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Old 01-08-2008, 11:00 AM
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How to correctly set the timing?

I feel pretty dumb asking this considering I assembled my engine, and the only work I didn't perform was the machine work to the block and heads, but what is the correct way of determining the timing on a small block chevy? I've always tuned by ear and vacum, but would like to know exactly what it's set at.

Currently, with a timing light, at 750 rpm it is reading on my C.A.T. fluid damper about 38-40* at the 0 mark, with the Accel adjustable vacum advance unplugged, and the lightest set of springs in from a Mr Gasket curve kit. I also ground some of the small end of the counter weights off to prevent some binding/catching that was taking place.

I guess my question is, with an aftermarket timing tab (Mr Gasket chrome one that I dremeled into a V so I could read where 0 was at easier), and balancer (etched with timing marks), how do I tell my initial advance, mechanical advance, etc?

Thanks in advance!

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Old 01-08-2008, 12:32 PM
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Down and dirty....

start the engine set it at like 1000 rpm, disconnect the vacuum advance, plug the port on the carb. Set your timing to the specs on your Cam Card. no cam card? start at like 8 degrees BTDC if you are reading 38-40 at this point then you are way off.

That is initial timing,

plug the vacuum advance back in, set it to 2000-2300 rpm check what you have for a reading, this is your total advance. Should be about what you were reading the first time (32-38)

With it still going that speed, disconnect your vacuum advance plug the port and check what you have...subtract your initial advance...this is your mechanical advance.

This is just off the top of my head, there may be different opinions on what RPMs to set it at but you can always play with it to see what works best for your motor.
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Old 01-08-2008, 12:45 PM
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THANKS!!

So, should I be reading the 8* at the 0 mark on the pointer?

I tried dialing it back that far while it was hot and running, but about the time I get to 20* it starts to want to die- I'll see if bringing the rpm's up to 1k will help.

I noticed when I was revving that it would get as high as 50-60*.

Hooking up the power wire for the new electric choke tonight- I'll have to check it out then.
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Old 01-08-2008, 01:05 PM
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Sounds like you may have either the wrong timing tab, wrong balancer or tape on the wrong place. If it wants to die at 20, something is wrong.

Mark
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Old 01-08-2008, 01:10 PM
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Bolt on timing tabs are not accurate. They are always off the mark. You need to find true TDC using a piston stop then adjust the tab and weld the timing tab onto the timing cover in the correct position.

If the motor has a big cam in it you need to modify the distributor advance curve. This involves more than changing the springs.
You want around 24 deg at idle and 34-36deg at high rpm + about 12-15deg of vacuum advance at cruise.
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Old 01-08-2008, 01:15 PM
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Yeah, I would assume that something is wrong there. You have the timing light on the #1 plug wire right? Here is a picture of what your timing tab and balancer should look like at top dead center on the compression stroke on the #1 cylinder. If it does not look like this then you will not have accurate readings. On my tab 0 is at the bottom of the tab and yours is probably in the middle. I have a programable timing light so I just set the advance I want and bring the mark back to zero.
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Old 01-08-2008, 01:38 PM
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That might be where I've messed up then.....my balancer is a C.A.T. 6.25 , and the timing tab is a typical Mr. Gasket parts store item...not sure what size it's meant for, it was just something that I assumed would work.

Should I look into a Tavia/summit style timing tab like this http://store.summitracing.com/partde...5&autoview=sku

As far as welding, that's out for me...I have no welding equipment, or buddies with any for that matter.

Engine is a warmed over 312 SBC. The cam is 214/224 @.050, .442/.465. I'm running an OE distributor housing w/ an Accel Supercoil, Accel ICU, Accel Adjustable Vac Advance, Mr Gasket curve kit (Lightest springs w/ modded weights), Unilite capacitor and harness, Accel cap, Taylor Thundervolt wires.

I will check TDC tonight once I finish on the choke- my 0 mark is more in the middle/middle to passenger side. I don't *think* I advanced or retarded my cam when I installed the gears, but I might be pulling the cover if TDC isn't checking out.
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Old 01-08-2008, 01:44 PM
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Quote:
Originally Posted by Double_v23
Yeah, I would assume that something is wrong there. You have the timing light on the #1 plug wire right? Here is a picture of what your timing tab and balancer should look like at top dead center on the compression stroke on the #1 cylinder. If it does not look like this then you will not have accurate readings. On my tab 0 is at the bottom of the tab and yours is probably in the middle. I have a programable timing light so I just set the advance I want and bring the mark back to zero.
Yes- light is on the #1 cylinder wire. Like I said above, mine is waaaay off compared to that.

Could it be b/c the timing cover that was originally on the engine was the style with the hole welded at about the 12 o'clock position so you had to look down the back of the water pump? Would that affect the keyway placement on the crank?
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Old 01-08-2008, 01:59 PM
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For that cam I would suggest 12- to 16deg initial at idle 34-36deg at 3000rpm +/- ... Then 15deg of vacuum advance. Sounds like you may have fubared the advance weights.
The lightest tension springs are too light and result in a unstable advance curve. use one med and one light spring. you want a smooth curve that starts at around 1100-1300rpm and peaks at 3000rpm +/-

slow down the engine idle speed as slow as it will idle when setting the initial timing to be sure you're on the base of the advance curve.
Check and verify the max advance. will probabily need the large diameter advance pin stop bushing.
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Old 01-08-2008, 02:15 PM
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Quote:
Originally Posted by F-BIRD'88
For that cam I would suggest 12- to 16deg initial at idle 34-36deg at 3000rpm +/- ... Then 15deg of vacuum advance. Sounds like you may have fubared the advance weights.
The lightest tension springs are too light and result in a unstable advance curve. use one med and one light spring. you want a smooth curve that starts at around 1100-1300rpm and peaks at 3000rpm +/-

slow down the engine idle speed as slow as it will idle when setting the initial timing to be sure you're on the base of the advance curve.
Check and verify the max advance. will probabily need the large diameter advance pin stop bushing.
I'll give that a shot, as well as the set of weights from the other kits (I have another Mr Gasket one, and an Accel kit laying around).

Question of ignorance...is the bushing you talk about the ones that don't have a sholder and don't fit into the weights? That might be part of my problem, as i don't think that I've installed those into the 2 posts that go through the plate under everything in the distributor.
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Old 01-08-2008, 03:49 PM
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You want about 20deg of mechanical advance travel for the cam you chose. If you have more than that you have to install a different advance stop limit bushing on the advance limit pin that runs in a slot on the bottom of the advance mechanism. (GM HEI)
Sometimes the shape of the wings on the end of the GM HEI advance weights set the advance limit by contacting the advance center piece at full advance, but I've never found this to be consistent.

Sometimes I just weld up the end of the limit slot and regrind it out for the amount of advance limit I want to achieve, When setting up a distributor.
If you use that method to limit the advance make sure you're welding up the right end of the slot or the springs won't have proper tension at idle.
Requires disassembling the distributor drive gear, shafts and advance mechanism.

Once you've found true TDC using a piston stop you can bend the bolt on timing tab and or loosen the timing cover bolts that attach the tab and move it as necessary to get the 0 mark lined up correctly with the TDC mark on the balancer and retighten the bolts. If you don't tack weld the tab to the timing cover at that point and you disassemble the timing cover later on, you probabily won't get the tab back in the exact right spot again.
Mine was out by 4 degrees.

Last edited by F-BIRD'88; 01-08-2008 at 03:58 PM.
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Old 01-08-2008, 05:50 PM
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Remember that there are at least two different balancer/tab combinations used on SBCs. The cover/tab combination pictured in an earlier post is usually listed as a balancer with a 2:00 o'clock TDC. The original cover you removed was designed for a balancer with TDC at 12:00 o'clock (straight up).

You need to look up the specs on the balancer you bought, and make sure you are locating the tab in the right place.

Bruce
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Old 01-08-2008, 08:03 PM
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Quote:
Originally Posted by 75gmck25
Remember that there are at least two different balancer/tab combinations used on SBCs. The cover/tab combination pictured in an earlier post is usually listed as a balancer with a 2:00 o'clock TDC. The original cover you removed was designed for a balancer with TDC at 12:00 o'clock (straight up).

You need to look up the specs on the balancer you bought, and make sure you are locating the tab in the right place.

Bruce
This is the one that I purchased....

http://paceperformance.com/index.asp...&ProdID=136874

It is a 2:00 position- but mine seems to have Zero at 12:00......could I have miffed it 90* when I installed the distributor?

To give you an idea of which way the distributor is pointing, the pickup, power, and tach wires that lead into the coil are pointed at 3:00 if you are at the front of the engine looking towards the firewall.

Going out shortly to check TDC....just got my brand new laptop and setting it up and snaking wireless off a neighbor lol!
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Old 01-09-2008, 10:21 PM
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Finally got around to messing with the car tonght.

1. Hooked up choke power wire to battery, as the battery to my voltmeter went dead. Murphy's law is in force still I reckon.

Car didn't want to start, but finally would after pumping gas about 10 times, and messed with timing. After car ran and just started to approach warming up, it died.

Pulled #1 plug. Running rich.

Rotated engine to find TDC w/ finger and a screwdriver in the hole. TDC is within 4* of where my pointer is marking 0.

2. Pulled the 'fubar'd' weights, centerplate, and 1 of the lightest springs out (black), and put in the untouched weights, one medium spring, and matching centerplate for that set. Also pulled the narrow bushings out of the weights, and added the large diameter bushings (no shoulder, fits loose on the posts).

Car didn't want to start initially, but after messing with timing and adjusting the choke she finally did. She ran fairly well, (better than before) but was sluggish under throttle of any amount.

Fired right up to 1200 or so, dropped down to 500, died. Kept messing w/ timing and choke, got it to run at roughly 1200, but then would drop down to 1000, pop/slight backfire through the exhaust, then rpm would jump about 200, and slowly decrease back to 1000, pop rise, and slow, until finally, it slowed gradually to 500 and died.

I had a LOT of popping through the exhaust during any revving, at all rpms, which leads me to believe I should re-set my lash a bit looser.

I'm L O S T.

What's next? Pull the timing cover and check the timing marks on the sprockets? I also have no idea how old the distributor is- replace it with a new one?
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Old 01-09-2008, 10:23 PM
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Or is it possible that instead of having the distributor off 180*, I have it off 45 or 90*?

It's fully seated against the intake.
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