Stock SBC 350 Crate Motor valve chatter under load - Hot Rod Forum : Hotrodders Bulletin Board
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Old 01-06-2013, 04:12 PM
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Stock SBC 350 Crate Motor valve chatter under load

I'm getting valve chatter under load on my stock 290 hp GM Perfomance 350 crate motor.

I have replaced the plugs, plug wires, distributor, and did a full valvetrain check and valve adjustment just in case.

Its running a late model Rochestor Quadrajet carb with electric choke. The only aftermarket parts are a set of aluminium valve covers, MSD E-Curve distributor, Blaster coil, 8mm Autozone plug wires, Champion platinum plugs, Sanderson QP1000 headers, and an Edelbrock air cleaner.

Right now I have the total timing set at 32 degrees and 12 degrees at idle. I have also tried 34 total and 14 idle too and it still chatters.

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Old 01-06-2013, 04:28 PM
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Quote:
Originally Posted by 71fj40guy View Post
I'm getting valve chatter under load on my stock 290 hp GM Perfomance 350 crate motor.

I have replaced the plugs, plug wires, distributor, and did a full valvetrain check and valve adjustment just in case.

Its running a late model Rochestor Quadrajet carb with electric choke. The only aftermarket parts are a set of aluminium valve covers, MSD E-Curve distributor, Blaster coil, 8mm Autozone plug wires, Champion platinum plugs, Sanderson QP1000 headers, and an Edelbrock air cleaner.

Right now I have the total timing set at 32 degrees and 12 degrees at idle. I have also tried 34 total and 14 idle too and it still chatters.
What type of noise are you hearing is the valves rattling or is the engine knocking from detonation.

Have you adjusted the valves.
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Old 01-06-2013, 04:35 PM
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Originally Posted by hcompton View Post
What type of noise are you hearing is the valves rattling or is the engine knocking from detonation.

Have you adjusted the valves.
It sound like valve rattling to me. I just adjusted the valves again this morning.
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Old 01-06-2013, 05:23 PM
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If it's only while loaded, I suspect it is detonation. Have you verified TDC and your pointer/damper marks?
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Old 01-06-2013, 05:38 PM
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If it's only while loaded, I suspect it is detonation. Have you verified TDC and your pointer/damper marks?
Yes TDC was checked vs the damper mark. It is correct. I also installed a new MSD timing tape before I put in the new E-Curve dizzy.
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Old 01-06-2013, 05:52 PM
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Detonation.
Excessive valve lash (or bent push rods) would rattle just as much at free rev as under load. Plus you would probably hear it at idle.

Verify timing marks and pointer as stated above.
Initial advance at 12 might be a bit much, especially if your running 87 octane.
Also, check vacuum advance operation, if it isn't working right you'll have too much advance when you press the throttle under load.

Is this a new engine or did you change anything just before the noise started?
If the engine was running fine and then starts pinging w/o changing ignition/timing, then it could be running lean (causes detonation). If so check fuel delivery to carb, read the plugs, etc. With the ethanol in todays gas, it doesn't take long before the moisture can accumulate in the carb and cause corrosion and mess up your mixture.

Good luck.
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Old 01-06-2013, 06:56 PM
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Originally Posted by starnest View Post
Detonation.
Excessive valve lash (or bent push rods) would rattle just as much at free rev as under load. Plus you would probably hear it at idle.

Verify timing marks and pointer as stated above.
Initial advance at 12 might be a bit much, especially if your running 87 octane.
Also, check vacuum advance operation, if it isn't working right you'll have too much advance when you press the throttle under load.

Is this a new engine or did you change anything just before the noise started?
If the engine was running fine and then starts pinging w/o changing ignition/timing, then it could be running lean (causes detonation). If so check fuel delivery to carb, read the plugs, etc. With the ethanol in todays gas, it doesn't take long before the moisture can accumulate in the carb and cause corrosion and mess up your mixture.

Good luck.
The motor has 60,000 miles on it. It was running fine then I cleaned the engine bay and got some water in my old MSD pro billet dizzy from that point it went south. I started by checking and replacing all the plugs, then wires, then the cap and rotor, and finally the distributor.
If I have it set to anything less than 12 at idle I get valve chatter and it idles rough.
The chatter also started before I did the valve adjustment.
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Old 01-06-2013, 09:08 PM
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Stock SBC 350 Crate Motor valve chatter under load

Check to see if the rotor is pointing to #1 sparkplug wire on the distributor cap when it is at TDC or between 12*-18* BTDC. Do this with a breaker bar and socket by hand not with the starter motor. If you are using the rev limiter set it at 5500 rpms. What are the settings on the electronic mechanical advance curve? Are you using vacuum advance also? Is there a vacuum line used from the carburetor to this distributor? I was wondering about this because the directions say if vacuum is not wanted simply do not connect the vacuum port. Post back the settings. Another possibility is you have some bad gas (water in the gas). To a half of tank of gas add 1 bottle of Chevron Fuel System Cleaner that treats 20 gallons of gas and a bottle of STP water remover. Drive it around about 20 miles to see if there is a improvement. If it is detonation try putting about 5 gallons of 93 octane to what is in the tank now. Try for a half and half mixture to the amount of gas you have. This should stop that. Post back the results.
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Old 01-06-2013, 09:42 PM
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Originally Posted by cdminter59 View Post
Check to see if the rotor is pointing to #1 sparkplug wire on the distributor cap when it is at TDC or between 12*-18* BTDC. Do this with a breaker bar and socket by hand not with the starter motor. If you are using the rev limiter set it at 5500 rpms. What are the settings on the electronic mechanical advance curve? Are you using vacuum advance also? Is there a vacuum line used from the carburetor to this distributor? I was wondering about this because the directions say if vacuum is not wanted simply do not connect the vacuum port. Post back the settings. Another possibility is you have some bad gas (water in the gas). To a half of tank of gas add 1 bottle of Chevron Fuel System Cleaner that treats 20 gallons of gas and a bottle of STP water remover. Drive it around about 20 miles to see if there is a improvement. If it is detonation try putting about 5 gallons of 93 octane to what is in the tank now. Try for a half and half mixture to the amount of gas you have. This should stop that. Post back the results.
I just filled it with gas Friday. I will try the fuel additives you recommended.
I don't have the vacuum advance hooked up currently. I wanted to get the base timing issue resolved first before I start mucking around with that.

Right now I'm using the "G" 20 degree advance curve.
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Old 01-06-2013, 10:11 PM
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Stock SBC 350 Crate Motor valve chatter under load

Try F to see if it makes any difference. G is all in by 2500 rpms. F is 3000 rpms. After adjusting settings rev the engine to 3000 rpms and check total timing for 32*. GM recommends 34* on 87 octane. But you might have to wait until you solve this problem. If you can check the oil on the dipstick see if it smells like gas. If it does change it. Get a vacuum gauge and tune the carburetor and do some of the other checks in the instruction book. When you are able to get it right and want to hook up vacuum advance try F3 #1 knob 4, #2 knob 6.
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Old 01-12-2013, 05:48 PM
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Ok I topped off half the tank with 91 octane along with using the water remover and Chevron fuel treatment. I put about 20 miles on it and the chatter is still there. I also changed the curve to all in at 3000 rpm along with adjusting the total timing to 34 degrees. at idle i'm at 14 degrees.
Unfortunately the chatter under load is still there. Here are 2 videos I made of the noise.


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Old 01-12-2013, 06:48 PM
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Stock SBC 350 Crate Motor valve chatter under load

Pull a valve cover and look to see if the lifters and rocker arms are getting oil. Watch out if you rev it too high oil will squirt all over the place. Be sure and check it at idle and giving it some gas pedal. How long have you had them AutoZone sparkplug wires? Fire it up at nighttime completely dark. Check for spark around the boots and where they plug into the cap. Next time it comes time to replace them try the AC Delco Part No. 9608U $62.99. These wire last a long time. They are 8MM wires with a lifetime warranty too. Order them online and pickup at the store for a 20% off.
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Old 01-12-2013, 07:25 PM
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Originally Posted by cdminter59 View Post
Pull a valve cover and look to see if the lifters and rocker arms are getting oil. Watch out if you rev it too high oil will squirt all over the place. Be sure and check it at idle and giving it some gas pedal. How long have you had them AutoZone sparkplug wires? Fire it up at nighttime completely dark. Check for spark around the boots and where they plug into the cap. Next time it comes time to replace them try the AC Delco Part No. 9608U $62.99. These wire last a long time. They are 8MM wires with a lifetime warranty too. Order them online and pickup at the store for a 20% off.
Plug wires are brand new and there is no visible sparking.
I just did a running valve adjustment using some old steel cut out covers. The rockers are definately getting oil at idle and when the engine is reved.
This issue is stumping the hell out of me.
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Old 01-12-2013, 10:54 PM
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quite possibly you could have bad valve springs even if one is weak then its going to cause the valve to bounce off the seat as it closes instead of closing and sitting still which in turn will cause a horrendous ticking or tapping from the valves
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Old 01-13-2013, 12:41 AM
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Definitely an unusual noise. I was thinking it could be a broken damper or 2. Or like the previous post a bad or weak valve spring. Does it chatter in the driveway if u rev it up? If so remove the valve covers and try revving the motor up and see which valve springs are making the noise

Last edited by cadillacdave1; 01-13-2013 at 12:46 AM. Reason: add to post
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