Hi Guys.

Looking for any advice to help me diagnose a rattling noise I have in the engine in my '70 Cutlass, which has it's original L-33 455.

First, the rattle sound similar to a quarter rattling around in the dryer, or maybe a rock inside your hubcap like the guys liked to do back in high school... i.e., it isn't a consistent noise that tracks RPM. I took a video (link below hopefully), and there it sounds like a knock that happens for about 6-7 seconds, then disappears. I guess it varies.


The car started running rough suddenly a few blocks from home a while back, pulled over, and couldn't find anything out of whack under the hood (i.e. plug wire popped off etc); and it took a while to get it to re-start so I could turn around back home. Engine was hard to crank like there was backpressure; until it cooled down. Temp gauge (which works) was never past middle-dial.

Now, it catches on the first turn and seems to run smoothly, but with the rattle. Have only run it prob 15 minutes in short intervals while trying to figure things out, as am nervous about damaging my #'s matching block.

I've been trying to figure it out on my own for a few weeks, and have searched the forums and tried different things, but am stumped. I have little experience with internal engine stuff, so not surprising!

Here's what I've done so far:

1) Pulled all the plugs to see if any certain cylinder looked like it had a problem. Plugs all looked fairly uniform, no oil on them, but a bit black/carbon coated. Put in new plugs, noise still there (as expected).

NOTE: The car has all fairly recent tune-up parts, including electronic ignition (pertronix type), good MSD wires, recent dist cap. The quadrajet was re-jetted and timing dialed in last spring by hot-rod shop. (I swapped out the orig 2bbl about 5 years ago for a stock '70 442 quadrajet on a cast-iron olds manifold).

2) Took off the valve covers to see if there was any clear smoking gun. My neighbor who has built several engines came over and looked at springs, felt rocker arm play, pushrods etc. but nothing was obviously wrong to him.

3) Did a compression test with a borrowed gauge. Pulled all the plugs, and checked each cylinder, with results ranging from 150# to 170#. NOTE: the needle on this gauge didn't lock at the highest reading, so probably not super accurate numbers as I had to run back and forth from the key to the gauge as it was going down... but did not see any super low readings so moved on...

4) Drained the oil into a clean pan and sifted around with a magnet to see if there was metal in it. Came up a little metal furr, no big chunks. Picture the top 1/8th of an inch a Q-tip and that's how much. Didn't strike me as anything to worry about but maybe ya'll will advise differently.

5) Put things back together and checked the timing, as it was suggested that a failing timing chain would show the timing "wandering" around. I didn't have my dwell meter, and my Parts Place repro tic-tach broke years ago (the toc still works), so I couldn't be sure of the RPM but it was at fast idle and it was within a couple degrees (8 deg BTDC if I remember) of spec. Anyways, it wasn't wandering around and wasn't off the chart.

Any ideas about what I've got, and further testing I can do myself before I take it somewhere?

Thanks - Dan

 

If it's the original timing chain - that's what I'd be looking at. As it gets warm, it loosens up.
Easy check: Pop the dist. cap out of the way and move the lower pulley back and forth.
If you can move the pulley more than a 2 inches, either way, before the rotor moves, replace the chain.

 

Thanks, I'll check that out.

My neighbor stopped by this evening and checked out my oil. His opinion that the fine silvery metal in my oil was remnants of a bearing & too much metal, so he thinks rebuild time.

Had taken a second video which shows the sound better:

 

It sounds like piston slapping or even worse ( rod) mine started to sound exactly like that and get worse,ate up all bearings at the end. I wouldn't drive it,drop the pan and take a closer look. Here is how mine sounded at the end.

 

I agree. Bad sound. Unless you can find something loose, like a loose or cracked flexplate, I'd guess a rod.
(Much easier to guess actually being there than hearing it on YouTube).

- Eric

 

Its time for it to come apart! Doesn't sound good.

 

Had the exact sound you are hearing. Pulled my engine and found the problem to be a loose piston rod cap. The noise was more visible when you revved the engine just a little as the engine wound back down. Sorry about the bad news, but hopefully you can get it resolved before any real damage.

 

It sounds like something is moving around in lower end. It is not a really rhythmic.(yet) Normal that is something loose.

Best bet is to pull the pan and check out the bottom end. Check all caps and, cylinder walls. If you don’t see anything that would cause it, look at the piston pins.

For numbers matching, pull it and check it out before the really hot season is here.

So how many miles?
Do you let it sit without running?
Did you nail it and this started?

The other way to look at it is to keep running it until you recognize what it is. Normally, that is a rod or piston that makes for a depressing paper weight.

 

I had the same sound and it went from that light "tap" to a squeek. End result was a rebuild. The #3 rod bearing was razor thin. It messed my crank up too. I had to buy a new one.

I think you have enough video evidence not to start it up again. Every start-up is more grinding the bearing down. IF, that is what it is. Im sure it could be something else.

Take it apart and see.

 

FYI,

Heres the link to my thread on this noise.

https://classicoldsmobile.com/forums...eek-noise.html

 

Thanks for the (depressing) video links!. No seriously, helpful.

I agree, I'm not going to start it again. I think it needs to be pulled and taken apart, and prob a full rebuild.

But, it's 43 years old, has 110K orig miles on it, and I don't think it's ever been out of the car. So it's due. Heck, I've done just about everything else on the car but the engine.

OL Speedster - No, I hadn't stomped on it the day it happened... but I have before Its a convertible in rainy Seattle, so it does sit. But rarely without being started for more than three or four weeks.

I'm sure I will be reaching out to ya'll more when I get my game plan together. Haven't pulled an engine for many years!

 

Dan,

If you need info on a good rebuild machine shop. Here is the guy I used on my 48 build. Has lots of Oldsmobile experience. C & D Auto Rebuild. Give Chuck a call 425-821-7172

I live in Bothell WA if you need a hand give me a call

Pat

 

Pat, thanks for the reference and the offer to help. Careful, 'cause I just might need it!

So, maybe a dumb question, but I want to call a few local machine shops and check their price, and of course availability / lead times.

My plan would be to do a full rebuild to more or less stock specs (except to account for modern fuels?). Maybe a slight cam upgrade if you guys talk me into it.

Given the miles on the engine, I assume that means boring out the cylinders, new pistons, camshaft, and all other parts. The crank is probably a wait and see?

I guess my question is, can I come close to defining the scope of work to these guys over the phone before the engine comes apart? Is there a standard to-do list that applies here? I've read lots of rebuild posts here over the years with interest, but have never been sure what parts are being changed due to normal maintenance, and what are being changed solely as a performance upgrade.

Again, thanks.

 

this is a long shot but check it anyway. I have seen exhaust leaks cause a sound close to that so check it first for that. I would also double check the oil level.