Spark knock?

[Just.Ice.T]

So, I have a ‘79 510 with a dual plug head (Cali emissions) z20s from an ‘80 510 in it. Under acceleration, engine completely warm, I hear a loud chatter/knock at about 2k+ RPM. The timing is set right. I also have tried different grades of fuels. It does it regardless. Any remedies? Carbon buildup perhaps?

 

    It doesn’t do it at idle, so I ruled out exhaust leak for now.

 

Thanks in advance

[datzenmike]

The Z series engine timing should be around 3-5 degrees, much different than the L20B that's at 12.

[Just.Ice.T]

So you think it’s a timing thing? Is this what people mean by “pinging” when the timing is too advanced?

[datzenmike]

It could be. The dual plug design means less advance needed. If this was set by someone not knowing what engine was swapped in, may have set it to '79 L20B specs.

[Just.Ice.T]

It came with a 4-plug dizzy, running only the plugs on the exhaust side. The sticker under the hood says 8 degrees for stock, but I have it running at 10 ish to compensate for having only 4 plugs, instead of 8. I’ve tried backing it off (retarding) further than 10, but the car starts/runs much worse. 

[banzai510(hainz)]

Try running on the intake side.better yet run it like it’s supposed to with both or adjust the timing 

[datzenmike]

Ahhh early non California ones were 4 plug but all switched to 8 plug for '81.

 

If it's supposed to be 8^o then set it at 8^o.

 

Agree with Hainz. Run intake side. BP6ES.... must be NGK plugs

[Just.Ice.T]

I’ll try the intake side, but running both would entail getting an 8 plug dizzy and another coil. 

 

I’m mainly just trying to make sure I’m diagnosing the noise properly. 

 

I’ll see if swapping the sides will work though, thanks for the replies 

[datzenmike]

Don't forget to pull the plugs and clean/check them. They've not been firing and may be dirty. Spark plugs are self cleaning if running. Check they are NGK BP6ES

[Crashtd420]

Is it possible this noise isnt a knock?

If your in to high a gear trying to accelerate from a low rpm you might be doing what's called lugging the motor....

That sounds kind of rattly too....

 

[datzenmike]

Exhaust leak sound will be louder with more load and sometimes louder at certain RPMs. Idle will be the quietest usually and often it can be loudest when cold and quieter as metal heats and expands. If you are quick, start it up cold and reach around the exhaust manifold and joining to head and the down pipe. You can feel the puffs of exhaust from a bad gasket or crack. You have 5-10 seconds before the pipes become uncomfortably hot.

 

The extra spark plugs that are not used might be ignition points. They are exposed and sharp edged and get very hot. With dual plugs the exhaust side are BP5ES one range colder because they are so close to the exhaust valve.

 

Examine the plugs. They may be carboned up from poor firing or over rich carb setting... perhaps the choke is stuck on? Carbon will get glowing hot and can be an ignition point during the compression stroke or shortly after the plug fires and the pressure in the combustion chamber spikes. Dual plugs avoid much of this because the timing is necessarily much less.

[Just.Ice.T]

So I swapped the plugs from the exhaust side to the intake side. For whatever reason, it seems to run a tad smoother now, on the intake side. I’m still getting that noise, but after doing that quick check with the exhaust cold, I feel a leak right where the tri-bolt flange connects to the manifold. The bolts are tight... so I’m not sure how to fix that. Maybe that’s causing my noise, and I only hear it at higher rpms?

 

the new plugs I put in were NGK BPR6ES. The old ones that are unused (now in the exhaust side) at the moment were nasty looking. Had pretty decent carbon deposits on the ground. I’ll be replacing those very soon. 

[distributorguy]

Take out those resistor plugs.  The R means there's a 5000 Ohm resistor in each plug.  You do NOT want that.  I'd speculate your plug wires have another 7000 Ohms each or more.  You want a total of 2000 Ohm or less between the plugs and wires, per cylinder.  

[Just.Ice.T]

1 hour ago, distributorguy said:

Take out those resistor plugs.  The R means there's a 5000 Ohm resistor in each plug.  You do NOT want that.  I'd speculate your plug wires have another 7000 Ohms each or more.  You want a total of 2000 Ohm or less between the plugs and wires, per cylinder.  

 Oooo... thank you for this. I’ll get em swapped out ASAP.

[Crashtd420]

I took distributorguy's suggestion and was able to get my wires to less than 1000 ohms... I think the one from the coil was 500 or 700 ohms....

Msd makes a nice low resistance wire set, 500 ohm per foot,  for a v8 so you have 4 extra main wires if I want to route it differently later..... these are a make your own type, on one end and they give you a crimp tool.... 

 

MSD 5551 Street Fire Spark Plug... https://www.amazon.com/dp/B001BDSVOM?ref=ppx_pop_mob_ap_share

 

[Just.Ice.T]

Well I just got some BP6ES’s put in there, no resistor this time. What’s a good way to check the ohms? Or is that a easy google question? 

[banzai510(hainz)]

I just buy NGK plug wires and all mine have been fine. Othewise you have other issues

[Crashtd420]

51 minutes ago, Just.Ice.T said:

Well I just got some BP6ES’s put in there, no resistor this time. What’s a good way to check the ohms? Or is that a easy google question? 

Do you mean for the wires?

Remove the wire and connect a volt meter set to ohms . one lead from the meter to each end....

[distributorguy]

On 10/29/2019 at 11:37 AM, Crashtd420 said:

Do you mean for the wires?

Remove the wire and connect a volt meter set to ohms . one lead from the meter to each end....

 

And the same for the plug wires.  Measure end to end.  If the meter is set too low, it'll read as an open circuit.