Results and Repair for "warrenmj" Engine Problem Post
01-29-2019, 10:24 PM
#61
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I was looking at this thread and noticed that it was commented that if the TDC line on the damper aligns with the keyway, the damper has slipped - this is not necessarily correct! Prior to 1969, the harmonic dampers had the TDC line aligned with the keyway! So, if one is using a 1966 timing chain cover, the damper should have TDC and keyway alignment! In the case of the OP, the timing chain cover appears to be a 1966 version, so therefore, the OP should use an early damper having the TDC line aligned with the keyway.
With later dampers, the TDC line is shifted 10 degrees CCW. This is characteristic of this thread's replacement damper mentioned earlier. If timing is attempted with this new damper and the old timing tag, the timing will be 10 degrees RETARDED from indications! Beware!
HOW TO TELL AN EARLY FROM A LATE HARMONIC DAMPER...
An easy way to tell an early damper is when the TDC line aligns with the keyway. But if you can't see the keyway, eyeball the TDC alignment compared to the nearest pulley bolt - if it does align, it's an early damper because the pulley bolt hole always aligns with the keyway. If the TDC line appears about 1/2" to the left of the pulley bolt, it's a later damper. In any event, best practice is to always find true TDC prior to working on any unknown engines.
With later dampers, the TDC line is shifted 10 degrees CCW. This is characteristic of this thread's replacement damper mentioned earlier. If timing is attempted with this new damper and the old timing tag, the timing will be 10 degrees RETARDED from indications! Beware!
HOW TO TELL AN EARLY FROM A LATE HARMONIC DAMPER...
An easy way to tell an early damper is when the TDC line aligns with the keyway. But if you can't see the keyway, eyeball the TDC alignment compared to the nearest pulley bolt - if it does align, it's an early damper because the pulley bolt hole always aligns with the keyway. If the TDC line appears about 1/2" to the left of the pulley bolt, it's a later damper. In any event, best practice is to always find true TDC prior to working on any unknown engines.
This is correct, and thanks for pointing that out. In the case of Mark's car, the engine had actually been replaced after the original L79 was destroyed. So the later-model damper was used to align with the later-model timing chain cover (and timing tab) installed on his engine. Any time you do balancer work, timing chain work, swap timing chain covers, or install a different timing pointer, TDC should always be checked and verified. I have made editorial changes to the technical write-ups in the two posts above to clarify the importance of verifying TDC and to make sure ytou are using the correct balancer (damper) for the application. Drop me an e-mail request if anyone needs a copy of my TDC verification paper.
Lars
V8FastCars@msn.com
Last edited by lars; 01-29-2019 at 10:46 PM.
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03-10-2019, 09:44 PM
#63
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Proform part number 66514, available from Summit Racing:
https://www.summitracing.com/parts/pro-66514/overview/
Lars
https://www.summitracing.com/parts/pro-66514/overview/
Lars