[StrokedNova]

I got a 75 nova with a in line 250ci 6Cly that has a knock at speeds over 60-65. i can get it to go faster but i have to accelerate slowly and forget any type of up hill. also does it when i first start up but stops when i pump the accelerator. any help would be great and keep it simple don't know much.
has about 86000 miles on it.

Thanks

 

[Siggy_Freud]

Could try backing off the timing a bit.

 

[StrokedNova]

k i'll try it just a degree or 2 at a time right

thanks for the reply

 

[lluciano77]

Kick it back about 6o the first time. See if it stops making the noise. If 6o doesn't make a huge difference, there is something else going on. Don't go 2o at a time.

 

[StrokedNova]

ok, is there any thing else that it may be other than the timing(just woundering). I've had the problem withlow oct. gas so i know its not that this time.

 

[docvette]

Knock

Doc here imp:

Just fur grins...What does this "Knock" Sound like...?

Is a pinging or rattling? or a heavy knock? or a double knock?

Pinging or rattle under accel is usually timing / octane issues.

Heavy Knock under accel is usually Rods bearings..

Double knock is medium in tone and is usually wrist Pins...

Which is yours?

Doc

 

[StrokedNova]

Its a scary kind of knock that when i first heard it makes you back of the throttle fast and wait for the bang. Its a lot like a machine gun a fast metal to metal sound that you can hear pretty well unless the windows are down the stereos loud. Worst than the Oct. ping it does that when i really put my foot in it at low speeds.(and yes i use 87 Oct regular)

any help is appreciated

 

[78novaman]

My nova's 250 makes all kinds of "ping" or "knocking" noises when it's cold and under acceleration. Had it checked out and it's just the hydraulic lifters not getting pumped up until it's warmed up. Not too terribly bad for the engine but will scare the piss out of you the first time it happens. It kinda sounded like someone was hitting the pistons with the ball part of a ballpeen hammer in rapid succession. Really high pitched, loud, but deeper than an octane ping. Does that sound description make any sense???

 

[jimfulco]

Check your EGR valve. I disconnected mine on my '77 Nova 250 and it would ping at light throttle around town & at any speed over about 60. I reconnected it & that fixed it. Also look at the temperature-controlled vacuum switch in the EGR line. It may be sticking in the "cold" position & not allowing the EGR to activate.

78Novaman, it may be piston slap if it quits when it warms up. Generally not a big deal, it's just a little extra clearance when the motor's cold.

 

[StrokedNova]

I really want to swap out the 250 for a 350, i'm getting 12mpg now. so the engine has more than knocking problems, it may be better to just switch it out. I'll most likely be happier with the 350.

But none the less thanks for the tips and i will try them, its got to run for awhile longer so thanks for the tips.

 

[novadan]

I got a 1973 nova, it had a 250 ci inline six. the gas mileage was about the same as yours and my motor only had 40,000 miles on it. you should consider doing the 350 motor swap. I did a 383 stroker swap with the six cyl, and boy is it a blast. still uses the same amount of gas though. Does the pinging you have sound like almost like a crackling. The 383 does this (probably a pinging a degree or 2 to high or too low of octane) It reminds me almost of a crackling in the motor. It does it only when I'm on the highway going really fast (about 85 to 90) I don't do this all the time. I'm not sure if it is the timing a little to high (motor is running perfect at idol and crusing speed) or the motor is running at a lower octane, but I always use 93 octane.
Dan

 

[Simo]

My nova's 250 makes all kinds of "ping" or "knocking" noises when it's cold and under acceleration. Had it checked out and it's just the hydraulic lifters not getting pumped up until it's warmed up. Not too terribly bad for the engine but will scare the piss out of you the first time it happens. It kinda sounded like someone was hitting the pistons with the ball part of a ballpeen hammer in rapid succession. Really high pitched, loud, but deeper than an octane ping. Does that sound description make any sense???

The lifters can warm (rattle till pumped) be nice and quiet till the revs get to a stage where the lifters have to cope with more hydraulic load , if they cant hold the dampening fluid (leak down)
they will colapse causing noise at revs ,

 

[StrokedNova]

Nope its a knock not a cracking Dan i've been told it could be a rod about to be thrown but he who told me is not a mechanic and hasn't heard the noise so i figured it would be best to ask people who have worked/are working on cars for a while.