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Old 09-05-2008, 04:22 AM
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400 Small block making banging noise when trying to start

Hi.
Well I finally figured out the flex plate problem, and thought all I had to worry about was getting the body ready for paint?
I have a small block 400 with 12:1 compression pistons, dual 500 eldabrock carbs, I bought the motor pre built, was a great deal at the time, had it running and had tons of power!
I only got on it one time and did a burn out for about 150 feet?
everything seemed fine, tonight i pulled the rod out on the driveway to have more room in the garage to work on the doors. it acted like it didn't want to start? so I turn the distributor just a tiny bit, about an 1/8 inch? not even a quarter. Well it started and I figured it had just turn a little on the distributor cause I didn't have it tightened all the way down yet as I need to fine tune it.
Anyway when I went to start it up again, and it cranked over and all of a sudden it stoped and made a banging type noise! not a back fire but a banging noise like a hammer hitting a plate of metal? It never did actually start. I tought ***? anyway I got out and turn the distributor back, the other way like 1/8 an inch just barley, got back in the car again, hit the starter and it cranked and then BANG, same thing? So now I am wondering if it jumped timing on the timing chain and the noise I hear is a piston hitting a valve? With 12:1 I know they are close, the motor is supposed to be all rebuilt with new parts? So I am thinking they must have only used a single sprocket timing gears and chain? or they used and old setup? Cause like I said the one time I did get on to it, it hauled ***.
What do you guys think? any info is great!
Gary

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Old 09-05-2008, 04:30 AM
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Check the starter and flexplate again. Or, have a friend turn it over while you observe the starter. Also make sure the starter gear isn`t making contact with the flexplate. You said you replaced the flexplate, are you certain you used the correct one?
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Old 09-05-2008, 04:37 AM
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yes sure on the flex plate

yes it is the corect plate and it is aliened correctly to the starter.
It, the starter and flex plate have been working great till this new problem.
I hope that whenI did get on it the one time that I didn't damage the cam or trow the timing a few teeth? cause it does sound like a piston hitting a valve
When I crank it over now. I guess the only sure way is to pull the front apart and check the gears and chain?
Gary
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Old 09-05-2008, 04:46 AM
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Check every other obvious area before you start tearing it apart, make sure nothing is in the fan or hitting anything, loosen the belts and start it and see if the noise persists. It`s not likely it jumped time on the chain, if it did so after you did the burnout you would have known it. Being it ran fine after the burnout says the timing chain is fine. Flexplates are known to make noise that sounds like a hammer hitting a piece of steel as you discribe. Once before when I delt with a cracked flexplate not only did it make the same noise it also sounded like a rod knocking. Inspect everything with a fine tooth comb before you start tearing it down as I would hate for you to have to tear down a engine that pretty only to find the problem was external. Good luck Gary.
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Old 09-05-2008, 04:52 AM
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Ok thanks for the info

I will go over it first like you said.
Thanks for your info and time.
Gary
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Old 09-05-2008, 09:49 AM
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Quote:
Originally Posted by Aboveknee
So now I am wondering if it jumped timing on the timing chain and the noise I hear is a piston hitting a valve? With 12:1 I know they are close, the motor is supposed to be all rebuilt with new parts?
Gary
If it was rebuilt with flat top pistons & 305 heads it would have 12 to 1 compression.
400's don't require domed pistons to have high compression ratios when using flat top pistons.
Are you using pump gas with 12 to 1 comp.?
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Old 09-05-2008, 10:29 AM
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If it is a stock style starter do you have the rear brace on it. A 12:1 engine is going to put a lot of stress on that starter. It may be getting out of alignment due to the increased torque it takes to turn thaat engine. You can prove if it is timing, disconnect the coil wire and crank it and see if it still does it. You could also pull all the plugs and spin it over to check the valve into the piston theory. I doubt this is your issue as it would be more likely to make contact while running and if it hit once that would most likely be catastrophic.
Check the starter real good, I think that is where your issue is

Chet
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Old 09-05-2008, 06:01 PM
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you mite be right?

You know i sleept on it, and it did seem like the battery mite be a little on the low side? and if it was turning over just a little slower it mite have put mor stress on it and cause the starter teeth to jump out? would that kind of thing happen? I mean it sounds like a bang or a big ping? I am going to inspeak the fly wheel close and super charge the battery, I am afaraid of cranking it over anymore and causeing more damage?> but then again how will i find the cause? I think I dont have much choose but to try and turn it over and find the problem again, another person was asking about the heads and pistons? it has standerd 44 heads the pistons I belive are domed but iam not sure? I didnt build it. I do know this, when the pulgs are out of the heads you can look into the spark plug hole and see the pistons , there is a noth so the plug clears and the piston looks like it comes up higher the the plug hole.
The motor was build by a guy who drag race's all the time. I which i knew more. Gary
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Old 09-05-2008, 06:25 PM
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Quote:
Originally Posted by Aboveknee
Hi.
Well I finally figured out the flex plate problem, and thought all I had to worry about was getting the body ready for paint?
I have a small block 400 with 12:1 compression pistons, dual 500 eldabrock carbs, I bought the motor pre built, was a great deal at the time, had it running and had tons of power!
I only got on it one time and did a burn out for about 150 feet?
everything seemed fine, tonight i pulled the rod out on the driveway to have more room in the garage to work on the doors. it acted like it didn't want to start? so I turn the distributor just a tiny bit, about an 1/8 inch? not even a quarter. Well it started and I figured it had just turn a little on the distributor cause I didn't have it tightened all the way down yet as I need to fine tune it.
Anyway when I went to start it up again, and it cranked over and all of a sudden it stoped and made a banging type noise! not a back fire but a banging noise like a hammer hitting a plate of metal? It never did actually start. I tought ***? anyway I got out and turn the distributor back, the other way like 1/8 an inch just barley, got back in the car again, hit the starter and it cranked and then BANG, same thing? So now I am wondering if it jumped timing on the timing chain and the noise I hear is a piston hitting a valve? With 12:1 I know they are close, the motor is supposed to be all rebuilt with new parts? So I am thinking they must have only used a single sprocket timing gears and chain? or they used and old setup? Cause like I said the one time I did get on to it, it hauled ***.
What do you guys think? any info is great!
Gary
This is a little information that may help, or not.

Years ago, when I was a crew chief on a 1/4 mile drag boat, I loosened the distributer to set the timing. It instantly lost oil pressure, so we pulled it out, and tore it apart, and found nothing wrong. We put it back in, and it did the same thing again. It turned out to be the thickness of the intake manifold being too thick, allowing the distributor to lift off of the oil pump drive.

I hope this is not what your problem is. It could be expensive.
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Old 09-05-2008, 07:35 PM
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Double check your timing with a timing light. A couple times when I "play" with the distributor I accidently knock it way advanced and dont notice so that it makes loud knocks when I try to start it. (Simple to check)
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