Timing chain adjustment - Pontiac GTO Forum
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post #1 of 5 (permalink) Old 08-14-2018, 02:06 AM Thread Starter
 
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Timing chain adjustment

Hey everyone! First of all let me start by saying this is my first restoration/rebuild and I am still learning. I have been relying on numerous publications to get me through the restoration process. I recently purchased a rebuilt 389 that has been sitting for years (YS motor from a 66 GTO). I will be using this engine for my 69 GTO RAM AIR IV restoration. I will be putting Edelbrock 82cc round port heads on shortly. Anyways.... because the engine was sitting so long, I wanted to make sure everything was lubricated and ready to rock n roll before I start putting it together. I noticed the cam gear dot and the crank gear dot do not line up at the 12 o'clock position. I turned over the engine a few times hoping the dots would line up at 12 o'clock but no luck. When my 1 cylinder is TDC, the cam gear is just about 6 o'clock and my crank is at 4 o'clock. I attached a few photos for you to look at. Here are my questions....

1. is this an issue?
2. how do I go about fixing this?

Thanks in advance!
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post #2 of 5 (permalink) Old 08-14-2018, 07:51 AM
 
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Looks to me like you just need to rotate the crank slightly counterclockwise to line up the dots.

That set appears to have 3 keyways: standard, 4 advance, & 4 retard. Make sure you're looking at the right dot or mark that should be used for the keyway you used.

Assuming the dots/marks are in the correct place, always move the crank dot/mark to 12 O'clock. Then rotate the cam til you can line up the cam gear dot with the crank gear dot/mark. It's easier to line up, with the dots/marks at 12 & 6, rather than 12 & 12, because they are closer together.

You just have to remember that at 12 & 6, you're on the #6 compression stroke. Rotate the crank 360 & your dots/marks will be at 12 & 12, and you'll be on #1 compression stroke. This is because the crank turns 2 revolutions every time the cam turns one revolution.

Makes no difference whether you line 'em up at 12 & 6, or 12 & 12, as long as you position your #1 plug wire on the dist cap near TDC of the compression stroke of #1 cylinder. Then, of course, arrange the rest of the wires in the correct firing order in a counterclockwise direction.

I like to line 'em up at 12 & 6, to install the timing set, then rotate to 12 & 12 before installing the timing cover.

But, some like to put a finger in the #1 spark plug hole while turning the crank. When the compression tries to push the finger out of the hole, you know it' on the compression stroke. So, assuming your timing mark is on the balancer is in the correct location, you can just rotate the crank to where that mark is lined up with zero on the timing tab.

When the timing mark is on zero, I like to rotate the dist to where the rotor is pointing just past #1 wire terminal, in a counterclockwise direction. Most guys seem to like 12-15 ignition advance, at idle. Since the wire terminals are 45 apart, you don't want to go over 1/3 of the distance to the #8 wire terminal, since 1/3 of 45 would be 15. Somehwere just short of 15 should easily start the engine. It will at least put you in the ball park.

Some guys will just fish around, by rotating the dist while trying to crank. I've done that too. But, I now prefer the method described, especially for the initial start up of a new engine.
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Last edited by bigD; 08-14-2018 at 08:14 AM.
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post #3 of 5 (permalink) Old 08-14-2018, 08:05 AM
 
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As bigD stated, it appears you have a 3-keyway crankshaft gear, allowing the use of factory, advanced, or retarded camshaft timing. Your engine appears to be set up with advanced timing (note the "A" stamp at the keyway being used). In this case, you use the "A" mark on the gear face instead of the factory timing "dot" in the gear alignment process.

The amount of advance (or retard) can vary with these sets, but typically it's a couple of degrees of cam rotation (or 4 degrees at the crank)... in your case the advanced setting will result in slightly more low rpm torque than the factory timing. Retarded camshaft timing will conversely result in slightly more top end horsepower than stock timing.

Here's a link that might help explain: http://www.cloyes.com/Images/Instruc...0(general).pdf
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post #4 of 5 (permalink) Old 08-14-2018, 08:56 AM
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As has already been said, you're good. Notice that your crank gear has more than one key way cut into it and that it's installed using the one marked "A" (for Advanced). What you've got there is a timing set that allows the cam to be installed "straight up", slightly advanced, or slightly retarded. There will be a different timing mark on the crank gear that corresponds to each of the different key ways.

Note that just because things are installed using the "A" key way and corresponding mark that does not mean necessarily that the cam actually *IS* advanced. Cam suppliers provide specs on how they intend for their cams to be installed expressed as an "intake centerline" value (ICL). You'll sometimes see this reflected in conversations via phrases like "installed at xxx degrees btdc". What this means is that the intake lobe of the cam reaches it's peak lift point when the crank is xxx degrees before top dead center. Setting things up is called "degreeing a cam" and you use a degree wheel and dial indicator to do it. Getting a cam installed to exactly the spec provided by the cam manufacturer sometimes can require "moving" it slightly from the factory timing marks on a factory timing set. Using a timing set with multiple key ways on the crank gear with corresponding marks is one way to do that. Another way is to use keys that have a sideways "offset" in them. Advancing or retarding a cam such that it's installed on a intake centerline different from what the cam supplier recommends is something that should only be done in very specific cases and then only if you've already run the car with it installed as recommended, are seeking a specific result/change, and have good reasons for doing it.

The fact that you've got this timing set in that engine is a clue that someone has been "into it" before. I'd be a good idea to examine everything in it closely to find out exactly what's been done to it.

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post #5 of 5 (permalink) Old 08-15-2018, 12:53 AM Thread Starter
 
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Thanks guys! Makes sense now. The cam lines up with the “A” mark on the crank gear. I really appreciate all help
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  Pontiac GTO Forum > The 1964-1974 Pontiac Tempest, Lemans & GTO > 1964-1974 Tempest, Lemans & GTO Complete Engine Compartment Discussion

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