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Old 07-22-2011, 12:15 AM
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Please Help with a rebuilt 350 bored

Hey guys I really need some help I am at my breaking point. I have a 69' chevrolet with a rebuilt 350 bored over, flat tops, 202 camal hump heads. Im have trouble getting it tuned, I've pulled the top end off and distibuter multiple times. And I talked to a guy from a machine shop and he said that the cam and the crank dots are suppose to be both at 12 o'clock. Which is different from what I was taught, were the dots were suppose to meet, crank at 12 and the cam at 6 but he said this was tdc for the number 6 cylinder. Which is right? But when the dots meet it spudders at low rpm like its missing. And runs desent at 22-40 degrees and put new plugs. please help any advise would be awesome.

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Old 07-22-2011, 03:24 AM
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You want to verify that you have the Number 1 cylinder at top dead center on compression. Then look at the timing marks on the cam and crank gear and see where they line up. All timing is set off the number one cylinder.

If you have a timing set with multiple marks, that can throw you off.

What kind of cam do you have?

Did you check all the other systems?

Did you check for vacuum leaks?

Is the carburetor calibrated properly?

What kind of ignition system are you using and is it functioning properly?

Do you have enough fuel pressure?

Float bowl height ok?

Did you do a bunch of changes and lose track of where you were?

Did you break in the cam properly, if it's a flat tappet? ( Lose a lobe, it'll sputter and miss )

Did you set the valves properly?
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Old 07-22-2011, 04:11 AM
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Ok so what I know is that the piston was at tdc will dropping the distributor. Even with all other systems not running properly doesnt explain why truck runs fine at 22-30 degrees. I know my cam is a rv cam, nothing to big. Carb is a little to big for the motor, yet that would only cause over fueling. No vacuum leaks. Possible flattening of cam lobes, that would cause sputter at all rpm ranges. And my valve adjustment should be good spark plugs seem in good condition for overfueling. Their is a possibility that something could be wrong with distributor HEI.

Question which way are the dots on cam and crank suppose to be faceing 12 and 12 or 12 and 6. I thought dot to dot (12 and 6 o'clock) Cam at 6 and crank at 12
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Old 07-22-2011, 04:13 AM
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Sorry and their is no other marks on timing chain
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Old 07-22-2011, 04:40 AM
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The crank turns at twice cam speed. The dots are properly aligned with the cam gear at BOTH 6:00 and 12:00. The only issue is getting the distributor in correctly- one orientation will have no 1 at TDC on the compression stroke and the other on the exhaust stroke, at which point you need to rotate the distributor shaft 180 deg.
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Old 07-22-2011, 04:54 AM
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I know that I'm at tdc. I pull number 1 spark plug and turn the motor over until I can feel air push my finger from the hole and the exhaust stroke I could see the exhaust lifter commpressed. I'm thinking my timing is good maybe my distributor is bad or wires
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Old 07-22-2011, 05:12 AM
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Quote:
Originally Posted by importeater33
I know that I'm at tdc. I pull number 1 spark plug and turn the motor over until I can feel air push my finger from the hole and the exhaust stroke I could see the exhaust lifter commpressed. I'm thinking my timing is good maybe my distributor is bad or wires
Bottom line on the timing set dots:

If the dots are at 12 o'clock on the cam gear and 12 o'clock on the crank gear, cylinder #6 is at TDC compression (firing).

If the cam gear is at 6 o'clock and the crank gear is at 12 o'clock, cylinder #1 is TDC, firing.

In EITHER position, cylinders #1 and #6 will be at TDC- but on different strokes.

In your case, be sure the plug wires are correctly run: 1-8-4-3-6-5-7-2, CW on the cap. Be sure #5 and #7 cylinders are not swapped at the cap or at the plugs- they are next to each other physically and in the firing order.

Be absolutely sure the valves are not set too tight- this will cause the engine to run poorly.

Be positive the timing mark on the damper and the timing tab are correct. The following is from another post I made on this:

Quote:
There are several different dampers and timing tabs. Both the diameter, thickness and the placement of the line on the outer ring of the damper can differ, as well as how the timing tab is positioned. So you need to know what damper you have, to know what tab to use.

The three most common locations for the timing mark on the damper:

The exact years of the type of damper timing marks overlap one another, depending on the exact application.

The pre-'69 damper has the TDC line on the outer ring at the 2:30 o’clock position- or 2º before- (i.e. to the LEFT of the keyway, looking at the front of the engine) the keyway centerline. The keyway is seen in the ID of the damper.

The damper used from '69 to about ‘84 has the TDC line at the 2 o’clock position- or 10º before the keyway. You'll find that aftermarket dampers are the 10º type, as are the bolt-on tabs sold in the aftermarket, unless they're adjustable.

A third timing mark was used from about 1978 to about 1995. It is at the 12 o’clock position- or 40º before the keyway. This damper uses a timing cover that has the tab welded on at about the 12 o'clock position. Professional Products lists the years for this type damper line as being ‘84-’95 and is a 6-3/4” diameter damper.

If you're unsure, or just want to check the accuracy of the tab/mark for TDC, DETERMINE TDC and MAKE A TIMING TAPE will help you to see for yourself.
PHOTO OF RELOCATED DAMPER LINE-
The damper is a "12 o'clock" version, the tab is a 2 o'clock version. The difference in the lines looks like (photo from here):
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