Jumped Time ? - Team Camaro Tech
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post #1 of 11 (permalink) Old Jul 21st, 02, 03:49 PM Thread Starter
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I know just enough about working on engines to get me in trouble. I adjusted the valves on the old '74 Chevy truck (350 ci - 99,500 miles) because some of the lifters would tap at times. I did it with the engine running - backed them off till the rocker rattled, turned it back until it quit, then another half turn. Some of the ones I did seem to almost choke the engine down, and then it smoothed out. Overall, it seemed to help it run better. After it set for a couple of days, I couldn't get it started. A friend told me it seemed advanced too much. I didn't think that was the problem, because I had checked it, and it was 8* BTDC before I adjusted them. I retarded the distributor anyway, and it started; it was way too much advanced even after retarding it as far as I could turn it. The only way I'll be able to set the timing now is pull the distributor and start over, but I'm afraid that will be a waste of time. Is it possible that the timing chain could jump a tooth and the engine still run ? That would put the cam and crank out of time. Has this happened to any of you guys, and would adjusting the valves to tight cause it to happen, or is it just a high milage thing ? I guess I need a new timing chain and gear now ? Thanks, Ron.

[This message has been edited by Rons68 (edited 07-21-2002).]
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post #2 of 11 (permalink) Old Jul 21st, 02, 04:53 PM
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Hydraulic lifters tend to pump up when you take the preload off of them with the vehicle running. This does put a little added stress on the cam when you relash the valves. With 100K right around the corner and the fact the stock cam gear has nylon teeth leads me to believe you need a new timing gear set. I also have a '74 pickup with 97K on it and had to replace the cam and lifters too because these cams were notorious for loosing lobes. Sorry I had to ruin your day.

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post #3 of 11 (permalink) Old Jul 22nd, 02, 04:33 AM
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If anything slipped, highly unlikely, it would retard everything. If something slipped a tooth (either the cam sprocket, crank sprocket, or distributor gear) I doubt she'd run.

You say she ran fine after the valve adjustment, but wouldn't start after sitting a while.

Back to basics...here's a few things to look for:

bad fuel,
moisture in the distributor cap,
fuel pump,
carb needs a rebuild,
plug wires are bad,
cap and rotor need r&r,
low compression,

Do a search here on how to static time your ignition for start-up if you're still having trouble gettin' her to fire. After she's running, you can set the initial timing. But my guess is, you need to inspect and replace some ignition parts and/or inspect and replace some fuel delivery parts...a carb rebuild might be in order.

Let us know what you find and good luck!
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post #4 of 11 (permalink) Old Jul 22nd, 02, 05:33 AM
 
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how you doin
you said you timed it to 8 degrees but did you remove the vacum advance from the dist. before you did so if not your timing would be set way off and reset idle speed after timing and recheck also make sure that the vacume line is not holding vacume after you shut the engine off witch will hold the advance on. worth a try!!! good luck
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post #5 of 11 (permalink) Old Jul 22nd, 02, 05:27 PM
 
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Sounds like your chain to me. It jumped to the advanced side--hence it grunts when you try to start it in the normal postion. You can check it by putting timing mark at TDC (o) and then remove #1 plug. Insert a drinking straw in hole so it is touching piston. Turn motor in normal direction.(best by hand if you can) If outer edge of straw goes down it means piston is still rising which means it is out of time.If it was at TDC as indicated the straw should raise on outer edge as the piston should be on it's way down. Hope this is not to confusing.( confused me some and I wrote it!!)
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post #6 of 11 (permalink) Old Jul 22nd, 02, 05:52 PM
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Since the timing mark is on the balancer on the crank, not the cam, this will prove nothing. Trust me, I've changed enough of these to know. If it's the original timing set, it's shot.

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'69 RS Camaro
355 5-speed 4.11

[This message has been edited by 1 2RUN (edited 07-22-2002).]
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post #7 of 11 (permalink) Old Jul 22nd, 02, 06:44 PM
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I've seen three different vehicles with timing chains that have jumped a tooth. In very case, the car ran fine until it was shut off, then would never start again. Even if it hasn't jumped - if the timing chain and gears are stock original, replace them.

-dnult
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post #8 of 11 (permalink) Old Jul 24th, 02, 03:38 AM Thread Starter
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I brought the timing mark around to TDC on the compression stroke and checked the position of the distributor. It was way past number one; it was in the number 4-3 range.

I guess I'll be putting a new timing chain set this weekend. I just hope that none of the valves got damaged. I didn't hear any bad noises the last time it ran. I don't want to put a lot of money in this thing, I already have a '68 money pit. I'm kind of looking forward to pulling the pan to see if it has a four bolt main and a steel crank.
Thanks for all the replies, Ron.
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post #9 of 11 (permalink) Old Jul 24th, 02, 06:37 PM
 
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It will if you watch the rotor button at the same time which I forgot to mention.( told you I was confused to). Sorry!
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post #10 of 11 (permalink) Old Jul 28th, 02, 03:45 PM Thread Starter
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Well, I put in a new timing chain & gear this weekend. To my suprise, the old cam gear was steel (it said GM on it & Dad said he had never replaced it), and it had not jumped time ! The timing dots still lined up even though the chain did have some slack in it.

Then I got to thinking, I bet the cam or distributor gear is worn out. I pulled the distributor gear and it looked good. Looking through the distributor hole in the intake with a flashlight, I took a piece of coat hanger wire and ran it through the gears on the cam; they looked OK too. I did notice that the wear pattern on the distributor gear was near the bottom of it. Somehow it must have jumped up and skipped a tooth on the cam, because the problem didn't happen at the timing chain. The distributor bolt was always tight too.

I'm very puzzled by all of this, but now it runs better than ever, and now I know it's a 4 bolt block too ! I think it has a cast crank though; I'm going to post the crank number on Tag Team. Thanks for everyone's help, Ron.
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post #11 of 11 (permalink) Old Jul 29th, 02, 12:59 AM
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Some truck engines had a steel camshaft sprocket.

There may have been enough slack in the chain to give the symptoms of retarded cam timing.

A '74 w/ 100K miles? Not bad, not driven much.

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