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In this Discussion
- martyweir February 2008
- MikeKy55 March 2008
- Oldcar_Mechanic February 2008
- Steve E. February 2008
Chevy 350 Valve Clatter (clacking noise)
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Howdy All,
I own a 76 CJ7 which has a chevy 350 in it. The engine came out of a 70-72 c20 pickup I think. I have been struggling to eliminate an annoying clacking noise coming from the valvetrain.
The clacking is not constant or isolated to one valve when the engine is cool. I will hear a valve or two clack 6-8 times, then it goes away for 5 to 10 seconds, then comes back. It does this until the engine gets hot, then it seems to spread to several of the valves and is more constant. I have adjusted my valves a few times, loosening them till they rattle, then tightening them till quiet, then 1/4 turn more. No luck.
I have come to the conclusion that the cause of the clacking or clatter is oil starvation, because when adjusting the valves I noticed that oil was not squirting out of all of the push rods - three or four were running dry. There is also quite a bit of crud (burned oil? real gritty & dry, doesnt' look like sludge - no metal in it) built up on the heads, so I pulled the push rods and cleaned them out - several were totally clogged. I added an oil cleaner flush additive, and ran it through. After this, I noticed that one pushrod had no oil coming out, but the one next to it was squirting oil so hard it was squirting out of the engine compartment for about 30 seconds then it slowed down.
The former owner "rebuilt" this engine. When I got it, I changed the water pump, thermostat & oil pump are next. The timing was off, as was the mixture, causing the engine to run hot. Also, the PCV was not connected to a vacuum line. I think all of these conditions could have caused burned oil / crud buildup in the engine. I have good compression, and when i checked w/ vacuum guage, it hovers right around 20. Weird thing is that the oil pressure is pretty steady around 18 - 20 @ Idle, then up to 40 at mid RPMs. Seems normal. The engine seems sound & worth the effort. It runs well, the clacking initially annoyed me, but now it has got me worried.
1. Does it sound like the clacking is caused by oil starvation?
2. How much oil should be coming out of the pushrod holes? Does my oil flow sound bad?
3. Any other cause of burnt oil I am overlooking?
4. I'd like to check my lifters & clean them too. Can I pull them without pulling the heads? Is pulling the heads a good Idea to flush engine?
5. I have been told to fill the crank case w/ diesel & dry crank (pull plug wires) to flush the crud / clean the case out. Is this acceptable & will it work? Any other suggestions for a good flush to get oil flowing better?
6. I have heard folks talk about "boiling" cylinder heads. Is there anywhere I can learn about this procedure? Is this reccomended?
Thanks for any help you can offer!!! -
Sounds like possible culprits could be the lifters are full of crud and/or possibly the oil galleys that feed the lifters.
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Thanks Steve. I guess That's what I suspect too.
BTW, Can the lifters be pulled w/o pulling the heads on the older 350's? I'm trying to avoid buying a $30 lifter puller that I'll use once... Any DIY tools that will do the trick? -
I have to agree with Steve. It does sound like the lifters being cloged was stopping the oil from getting to the rockers (hence, no oil squirting) and they were not pumping up enough to stop the clatter.
18 to 20 p.s.i. on an oil gauge sounds like there is no need to change the pump to me.
Quite possible, if you had a bad water pump, the engine was probably running way to hot and allowing the oil to cook onto the heads.
You should be able to remove the lifters just by removing the intake, losening the rockers and taking the push rods out of the way. You could take the lifters apart and clean them, but you may be better off just buying new ones.
If you want to flush the engine with diesel fuel you could do that. After draining the old oil, fill the crankcase with the diesel fuel, remove the distributor and take a cut-off screw driver chocked in a drill and run the pump till you see the oil flow from the rockers. That way there would be no need to run the engine. After you drain the diesel fuel out and replenish the crankcase with good motor oil, run the pump again so that everything is well lubricated.
Of course, all of this is subject to how crudded up everything is. If it's real bad, it may be time to do a complete disassembly or overhaul.
Ron -
Another thing to check oddly enough is the fuel pump. I went through the valves on a 350 I build once at least 3 times and the tapping kept coming back. It turned out to be the fuel pump. The return spring was weak and allowed the pump push rod to bounce. It sounded exactly like a lifter tap. It's an easy test. Just remove the two bolts holding the pump to the block and pull the pump away from the motor and start it. It will run long enough on the fuel in the carb to know if the tapping has stopped.
