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Hi guys, 

I went through most of yalls posts on Harmonic balancer pics... but none have the markings I have. I’m trying to set the timing; If y’all can give me a breakdown of what ATC & BTC mean that would be really great help. Yes I know the engines had better days but the cosmetics are the last of the upgrades thanks :)


Edited by kiko619
Left out the specifics

1972 Mach1 H-code 351C - 2V - bought 10/5/2010 still a headeache

1972 Grande coupe Inline 6 1bbl - dad bought in 90's Sold




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  • kiko619 changed the title to 351C Harmonic Balancer

BTC is Before Top (dead) Center, ATC is After Top Center. In your picture the pointer is at approximately 2° BTC. Depending on engine components you'll want to initially set the timing between 6° and 12° BTC.

Edited by Don C
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“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein


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It's rather simple when you look at it. Obviously, the "TC" is short for "top center", and is the zero mark. Your engine turns clockwise, when running,  as viewed from the front. The ATC means "after top center", anything firing here is a retarded spark firing. The BTC side is "before top center", and is where the pointer will show any timing advance. The "advanced" firing markings are used to set initial, and total timing when tuning your engine, the "total advance" being most important, and can play a part in how much initial is used. On these older engines, it is always cautious to remember that the elastomer rubber insulating ring on the harmonic balancer, can deteriorate over time, and allow the outer ring holding the numbers to shift. This doesn't always happen, just be aware that it is a variable when searching for a tuning gremlin 

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