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#1
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Finding TDC Land
We have been reading the MOPAR small block racing book, and are performing the TDC timing mark verification section (from the book) to see if the timing marks on the harmonic balancer are accurate.
This is a 360, externally balanced small block. Heads are on. So we are doing the procedure where we have screwed a special plug into the #1 spark plug hole that is definitely so long that the piston hits it as it comes up. We are being very careful to turn the crank bolt ever so slowly so as to not poke a hole in the piston or rip the spark plugs threads out. We have NOT installed a degree wheel; rather we are just making marks on the factory harmonic balancer (HB). Early testing shows that coming up to TDC from one direction, the interference happens at 1 7/16" from the factory groove on the HB. But coming up from the opposite direction the interference happens at 1 1/4" from the groove. I believe that this 3/16 inch difference is significant and probably will convert to 3 to 5 degrees. So here are my questions: 1) Is this testing method faulty? 2) Is it common for a HB to be this far off? 3) If I just make a new "TDC" mark on the HB, I would be worried that the HB might easily slip again (since it obviously has slipped in the past). Are my fears warranted? 4) If I do need to buy a new HB, what is a good choice? This is NOT a high power engine, has been estimated to have only 325 HP at the flywheel. Will the new HB have the correct "externally balancing"? 5) Are there some considerations that I have spaced on? Thanks for your input, T |
#2
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I have used a dial indicator through the spark plug hole before, that worked. The "bolt" screwed in method never appealed to me, for the same concerns you stated. You can spend a $285 or even more for a racing type H.B. but if you are not trying to pass tech at some race track this is not neccessary. I have seen replacement ones for $50-60. There is always the salvage yards too.Stock mopar ones rarely slip, although they can. I used a stock one on my drag car until they "forced" the issue. (by a rule change)
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#3
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Try a shorter or longer "specal" plug and see if you get the same reading
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#4
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The method that you used is valid and accurate. It is not unusual for a factory balancer to be that far off. I would mark the correct 0º mark and then check it again after another 500 - 1,000 miles of driving. Then do the measurements again. If the new 0º mark is still in the center, then the balancer is not slippin
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#5
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Yeah, that is THE method, period. It would be the same with a degree wheel, but you wouldnt have to measure with a tape, just devide the degrees in half and scratch a new mark.
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#6
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Finding TDC
Thanks guys!
I guess I will use the old HB. I am just surprised that the factory can be that far off. Tim |
#7
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They're not that far off when new but the ring does slip with age. If you merely make a new mark ir will eventually spin again and the mark will be off.
Get a new one or have yours rebuilt. |
#8
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Paint some marks on both parts of the damper, so you know if it slips more later.
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#9
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Quote:
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#10
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Wohooo! I wrote something right!!!
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#11
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FYI, Iv'e seen two stock damper rings slip, by a bunch! One was mine, found to be 10 deg. off during assembly, the other, my buddy's, while we were driving it for the first time and trying to set the timing. Slipped each time we drove it! Now I can't bring myself to trust a stock one ever again!
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#12
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P.S.- That is a good damper 'Quich Check' idea you have 'Rusty'!
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#13
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I am just too lazy to measure everytime I set the timing...
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#14
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HB was 2 degrees off, now is OK
Thanks to all for the discussion. I redid my measurements and determined that my HB was ONLY 2 degrees off. I measured it with 3 different "piston stop" heights such as 23T suggested, and got the same answer each time. Then I "dremeled" a new groove at the new zero place, and applied a mopar timing tape using the new zero. Then I "dremeled" some small cuts into both metal pieces, crossing over the rubber boundary, just as Rusty suggested so I can easily detect any future slippage.
Rusty, you are a genius. Tim |
#15
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Uh, sure, whatever...
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