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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.
 
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#38 ·
Too bad you did not take advantage of the situation and degree and advance the .450"in.460" ex camshaft in this motor.
( If you were to degree it you would find it is retarded (115in/113ex C/L's) 114LSA (retarded by 1deg)
Moving the cam to a new 107in/121ex C/L position (7degree advanced) will wake it up and make more torque in this low cr engine. as the intake valve will close sooner.
This cam was GM's origional 1969 11:1 ccompression 350-350HP L-46 cam.
As installed it is a mis match @8.5:1cr. It need to be advanced.

If the new head gasket is thicker than the old stock head gasket the compression ratio wil now be even lower.
Should have wacked some off the heads (.050") and used a felpro shim head gasket.
I would have home ported the heads too.
When I had the heads off I put it to TDC and it was already set to 6 degrees advance.
Unfortunately I ran into more delays today. Got everything put together, but when I fired her up she ran for about 20 second then died. Need to trouble shoot tomorrow and do the final dial in on the timing and valves.
 
#41 ·
Quick update, finally got the FJ40 running and idling smooth. Timing is all set and I finished half of the final running valve adjustment. All I have left to do is finish the the passenger side valves.
So far all of the previous issues are gone. No detonation/valve chatter, no single tick when I turn off the motor, all the pistons are firing perfectly. Can't wait to test drive it tomorrow night.

On another note....I really like the MSD Digital E-Curve distributor. After I learned how to set it up it's so easy to deal with. Nothing like being able to change the curve in just a few seconds.
 
#43 ·
So throughout the repairs or tear down of the top end, did you ever really nail down what was causing this "rattling" ... was it valves floating with really weak springs or perhaps preignition due to an extreme amount of carbon build up and was that from too rich a fuel mixture or was it using excessive amounts of oil ? . Then the matter of the mystery air loss in two cylinders as you pressured them up. Just curious to find out what was really going on inside that engine.
 
#44 ·
I'm going with the extreme amount of carbon. It was really caked on the piston faces and the heads were covered in sludge. This was most likely caused by oil getting sucked up through the PCV valve since my valve covers had no baffles. It also looked like there was an issue on the old head gasket between those 2 cylinders. The gasket came of clean and you could actually see an issue.
 
#45 ·
I wonder if the sludge was that bad that it held the oil back from flowing out of the heads { assuming you meant sludge on top of the heads } that it helped promote the PCV to suck up oil .. its only a thought. Do you know the past history in how often the engine oil was changed and what brand of oil was used and what I am driving at there is the fact the oil wasn't doing a very good job at keeping the sludge at bay or somewhere along the line the PCV valve plugged up, a thermostat not keeping the engine up to temperature etc. I realize the humidity factor of your area could be an issue in keeping an engine cleared out of moisture but can't be worse then the south eastern states or for that matter up here in the winter.

I just know with my own 1995 350ci, in sorting out my own engine miss issues I had the valve covers off and I was surprised to see how clean it was, just a slight discoloration film on the rocker arms and the head surfaces were spotless and only a thin layer of build up in the very front end of each valve cover. I have used 0W-30 synthetic all along from Imperial .. now Mobil and change it every 3000 miles and the engine has 186000 miles on it. Hard to say if it would have looked the same with another oil as I have nothing to compare with.

It may not hurt assuming the combustion chamber cleaning products work, to run some through on a regular basis and hopefully keep the carbon build up down. At least as time goes on you can pop the valve covers off and see how the top side of the heads look.
 
#46 ·
I wonder if the sludge was that bad that it held the oil back from flowing out of the heads { assuming you meant sludge on top of the heads } that it helped promote the PCV to suck up oil .. its only a thought. Do you know the past history in how often the engine oil was changed and what brand of oil was used and what I am driving at there is the fact the oil wasn't doing a very good job at keeping the sludge at bay or somewhere along the line the PCV valve plugged up, a thermostat not keeping the engine up to temperature etc. I realize the humidity factor of your area could be an issue in keeping an engine cleared out of moisture but can't be worse then the south eastern states or for that matter up here in the winter.

I just know with my own 1995 350ci, in sorting out my own engine miss issues I had the valve covers off and I was surprised to see how clean it was, just a slight discoloration film on the rocker arms and the head surfaces were spotless and only a thin layer of build up in the very front end of each valve cover. I have used 0W-30 synthetic all along from Imperial .. now Mobil and change it every 3000 miles and the engine has 186000 miles on it. Hard to say if it would have looked the same with another oil as I have nothing to compare with.

It may not hurt assuming the combustion chamber cleaning products work, to run some through on a regular basis and hopefully keep the carbon build up down. At least as time goes on you can pop the valve covers off and see how the top side of the heads look.
The sludge and oil was actually on the cumbustion chamber side along with the inside of the head. I have no doubt that it was effecting the way the valves worked. There was a lot of oil getting sucked into the intake.
 
#47 ·
Oh I get you now, I just associate sludge with the topside of heads, lifter valley and oil pan. So where it came from, ether the PCV valve and may or may not mean excessive ring blow by or you also had intake gaskets leaking from underneath, this is assuming your valve guide seals really are good .. hope so after having the heads checked out!. I would think you would have been going through a certain amount of oil, consumption wise then in the last while.
 
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