307 sbc w/416 heads, unknown (stock prob.) cam, rest is stock. Sitting still in idle, intermittent knock sound from front of engine, have pulled plug wires and isolated it to #4. 60 psi oil pressure, no smoke, put it in gear and knock goes away, driving it, its dead silent and runs great. Have not adj. valves yet and am suspecting wrist pin problem. Any ideas on what it might be? I'm not thinking a rod because it occurs just at idle. Have pulled all belts and its still there, fuel pump also sounds great thru a scope.
Are you wanting us to tell you to just keep driving it, and see if it gets worse? Because it probably will be fine, especially if you just drive around town. But if you're the courageous type, we'll all tell you our stories about driving a car with a little bit of a rod knock on road trips for thousands of miles, and made it home OK. Here's my Corvair rod bearing pictures. 5000 miles to California, up the coast to Seattle, back down to Monterey, then up to Utah for the eclipse, and back home. No problem with the little knock at light throttle at speed.
^^^^^ both 56’s have a couple of bearings like the one on the far left. Nothing has left from within for years.
Check the mechanical fuel pump if that is what you have....had this on a sbc Yep, Ran a Gm v6 for couple years with a bottom end knock at idle/low speed, was still going when I decided to put in a v8
On this one you mention, “intermittent knock sound from front of engine”. Have you checked for timing chain slop?
There is a knock adjustment knob usually found on the dash. On cars so equipped, there are two knobs, a left and a right. The left knob turns the knock adjustment on. The right knob is used to find the loudest knock eliminating noise. This can be musical, talk or a combination of both. Once the loudest knock eliminating signal is found the left knob is adjusted until the knock goes away. On cars not equipped with the knock eliminator on the dash, a female passenger is recommended.
Reminds me of when I worked for a Dodge dealer. We had just sold a used Chevy pickup and the customer brought it back with an engine noise. The owner's son, an excellent mechanic, called me to listen to the noise. He thought it was carbon on top of a piston. I thought the noise was much lower in the block. He proceeded to spray water in the carb while revving the engine. Then he took it for a test drive. It was setting in the show room with the salesmen watching As The World Turns (Meg Ryan was hot). The dealer's son came in and said the noise is number 5 rod. His brother asked how the heck did he know it was number 5 by just driving it? His reply was that he could read the number on it.
I have been fooled by this type of knock being a loose or cracked flex plate. However, if it goes away by shorting number 4 cylinder, I think you have bigger problems. A loose rod bearing will quit making noise under load, but rattle during coast down.
Yup, I second the flex plate being cracked. especially if it goes away when you put it in gear. Maybe shorting number 4 makes it run just rough enough to hide the noise from the crack. Remove the flywheel cover and look up at the crank flange, turn it all the way around, they are not always easy to see, this is where the flex plates usually crack. I had one once where the converter bolts came loose
I also had a loose converter bolts once, not sure how they loosened because as far as I knew it had never been removed or worked on. It was a straight six and sounded like the engine was going to come unglued at idle but went away at speed. Fairly easy to check for loose torque converter bolts and cracks. Not sure how to check for loose flex plate to crank bolts - wiggle maybe? Dan
I know that sometimes its hard to pinpoint a noise and its sounds like its one place when its actually somewhere else. Checking torque converter bolts is easy, but usually when thats the problem, it persists and doesn't go away . You haven't checked rocker arms, and it could be a lifter sticking and then going away. Might try an oil additive just to see what happens. I've had a lifter that would tick on occasion but it seems to have healed itself. Could be a piston slap that goes away after warm up. I'd keep driving it a while longer unless you use the vehicle for long drives, and just see if it gets worse or goes away.
I think we should pool our money & buy a cannon , that way we could load it with all kinds of crap & shoot it at a wall to see what sticks !
The OP asked for opinions. To that end he will get - hopefully real world experience on what is causing his knock, so yes he will get a shotgun response. I posted that I had similar experience ie: the engine knocked terribly at idle but went away when I drove. I had an old school mechanic friend look at it. The first thing he asked was “have you removed the transmission in the past” no I haven’t. He said your torque converter is loose. Sure enough he knew because he experienced the problem before, probably more than a few times. Good luck OP Dan
Tks to those replies that were serious and to the point...good ideas... I'll check the flexplate bolts first, and I don't know anything about the guts of the engine, but my guess is bone stock. Have checked the balancer for movement, solid. My thought also was a can of additive to the oil but my chicken side has made me hold off on that. Its one of those things you just know is there and every time you drive it you listen for it, as if its going away on its own. Had a lot of sbc's with every problem i thought existed, well...no.
My self @ one time have experienced pretty much every symptom mentioned previous thats above, & another one that took some time to solve ,Middle of engine, A Worn valve guide , a single knock sound about every few mints ,
One other thing that didn't get mentioned is that an exhaust leak can sometimes sound like a ticking noise. That aside, I think I would try to notice each time you start the engine what the atmospheric temp is and whether it makes the noise....or not. And if it makes the noise only when the engine is cold or does so when fully warmed. And does it go away ................what are the conditions when it does not make noise. Just try to notice when stuff happens. Good luck with it.............
Had 2 off topic Chevy trucks with cracked flex plates. Both brought vibration with the noise. That problem that @19Eddy30 just mentioned has tormented many owners with mystery. My Pops Impala ran with a wrist pin noise when cold, for like EVER.
Well, decided to get nasty greasy on Christmas Eve since other option was in the house with wifey and cooking. Checked converter bolts, flex plate solid, etc. Converter bolts about a 1/2 turn to max tight, think they were torqued originally but tight now. Haven't checked it yet , but that end seems o.k. The idea of a worn valve guide is new, those heads are from who knows what and what shape they were in when installed. I'm trying to go as long as I can with the engine, of course I'll prob. put a 350 in it when/if it craters. Its a great little street motor.
As said before, if it concerns you, keep things to local runs. Otherwise get the next engine ready for the (maybe) failure and plan for the long trip then.
when the flex plate cracks first start they are very hard to see. They crack between the bolt holes where it bolts on to the crankshaft hub. shine a good flashlight up there and look close it is hard to see because the conv is close, turn it a full revolution a little at a time and look real close
Been thinking the same thing since its just intermittent. Pulled the valve covers though and the engine there is as clean as any i've seen, but the heads could have been just put on a "dirty" engine inside. If I can muster up enough guts i might add a can of additive to the oil and see if it helps. Don't like the idea though.
Might take a look at Liqui Moly, it targets lifter noises. Lots of additives out there, so make sure you choose one that addresses your issue.........Marvel Mystery Oil also has a good rep for solving problems .
As mentioned a couple time's above, Those had aluminum/ nylon (dry up ,crack) timing set's if factory, Chain could be banging around... Pull the dis. Cap, An turn crank back/forth, see how much slop is in the chain..
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