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timing chain broke????

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Old Dec 8, 2007 | 09:42 AM
  #1  
gapimpin's Avatar
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From: waco,texas
Car: 1991 Pontiac Firebird
Engine: 383 LT1
Transmission: built 700r4 and fuddle 3500stall
Axle/Gears: 4th gen 3.42 auburn
timing chain broke????

I was manually shifting my built 700r4 and didnt get it out of 1st till the tach was pegged at 6k. im guessing i got up in the 6.5-7k area and heard a pop.
the car shut off quick and my friend that was in a car next too me said he heard a loud rattling noise.

We pushed it off the road and started looking at it. the rotor had come off the dizzy and was knocking around inside the cap. we also found that the dizzy doesent turn with the motor.

I took off a valve cover and cranked it again. none of the rockers moved so the cam isnt spinning.
Is it possible i broke the double roller timing chain or would the cam sproket maybe come off?

what do you guys think happend with those symptoms?
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Old Dec 8, 2007 | 10:30 AM
  #2  
Comp788's Avatar
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Joined: Sep 2006
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From: Reno, NV
Car: 1982 Z28 & 1967 RR/SS 396
Engine: ZZ383 & 375hp 396
Transmission: T56 & factory TH400
Axle/Gears: 9" ford & 12 bolt 4.10
Re: timing chain broke????

Anything is possible... You might have sheared the keyway in the crank, had the bolts cole loose/out of the timing chain sprocket, or had the timing chain break...
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Old Dec 8, 2007 | 01:56 PM
  #3  
Apeiron's Avatar
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From: Mercedes Norte, Heredia, Costa Rica
Car: 1984 Z28 Hardtop
Engine: 383 Carb
Transmission: 4L60
Axle/Gears: 3.54 Dana 44
Re: timing chain broke????

Does your belt turn when you crank it?
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Old Dec 8, 2007 | 03:15 PM
  #4  
AlkyIROC's Avatar
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From: 51°N 114°W, 3500'
Car: 87 IROC L98
Engine: 588 Alcohol BBC
Transmission: Powerglide
Axle/Gears: Ford 9"/31 spline spool/4.86
Re: timing chain broke????

The chance of breaking a double roller chain is possible but slim. As mentioned above, the keyway could have broke. The crank gear could have split and broke. The cam gear bolts could have fallen out. The camshaft could have broke. The front of the crank could have broke preventing the timing chain from rotating. Is the balancer rotating while cranking over the engine?

If the cam stopped rotating for any reason and the engine died, then the pistons were still going up and down while the valves were open. There's a good chance you have some bent valves.

You're going to need to do a complete tear down to inspect for damage. Start by pulling the spark plugs to check for damage. Pull the oil pan and see if there's anything sitting in the bottom.
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Old Dec 8, 2007 | 04:40 PM
  #5  
dayton's Z's Avatar
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Joined: Jun 2007
Posts: 34
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From: dayton, oh
Car: 85z-28
Engine: gm goodwrench 350
Transmission: t-5
Axle/Gears: stock, 3.08 one wheel peel!
Re: timing chain broke????

get ahold of a pressure tester make sure you have compression in you cylinders to check for bent valves.

and good luck hope its something minor as minor can be in this situation
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Old Dec 24, 2007 | 10:49 PM
  #6  
gapimpin's Avatar
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From: waco,texas
Car: 1991 Pontiac Firebird
Engine: 383 LT1
Transmission: built 700r4 and fuddle 3500stall
Axle/Gears: 4th gen 3.42 auburn
Re: timing chain broke????

ok so a little more info....
It wasnt a double roller just a stock roller chain. we found the chain lodged in the top of the timing cover and all the teeth on the crank sprocket had been sheared off. we replaced the timing set and the motor turned over first try but it was running rough like it was running on 4cyl. I didnt hear any rod knock but the motor stopped and wont turn over now. when i hit the starter it moves a little but not much and goes back when i let off the starter. could i possibly have bent a valve and its keeping the piston from going to tdc?
we didnt see anything in the oil when we drained it. Ill pull the heads sometime this week just havent had a chance to yet cause the car is down in austin and i live 120miles away in waco.
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Old Dec 26, 2007 | 02:23 PM
  #7  
Damon's Avatar
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Joined: Sep 1999
Posts: 7,072
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From: Philly, PA
Re: timing chain broke????

Yeah, you probably dinged some valves crooked the first time you lost the chain. Then when you fired it again with the new chain something got wedged and stopped it from turning any further. When you lose a timing chain at high RPMs bent valves are a practical certainty.
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Old Dec 26, 2007 | 02:37 PM
  #8  
AlkyIROC's Avatar
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From: 51°N 114°W, 3500'
Car: 87 IROC L98
Engine: 588 Alcohol BBC
Transmission: Powerglide
Axle/Gears: Ford 9"/31 spline spool/4.86
Re: timing chain broke????

Well a factory chain is a different story. Normally the plastic teeth on the cam sprocket fail first.

As mentioned above, you'll have bent valves. Price out some replacement heads. They may be cheaper than getting the ones you have repaired. Don't buy anything until you pull the heads to asses the damage. If a piston is damaged, you might as well price out a rebuilt engine.
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Old Dec 26, 2007 | 03:20 PM
  #9  
ibmtech's Avatar
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From: Glen Park, NY
Car: 1987 IROC-Z
Engine: TPIS II Supercharged w/Nitrous
Transmission: 700R4 Probuilt
Axle/Gears: 3:73 Richmond 12 Bolt
Re: timing chain broke????

You will have to look at the top of your pistons for damage. I had a 3.1 Regal engine that some idiot (ME!!!) accidently swapped the push rods on.. I got the blue and the orange rods mixed up on 1 cylinder.. After I started it up.. I thought I had dropped a rod so after a few more hours, I pulled the motor to inspect for damage. Once I got the heads off again, I found the mistake and had to do a little grinding on the piston and it worked ok.. I was extremely lucky and sold the car and it never had another problem.. You don't sound like you can be that lucky.
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Old Dec 31, 2007 | 10:32 PM
  #10  
gapimpin's Avatar
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From: waco,texas
Car: 1991 Pontiac Firebird
Engine: 383 LT1
Transmission: built 700r4 and fuddle 3500stall
Axle/Gears: 4th gen 3.42 auburn
Re: timing chain broke????

well we pulled the heads and it did have some bent valves. all the walls looked fine and the pistons looked fine. it got dark and cold out though so we didnt have time to try and turn it over again. only one of the valves was bent bad enough to keep it open a little all the rest looked closed. im betting when i take off the springs though its gonna be hard to get them to move. i really hope i didnt damage a bearing. thats what the guy at the local speed shop said probably happend. we will see when i try to crank it by hand though.
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