Have a sbc in an elco. Holds 60 psi pressure running, about 40 at idle. At idle I hear a small knock from the front of the engine, have checked alternator, P/S pump, A/C compressor, fuel pump. (did it the old way, with a hose), Its not there all the time, just every now and then and runs fine on the road, no noise-still I'd like to find it, don't want a fail on the road. I've thought about the pump rod, but think i would have heard it. Any opinions?
Good question. Got the engine with the car and it was/is fine for a long time. Don't know what the chain is (single/double row) or anything else about the internals. Has 416 heads on it (307 c.i.) which are the better ones and not stock, so i'd guess the chain was changed.
You should be able to get an idea of timing chain slop by removing the dist cap then grab the balancer and move the balancer back and forth (easier done with plugs removed) while watching the dist rotor. How much can you move the balancer without the rotor turning is the question. I have removed timing covers and found evidence of the chain being loose enough to contact the cover, which could possibly be your noise. I chased what I thought was lifter tick in a SBC that did end up being nothing more than the spring in the fuel pump. New fuel pump fixed that issue.
You could pull the fuel pump and run the engine from a IV gravity feed and see if the noise goes away. Also may be able to access the timing chain through the fuel pump hole, don't know if that works on a sbc.
Pretty sure that won't work. See pic here: https://www.jalopyjournal.com/forum/threads/sbc-fuel-pump-mount-question.1147088/
Yup, like I said I didn't know if it would work. It works on a lot of engines, but I don't have any experience with sbc engines. Thanks for clarifying it.
If it is a deep knock, I would look at the harmonic balancer, the torque converter bolts and at worse ,it may be thrust bearing worn
Came here to day that. I have known a few people that replaced and engine over that, failing to check first.
Like said check crank end play by prying the hormonic back & forth in unison with flex plate or flywheel.
It's a turbo 350 auto. Has about 3K on the trans (rebuilt before installation) and new converter and flex plate-torqued up to specs. Knock seems to be right at the very front of the engine, balancer is a 3 belt type, no rubber. Lots of good ideas here, thanks guys. With the oil pressures being high (no doubt, hi volume oil pump, not stock) and the upgraded heads, I have to think the engine was built right, hopefully with a new chain. I'll try the easy things first (lazy) like belts and then go from there. BTW, the damm knock seems to come and go, not constant.
If its the thrust bearing on the crank it will do it after warm up & at idle, if really bad at fast idle. The reason I bring this up again is that it's a SBC! And the sound will have you going in all direction, stand at front sounds like in the rear, visa versa. Stand on left side it can sound like from the right.
Ah, the joy of chasing intermittent noises. Does engine cold or at operating temp make a difference? If there, engine cold and goes away engine hot, possibly piston slap. (Usually on a high mileage engine.) Also buggered rocker arm, ball or pushrod end. Worn valve guide? Header/exhaust manifold gasket? Heat riser? At any temp, look for loose mounting brackets or bolts that allow vibration at low, no load idle speed but get put under tension at higher engine speeds. Afore mentioned flexplate. (Usually goes away when put in gear. Puts a load on the crack, esp. if engine speed is raised.) I've had success using a screwdriver as a stethoscope by wrapping my hand around handle and putting my thumb in my ear. Wooden handles seem to work best.
I had 64 Grand Prix that had this odd sound. it turned out that the flex plate bolts loosed up enough to then allow the flex plate to crack....
Ha! I might have the solution-easy peasy! I wear hearing aids, maybe if I just take 'em off when I drive it or listen to it under hood the sound will go away!
I have had the pulley crack out around the bolt circle on one multi belt pulley. With an automatic flex plate noises can usually be heard at and idle with no load or when you let off and unload them but will go away if you put it in gear with the brake on and give enough gas to put a load on it. That was the reason I got the free Olds 350R that I had in my 51 Merc for years. It was in a Chevy pickup and there was a knock in it and a guy who had it gave it to my buddy who then hauled it to my house and gave it to me. You can pop the distributor cap and move the crank back and forth with a socket to see how much slack you have in the timing chain. Just in how far backwards or forwards does the crank move before the rotor moves. If the engine came out of a donor with a stick and especially a truck with a heavy clutch the thrust surface on the crank could be worn enough so that the crank moves back and forth. A good shop should catch that but a guy doing a home rebuild or a ring, rods and mains refresh might not catch it.
I had a knock in a 472 Cad motor at startup. Turned out the stock torque converter bolts bottomed out on the new replacement torque converter, so it didn't pull it up tight against the flex plate. Shorter bolts fixed the knock.
Young guys turn up the radio volume to override engine noises, us old farts turn down hearing aid sensitivity! it's the KISS principle in action!
Checking ALL above , & illuminating what has been mention, Here is another One to Add to list to check !! A Bad Valve Guild & Warn Stem will make a Weird Sound , I chased the Sound for close toWeek , Taken off parts , / disconnecting The Sound Started , Me Hearing ,would come & Go about every 30ish seconds To Little over a minute in between , The Sound would Last about 2-4 seconds,,!!! @ Idle , (Longer to hear to come back around) When the Valve would Open , Then Go to Close , Vale was trying to Find """Center""" On Valve Seat when Valve Closing,, Also , a Broken Valve Spring will make Sounds @ different Times ( Not consistent)
I had (actually still have) a 350Chevy that sounded like a diesel at idle. Checked everything that could be checked in the truck without pulling the heads off and pistons out. Still rattled. Probably put 30,000 miles on it before it got pulled and overhauled to go in a different vehicle. No more rattle. My conclusion was that it had a bad wrist pin. It's got another 50,000 on it now and still quiet.
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