Rod knock on an engine with 4000 miles??????

[americanmusc1e]

my motor was rebuilt 4000 miles ago and today it started making death noises,
at Idle and anything below 2500 it runs perfectly normal
above 2500 it sounds like a really bad diesel motor and won't rev past about 3000(the noise gets worse the harder you press the gas)

rod knock??? what else could it be????

[americanmusc1e]

another thing to mention is that it only knocks in gear. tried to get it to do it in drive with my foot on the brake but I couldn't get it to rev to 2500 without it taking off. The 700r4 is new, less than a month old. I guess it could be the transmission but it sounds like its further up.

[ZombieWeinerDog]

Originally Posted by americanmusc1e

another thing to mention is that it only knocks in gear. tried to get it to do it in drive with my foot on the brake but I couldn't get it to rev to 2500 without it taking off. The 700r4 is new, less than a month old. I guess it could be the transmission but it sounds like its further up.

clutch maybe? im no expert. keep me updated, im interested

[t&tkennels]

maybe check the torque converter bolts. they can make a pretty bad knocking sound when loose

[paaw]

Also check your flywheel (flex plate) mine was cracked, thought i had a rod knocking

[americanmusc1e]

Ive had a cracked flywheel before, this knock isn't a gentle tapping.
It sounds like someone is banging on my engine with a hammer

[spinning wheels]

Sound travels thru an engine, so it can be hard to pin point what is causing the sound. Use a set of stethoscopes, (you can get them at Harbor Freight real cheap). This can help you pin point the noise better. Just throwing this out there, I have heard of water pumps making the thumping sound. The only time I had an engine make that sound, it was a rod knock

[kdailey4315]

I was thinking flexplate also. If you want to check to pinpoint the noise like spinning wheels said you don't need a scope. Just get a long screwdriver. Good luck though. Did you have a shop do it? Is there any kind of warranty with it?

[chev-obsession]

did you have your foot in it a lot before it started making these god awfull noises?

[americanmusc1e]

Originally Posted by chev-obsession

did you have your foot in it a lot before it started making these god awfull noises?

yes

[rob32472]

it sounds like you know what it is..... if you have a warranty see what they will do. if not....... when i was younger my dad told me that when it comes to driving my foot would be the bigest money saver in my life... didn't understand until i bought tires, brakes, drive shafts, rear ends, motors and was constantly workin on my truck then it just hit me and now i spend my money on things i want instead of what i have broken. lil off topic but just my two cents.... hope it works out

[americanmusc1e]

well, I must have been having a bad day yesterday. Today the truck is almost normal. Its still making a little noise but its not near as severe as it was yesterday. I'm gonna give the truck a tune-up and see if that helps.

[americanmusc1e]

It did it again today, I finally checked my oil pressure gauge. when its acting fine I have about 30psi at Idle and about 70psi max.
when it starts making noise it drops to 0psi at Idle and around 20psi max.

[VetteVet]

Rod knocks are usually heard when the engine is under load like when accelerating or climbing a grade. It shouldn't take anywhere near 2500 in gear to hear a rod knock. I would try taking it out on the road and pulling one spark plug at a time and see if the knock goes away. This relieves the combustion pressure on the cylinder and if the knock goes away then you've found the bad cylinder.

[special-K]

I`d still look into the flex-plate/torque convertor area,first.It doesn`t always make the same noise and definately can sound like more than a tap.More times than not it sounds like the bottom end is coming out of it.Drain oil into an absolutely clean container and do an oil analysis.Take a piece of something clean,rigid,and white(like corrugated sign board from Walmart),pour oil a splash of oil on there and let it flow down.look for metal bits.If you can`t see anything,run a rare earth magnet over it or even scrape it across with the tail end dragging.If there are no fragments there is no internal damage.I`d also tear the filter apart and see what`s in there.

[cdowns]

an old harmonic balanced on a worn crank snout can sound and feel like rod knock too //just look at it and see if its wobbeling

[DANTIP]

Is your oil-pressure normal? You also said it only knocks in gear, does that mean it does not knock in Park or Neutral?

[70rs/ss]

Low on oil?? And except the oil pressure, I was thinking a ping (detonation) vs knock but a ping wouldn't lower the oil pressure.

[special-K]

When did you change the oil?How many times?How long has it been?Have you smelled the oil?I wonder if you have drain back from the carb.Or,a wiped bearing?Once the oil warms up oil pressure is low.The crank could be turned a bit beyond tolerance.Was it ground?Undersized bearings?The oil test I described would help narrow down if it`s improper tolerances.There wouldn`t be any grindings.

[americanmusc1e]

Originally Posted by special-K

When did you change the oil?How many times?How long has it been?Have you smelled the oil?I wonder if you have drain back from the carb.Or,a wiped bearing?Once the oil warms up oil pressure is low.The crank could be turned a bit beyond tolerance.Was it ground?Undersized bearings?The oil test I described would help narrow down if it`s improper tolerances.There wouldn`t be any grindings.

Oil is changed every 3000 miles. changed oil less than 1500 miles ago.
4 quarts valvoline racing 20w50 1 quart marvel mystery oil

I noticed this after the noise started so I guess its connected. usually my oil pressure runs between 40 and 60psi

[highperf4x4]

I can tell you real quick how to check the main bearings and rod bearings. If you have a garage pull the front of the truck inside the door. If not, put the passenger side as close to your house or other wall/fence as you can get it and roll the window down. Bring the engine up to a constant 3000 rpm. After a couple of seconds, let up on the accelerator only SLIGHTLY so that it doesn't drop more than a few hundred rpms. Do this several times. If it's a rod or main it will make a dinstinct clanking noise each time you do it. A loose torque converter will also do the same thing however, you said it does it under a load and a torque converter usually will not so I'd rule that out for now.

With the engine idling, you can also take a wooden handle (like a broom handle minus the broom) and put one end against the engine block and wrap your hand around the other end (flush with the end) and then lay your ear on it like listening through a wall. If you have something knocking you will hear it through the handle and this saves you having to buy anything to listen with.

Not to throw a damper on anything but if your oil pressure is varying from 30lbs to 70lbs, you have a main bearing problem. It could be a gauge malfunction though so who knows.

[68C15]

I'm thinking a spun main bearing or two.
the pan needs to come off, NOW

[americanmusc1e]

Originally Posted by 68C15

I'm thinking a spun main bearing or two.
the pan needs to come off, NOW

should i pull the pan???????? or just bite the bullet and pull the motor????????????????????

[71 super]

Do you lose pressure when you accellerate and gain pressure when you let off the gas. If yes to either of these pull the motor the lower end is trashed and crank and bearings with line bore are in your future.

[americanmusc1e]

Originally Posted by 71 super

Do you lose pressure when you accellerate and gain pressure when you let off the gas. If yes to either of these pull the motor the lower end is trashed and crank and bearings with line bore are in your future.

not really. when it starts acting up it just drops the oil pressure down but it still acts normal