Estimating timing chain wear
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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. | ||
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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 | + | ==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. | ||
| + | ===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. The chain doesn't transmit the harmonics like a gear drive, and has been found to give good service at a reasonable cost. | 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. The chain doesn't transmit the harmonics 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|Roller chain]] | ||
| + | |[[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. Many timing sets have multiple keyways (seen above on the chain and gear-type timing sets) or other forms of adjustability (as seen on the belt drive above, where the cam gear is adjustable) that allow changes to the cam phasing. 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. | ||
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[[Category:Engine]] | [[Category:Engine]] | ||
[[Category:Adjust valves]] | [[Category:Adjust valves]] | ||
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