Engine knock with good oil pressure

I was listening to a guy's 235 Chevy engine at idle that seems to have a slight rattling or knocking sound.It's not real noisy but someone familiar with engines listening while the hood is open might hear it.Sounds like it coming from the middle of the block on all cylinders.Same on the left and right side.It's less noisy under neath the car.The noise is a bit less when the engine is cold.The oil pressure is good for a 235,25 psi at a hot idle,40-45 driving down the road.The engine runs smooth and strong with a slight trace of blowby ,solid lifters are quieter than most of these engines.Pushing in the clutch changes the sound slightly but I think it's just tranny gear rattle in neutral.
I'm thinking it's just worn pistons and nothing to be concerned about. What do you think,yes noises are hard to hear on the Internet

 

Older motors were noisier than modern motors. A 235 Chev has wrist pins that ae often the source of a noise, as well as piston skirts. If is not to bad, run it. After a complete overhaul, it will give years of reliable service, if done right.

 

Sounds like piston slap.

 

If the engine was setting a while before being driven agin it could be carbon on th top of a few pistons, that will make the sound you descibe......
get an old Windex bottle with some water in it, take the air cleaner off and while rvving the engine spray it in the carb till it dies down....
repeat this about 6-8 times revving it up high and spraying the water in the carb.... this would remove it if carbon is the culprit......

 

This engine has been in steady use.The owner recently noticed the noise,not to say it wasn't always there and not noticed.Driven about 1000 miles and the noise hasn't gotten worse.He even ran the engine up to near 4000 rpm in the gears a few times to see what happens...
I forgot to say,increase the engine rpm to around 1000 rpm and the noise pretty much disappears.
The sound does not have a on time steady beat like a bearing knock but more "rattly"
I checked the damper and it's seems fine.

 

Back off the advance a little & see if that changes it.

 

Check the crankshaft end play.

 

Are you being serious?

 

Yes he is. Used to use it myself, passed down by my father. Saves taking the head off to clean the carbon & LEAD deposits. When there was lead.

 

Reijer Yes the water thing is serious, you can also use transmission fulid just pour a little at a time and keep RPM,s up and it will smoke like hell.
As for the knock do you think it could be this great gas we how have to use?

 

Engines ping at idle? No sign of pinging when driving the car.

I just checked the crank end play at the flywheel with a dial indicator,about .008-.010

 

I broke a flex plate in my Studebaker, sounded like a rod knock.

 

Fuel pump spring.

 

This was my first thought!

 

A cracked flexplate could be another source of the noise. The flexplate/torque converter bolts could be loose as well.

 

What are the specs for proper crank endplay?

 

Hmmm... had not heard that before. Still, I wonder if the engine is smoking because carbon build up is being burned away, or because something other than the fuel-air mixture is being burned in the cylinder heads.

 

Ummm, nevermind.....manual trans...

 

The car owner looked through the papers he got from the previous owner....Nothing about a engine rebuild but there's receipts for head milling ,valve job and a M4F camshaft grind and new aluminum timing gear.The engine does have two carbs, short tube headers and has a slight lope at idle.
A experienced mechanic came over to listen .He thinks the noise is a combination of slight piston slap,steel tube header "ping" and gear backlash rattle from the aluminum timing gear....................Nothing to be concerned about he says............

 

Some guys swore by using a can of Coke instead of the water. I've used the water method plenty of times.

Bob

 

An out of round piston skirt noise is more evident when it's cold. Piston pin knocks are a double-rap. Can it be isolated to a specific cylinder when you short out the plug wires one at a time? I would first try a heavier grade oil, maybe a straight 40 since the weather is warmer and see if the noise changes.

Bob

 

I pulled the vacuum line off while the engine was idling once. It sounded like every bearing in it was bad. I QUICKLY pushed the vacuum hose back on and it was back to normal,try it for a second. You might have a weak vacuum hose. Mine is a 56 year model 235.

 

The engine has 20/50 Brad Penn oil in it.The noise doesn't seem to be as obvious when cold.I'll try grounding out the plugs one at a time to see what happens
read my last post above but the mechanic's comment on the noise...........

 

That diagnosis is still possible, header ping is a thought as cast iron manifolds do absorb combustion noise, did it do this before the headers were put on? You seem to have a heavy enough oil in it. I would still try to isolate it to a cylinder, maybe get a local HAMBer to take a listen to it.

Bob

 

Ever pull apart an engine with a blown head gasket? The pistons in the bad cylinders are shiny clean. The coolant sort of steam cleans then.

 

Never pour Coke, beer, Kool-Aid or anything else containing sugar down an engine! Sugar plus heat makes candy, something you don't want inside an engine. Water, kerosene, diesel fuel, all OK in small amounts. The steam blasts carbon loose.

 

If you are adventerous, its easy to pull the pan and check the main bearings : use caution...those old mains .. more often than not had brass shimms under the main caps to correct poor tolerances in machining. Keep close track as to where they go!! Use some plasti gage to check clearences. If bearing looks good you can adjust the shim pack to get rid of excess gap, but only if needed. bearings worn out? pitch them and replace with new...re adjust shim pack. LONG LIVE THE 235 !

 

Worked in a machine shop 68-69 before I got drafted. I saw several instances of steam cleaning off carbon. My boss used to use the clean parts to show the customer just where the head gasket had let go.
We had one once that the customer had shut down quickly when he suspected something wrong. Two cylinders were only half clean, the engine hadn't run long enough to completely clean the two cylinders where the gasket had let go.
I saw the water, and ATF trick done tons of times, almost all with some positive results.

 

Very old trick, probably as old as the internal combustion engine. It works very well.
The carbon isn't being burnt off as much as its being removed.


Op, on strange noises

I find it interesting that pushing in the clutch changes the noise. Does it make the same noises in neutral as well as the other gears ? A flex plate issue will cause similar noises, also a pressure plate or clutch disc issue will do almost the same thing.

An increase in rmp increases centrifugal force on the rattling parts and they become quiet.
Worth a look

 

Everything has to be listened to. I'd get the car on a lift and use the old wooden dowel trick. Have someone up in the car, work the clutch and give it a listen. TO bearings can be noisy and go with the clutch pedal thing.

Bob