SBC mystery knock

hey fella's, i got an issue in the engine in the 55. so first off, some background, its a crate goodwrench sbc, miles unknown. i started it up a couple weeks ago and the damn thing started ticking. i thought it was just a little lifter noise as it was a little cold out. anyhow, so i have been trying to figure out the noise. it now will not make the noise when started cold, it will begin making this knock after about 10 minutes of driving and will progressively get a little bit louder and initially only under load (at idle, in drive) after about 20 minutes. damndest thing is it wont ALWAYS do it in neutral or park often times it just subsides or gets quite enough that it is no longer audible, only after driving the car for quite some time, will it finally persistently do it in park or drive. the knock will become more rapid and speed up and down with the RPM's, and like when leaving a stop light when the RPM's climb rapidly the noise will speed up with the RPM, as the knock increases in rapidity it almost becomes a whine

so what is it? spun rod bearing? main bearing? doesn't sound like water pump.. i pulled the valve cover on the passenger side (the side where the noise seemed to be coming from) and watched the valve train, and all rocker arms seemed to be moving in equality so i'm thinking it is not in the valve train. IM BAFFLED!!! any body experience this before? any clues as to what this bastard knock is?!


thanks for your help guys

-Jr

 

Wrist pin? It will make noise when the motor is at temp if you have a problem.

 

Hi Jr,
I had a 283 in a '67 Impala Sport Coupe and it had a crazy little knock too. Found it with a piece of rubber hose...and it was the fuel pump, up front. Just a thought... Old piece of hose can come in handy for some noises. Good Luck...duane

 

yes , i once had a strange tick that came and went in a sbc .....it was from the fuel pump too

 

I have the same knock on my 283. I think it is the fuel pump rod. Drove it to Chicago from L.A. and more. No trouble yet.

 

When it's making the noise at idle, start pulling plug wires and when the sound goes away you found the rod that's giving off the noise.

 

wife's 55 did this for quite a while--early 327--drove it like that for a long time--thought it was a lifter or something--changed fuel pump and rod as a piece of hose led me there--end of knock

 

Mine use to break the spring on the fuel pump arm. Also a cracked piston skirt will make a weird noise also. Lippy

 

hmmm a whole new world of possibilities, i will grab a hose and start tracking around the fuel pump.. any other common knocks that begin AFTER warm up??? weirdest damn thing.

 

There are many things that can cause such a noise;a bad harmonic balancer for one.I had this problem on my 55 Pontiac and it sounded for all the world like it was coming from the fuel pump.Drove me crazy!Is your balancer a press on on held in with a bolt?If a bolt check to make sure it is still there.If a press on,check the belt alignment to make sure it hasn't walked out.
Another can be(very rarely)a broken crankshaft.A friend of mine had a 327 that developed a slight knocking sound that would come and go.Finally tore down the engine and found that the crank(forged)had broken at the #1 journal and the only thing holding it together was the unevenness of the break.

 

broken flex plate..happens all the time to gm's

 

AHH yes, broken flexplate, I should know that one my 79 chev p.u. has one ticking now!! Also loose convertor bolts will do it too, it's more of a knock though.from the bolt deal. Yep, can be a lot of things. Try to isolate it I guess. Lippy

 

ground pounder

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I was going to say the same thing as theses two guys....

so my vote is !!!!!!!

 

yeaaaa, this looks like its really not going to be easy to deduce. just to make sure i adjusted the rocker arms right.. to adjust with hydraulics you bring the cylinder to TDC, tighten the rocker arm then back it of 2 turns correct? just want to make sure i did not over tighten them before i take the car out today.

 

now, a would a broken flywheel only knock after the car is warm? i honestly dont know, but seems like it would be all the time, then again, you guys have the experience not me.

 

as mentioned mech fuel pump can make all kinds of racket.

# 1 rod on sbc chevy is a notorious trouble maker, last one in line for the oil, run er a bit low and bye bye. That said, I have had sbc's with a weak #1 rod go for as long as I wanted them too, as long as I kept making sure it had plenty of oil.

My bet is #1 wrist pin

 

also, just to make sure i did not over tighten the rocker arms, the correct way to tighten with hyraulics is to bring the cylinder to tdc, tighten the rocker arm down, then back it off 2 turns correct?

 

This sounds wrong to me.

 

There are as many opinions on how to set hydraulics as there are people setting them. I won't be the one responsible for your bent push rods

This guy does it the way I do.

http://www.4secondsflat.com/Hydraulic_lifter_cams.html

 

No that is not correct,bring up to tdc on comp tighten to 0 lash then down 1/2 turn.Some say 1 turn some say 1/4 turn.This should get you in the ball park

 

as long as he hasn't already collapsed em by setting them too tight

 

yea, see the way i had always been told to do it is to start the engine, loosen the rocker till it starts ticking then slowly turn it down till the ticking stops, is that about right?

 

I would watch the oil pressure closely, if it don't have a direct pressure guage I'd put one on. Then I would take the oil filter apart every hundred miles or so and see if it's making metal.

 

With the lifters full of oil this is probably not the most accurate way to adjust the rocker arms. I usually loosen the rocker until there is some play in the pushrod (ie, you can wiggle the pushrod very slightly. This play indicates that the lifter plunger is all the way at the top of the lifter. Then I tighten the rocker arm until the play is just barely gone gone, and give it another 3/4 turn.

Doing it the way you describe, if the lifter doesn't bleed down quickly, you may well end up with too much clearance.

Yes, this is another way to do it, although likely much messier. If you do it this way, loosen until it clicks, then tighten until the clicking is gone, then give it another 1/2 to 3/4 turn. This should get the lifter preload pretty much where it needs to be.

 

To avoid the mess of adjusting valves with the engine running, you can cut the top middle section out of an old valve cover. then bolt it on while adjusting the valves. old trick i learned from my pops.

 

Make it 4 votes for flexplate.I'd pull the flexplate cover and have a peek. sometimes you can see a hairline crack around the crank bolts.

 

Check the big brain on Dan!!
A FNG with a good idea!!

Just kidding Dan , that is a good idea though , I will use it in the future.

 

ok so i was remembering half right.. almost.. haha i will go back through them before i take off.. any thing else as far as the knock goes? easy ways to diagnose (other than the hose trick)?

 

A long screw driver is ok for listening to sounds. Place it around the motor to help locate the noise. [ metal tip on the motor , ear to the handle ]

 

long screwdriver works. or you could use a mechanics stethoscope.