. . Timing is Everything
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Intermediate
Joined: Jan 2017
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From: Colorado
balancer
. . I never said it detonates. . This whole thing started with an overheating issue in stop and go traffic. . And no, I have not verified that with an IR gun but have one on order now. .
. . The timing question came up because the previous owner put an 8" balancer on the crank and the timing tab on the cover was gone. . The mark on the balancer was way up, about the one o'clock position. . Far higher than the original 6" balancer would have been. . I found out later that the 8" balancer mark is about 10 deg before the keyway while the original 6" was about 2 deg. .
. . So pulled #1 spark plug, found what is real close to TDC, installed an aftermarket degree tab on the timing cover, checked with the 8" balancer mark and it was a degree of 8. . So calculating the math, if a balancer with a 2 deg offset from the keyway reads TDC on the tab then a balancer with a 10 deg offset should read 8 deg. . Added 10 deg and set it at 18 on my non original balancer setup. . It's also a bit lower than what the previous owner had. . Sounds smooth, will drive it when the rain stops. .
. . The timing question came up because the previous owner put an 8" balancer on the crank and the timing tab on the cover was gone. . The mark on the balancer was way up, about the one o'clock position. . Far higher than the original 6" balancer would have been. . I found out later that the 8" balancer mark is about 10 deg before the keyway while the original 6" was about 2 deg. .
. . So pulled #1 spark plug, found what is real close to TDC, installed an aftermarket degree tab on the timing cover, checked with the 8" balancer mark and it was a degree of 8. . So calculating the math, if a balancer with a 2 deg offset from the keyway reads TDC on the tab then a balancer with a 10 deg offset should read 8 deg. . Added 10 deg and set it at 18 on my non original balancer setup. . It's also a bit lower than what the previous owner had. . Sounds smooth, will drive it when the rain stops. .
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Detonation is usually from too much advance.
I agree with Duke in that without VAC, you likely have too little advance, especially at idle, which may be a factor in your heat problem.
I agree with Duke in that without VAC, you likely have too little advance, especially at idle, which may be a factor in your heat problem.
Team Owner
Joined: Oct 2000
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From: Washington Michigan
Detonation is frequently described as a "tinkling" sound, like shaking a tin can with some BB's in it.
What you appear to have is a '69-up 8" balancer - they moved the timing index line about 9* counter-clockwise from its original TDC position (in line with the keyway) in 1969 to accommodate the all-new small-block accessory drive system with the new "long" water pump and the alternator on the passenger side. This change did NOT affect Corvette until the late 70's or early 80's. That's why you really have to remove the balancer bolt and washer on an unknown engine and see where the keyway is relative to the timing index line on the OD of the balancer so you know whether you're dealing with a stock Corvette 8" balancer or a '69-up 8" passenger car balancer. The 1969 balancer timing index line change also affected the orientation of the timing tab on the timing cover.
What you appear to have is a '69-up 8" balancer - they moved the timing index line about 9* counter-clockwise from its original TDC position (in line with the keyway) in 1969 to accommodate the all-new small-block accessory drive system with the new "long" water pump and the alternator on the passenger side. This change did NOT affect Corvette until the late 70's or early 80's. That's why you really have to remove the balancer bolt and washer on an unknown engine and see where the keyway is relative to the timing index line on the OD of the balancer so you know whether you're dealing with a stock Corvette 8" balancer or a '69-up 8" passenger car balancer. The 1969 balancer timing index line change also affected the orientation of the timing tab on the timing cover.
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Duke
