More like a "thock thock" sound. Any thoughts? Goes away once engine reaches operating temp.
Motor and trans are out of an '86 Vette. I bought it in 2006, unknown condition, fired it up in 2013. I've put about 600 or so miles on it and the sound hasn't gotten better or worse. 5w-30 oil, 50 psi when cold, I believe 10 psi at idle when warm. No change in oil psi from 2013 to now. I've had the intake and valve covers off and the motor looked clean and cared for / low miles in those areas. No loose rockers although I'm thinking of running the valves eventually. Doesn't "tick" anyway.
Sounds loudest on passenger side. No more air injection pump, new water pump, all belt drive accessories turn freely. Noise is not back near the flywheel although I don't remember ever separating the trans and motor. A visual from underneath looks good. Working on doing a compression check right now.
You have to use a locator devise, anything from a broom handle to a stethoscope. You have to isolate where it's coming from. P.S., I can't tell you how many times I have found a sound like that is either timing or exhaust/headers leaking or both. Sounds exactly like something thocking/knocking or ticking. I'll bet you my piggy bank that's what it is. Whatever it is, goes away after warm up because of expansion. Your motor may have a detonation sensor/knock sensor. If it fails, motor may detonate and make that sound. http://www.oreillyauto.com/site/c/d...nation+sensor&pt=02200&ppt=C2179 However, the symptoms for that are knock under load or highway speeds. At idle like yours: My guess, Exhaust leak.
Don, I'll double check the flywheel but, the sound is up front.
Bartamos, I believe last time I used the ol' gigantic screwdriver but I have an electronic ear at work that I'll borrow. I'm leaning towards the valvetrain as the knock is one half of what the crank turns. That would include one exhaust port leaking. I'll have a closer look at those stock headers. The only change they went through, beside coming off and on the motor, is me welding up the air injector bungs. It might be possible that I missed a spot.
You have a piston with a little too much skirt clearance. Once the engine reaches operating temp, the piston slap goes away due to heat expansion. While it's knocking, disconnect the spark plug wires one at a time. When you find the cylinder with the knock, it will either disappear, or change to a double noise if it's loose enough, kind of a "Ka-thunk" sound as the piston flops around without any combustion pressure keeping it pressed tight against the cylinder on the down stroke. I'm betting the noise will stop since it self-corrects when warm. Use a long screwdriver or a broomstick held to your ear as a stethoscope and the noise should be pretty easy to locate. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
Doing a little new school, Jerry. Brought home the electronic stethoscope and the scope to peer inside the spark plug holes. Maybe get a look at the cylinder walls.
But first, a new experience for the kids. Let them pick out some Safe and Sane then buy them dinner. I'll get back to it before the night is over.
I use a 5MM USB borescope that projects a full-screen pic on my laptop, for both gunsmithing and engine inspections. The scope won't show a collapsed piston skirt, however. I still get along with the oldtime probe-type stethoscope for the time being. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
More like a "thock thock" sound. Any thoughts? Goes away once engine reaches operating temp.
Common small block problem. If I remember correctly GM changed piston design going with a smaller piston skirt. So tendency to develop a piston slap when the engine is cold.
Being the noise goes away after the engine warms up is enough to confirm that piston slap is what you have. Save your money buying any listening tool. And bore scope's are not going to show you anything concerning piston slap.
I switched from 5w 30 oil to 10w 30. That helped reduce the noise and shortened the time needed for the noise to go away.
Then I told the wife that she must warm up the engine and wait for the noise to go away before she puts the suburban in gear.
At least 25,000 miles with cold engine piston slap. I am living with it. And I know of others that have done the same.
And I would not call that sound a knock. Main bearings, connecting rod bearings, that's a knock.
I don't have as high tech as yours, Jerry. But neat little toy, none-the-less. Not a whole lot of carbon build up in 2,4, 6 and 8. #2 had a bit of deep scoring. #4 looked like it had a couple of rust spots on the wall.
Jerry: Once he does the sparkplug test and does find a cylinder making the noise, then what? I've read many folks having 350 noise problems but they were motors from the 1990's. They more or less live with it or try different weight oil.
The only sure fix is to swap pistons. We used to run a knurl on the skirt area to decrease the clearance a little, but recently the cost of parts has gone down and labor has gone up so it's impractical to patch on anything- - -just install new parts once the engine is torn down. Modern hypereutectic alloy pistons work with spooky close tolerances (.001"-.002") since there's virtually no heat expansion. Jerry
"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt! There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway Love your enemies and drive 'em nuts!
The overwhelming response on the internet is to forget about it. It is common in Chevy V8's. This forum is also the internet and has many experienced motormen. You asked and got good info. It is hard to decide on a problem with a risk factor like this. Let us know if the spark test shows anything. I am sticking with exhaust noise, because it's cheaper. Warm it up before driving. I had a 56 Chevy 210 with a 265 when I was a teen. It smoked like crazy, used 90wt gear oil in the crankcase. Still smoked. Don't think oil will fix yours either.
Its a 350 and you likely don't have a lot of money tied up in it. I say run it like you stole it until you have to add more oil to it than gasoline, then rebuild it. Carl
1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission
Stethoscope says #2 piston is slapping and #8 injector is very weak. Plus the #8 spark plug told me that. Maybe I'll try some fresh injectors and see if the idle will smooth out some.
Its a 350 and you likely don't have a lot of money tied up in it. I say run it like you stole it until you have to add more oil to it than gasoline, then rebuild it. Carl
1950 Chevy Advance Design 3100 in Scotland In the Stovebolt Gallery More pix on Flickr. I've definately got this truck thing in my blood ... my DNA sequence has torque settings "Of all the small nations of this earth,perhaps only the ancient Greeks surpass the Scots in their contribution to mankind" Winston Churchill.
