Hey Again,

Well I as many of you know I posted "i think that it is time to buy a chevy"

We all talked about how that pinging/ dieseling sound should be something to do with timing, ignition, bla bla bla.

Anyways today i put some deep thought into it and thought of this conclusion!

First if you arent familiar with what i am talking about just read my "I think its time to buy a chevy post."

Anyways my conclusion is:

Is it possible for a crank bearing to be going bad and letting enough play free at that certain RPM (between 40 and 70 miles an hour) that what i hear is a piston rod knocking? Or anything else hooked to the crank that might knock once it has a little play?

I mean this makes sense to me that the dieseling noise is something as bad as that because I have tried everything to do with timing, ETC. The only thing that i dont know for sure is if my my valve springs are good or bad... That is the only thing that i am not sure of.

Any help would be great, also any further questions about the sound i hear i will try to describe it better.

Thanks

KMAN

 

kman,

Rod bearings can make a knocking/dieseling sound. I reviewed your other post to determine when it is making the noise. You say only on deceleration. Generally a rod bearing will rattle the most when the engine is unloaded. This can happen on VERY light deceleration. Usually you'll hear it when you have the engine with no acceleration or decceleration. The knock will usually go away with power added or foot completely off the accelerator (when your moving down the road). I hope you get what I'm trying to say. Another note, U-joints noise will act the same way. Loading or unloading the drivetrain "tightens" everything up so you won't hear the noise.

Randy

 

KMAN, I just read your previous post and noticed how everyone was hung up on pinging and or preignition troubles. Did anyone mention piston slapping? If the piston skirts are loose in the cylinders the piston will rock under some conditions. Possible at idle but very light, usually not under full load but possible under light acceleration, (revving in neutral) and the clue that tips it off is the noise when decelerating. I've never heard of pinging/preignition when decelerating. When decelerating the engine is acting on a vacuum, the loads on the pistons have changed, and is not making any power so fuel ratios and timing adjustments are a moot point.
I know it's hard to diagnose noises by a description but it sounds like the problem is a little deeper than a carb or timing adjustment. Sorry.
Hope this helps.
Greg

 

ok kman i have read all these posts and replies and now i figured i'll throw my two cents in. when you replaced the cam, did you use new lifters, or old ones? And did you lube the cam and lifters and allow for a break in period? Your problem may be that you are wiping either the cam lobes or the lifters, which is causing certain cylinders to not breathe enough which will cause a horrible noise which sounds like someone banging on a tin can in your engine (certainly not pinging.) my advice would be to pull your valve covers and check your rockers. If you have any unusually loose ones than there is your problem. Also, put a vacuum gauge on your engine and rev it a couple of times. As your vacuum rises and falls, it should do so evenly. If it jumps around at all, there is a problem there with your valves. Also while your valve covers are off do some "idiot" checks to make sure you put the camshaft in correctly. Roll the engine by hand and check to make sure that the intake valve, exhaust valve, and distributor rotor are all jiving together. my focus would be on the camshaft and valve train.

 

Hey,

I am so thankful that somone could think beyond ignition!

I feel that it is my crank bearings now becasue of the dscription of symptoms i have recieved!

Also, before i deterime that it is my rod bearings I am going to check my rockers and valve train first to see if there could be a possible fix rather than rebuild.

Also, I did replace my lifters, and i allowed a breakin period with lifter lube.

I would appreciate any furthermore thoughts if anyone has any?

Thanks

KMAN

 

Hey,

How could i tell if my rod bearings were going out?

I am not sure if it is my rod bearings, but thing its a possibility?

I also think that it could be my valve springs?

Does any one know about valve springs or how to tell if its rod bearings?

(There is no metal shavings in my oil)

PLEASE HELP

THANKS

kman

 

hey

I heard that if i check my compression and it was below 90 that my problems would liie somewhere in the valve train!

Is this true?

Thanks

kman

 

I had a Mazda B2000 with bad rod bearins, not a hint of rod knock, but at higher rpms, would rap. Sounded like a bad lifter, but it was solid cam followers. Finally blew the motor, and when I pulled the head off, there were marks all over the pistons from where they were smacking the head! The rod bearings had visible play in them. Another thing to consider, is if it is a high mile engine, it could be worn more than .010" from new in the bores. A piston that is small, but still within spec, plus worn-out bores= slap. Another thing to keep in mind is the EGR system. This operates primarily under cruise, and if it is TNF, it will cause a knock. Just something to keep in mind. Also, vacuum leaks causing an overly lean mix. It may be benificial to find a shop locally with a 5-gas analyzer, and have them test drive the truck with that. Excessive NOx means overly lean/ overheated combustion. High CO readings combined with high NOx means too lean. Hope this helps you.

 

Hey Ford-Six

First whats TNS?

Second what did it sound like at those higher rpms?

Did it sound like a diesel kindof.

Mine Sounds like a diesel kindof, once i get to 45 miles an hour then dont accelerate but maintain the speed it makes a diesel sound. Also, if i accelerate then it doesnt make the sound until about 65 or 70, then if i completely let off the gas pedal , then it makes the diesel sound very quickly in a short burst then quiets down till idle!

Does this sound like bearings?

Also, when i am going at normal speeds on the road if i listen i can hear something that sounds kindof like a whistle! Not high pitched just a lower constant whistle!

Any ideas?

Thanks

Kman

 

Whistle and rattling sound? Could be the guts of the catalytic converter. If they're plugged they'll cause a whistle and if the honeycomb mass is breaking down and loose in the housing it'll cause a rattle.
Maybe?
Greg

 

No its not my cat!

I know that for sure!

The whistle is coming from the heads, I think?

All i know is i can hear something that sounds like a low pitched kindof humming coming from the engine during light acceleration!

someone said that valvesprings make an air sound, could this be what they are talking about?

Thanks kman

 

Check the air injection fittings on the back of the heads. There's a check valve there that could have gone bad or rusted out.

 

Don't know what the whistling sound is all about but the dieseling sound at the times you describe still sounds like rod bearings.

Randy

 

Does the noise go away when the truck warms up? My truck would make a similar noise, and it turned out to be that check valve on the back of the motor, the rubber hose was letting the air from the smog pump get discharged into the air, and for some reason the smog pump makes a dieseling sort of sound (at least mine did). Could be something else, but this is an easy thing to check, and one less possibility if it's not the problem.

 

The possible reason why it may have been thought to have led to timing issues, I noticed after I said the heck with it and moved on to other posts, is the description of the type and frequency of sound would change a bit throughout the thread. You need to take the truck in to a few different shops to have them listen to it. WIth the mileage what it is, and the year of the truck, I would simply look forward to building a new engine for it anyway, and do it right the first time, building a balanced package around what kind of performance you want out of the truck.