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Old 04-04-2004, 12:08 PM
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engine has to much vacume?

drove the car yesterday ran great,today i changed the oil and started it up and the engine started knocking pretty loud,never knocked before ever,and i pulled the oil cap off and the knock was gone and the car ran perfectly.put the cap on and the knock came back.timing chain cover is tapping when the cap is on.

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Last edited by 73chevyhelp; 04-05-2004 at 11:09 AM.
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Old 04-04-2004, 12:18 PM
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More details? Is this a fresh engine? What is your oil pressure like? Solid or hyd. cam? What kind of rockers/nuts?

Royce
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Old 04-04-2004, 12:29 PM
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the cam and lifters are new changed the oil and im guessing the lifters are to tight on one cylinder causing the knock,setting the lifters now
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Old 04-04-2004, 12:54 PM
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That's a good place to start. Spin your push rods while you're in there to make sure they aren't bent as well.

Royce
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Old 04-04-2004, 12:58 PM
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ok lifters are fine,the noise is a knocking sound like metal tapping but it only comes when i put the oil cap on,if i take it off it stops knocking and runs normal,you can hear the suction of the cap when u take it off there is so much vacume on it,checked the vacume lines and there ok.dont know what it is now lol,
350 sbc stock engine.

Last edited by 73chevyhelp; 04-04-2004 at 01:07 PM.
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Old 04-04-2004, 01:43 PM
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Could this be your PCV valve rattling?
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Old 04-04-2004, 02:05 PM
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pcv valve is brand new this is a loud knock not spark knock and only occurs when u put the oil cap on,when u take the cap off it stops knocking and the car runs great?lol, the pvc valve is on the driver side of the cover,the oil cap on the passenger side does the passenger side suck vacuum?this is very strange to me,the valve covers are new and i remember having an oil cap that was different than the one i have now,the current cap is solid,the previous cap had breather holes around the bottom of it,was shaped like a short stubby oil filter.would a soild oil cap cause the motor to cut air flow and cause a need of unusuall vacuum?

Last edited by 73chevyhelp; 04-04-2004 at 02:23 PM.
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Old 04-04-2004, 02:30 PM
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Are you sure that a rocker is not hitting the inside of that oil cap?
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Old 04-04-2004, 02:37 PM
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the lifters and rods are fine they arent the noise i hear when i put the oil cap and they arent any noises ,its gotta be vacuum vacuum vacuum! the gasket around the distributer base bubbles if the cap is on and stops when the cap is taken off,no knock when cap off,knock when cap is on.thats why im asking about the solid oil cap being a problem,doesnt make any sense but thats where i am.engine is rebuilt with about 40,000 on it,never ever ever tapped before,and this tap is in the front of the motor,ive tried to determine the tap by listening to everything on the engine,not the valves,rockers,lifters,fuel pump,water pump,u cant feel the tap coming from anywhere.its baffling me why the tap goes away when the cap or the pvc valve is removed i tried switching the cap and pvc around but same thing.has to be vacuum because the cap is being sucked on,when u pull it off you can feel the vacuum and hear it go shook when the cap is removed,maybe someone can go over the whole vacuum process with me to help me better understand.

Last edited by 73chevyhelp; 04-04-2004 at 02:45 PM.
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Old 04-04-2004, 02:41 PM
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Too much crankcase pressure. You need to vent the crankcase better. However, something is causing this pressure. Bad head gasket, blowby on rings, valve seals...........

Nothing to do with vacuum.
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Old 04-04-2004, 02:48 PM
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how would i vent the crankcase better?im guessing the vented oil cap? the pressure i dont understand,never used this cap before on this engine its always had the tall ported cap on it sorry to be so aggravated with this its just strange to happen all of a sudden and knowing the changed cap is the only difference.
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Old 04-04-2004, 03:31 PM
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Hmm, If you install the oil cap, it knocks, you remove the cap and the knocking stops?

If you have good vacuum from the PCV valve and don't have a good vent on the other valve cover, the suction from the PCV could be pulling down on the valve cover causing one of the rockers to strike the cover or oil cap. Look at the underside of the cap and see if something has been hitting it, (usually on aftermarket non-baffled covers).
Ck the vent on the opposite cover to see if its clear and clean.
Are they stock valve covers? if so, you can put them on wrong and the rockers will hit on the inboard side of the covers.

Mark
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Old 04-04-2004, 03:35 PM
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Mark, I think you hit the nail on the head. He needs to install a breather on the other side.

Royce
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Old 04-04-2004, 03:49 PM
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!

That must be one heck of a PCV valve!! LOL
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Old 04-04-2004, 03:56 PM
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the valve covers are eldebrook covers from advance,i looked at the covers and cant tell the have been hit,rubbed or damaged, the covers have baffels on both holes where pvc and oil cap go,pvc works good and is new,the cover with the oil cap has no way to vent cause the cap is solid and not vented.camaroman7d says i need a breather cap like i had before on the cover,thats what im guessing to!
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