How to fix timing. tdc is at about 8-12 degrees not zero. - Hot Rod Forum : Hotrodders Bulletin Board
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Old 03-02-2004, 11:08 AM
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How to fix timing. tdc is at about 8-12 degrees not zero.

Well i was trying to get my truck to run good, so i got it to(supposedly) top dead center and got the rotor turned to where cylinder 1 fires. and we turned the distributer to try to get it fired up but it just backfires and flames out the carb. So we stuck some kind of long object into the first cylinder and we couldn't feel the piston come up till about 8-12 degrees past tdc. so how am i going to fix this? is the timing off a couple teeth maybe??? Could it be anything else?? how do i know where the belt should go???

I'm worken with a chevy 307

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Old 03-02-2004, 11:36 AM
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The piston doesn't come up past TDC ... it's the guy that marks where TDC is. That means your distributor is firing about 8-12* before the piston reaches TDC which is about kinda where you want it depending on setup.
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Old 03-02-2004, 11:40 AM
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Pull the drivers side valve cover and confirm you are at TDC on the compression stroke. That will be right after the intake valve on #1 cylinder opens and closes.

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Old 03-02-2004, 11:40 AM
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nah it's a gauge mounted on the side, it's not drawn on there. it's definatly not good when tdc is at 12 and not 0 where it should be. its on the compression stoke, we took the spark plug out and felt for compression while i turned it over.
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Old 03-02-2004, 12:15 PM
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First off, for checking the TDC mark, it doesn't matter whether you are on the compression stroke or not. The piston will be at top dead center every revolution, and checking for the timing mark can be done on any revolution. Now if you're setting the distributor timing, then finding the compression stroke is important.

Just to make sure you are getting a true measurement, it's best to use a piston stop, or at least a dial gauge so that you can really find true TDC. The piston should be measured at say a half inch before TDC on clockwise movement with the damper marked, and then rotated counter clockwise until the same stop is touched and another mark is made. Your TDC will be in the middle of the two marks. It is too imprecise to attempt to guess when top dead center occurs by just rotating the engine one way and feeling when you think it has hit its peak.

If the factory inscribed mark doesn't agree with your new found TDC, then either the chain is a tooth off or the balancer ring has slipped on the hub.
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Old 03-02-2004, 12:20 PM
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Want to find TDC?


take an old spark plug, break out the middle part, porcelin and all. Take a bolt that will go down through it and extend a ways into the cylinder and hit the piston. Weld it to the plug housing.

Take all your plugs out. Thread this plug with the bolt into #1 sparkplug hole. Turn the engine over by hand until the piston contacts the bolt. Make a mark on the harmonic balancer corresponding with the 0 mark on the timing tab. Turn the engine the opposite way until the piston contacts the piston again. Make another mark on the balancer at the 0 mark. Measure the distance between the marks. 1/2 of that is exactly where TDC is......
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Old 03-02-2004, 01:25 PM
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i know just feeling it won't tell me where tdc is but it's still going up after tdc when it should be going down.
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Old 03-02-2004, 04:15 PM
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Sounds like your balancer ring has slipped. This will cause timing to show incorrectly. Get a new one.

Chris
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Old 03-03-2004, 12:12 AM
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yeah thats what happened i got it to where i could look in the piston to see where it goes up and starts to come down, it said it was at 8 degrees on the gauge thing on the pully so i put the rotor pointing to the first cylinder and it started up and we timed it to 12 , runs like it always has and it needs to new points, i picked new ones for like 2.49. i hope it helps a lot cuz that would be cool, i think it runs good now, lets see how it is after i swap in the new one.
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