is standard equipment, the best choice for the majority of engines/applications is to use a true roller chain and gears. A chain doesn't transmit the harmonics from the crankshaft into the valve train like a gear drive, and has been found to give good service at a reasonable cost. | ||
| + | |||
| + | ===Belt drive=== | ||
| + | Recognized by many as the ultimate method to drive the cam, a belt drive timing set does not come cheap. But the upside is they're very durable, accurate, and they do not transmit harmonics between the crank and valve train; the belt acts as a kind of "shock absorber" to keep the cam from being affected by the erratic motion of the crankshaft when the engine is running. | ||
| + | |||
| + | {| | ||
| + | |[[File:Float idler gear cam drive.jpg|thumb|center|300px|Gear drive]] | ||
| + | |[[File:Double roller timing set.jpg|thumb|center|200px|Chain drive]] | ||
| + | |[[File:Belt cam drive.jpg|thumb|center|300px|Belt drive]] | ||
| + | |} | ||
| + | |||
| + | ==Adjusting the cam phasing== | ||
| + | Cam phasing is the relationship of the camshaft position to the crankshaft position in reference to TDC. A change of 2 degrees at the cam gear equals 4 degrees at the crank. Many timing sets have multiple crankshaft keyways that allow changes to the cam phasing like seen above on the chain and gear-type timing sets. There are other forms of adjustability like seen on the belt drive above where the cam gear is adjustable (there are chain-type timing sets that use this as well). | ||
| + | |||
| + | On timing sets that have no built-in adjustability, the cam phasing can still be adjusted in many cases. This is done by drilling the dowel pin hole of the cam gear oversize in order to use a bushing to advance or retard the cam gear. On engines where this isn't practical, an offset crank gear Woodruff key can often be used instead. | ||
| + | {| | ||
| + | |[[File:Cam bushings.jpg|thumb|center|280px|Cam gear bushing selection]] | ||
| + | |[[File:Cam bush captured.jpg|thumb|center|250px|Bushing ready for installation]] | ||
| + | |} | ||
| + | |||
| + | {| | ||
| + | |[[File:Offset crank keys.jpg|thumb|center|280px|Crank gear offset key selection]] | ||
| + | |[[File:3 key crank timing gear.jpg|thumb|center|250px|Crank gear with multiple keyways]] | ||
| + | |} | ||
| + | |||
| + | In the majority of cases, installing the cam "straight up" (without any advance/retard added by the installer) is the correct way to install the cam and timing set. Many cam makers have already advanced (in most cases) the cam timing when the cam was made, to suit the application. Unless the builder has access to an engine dynamometer or has advanced knowledge of the dynamics involved, advancing/retarding a cam is nothing but a shot in the dark as to whether it will result in any benefits at all. And there's the chance the engine output could be adversely affected by indiscriminately changing the phasing of the cam. | ||
| + | |||
| + | ==Effects of changing cam timing== | ||
| + | When advancing/retarding the cam, be sure to check valve to piston clearance. Each degree of change effects valve clearance approximately 0.010". Example: If you advance the camshaft 4 degrees, you will '''lose''' about 0.040" clearance between the intake valve and piston, and you will ''gain'' about 0.040" clearance between the exhaust valve and piston. It will be the opposite if the camshaft is retarded. | ||
| + | |||
| + | ===Advance timing=== | ||
| + | *Open Intake Valve Sooner | ||
| + | *Builds more low-end torque | ||
| + | *Decreases piston to intake valve clearance | ||
| + | *Increases piston to exhaust valve clearance | ||
| + | |||
| + | ===Retard timing=== | ||
| + | *Keeps intake valve open later | ||
| + | *Builds more upper RPM power | ||
| + | *Increases piston to intake valve clearance | ||
| + | *Decreases piston to exhaust valve clearance | ||
| + | |||
| + | ====Ford retarded timing sets==== | ||
| + | ;According to [[Media:Crane roller cam instruct.pdf|Crane (page 3)]]<nowiki>:</nowiki> | ||
| + | <blockquote> | ||
| + | '''Note:''' Many 1972 and later Ford-Mercury V-8 engines are originally equipped with a retarded crankshaft sprocket. This may cause idling and performance problems when installing aftermarket camshafts. Eliminate this problem by installing a pre-1972 crankshaft sprocket, (the non-retarded sprocket will have the alignment dot and keyway slot directly in line with each other), or by degreeing in your camshaft, or with appropriate Crane timing chain and gear set. | ||
| + | </blockquote> | ||
| + | |||
| + | An aftermarket performance timing set is a good choice (Cloyes, etc.). Regardless of the timing set that's used, it is always best to degree the cam. That way you will know ''for sure'' where the cam is in relation to TDC. Degreeing the can will also show if the cam or timing set was made wrong, and will give the opportunity to correct for any errors/tolerance creep that can make the cam slightly out of phase. | ||
| + | |||
| + | *On a non-adjustable timing set having just one keyway, if it's a '''straight up''' timing set (no cam retard built into the timing set) the dot on the crank gear will be in alignment with the keyway. | ||
| + | *A set having the dot offset to the right of the keyway (as seen if you were standing in front of the vehicle looking over the radiator at the engine) will give '''advanced''' timing. | ||
| + | *A set having the dot offset to the left of the keyway (as seen if you were standing in front of the vehicle looking over the radiator at the engine) will give '''retarded''' timing. See the drawing below, left for an example of a retarded timing gear. | ||
| + | |||
| + | On a timing set having various keyways for advancing or retarding the cam timing, use the keyway that has the dot or pip mark directly above the keyway, not offset to either side if you want the timing to be straight up (having no advance or retard), like the 1972-back and 1987-newer timing sets. | ||
| + | |||
| + | {| | ||
| + | |[[File:Retarded ford cam1.jpg]] | ||
| + | |[[File:Straight up fprd cam1.jpg|thumb|300px|Example of Ford timing set adjusted to the "straight up" position]] | ||
| + | |} | ||
| + | |||
| + | ==Effects of changing lobe separation angle== | ||
| + | The lobe separation angle (LSA) is ground into the cam at the time of manufacture and cannot be changed by the installer. | ||
| + | |||
| + | ===Wider (larger number) LSA=== | ||
| + | *Generally >/= 112 degrees | ||
| + | *Raises torque to higher RPM | ||
| + | *Reduces maximum torque | ||
| + | *Broadens power band | ||
| + | *Reduces maximum cylinder pressure | ||
| + | *Decrease chance of engine knock | ||
| + | *Decrease cranking compression | ||
| + | *Decrease effective compression | ||
| + | *Idle vacuum is increased | ||
| + | *Idle Quality improves | ||
| + | *Overlap decreases | ||
| + | *Natural EGR effect is reduced | ||
| + | *Increases piston-to-valve clearance | ||
| − | == | + | ===Tighter (smaller number) LSA=== |
| − | + | *Generally </= 110 degrees | |
| + | *Moves torque to lower RPM | ||
| + | *Increases maximum torque | ||
| + | *Narrow power band | ||
| + | *Builds higher cylinder pressure | ||
| + | *Increase chance of engine knock | ||
| + | *Increase cranking compression | ||
| + | *Increase effective compression | ||
| + | *Idle vacuum is reduced | ||
| + | *Idle quality suffers | ||
| + | *Overlap increases | ||
| + | *Natural EGR effect increases | ||
| + | *Decreases piston-to-valve clearance | ||
| − | + | ==Resources== | |
| + | *[[Timing tabs and damper TDC lines SBC]] | ||
| + | *[[Determining top dead center]] | ||
| + | *[[How to make a timing tape]] | ||
[[Category:Engine]] | [[Category:Engine]] | ||
[[Category:Adjust valves]] | [[Category:Adjust valves]] | ||
| + | [[Category:Camshaft]] | ||
Your Privacy Choices