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Old 10-13-2008, 08:06 AM   #1
1965T5

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Default Timing Chain Install Help

Want to make sure I'm understanding the installation process right on my 425. First the crank sprocket goes on (I'll install straight up- meaning "0" degrees). Then comes my question since its been so long....

Do you rotate the crank until the "0" mark on the crank sprocket is at 12:00 - then install the cam sprocket so the "0" on it is at 6:00, so they are dead on...tighten and go?

Or is there more to it? Thanks!
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Old 10-13-2008, 08:44 AM   #2
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Default Re: Timing Chain Install Help

Been along time, but if I remember crank at 12, cam mark at 6 oclock
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Old 10-13-2008, 09:07 AM   #3
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Default Re: Timing Chain Install Help

Kevin is right, that's how it goes. Line up the timing marks on the "line" from the cam to the crank. Cam at 6, crank at 12.
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Old 10-13-2008, 09:24 AM   #4
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Default Re: Timing Chain Install Help

If you are using a multi keyed crank sprocket, you must refer to the instructions for the proper crank gear marker.
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Old 10-13-2008, 11:30 AM   #5
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Default Re: Timing Chain Install Help

That's true, on an aftermarket set, '0' is not necessarily always the same key position.
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Last edited by 7T2Z28 : 10-13-2008 at 06:35 PM.
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Old 10-13-2008, 12:11 PM   #7
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Default Re: Timing Chain Install Help

one more thing - when the crank is first rotated to get mark at 12:00 (independant of the cam with chain off) - does the cam need to then be rotated twice to get the cam mark at 6:00 and have consistant valvetrain position?

or is it better to remove old - not move anything - install new - rotate and check for alignment?
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Old 10-13-2008, 12:34 PM   #8
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Default Re: Timing Chain Install Help

install the new and line up the dots.. be sure to rotate the engine over several times to make sure you have the marks properly lined up... the best thing to do is degree that cam.. to make sure the timing chain isnt lying to you.. but for some ppl its a daunting task.
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Old 10-13-2008, 01:45 PM   #9
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Default Re: Timing Chain Install Help

one more thing - when the crank is first rotated to get mark at 12:00 (independant of the cam with chain off) - does the cam need to then be rotated twice to get the cam mark at 6:00 and have consistant valvetrain position?

or is it better to remove old - not move anything - install new - rotate and check for alignment?
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Old 10-13-2008, 01:50 PM   #10
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Default Re: Timing Chain Install Help

Quote:
Originally Posted by 1965T5 View Post
one more thing - when the crank is first rotated to get mark at 12:00 (independant of the cam with chain off) - does the cam need to then be rotated twice to get the cam mark at 6:00 and have consistant valvetrain position?

or is it better to remove old - not move anything - install new - rotate and check for alignment?
Unless the old chain has jumped the gears, you really want to rotate the engine to align the gears before taking anything apart. Some engines are interference engines, meaning the valves can hit the pistons if the timing chain isn't installed correctly. Rotating the crank or cam independently from each other can cause bent valves on these engines.

Having said that, you are really over-thinking this. Install the chain with the crank gear straight up and the cam gear either straight up or straight down. Since the crank turns at twice cam speed, either is correct. If you haven't pulled the distributor, then you don't even need to worry about where TDC is.
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Old 10-13-2008, 01:56 PM   #11
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Default Re: Timing Chain Install Help

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Originally Posted by joe_padavano View Post
Rotating the crank or cam independently from each other can cause bent valves on these engines..
Not if you remove the rockers to degree the cam.
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Old 10-13-2008, 02:14 PM   #12
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Default Re: Timing Chain Install Help

I know it's been mentioned a few times but I will say it again. You really should degree the cam to ensure it is where it is supposed to be. The last time I lined up the dots then buttoned the engine back up I had poor low RPM performance, and a subsequent check of the cam timing showed it was actually 8 retarded.
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Old 10-13-2008, 02:30 PM   #13
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Default Re: Timing Chain Install Help

[quote=joe_padavano;420553]Unless the old chain has jumped the gears, you really want to rotate the engine to align the gears before taking anything apart.

First - I believe the internals of this engine today are stock. I found this disaster waiting to happen by accident...when I opened the front cover, I found that the chain was very loose and riding on the gear tooth tips. Needless to say, the teeth on the cam gear are worn plenty off and the teeth are knife-edged. I'm unsure if it jumped a tooth. By the looks of it, it could have. I don't plan to degree the cam, as it's stock.

The distributor was out to swap to electronic before I found this. TDC was identified then as well. The chain is still in the engine.

All good advise so far and much appreciated. Any other comments considering this?
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Old 10-13-2008, 02:42 PM   #14
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Default Re: Timing Chain Install Help

Just realize that if you dont degree it now, you may have to tear it back down later if it runs slugish. The only reason you degree is to make sure everything is where its supposed to be, doesnt matter if its a stock cam or not. If the hole in the timing gear is machined just .020 of, your cam timing will be retarded/advanced. Youre basically checking that the part was made correctly, and in todays mass production facilities, they dont check every part for correct tolerance.

If youre doing this on a stock, never rebuilt motor, then you might want to check the oil pan for the plastic gear teeth that have dropped down there.
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Last edited by 70W-32 : 10-13-2008 at 02:48 PM.
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Old 10-14-2008, 10:06 AM   #15
1965T5

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Default Re: Timing Chain Install Help

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Originally Posted by 70W-32 View Post
If youre doing this on a stock, never rebuilt motor, then you might want to check the oil pan for the plastic gear teeth that have dropped down there.
That answers another question, as it's a metal gear set in there. I was wonering if this was a nylon gear originally (1967 425).
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Old 10-14-2008, 03:29 PM   #16
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Default Re: Timing Chain Install Help

Originally it would have a metal cam gear with a think nylon coating over the outer part of the ring and the gear teeth. When the nylon breaks off, the OD of the gear is smaller, the metal teeth that are exposed are thinner, and the ends of the teeth are very, very sharp. With the smaller OD and thinner teeth, the chain has a much greater chance of jumping a tooth due to all the slack in it.

Here's an image of an original nylon coated cam gear. If you look closely, you can see small cracks around the perimeter of the nylon/aluminum border. This is from a 50,000 mile 455 engine, by the way.
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Last edited by 71CutlassConvertible : 10-14-2008 at 03:34 PM.
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Old 10-15-2008, 10:52 AM   #17
1965T5

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Default Re: Timing Chain Install Help

thank you for posting that - mine looks like that one - less the coating and very sharp beat up teeth. Glad I found the problem before it got catastrophic.
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