Thread: knocking noise

Tweet

Yes I am an engine hypochondriac (there I said it). I am constantly "hearing" noises, but last time it was true, so now I am paranoid.

I have a knock in my SBC (now that I finally got it mostly running right). It is possible that it is timing, but not certain (yes I am working on finalizing the timing, but waiting for the piston stop to arrive). Qjet carb with HEI and adjustable vac advance hooked to manifold vac. Flowmaster super 40 (loudish) with agressive, noisy tires (and I still hear it).

It knocks NOT at idle at all. I hear it mostly at 2000rpm cruising, much more when the engine oil is not fully hot (oil pressure is still above 30PSI). It does not get worse or less at higher rpm's or under load. When engine is fully hot, I barely hear it. I'm running 93 octane fuel and have 9.5:1 compression.

Plugs are reading nice and clean. I can think of the following possibilities:

1) timing too far advanced causing spark knock - My timing marks are now off, I plan on 12 static, 12 vacuum, and 21centrifugal with medium springs. I mostly have that now except I'm not sure about the static for sure and have not adjusted the vacuum canister yet. I did reduce the timing by 5-6 degrees with no noticeable change at all in this noise

2) Unadjusted rocker arm (loose). I am thinking this is more of a tick, and I would hear it at other times. When I am at idle or cruising at 1500rpm, things sound PERFECT.

3) Rod knock. Bad, don't think this is it.

4) I'm crazy, it's a noisy SBC in a big Jeep, get over it and drive it until something seems really wrong.

All gauges read good (oil press, temp, water). No hot engine issues. Oil pressure when hot is a bit less than 10 per 1000rpm. Oil pressure is about 5-8 at idle.

Thoughts?

Let's get your paranoid levels to a new high...lol. Possible crank thrust clearance too loose. A lifter galley plug behind cam gear not unstalled or improperly installed causing your oil pressure to dip low. Thrust flange grooved or worn even to let crank "walk". Cracked crank? Creating flex at certain RPM. Busted piston skirt? Wrist pin bore has a flaw and now "talking to you (especially at 2000 rpm). Flywheel/flexplate loose at hub or outer bolt holes. Have I got your heart rate up yet? Can you duplicate this condition while up on jack stands and using someone to help you run this thing to simulate? Try it and use a stethescope or what you have at your disposal. Use some brake action to simulate load too. It will change the attitude of this thing will trying to duplicate conditions.

Thanks for the advice. I do not think it is physical engine damage like a skirt, I had it it apart this winter (Not bottom end, but oil pan off) and nothing looked broken when I inspected the lower end from underneath. FYI - I did do a Cam swap (related to the cam issues you mentioned) this winter and I'm pretty sure I got it all right.

If it were one of the bigger issues (like cracked crank) I probably would do nothing unless I was sure that was it (which I wouldn't know unless I did a teardown). By the time I got to determining if that was the issue or not, I would probably just tell myself I'm crazy, and just drive on.... When this one dies, good excuse to spend some $$ and get a modified LS6 or something.


I'll keep an eye on further responses, thanks.

We all need an excuse to build a new one....LOL. Just becuse we're paranoid doesn't mean that the gremlins aren't after us.....LOL.

if you are paranoid about engine noises then dont ever buy something with soild lifters haha i am constantly having to remind myself that i have them haha all the time im like "whats that noise" haha

Ran my 400 sbc hard once, spun some bearings and it was knocking. Replaced bottom end, ran it for a while then ran it hard another night and started knocking again, the same sound. Changed all bearings with motor in the truck, then it still knocked. It was the water pump.................i was only an ametuer at 16 yrs old but................................................................


On another note, you talking about being paranoid about noises..........I am VERY paranoid about the smell of smoke..........I am always afraid it is going to catch fire............If an oil burner (vehicle) is ahead of me on the highway and I smell burnt oil I start worrying its me, If someone is burning leaves and I smell it I start worrying its me.......................

Nothing wrong with being paranoid about our stuff.....keeps us sane.

i ran a 500 HP turbo 302 for a couple of months with STOCK connecting rod bolts...... finally one snapped and slowly ripped the rod cap off, mad a nice knocking noise, and a high pitch screeching.... destroyed the crank, block, all the other rods, put a hole in a piston, and bent 1 exhaust valve.... that was mess

Heard a noise and thought it was a loose rocker. Tightened it down and fifty miles latter was back again so I tightened the rocker down again, went another fifty miles and bang!!! oil out the exhaust and stuck on the side of the high way. While waiting for the highway patrol ( No cell phones in the late 60's) pulled the head off and found exhaust valve sucked off stem bounced around in cylinder cracked cylinder wall toasted piston and bounced back through head. Not a good day

Your knock could be a scored wall or piston. Strange as it sounds, you can usually tell a score by an acrid smell from the exhaust or crankcase vent. Smell it once and you'll never forget it.