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Old 10-12-2004, 01:26 AM
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What will an off harmonic balencer do???

Well i put my engine to tdc and i checked my harmonic alencer and it said it was 4 degrees After Top Dead Center what how will this affect my engine, it's performance, will it hurt it???

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Old 10-12-2004, 06:23 AM
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Balancers do not have adjustments. They slide on one way and thats it. I dont know how you found TDC, but this is usually done with the heads off and with a degree wheel,once you find TDC then your pointer is set to point to 0 on the balancer.

Ben
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Old 10-12-2004, 07:35 AM
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You didn't mention the motor this is on, but I'll bet it is a small block chevy. Later versions of the bigger small block balancer have the timing mark shifted, and the tab on the timing cover was different as well. So, if you run a new balancer with an older timing cover/tab, the marks are off 4 to 6 degrees or so.

I had this situation on the 327 in my 68. The new GM balancer I bought didn't match up with the 68 timing tab. I just set the engine at TDC, scored a straight line across the balancer to match the timing tab, and filled it in with a liitle silver paint pen. It showed up just fine under the timing light.

There's no issue with the machined groove on the balancer being a little off.
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Old 10-12-2004, 10:33 AM
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Harmonic Damper issue

Erictopless' reply is correct if you have a SB Chevy Damper. Pre '69 engines have the TDC mark 2 to the left of the keyway centerline. The '69 and later dampers have the TDC mark 10 to the left of the keyway centerline. Almost all aftermarket dampers use the later TDC position. If you have a pre '69 vehicle you can use one of the aftermarket bolt-on timing pointers to align correctly with the timing marks on your dampers.

Another possibility is if the damper is old and worn, the outer ring has moved relative to the hub which is keyed to the crank. The outer ring is pressed on over the rubber between the ring and the hub. Once this rubber gets old, it is possible for the outer ring to slip causing your marks to be off. If this is the case, you should get a new damper because it is possible for the ring to fly off the engine and it can do a lot of damage if it does.

A third possibility is that if it is a new or rebuilt damper that the ring has been incorrectly positioned relative to the keyway during the manufacturing process. Some of the cheaper replacement dampers on the market are not always exactly correct.
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Old 10-12-2004, 10:36 PM
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Yeah it's a 1968 SBC 307. it was rebuilt a while back, i'm not sure if they used the stock balencer or not when they rebuilt it but, i know i haven't replaced it. i hope it's just off. any way to look at it to make sure??
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Old 10-13-2004, 09:43 AM
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The simplest way to check it is to buy one of the bolt-on timing pointers. They are very inexpensive. Bolt it on, and then find tdc with your engine and if your TDC mark on the damper lines up with the pointer, which it should, then you know you are ok. There is no other way that I know of to check it other than having a measuring lab look at the damper and tell you where the TDC mark is relative to the keyway. As stated earlier, it is either going to be 2 degrees to the left of the keyway or 10 degrees. If it is 2 degrees your stock '68 pointer should line up. If it is 10 degrees, the aftermarket pointer should line up. If it is something other than those two measurements, then the ring has either slipped or it was made wrong to begin with. There is a good chance that when the engine was rebuilt they put a new or rebuilt damper on it and then there is about a 90% chance it has the later timing TDC mark.

I presume you know how to find TDC on your engine. The easiest way I know is to buy one of those TDC finders that screws into a spark plug hole or make one by welding a short length of rod into a spark plug. The rod should have a rounded end on it so it doesn't dig into your piston while checking for TDC. Turn the engine one way until it hits the plug. Draw a line on your damper that lines up with the pointer. Then turn the engine the opposite way until it hits the plug again. Draw another line on your damper that lines up with the pointer. Half way between the two lines you have drawn is your true TDC.

You didn't say how you originally found TDC on your engine to determine that the TDC mark was off. But if it wasn't something like I just described, possibly you made an error at that point.
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Old 10-16-2004, 03:24 AM
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It was a while ago but i belive we turned it slowly with my friends finger over the number one piston spark plug hole till he felt compression and i was able to get a flash light and my head down into the engine and i was able to see where the piston stoped going up and went down. got it right before it was going to go down and checked it!!! it was about 4 degrees off
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Old 10-16-2004, 12:27 PM
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I wonder if the rubber is broken and it slipped...I had one do that, it eventually went back against the timing cover...caught it by accident. I would use the head, with the valve cover off and the flash light thing to find tdc or close to it. When your at or near tdc the valves will both be closed and the push rods will be able to turn..ever so slightly. Then look at your timing marks. Are you SURE thats the right balancer....right year for the motor and right size? 327sbc and 305sbc and 350sbc balancers are all different.


Tazz


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Old 10-18-2004, 05:07 PM
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To: TM454

Except for 1984 and later engines, SB Chevys have only had two different locations for TDC. Up through 1968 was in one position and 1969 through 1983 was in a different position. These two positions are 6 degrees apart.

The SB Chevys primarily have had two different diameter dampers, 6.75" and 8" although there were some other oddball sizes too. But these dampers, depending on the years listed above, had the same TDC mark irresepctive of the diameter.

Since the method 61ChevyTruck used to find TDC was imprecise, I suspect his 4 degrees off was really 6 degrees off and was the difference between the early and late dampers.
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