Check for and adjust L timing chain stretch (L24 L26 L28 L28E L28ET)
02-02-2010, 07:12 PM
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Big Poppa
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Check for and adjust L timing chain stretch (L24 L26 L28 L28E L28ET)
thanks to datzenmike from ratsun for letting me re-post his article over here. he has years of valuble info to share about L series motors.
Check for timing chain stretch
A worn or stretched timing chain or a head that has been resurfaced will effectively retard the cam from it's factory setting that normally gives a good compromise between low speed driveability and high RPM power. Think of a retarded cam as having all valve openings and closings later than they would normally occur. Of all the valve events, late intake closing is the biggest detriment to engine running. Low/mid speed operation is the most affected as the piston is well on it's upward travel in the cylinder on it's compression stroke causing a reversal of flow back into the intake port. True, at higher speeds there is higher intake port velocity coupled with less time for this to happen on a properly timed cam, but on a retarded cam any advantage is moved well above the usable RPM range.
To check for stretch:
Set the motor to TDC compression on the #1 cylinder. Use the notch on the back of the crank pulley and align with the zero pointer on the chain cover on the L series. Or use whatever is your favorite method. The closer to perfect TDC the better. TDC must be set while turning the crank in a clockwise direction only, to keep the tension side of the chain tight. If you go past TDC, return to well before and try again. Remove valve cover.
Looking at the front, there should be finger sized holes around the cam sprocket below the teeth. Just below the topmost hole will be a number, probably a #2, (L16s are set #1 at the factory) look through the hole to the back of the sprocket and you will see a small V or U shape cut into it. A flashlight is handy for this. Just behind the V, etched into the cam retaining plate will be a small horizontal line. This line should be above an just slightly to the left of the V in the sprocket. If it is not, this means that the chain is stretched and the cam timing will be retarded. The etched line represents about 4 degrees of cam timing.
To correct timing chain stretch:
To advance the cam, slip a ratchet handle through one of the sprocket holes to lock the cam from turning and loosen the retaining bolt. Do not remove yet. Lock the chain in position to prevent the chain tensioner from falling out, similar to what you would do the remove the head. Remove the cam bolt, pump eccentric and cam sprocket and advance it to the next position, (#2 hole in this case) and install on the cam dowel with the retaining bolt lightly snugged on. Each number is a 4 degree cam advance.
Likely the TDC has been bumped, so reset TDC as per above. When done, the horizontal etch mark on the cam thrust plate should now be above and just to the left of the V in the sprocket. If this can't be done, the chain is too stretched and must be replaced. When tightening the cam retaining bolt, don't forget to install the fuel pump eccentric. This is easy to do and costs at most a valve cover gasket.
Advancing the cam back into correct time will improve idle, off idle and low mid range power and torque.
Check for timing chain stretch
A worn or stretched timing chain or a head that has been resurfaced will effectively retard the cam from it's factory setting that normally gives a good compromise between low speed driveability and high RPM power. Think of a retarded cam as having all valve openings and closings later than they would normally occur. Of all the valve events, late intake closing is the biggest detriment to engine running. Low/mid speed operation is the most affected as the piston is well on it's upward travel in the cylinder on it's compression stroke causing a reversal of flow back into the intake port. True, at higher speeds there is higher intake port velocity coupled with less time for this to happen on a properly timed cam, but on a retarded cam any advantage is moved well above the usable RPM range.
To check for stretch:
Set the motor to TDC compression on the #1 cylinder. Use the notch on the back of the crank pulley and align with the zero pointer on the chain cover on the L series. Or use whatever is your favorite method. The closer to perfect TDC the better. TDC must be set while turning the crank in a clockwise direction only, to keep the tension side of the chain tight. If you go past TDC, return to well before and try again. Remove valve cover.
Looking at the front, there should be finger sized holes around the cam sprocket below the teeth. Just below the topmost hole will be a number, probably a #2, (L16s are set #1 at the factory) look through the hole to the back of the sprocket and you will see a small V or U shape cut into it. A flashlight is handy for this. Just behind the V, etched into the cam retaining plate will be a small horizontal line. This line should be above an just slightly to the left of the V in the sprocket. If it is not, this means that the chain is stretched and the cam timing will be retarded. The etched line represents about 4 degrees of cam timing.
To correct timing chain stretch:
To advance the cam, slip a ratchet handle through one of the sprocket holes to lock the cam from turning and loosen the retaining bolt. Do not remove yet. Lock the chain in position to prevent the chain tensioner from falling out, similar to what you would do the remove the head. Remove the cam bolt, pump eccentric and cam sprocket and advance it to the next position, (#2 hole in this case) and install on the cam dowel with the retaining bolt lightly snugged on. Each number is a 4 degree cam advance.
Likely the TDC has been bumped, so reset TDC as per above. When done, the horizontal etch mark on the cam thrust plate should now be above and just to the left of the V in the sprocket. If this can't be done, the chain is too stretched and must be replaced. When tightening the cam retaining bolt, don't forget to install the fuel pump eccentric. This is easy to do and costs at most a valve cover gasket.
Advancing the cam back into correct time will improve idle, off idle and low mid range power and torque.
Last edited by SHADY280; 02-02-2010 at 07:23 PM.
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