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Old 05-06-2013, 01:07 PM
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Engine running at ATDC

I bought a 1978 Chrysler LeBaron with a 318 V8 engine. I bought this car from the original owner and the car still had the “Lean Burn System” which left me stranded when I tried to take the car to the transmission shop to repair the automatic transmission. Once the car was back at home I already had the electronic system from Jegs (ECU, Distributor and Wiring Harness) to replace the Lean Burn System. Before switching to the new ignition system I wanted to check the engine time and it was running close to 30deg ATDC , I blamed the “Lean Burn System” , which controls the time, for how rough the engine was running.

I made sure that my #1 was TDC at compression, mark on damper was right on 0 deg. And I installed the distributor with rotor pointing to #1 tower. Engine started with 2 or 3 cylinders, backfiring and only after I rotated the distributor clockwise and damper mark was again in the range of 30deg ATDC all the cylinders fired, any time I try to bring the time close to TDC it just stall. I have the shop manual for the car and It shows engine must be timed at 16deg BTDC.
I have been thinking that probably the timing chain has jump some teeth, what do you guys think about this problem?

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Old 05-06-2013, 02:12 PM
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I made sure that my #1 was TDC at compression, mark on damper was right on 0 deg.
Did you use a piston stop to determine TDC or was it just a SWAG?
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Old 05-06-2013, 05:47 PM
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With spark plug off you could see piston head as high as it can goes up.
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Old 05-06-2013, 05:59 PM
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Quote:
Originally Posted by cu42 View Post
I bought a 1978 Chrysler LeBaron with a 318 V8 engine. I bought this car from the original owner and the car still had the “Lean Burn System” which left me stranded when I tried to take the car to the transmission shop to repair the automatic transmission. Once the car was back at home I already had the electronic system from Jegs (ECU, Distributor and Wiring Harness) to replace the Lean Burn System. Before switching to the new ignition system I wanted to check the engine time and it was running close to 30deg ATDC , I blamed the “Lean Burn System” , which controls the time, for how rough the engine was running.

I made sure that my #1 was TDC at compression, mark on damper was right on 0 deg. And I installed the distributor with rotor pointing to #1 tower. Engine started with 2 or 3 cylinders, backfiring and only after I rotated the distributor clockwise and damper mark was again in the range of 30deg ATDC all the cylinders fired, any time I try to bring the time close to TDC it just stall. I have the shop manual for the car and It shows engine must be timed at 16deg BTDC.
I have been thinking that probably the timing chain has jump some teeth, what do you guys think about this problem?
I'll X2 Tech's comment and add that it's likely the cam and crank aren't on the same page anymore, as you suspect. Going over the top or bottom of the stroke there are a lot of degrees with little motion, following what Tech said without doing the positive stop routine you're left to assume that the when the crank is aligned to the TDC mark that the cam is also. Since wear on the timing set almost always retards the cam, you find yourself putting in more ignition advance to keep the rotor aimed at the proper distributor terminal because the cam is taking the distributor with it having no regard for where the crank is. If it runs long enough; a quick and dirty check with the timing light is to rev it up a bit then snap the throttle closed this will run in then back out the slack in the timing chain and gears so the timing will appear to wander. If it moves more than a couple/three degrees then it's probably time to replace the timing set.

Bogie
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