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Old 05-23-2007, 08:33 PM
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no start 350 chevy

Hey this may be a domb question, I shouldn't be stumped on a no start on a 73 chevy 350, but i am. I have good spark at all cylinders, fuel in carb and pumps out good through accelerator pump(quadrajet). ignition timing dead on, secondary ignition all good. I am wondering if the chain jumped and set my valve timing off because the compression is low and air is pumping out of the carb during cranking. Has anybody seen this before and does it sound like it just need new timing set? Any other checks i can do or suggestions would be great.
Thanks
joe

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Old 05-23-2007, 08:53 PM
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Have you recently re-installed the distributor? The timing may be 180 out. I have done it. Pretty easy mistake to make.
Just a thought.
You say the compression is low. I am assuming you have done a compression test on every cylinder? Some high some low?
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Old 05-23-2007, 10:41 PM
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Doc here,

IF the compression is LOW all the way around, The chain has jumped..

Timing CAN NOT be dead on if that is so.

#1 Cylinder, COMPRESSION, TDC, Both intake and Exhaust Valves DEAD closed, Timing marks lined up...IF you don't have this, your chain / gears are toast.

Pull the cap, Rotor should be pointing Dead on #1 Plug tower, traditionally, the 5 to 7 O'Clock position, IF the above is correct AND the rotor is out, reset the distributer to the Number 1 Firing position..AND while you have it out, INSPECT the dizzy drive gear and shear pin. IF needed, replace them.

Doc
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Old 05-24-2007, 07:45 AM
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re: no start 350 chevy

The distributor is in the correct place, I know for a fact the IGNITION TIMING is dead on as far as TDC w/ the crank, if the timing chain jumped the ignition timing can be set but the valve timing would still be off until you replace timing set. My question is can this be the cause of the air pumping out of the carb? I know there is fuel avalible at the carb, but the engine is not creating vacuum to pull the fuel out. I would like to verify that the chain jumped w/o pulling the cover off.
Thanks
joe
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Old 05-24-2007, 08:09 AM
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This might sound silly, but have you checked that the valves are fully closing ?. Are the rocker arms screwed down too far causing valves not to seat ?. They only have to be slightly off the seat for 150psi or so to squeeze past the seats and cause reverse flow.

The motor should still attempt to start unless all the valves are like it ?. Just a thought.
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Old 05-24-2007, 08:14 AM
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re: no start 350 chevy

Yea the the valves are closing ok, I have the valve cover off and when they are closed the rocker arm loosens up a little. I have pulled the distibutor and the gear and pin are in good shape and the distributor turns easy.
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Old 05-24-2007, 08:25 AM
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OK then. It certainly sounds like the cam timing is off. If it was way off the valves would be hitting the pistons.

I think you'll have to "bite the bullet" and pull the timing cover off and check it out. Unusual though for a SBC to jump teeth........unless it's an old stretched chain ?. Has it been doing it right from the start or did it back fire or something before this problem ??.
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Old 05-24-2007, 08:56 AM
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Quote:
Originally Posted by wrenchheads

The distributor is in the correct place, I know for a fact the IGNITION TIMING is dead on as far as TDC w/ the crank,

if the timing chain jumped the ignition timing can be set but the valve timing would still be off until you replace timing set.

My question is can this be the cause of the air pumping out of the carb? I know there is fuel avalible at the carb, but the engine is not creating vacuum to pull the fuel out. I would like to verify that the chain jumped w/o pulling the cover off.
Thanks
joe
Doc here,

IF the chain jumped, the Timing WILL be off at the distributer PROVIDING you DID NOT reset the distributer..AS it is driven by the CAM gear..SO if you did not set the dizzy...(or anyone else..it either IS or it ISN"T..) you COULD also be 180 out if you did reset the dizzy. (mark comes up twice..)

IF you are blowing air out the carb, you probably are sucking air in the tail pipe..bad mechanical timing (chain/gears)

TO VERIFY the chain/gears, AGAIN:

Quote:
Originally Posted by docvette
#1 Cylinder, COMPRESSION, TDC, Both intake and Exhaust Valves DEAD closed, Timing marks lined up...IF you don't have this, your chain / gears are toast.
Low compression numbers in like the 70''s all the way around indicated a jumped chain..

IF you reset the dizzy on a jumped chain, it will give the appearance of being correct BUT will be off, so you need to check compression and the above procedure.

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Old 05-24-2007, 03:40 PM
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Quote:
Originally Posted by docvette
Doc here,

...

IF you reset the dizzy on a jumped chain, it will give the appearance of being correct BUT will be off, so you need to check compression and the above procedure.

Doc

Can I tag on here? Doc, can you define "appearance"? Will it start, idle and shut down as if everything is normal??

I just swapped a cam in my 305 (boat) and after some starter kick-back and some distributor issues (being 180 deg off), I got it running very well. But, initial timing is now registering 36 degrees (verified w/2 timing lights and by pulling the cap and seeing the relationship of #1 firing and timing marks on balancer). Old cam intial timing was 10-12 degrees. Since this is a boat, I can only idle it in the driveway, with a slight rev here and there.

It was recommended to see if the balancer slipped, so I checked TDC last night and the balancer seems to be indicating correctly. It's easy for me to pull the cover, so I will do that tonight to see what's up with the gear indicators as well.
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Old 05-24-2007, 05:35 PM
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Timing

Hi,there Are 2 Different Sizes Of Balancers On The 350 Chev.i Believe The Sizes Are 6 1/2 And 8 Inch. You May Have The Wrong Timing Tab For The Balancer You Are Using. The Welded Timing Tab Is For The 6 1/2 Balancer And The Bolted Tab Is For The 8 Inch Balancer. Hope This Helps.
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Old 05-24-2007, 05:39 PM
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wrong post..sorry
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Old 05-24-2007, 06:51 PM
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Quote:
Originally Posted by D. Newland
Can I tag on here? Doc, can you define "appearance"? Will it start, idle and shut down as if everything is normal??

I just swapped a cam in my 305 (boat) and after some starter kick-back and some distributor issues (being 180 deg off), I got it running very well. But, initial timing is now registering 36 degrees (verified w/2 timing lights and by pulling the cap and seeing the relationship of #1 firing and timing marks on balancer). Old cam intial timing was 10-12 degrees. Since this is a boat, I can only idle it in the driveway, with a slight rev here and there.

It was recommended to see if the balancer slipped, so I checked TDC last night and the balancer seems to be indicating correctly. It's easy for me to pull the cover, so I will do that tonight to see what's up with the gear indicators as well.

Doc here,

If your talking a MARINE engine that's a different animal, for one thing the rotation is opposite a street engine IIRC..

The "Appearance" of being correct means if you look at it, it looks right (because it was reset) but the valve train is off however many degrees the chain jumped.

I am assuming from his FIRST post..this "just occurred" on a running engine..no chain covers were replaced, or distributer pulled , moved to a #1 fire position (on an off cam) or anything like that..

Different story if the engine were just put together, and this "First start" isn't happening..He needs to disclose that information.

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Old 05-24-2007, 08:58 PM
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Quote:
Originally Posted by wrenchheads
Hey this may be a domb question, I shouldn't be stumped on a no start on a 73 chevy 350, but i am. I have good spark at all cylinders, fuel in carb and pumps out good through accelerator pump(quadrajet). ignition timing dead on, secondary ignition all good. I am wondering if the chain jumped and set my valve timing off because the compression is low and air is pumping out of the carb during cranking. Has anybody seen this before and does it sound like it just need new timing set? Any other checks i can do or suggestions would be great.
Thanks
joe
Using TDC on #1 is fine to wire the ignition but the biggest mistake I see people make is that if the stock timing is BTDC when you hit the compression stroke on #1 the cylinder it has technically already fired - then when you located #1 on the cap you want it to be on the post it just passed not the next one inline (unless stock timing is ATDC normally not a GM motor)

I'd Re-check this and your firing order first that's much easier than pulling the timing cover and cheaper!
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Old 05-25-2007, 09:34 AM
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re: no start 350 chevy

I will be pulling the cover off, I am sure the chain jumped. I did reset the distributor and it is TDC #1. I will let you know for sure if it is the chain or not but I am sure it is.
Thanks for all the help and quick responses.
joe
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Old 05-25-2007, 10:36 PM
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stuff

just a thought, my brother could not get his motor to fire, all because of fouled plugs. all his high dollar electronic ignition, high buck wire's, and me donating a billet dizzy.

tc
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