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Old 04-17-2012, 11:37 AM
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Strange ignition timing readings

Hi guys. I need some help making since of these timing readings i am getting from my 383 sbchevy. When i start it up and check the timing at 1200rpm (which because of the hefty solid lifter cam is where it idles at) i get a reading of 31 degs. When i rev the engine up to 3500rpm i get a reading of 51deg. I know that every sbc engine i ever played with in the past ran best at around 32 to 35 degrees advance. But if i back off the timing to 32 deg, the engine will start popping and backfireing through the carb. I cant find any reason why this particular sbc wants so much ignition advance to run properly. Anyone ever have this type of problem?
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Old 04-17-2012, 11:57 AM
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First turn the crank until #1 TDC and see were the timing mark located. It should read "0". your harmanic dampener may be off.
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Old 04-17-2012, 12:04 PM
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Thanks lg1969. But i already checked that. I put on a new fluidamper a few months ago and checked the 0 mark on it and all is well.
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Old 04-17-2012, 12:18 PM
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1200rpm Idle sounds like a Hefty size Cam, which will require a lot of Initial timing. What Duration @.050" Lift?
Are you checking it with Vacuum canister disconnected & plugged?
If so, you'll need to limit your Mechanical timing advance.
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Old 04-17-2012, 12:22 PM
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Then there is a good chance the cam may be off by a tooth.
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Old 04-17-2012, 12:26 PM
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Let me refer to the cam card and I'll get back with you
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Old 04-17-2012, 12:40 PM
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Quote:
Originally Posted by Balls
Hi guys. I need some help making since of these timing readings i am getting from my 383 sbchevy. When i start it up and check the timing at 1200rpm (which because of the hefty solid lifter cam is where it idles at) i get a reading of 31 degs. When i rev the engine up to 3500rpm i get a reading of 51deg. I know that every sbc engine i ever played with in the past ran best at around 32 to 35 degrees advance. But if i back off the timing to 32 deg, the engine will start popping and backfireing through the carb. I cant find any reason why this particular sbc wants so much ignition advance to run properly. Anyone ever have this type of problem?
How much base timing and how much in the centrifugal and does it use vacuum advance?

Oh yeah what are the cam specs?

Bogie
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Old 04-17-2012, 02:08 PM
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If you were to use an early timing tab w/the afterrmarket damper, the result would be an abnormally high timing reading (~8-10 degrees).

What type of ignition are you using (what distributor, vacuum advance or not, etc.)?
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Old 04-17-2012, 02:21 PM
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check your vacuum advance, and also check that your 0 mark on your timing marker is exactly at TDC on #1 cylinder.

You don't need a timing tab or a correctly marked balancer to set the timing. I often move my timing indicator to where ever I have easy access to, put the engine at TDC on the compression stroke and put a mark on your balancer where the timing pointer is now pointing at. To set where you want your total timing marker at just figure out what the distance along the radius is for your diameter of balancer and desired total advance.
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Old 04-17-2012, 02:51 PM
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Cobalt327... i am using an old styie timing chain cover that has a welded on pointer with the fluidamper. Is that the problem u think? Cam specs are: at. 050 avg duration 262/274 lift. 543/.517 valve lash is. 22/.22. Ignition is an HEI MSD streetfire with a 6AL box and blaster 2 coil. I am using the vacuum advance.
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Old 04-17-2012, 03:47 PM
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Quote:
Originally Posted by Balls
Cobalt327... i am using an old styie timing chain cover that has a welded on pointer with the fluidamper. Is that the problem u think?
If the tab is the wrong one it could explain at least 8 degrees of error, anyway.

A couple pages that might be useful to you:

DETERMINE TDC. This will let you to be sure the timing tab and damper are correctly showing you TDC.

MAKE A TIMING TAPE. Useful for determining total timing, setting up the distributor timing curve, etc. w/o needing a dial back timing light.

Like mentioned earlier, there were three different sets of damper lines and timing tabs that go together. THIS page describes them. If these get mixed and matched wrong, you can get false timing readings like I mentioned before.

A "quick and dirty" method to see if there's a large error between the timing tab and damper line is to use a length of wire (like a foot long so there's no way to lose it down the plug hole) to show you when the piston is at TDC as you crank the engine over slowly by hand. The piston moves very little right before/at/after TDC, so this method isn't super accurate. But after you get a feel for it, you can get pretty darned close. And if it's easier to reach you can use #6- it comes to TDC at the exact same time as #1, just on a different stroke (like #6 will be on exhaust stroke when #1 is on the compression stroke).

Be sure to take all the plugs out so you're not fighting compression as you turn the engine over. You should have no problem using the damper bolt, but please be careful you don't accidentally over tighten the bolt.

Someone also mentioned the chance the timing set was installed a tooth off. Any chance that happened? Is the timing set the type w/multiple keyways for advancing or retarding the cam?
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Old 04-22-2012, 02:45 PM
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Okay guys thanks for all your input but here's what I found out. With the number 1 piston at TDC on the compression stroke, the timing tab is pointing directly at 0 on the balancer. Then being very careful not to rotate the crank i disassembled the front if the engine, droped the front of the oil pan and removed the timing chain cover only to find rhe marks on the crank and cam gears lined up perfectly with each other. So after reassembling everything and making sure the rotor tab was pointing at #1, i set my timing light at 35degs fired the engine up and after it warmed up i took a timing reading at 3500rpm only to find i had to advance my light another 16degs to get the 0 mark on the balancer to line up with my timing tab again. This makes my total toming advance an unbelievable 51degs. The engine runs great starts and shuts off fine and dosent run hot at all. I guess its just going to remain a mystery.
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Old 04-22-2012, 03:00 PM
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By the way, i did all that with the engine in the car. Talk about a *****.
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Old 04-22-2012, 05:17 PM
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51 degrees is fine- if the vacuum advance is hooked up.
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Old 04-22-2012, 06:57 PM
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It is. Thanks
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