Here are four ways to check a timing chain for excessive stretch:
1. On engines without chain tensioners that have distributors driven by the camshaft, watch the timing mark while checking ignition timing at idle. If the mark moves back and forth, the chain is loose.
2. To check a pushrod engine for chain slack while the engine is in the car:
* Remove the distributor cap and turn the vibration damper in one direction until the distributor rotor begins to turn.
* Then, turn the crank in the opposite direction until the rotor moves again.
* Observe how far the damper moves before the rotor turns.
o Because most distributors are driven by the cam, this is a good way to check for chain slack on these engines.
The engine may still run acceptably with 10° to 15° of chain slack. But ideally, movement should be less than 5° at the crank.
3. To check for a stretched roller chain, pull on the top of the chain while it is on the same sprocket. This can be done during a valve adjustment, while the valve cover is off. A worn chain will have considerable slack when tested in this manner; a new chain will fit snugly on the sprocket.
4. The most obvious way to check chain slack is to measure the slack during engine disassembly, after removing the timing cover.
* Be sure to turn the crank in one direction first, in order to tighten up one side of the chain.
* Then measure the amount of slack in the chain.
-Rob
May 10, 2008 at 7:31 PM
