So yesterday my 1990 GMC 3500 started making this noise from the motor. It is a metalic tapping that follows the enging RPM, sounds like a bad lifter, possibly a cam knock. It is coming from the front top of the motor. Definatly not a botom end deal after listening to it this morning. I think maybe the timing chain gave up and is slapping the cover? Or maybe a lifter collapased. It has 147K on it and I'm not sure it the timing chain has ever been done. Anyone have any opinions on this? Had similar experience?
Let me know what you think, I really need to find a definative answer soon so I can cure this thing. I pulled the belt and ran it, noise was still there, so definatly not an accesory. Got out a stethascope and gave it a good listen, tough to pinpoint because the noise is transmitting through everything. The timing also seemed to be jumping from 11*BTDC to 16* when I put a light on it.

Usally if the noise goes up with the RPM's its a rod.

I really don't believe the tone of this noise is a rod, it is metalic and tinty if you will, not a low thud like a rod.

UMMMMMMMMM

CALAPSED LIFTER....
LOOSE ROCKER.....
FLAT CAM.....
ROD KNOCK......
I DONT THINK IT WOULD BE THE CHAIN.......

This one has me a bit puzzeled, It is fucking loud, way louder than you would expext a lifter of rocker, guess I'll find out when I tear into it tomorow

I have an '85 3/4 ton burb w/ 454. I have the exact same noise comming from mine ! I have torn it down to timming gear, with nothing wrong. I have been advised spun bearring ? I am looking at a rebuild/replacment. Please let me know what you find out.:D

454 are well known asa RAT Motors ......

Rat motors because gen III and older had a design prob.

with the cam which was it ....the lifter ate the cam.....

rat....rat.....rat...sound

this problem was solved in gen IV and newer gen5 engines

92 and up

didn't the auto tranny equipped BBC trucks have problems with the torque converter ballooning under load and wiping out the thrust surface on the crank? That may allow the crank to walk far enough to cause all kinds of noises.

Well, after hammering the shit out of it on the way to work, speeds from 5 mph to 80mph, I have decided that it is either a collapsed lifter or bad lobe on the cam. Got a few farts through the exhaust too, but it didn't blow up:D I have narrowed it down to either # 2 or # 4 cyl. Gonna pull the rocker cover when I get home to see what is up. Should be pretty easy to see or feel.

Originally posted by Scoutillac
This one has me a bit puzzeled, It is fucking loud, way louder than you would expext a lifter of rocker, guess I'll find out when I tear into it tomorow


I had a motor do that about 1 1/2 years ago. It was a piston
slapping a cylinder wall. :(

Originally posted by SanDiegoCJ



I had a motor do that about 1 1/2 years ago. It was a piston
slapping a cylinder wall. :(

Did that have an affect on the general performance? At this point I have a noticable loss of power, stumble off idle, running a bit rough, and the ocasional fart in the exhaust.

Originally posted by pcelle
454 are well known asa RAT Motors ......

Rat motors because gen III and older had a design prob.
with the cam which was it ....the lifter ate the cam.....
rat....rat.....rat...sound
this problem was solved in gen IV and newer gen5 engines
92 and up

You sure about that? I kinda wondered how it got the name..

So why are SBC's called "mouse"? because the BBC was the rat? or for its own reason?

My buddy just had this happen to his 87 454. Kept on driving. Finally one pushrod came off the rocker and fell into the lifter galley.

Cause: One cam lobe flat.

Engine was filled with metal after he continued to drive.

Fix: Pulled the cam, flushed out the engine as best as he could, bought a new pushrod . He changed the timing chain also, and he slapped in a new hi-volume oil pump, since he had the oil pan tipped to get the timing cover off. (yes you can pull the pan in a 4wd frame.
). The thing runs like a raped ape now and I was amazed it didn't shell out after all the metal I saw in it.

First thing I thought of was loose rocker, since you said the top of the motor.

Run a compression check on it then pull the valve covers.

With you saying the timing is jumping I would expect the timing chain/gears need replaced. If you can’t find it in under the valve covers, I would probably pull it and go through it.
Poor man’s rebuild: Oil pump, bearings, timing set, rings, gaskets and seals, cam if needed. I know how these things grow, so but absolutely everything you need and try to do it all in a weekend. If not, you’ll end up boring it, new pistons, big cam, headers, nitrous, and so on.
Do it quick or it will turn into a race truck.
I’ve done several $100-200 rebuilds, if everything else is in fair condition, why not.

Originally posted by Eskimo


You sure about that? I kinda wondered how it got the name..

So why are SBC's called "mouse"? because the BBC was the rat? or for its own reason?

I thought it was named a rat after Big Daddy aka Rat Fink

http://www.ratfink.org/roth_book_ganahl/book.gif

When the small block introduced in 1955, it quickly became nicknamed the "Mouse" motor because it made big power in a small package. Because it was the small blocks big brother, it was only natural for the big block to be nicknamed the "Rat" when it debuted in '65.

Rat, rat, rat my ass!! :flipoff2:

mmm........

diferent story ......


like mine it has more fact´s


:)

Originally posted by Scoutillac


Did that have an affect on the general performance? At this point I have a noticable loss of power, stumble off idle, running a bit rough, and the ocasional fart in the exhaust.

Yup, it was like one cyl. was half dead.

Timing gear was chowdered, missing a 3rd of the teeth. Fired it up at 1 am and it seems to be happy and no knocking:flipoff2:

Great ! Glad urs is running so good ! Want mine ?

Originally posted by Scoutillac
Timing gear was chowdered, missing a 3rd of the teeth. Fired it up at 1 am and it seems to be happy and no knocking:flipoff2:

You had better drop the pan and clean the teeth out of the oil pump pickup or you will be replacing the lower end.
Butch

Originally posted by texican


You had better drop the pan and clean the teeth out of the oil pump pickup or you will be replacing the lower end.
Butch

dont you have to drop the pan to get the timing cover off, or can you weasel it out by prying it down? I thought you have to drop it on SBC and BBC's???



-Brett

Originally posted by cruiserbrett


dont you have to drop the pan to get the timing cover off, or can you weasel it out by prying it down? I thought you have to drop it on SBC and BBC's???



-Brett

I think he means the grindings and parts that broke off.
Good advice to pull the pan and have a looksie.

Originally posted by Jeepskickass
When the small block introduced in 1955, it quickly became nicknamed the "Mouse" motor because it made big power in a small package. Because it was the small blocks big brother, it was only natural for the big block to be nicknamed the "Rat" when it debuted in '65.

Rat, rat, rat my ass!! :flipoff2:

Getting closer.... before the SBC debut, the Mopar engines were kings of the drag strip. For their tremendous power, the Mopar mills were know as the "elephants". Then along came the SBC and they started winning back the bragging rights. Since the small block was so small and was "scaring" the elephants off the track, it was dubbed the "mouse". When the BBC came along, it was a natural progression to call them "rat" since they were the "mouses" big brother.

Was going to say when my BBC's timing was dancing all over.I changed the cam,timing gears and chain.Stopped the dancing and runs great now.:D