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Stock SBC 350 Crate Motor valve chatter under load

60K views 47 replies 10 participants last post by  UPandComing 
#1 ·
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.
 
#5 ·
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.
 
#6 ·
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.
 
#7 ·
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.
 
#8 ·
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.
 
#9 ·
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.
 
#10 ·
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.



 
#11 ·
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.
 
#15 ·
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
Once warmed up it doesn't make any noise at idle, but If I do give it some gas then I do here the noise. More so under a load.
 
#17 ·
After closer inspection with the valve covers off, the chatter seems to be coming from the valves above the #4 cylinder and 1 above the #1 cylinder. So I ordered a set of Edelbrock 5894 springs which are equivelent to the stock ones. Now I just have to reserve a weekend to put them in. The rocker arms and push rods checked out fine.
 
#18 ·
Good luck I hope it works, I would recommend putting compressed air to the cylinder your going to work on to prevent the valve from dropping into the cylinder and put a small magnet on the tip of the valve before compressing the spring to prevent the keepers from fallng into the cylinder head
 
#19 ·
Replaced all of the valve springs with a set of Edelbrock 5894 springs. When I lined up all 16 of the old springs it looks like 5 of them were noticeably shorter. After the new springs were installed and adjusted, I took it out for a test drive. The good news is the motor runs a lot better, power is good, and almost all of the mystery noise is gone. The bad new is I can still here it a bit while accelerating and when I hooked up the compressor to swap out the springs the number 4 cylinder was leaking bad and would only hold about 50 psi of air. The number 6 cylinder was also leaking air and would only hold 90 psi of air. All others seem to hold 120 no problem. When running theirs no smoke comming out of the exhaust and it doesn't burn oil. Any ideas why those 2 cylinders would not hold air?
 
#21 ·
Awesome progress, i can tell you with a certain degree of certainty that the 2 cylinders you are having trouble with either A) have a bent valve or B) are in need of a simple valve job, i dont recall what kind of heads are on the car are they stock? if so they probably need a freshen up, if they are out of the box heads and bolted directly on it is a COMMON problem that when new cylinder heads are built the tolerances are WAY wide, i would recommend taking the heads in to a machine shop have them cleaned inside and out get a 3 angle valve job done to guarantee a tight seal AND!!! when reassembling the engine remember to index the spark plugs, this last part is very important and will effect the overall way you're engine runs, the machinist should check valves for straightness, grind the tips if needed, test the spring pressures to ensure they are within spec, and new valve stem seals, i think if you go this route you will be VERY happy and satisfied with the result. also by removing the heads you will be able to inspect the cylinder walls ;) this will be good because if you have a broken ring (which i dont think you do) you will see heavy oily buildup on the piston face or even excessive wear on the cylinder wall its self, just remember what you do on one side you should do on the other otherwise you may end up chasing gremlins, and on a side note in regards to you're short springs, some engine have shorter springs on the intake side if im correct and there usually is shims underneath to set the proper height. i hope all my jawing helps out
 
#24 ·
I finally had a chance to pull the heads off yesterday and then dropped them off at the machine shop today for a full cleaning and valve job.

I checked all the piston walls for excess wear and everything looked perfect. all the walls were nice and smooth.

all of the piston faces had plenty of carbon build up except for number 6. It was pretty clean so they may have been some water leakage from that part of the head gasket.

I still need to check all the lifters for possible damage but I'm pretty sure the are fine.

I'll be putting everything back together next weekend so we'll see if that solves the valve noise problem.
 
#25 ·
I came across both of your engine threads this evening 70fj ( love those old fj Toyota's ) and saw your comment " I hope this solves my valve train noise problem " and F-BIRD'88 suggesting a cam change. Now while I am a total novice in a sense, I would seriously take that idea up of dropping in a new cam, lifters, timing set as its the perfect time since its mostly apart now with all fluids drained. At least down there in the States a cam kit is very reasonably priced and I would be surprised if you didn't find some excessive wear on a lobe or lifter and harder to tell, a lifter that is leaking down faster then it should. The bonus of the right cam for that 4x4 which flows like a brick through the air, you just might gain on mileage too, not to mention a stump pulling low end that just leaps from the lights or off road.

The reason for my little rant, I have an L05 series factory engine in my pickup thats been acting up lately and had it to a couple of mechanics and they thought for sure its worn valve guides thats causing it to miss sporadically at idle ... its more like constant now and am hearing some slight valve train noise. So on the weekend I do a compression test on all cylinders and the one they claimed had only 110 psi and was missing on their scope is actually the highest reading at 170 but I found its exhaust lifter to be bottoming out way too easy. I wish that's all that is wrong as I put a dial indicator on all valves on that head and I was blown away, my cam is melting away on all the lobes and although I will never know, I blame some of this on the newer oils. The point is, they missed what the real reason was and yet they knew these chevy engines have had cam shaft issues for years. I realize money is tight but ... it wouldn't hurt to think about that and do some pricing once you get some good cam grind profile ideas to look at. Then you will have covered all the basis and probably be ahead in the long run.
 
#27 ·
I forgot to add, if you did decide to change out the cam shaft, make sure your distributor gear and shaft play are good so there would be no chance of eating the gears off of both as its easily overlooked. At least a normal grade cast dist gear is very cheep to purchase if needed. I expect $300.00 would cover the cam kit, all gaskets for the timing cover and oil pan and dist gear if needed.
 
#30 ·
Heads are back from the machine shop. The owner cleaned all the oil and crud off them and checked them out. He stated they did not need a full valve job and were just fine. There was a fair amount of oil burnt on to combustion chambers, but now their all clean. Got to love dealing with honest people. He could have just did the full work and charged me but instead it only cost me $40.00. I will be installing an oil catch can inline with the pcv valve as I'm suspecting that oil is being sucked in the intake manifold and causing detonation that sounds like the valve chatter. I've also clean off the piston faces so everything should be all set.
I'll be getting an early start tomorrow and should have my motor all back together my noon.
 
#31 ·
awesome thats good to know, sometimes its better to spend a couple bucks and know what your working with, you do not need to run a pcv to the carb btw, all the pcv is way for the engine to vent combustable gasses back into the engine for better fuel economy so if this is not a pollution controlled engine then replace the pcv with a valve cover breather, and make sure there is one on each valve cover, i learned this the hard way
 
#32 ·
Well it's taking longer than I expected to put my motor back together. Ran into some delays cleaning off the burnt oil/carbon off the piston faces. The good news is I was able to really take a good look at every piston wall, all the lifters, and the cam lobes all check out fine.
The heads are installed, base valve adjustment complete.
Still need to install the intake manifold, carburetor, exhaust manifold, distributor, oil catch can set the timing, and do the final valve adustment.
Looks like I'm taking a day of tomorrow to finish.
 
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