Spark Knock troubles?

[emorybritt 13]

Hello, I have a 1969 mustang fastback that I built from the ground up and was finished about a year ago and there has always been this constant spark knock. I have messed with the timing in all different ways and it is currently at 6 degrees atdc. recently got a pertronix distributor put in. Today I changed the spark plugs and put in autolite copper plugs and new spark plug wires in and changed the coolant and also changed the oil and oil filter in hopes that something would change but of course it didnt. before the timing was at 10 degrees and that was terrible and its better at 6 but its definitely still there. im checking tomorrow for an exhaust leak but i doubt thats what it is because the knocking changes when the timing is changed. Any advice will be greatly appreciated I only have so much knowledge about this. 

[lanky 44]

Can you describe what type of sound it is, my car made a spark sound when my timing was too far advanced, I re-timed it and it was fine. Sounded like it had a fastener in the combustion chamber. Are you sure your new distributor has a proper curve? If I understand correctly vacuum advance distributors must have the springs/weights adjusted to take into account the vacuum advance, so as to not exceed maximum recommended timing...Someone chime in here but I believe this is correct. It's possible there is too much ignition timing, mine is set somewhere around 7-8 degrees .

[emorybritt 13]

sounds like a ticking and as i accelerate so does the knocking and before i have cut off the advance and still it knocks. I havent tried to cut off the advance since i set it to 6 degrees so i could try that and maybe the advance is turning the timing too far up. i can slightly hear the knocking when its idling but barely and when its in park and i turn the throttle up i still dont hear it but barely. But when its in drive and im just driving down the street in 1st at 2000 rps i hear it distinctly.

[Rsmach1 71]

What's your static compression ratio? No idea where the pic came from.

[emorybritt 13]

What's your static compression ratio?

what exactly is that? this shows my limited knowledge of all of this haha

[barnett468 418]

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your "knocking" is likely NOT detonation from your timing . . if it was advanced so far that you could hear it knock [detonate] at idle, the engine would not even turn over . . the only exception to this could be if you have a lot of timing on a low compression engine but that's pretty much unheard of.

[Print Dad 59]

Hello emorybrit,

Just to be certain we are talking the right timing - 

your motor should run fine at 8 degrees BEFORE top dead center.

In your original post it states "6 degrees atdc.

 

This could be a simple typo - -or it could indicate you are chasing the wrong 

direction on the timing. You want the spark to fire BEFORE the piston comes to

the top of the stroke.

 

It could be a simple fix - -perhaps you are timing to the wrong side of center

 

Trust me - we all make simple little errors but that is how we learn

 

Just wanted to double check before you get too far into this.

Of course a knock to your ear could be a tap to others,

The point is - -we gotta take this one step at a time till we figure

what is happening.

As others mentioned - -an exhaust leak at the manifold could sound like a

knock to some.

Please let the people here know what the timing is set to and they can help from there

 

Print Dad

[shaun071 62]

Have you fitted a new harmonic balancer? Sometimes the outer ring can shift on old balancers and put the timing marks in the wrong position in relation to TDC.

[Max Power 74]

You should never hear a spark knock at idle. I wonder if you are hearing a mechanical knock instead.

 

You said you built it from the ground up, meaning you should know static compression ratio, cam profile, advance curve, the difference between ATDC and BTDC, etc. All this information would be helpful to share so that people can better help you.

[Rsmach1 71]

I assumed when you said you built it from the ground up that you built the engine also. If you had the engine built for you find out from the builder what the compression ratio was, and what cam was used, including manufacturer and part #.

[emorybritt 13]

I'm about to hop under and check for any exhaust leaks because that would be an easy fix. But it's sounding like every time the distributor turns there's a ticking and the faster the distributor turns the faster the ticking is. This was a craigslist buy and the engine ran so I didn't do any work to it other than piecing it all together with a Holley 650 on that's why I don't know the compression ratio. I'm gonna check the timing and see if I can't get a picture of where it's at to post up

[emorybritt 13]

I couldn't manage to get a picture but the timing point is just to the left of the 10 degree mark. I'm not sure how to better word that

[emorybritt 13]

Definitely is at 6 degrees BEFORE top dead center that was a typo sorry for that haha but scared me enough to make sure

[Rsmach1 71]

OK, so it's an engine that came with the car and used, and probably no idea how many actual miles on it. Like Barnett468 stated it's most likely NOT spark knock.

 

Edit, sorry got pulled away.

So if you don't find an exhaust leak, start by listening on top of the engine, see if you can determine what side it's coming from to help narrow it down. May be something in your valvetrain.

[emorybritt 13]

I've tried many times to contact the owner before me but he has no intentions of telling me anything. Would it help to set the timing any lower than 6 degrees btc? Also what else can I do to pinpoint the problem

[LoneWolf2U 136]

Try taking a piece of pipe and hold it to your ear while running across the valve covers with the engine at idle. My bet is the valve train is loose.

[Rsmach1 71]

Yep was editing my post above, you can also use a long screwdriver to listen for the noise, place the blade on different spots across the valve cover and put your ear on the end of the handle. If you find the noise on one side you'll have to pull the cover and go from there. Do you have any experience working on engines? NOT MY DARN PIC!

[barnett468 418]

.

if you have a compression gauge, just take the compression with the coil removed and the carburetor jammed opened at least 1/3 rd of the way by opening the throttle and sticking a long screwdriver down the front holes.

 

turn engine over for exactly 4 seconds and tell us what it says.

 

if it is less than around 220, it should not detonate at idle. i know this because i've done it, lol. typical compression is between 135 and 180.

 

as far as the noise increasing with the turning of the distributor, it is exactly what it should do because in your case, as you tutn the distributor, the engine rpm is changing.

 

i can also tell you this . . if your engine rpm is increasing as you turn the distributor, you need MORE timing.

 

IGNITION TIMING

mustangs were delivered with less than optimal ignition timing . . . incorrect timing can easily cost 10 hp and i have seen gains as much as 40 hp when it has been corrected . . incorrect timing can also cause poor throttle response and bottom end power . . with the distributor vacuum advance disconnected, most street builds can run at least 10 at idle and around 34 at around 3000 rpm . . these numbers are on the slightly conservative side.

if it were me, i would disconnect the vacuum advance and check timing at idle, then rev it up until it stops advancing and note the timing and rpm.

if you dont have a tachometer but you have less than 30 degrees of total timing, its reasonable to guess that you could benefit from more.


The following quick and easy test will give you an idea as to whether your engine can benefit from more timing at idle or at high rpm . . You can try it before you do your cam but you must also do it after because the results will be different if your current timing chain is stretched much.

IGNITION TIMING TEST
 
Incorrect timing can easily cost 10 hp or more.

Too little initial timing can cause engine to idle hotter than it otherwise would.

Check for carburetor and intake air leak.
 
Plug the vacuum advance line.
 
With the engine warm/hot, loosen the distributor bolt 1/4 turn
 
Start engine and note the timing . . stock is around 6 degrees btdc, 8 – 10 is often better.
 
Rev engine to almost 1/2 throttle and note the timing . . if you have a tachometer, rev the engine slowly until the timing stops advancing then not the timing and the rpm.
 
Let engine idle and advance the timing 3 degrees.
 
If the rpm increases and the engine still runs perfectly smoothly, reset idle and advance timing 3 more degrees.
 
If the rpm increases and the engine still runs perfectly smoothly, reset idle and advance timing 3 more degrees.
 
Next, reset the timing and idle speed.
 
Turn up idle screw so engine is revving around 2500 rpm and note the timing.
 
Advance the timing 3 degrees.
 
If the rpm increases and the engine still runs perfectly smoothly, advance timing 3 more degrees.
 
If the rpm increases and the engine still runs perfectly smoothly, advance timing 3 more degrees.

Reset timing to previous setting and post results.

[emorybritt 13]

thank you barnett i will definitely try that tomorrow. today as i was driving after checking the timing to make sure it was at 6 degrees before and not after and as i would get on the gas it would sound like it would almost stall then then it would suddenly accelerate like a lag before it would kick in. and im going to do the screwdriver thing tomorrow to see if i can pinpoint the sound. from inside the car it sounds like it is on the driver side but i could be wrong since im on the drivers side when i drive. 

[barnett468 418]

ok, dont forget to disconnect your distributor vacuum advance hose and leave it disconnected until your problem is fixed then reconnect it to ported vacuum, not manifold vacuum . . if you have a dual diaphragm distributor its more complicated.

 

if you have a holley carb, set the gas level so it is just below the inspection holes when the car is idling.

[Rsmach1 71]

Hey Barnett468 check your pm's lol

[Ridge Runner 1,154]

Is this an actual tick of a jumping spark or pinging from detonation .If it is a spark tick check under the hood at night ,you will see a spark jump .Could be between the wires or a small split in the dist. cap .

[barnett468 418]

Hey Barnett468 check your pm's lol

 

lol, yeah i once again didnt see i had messages...sent a reply, thanks