Rattle Noise while driving

Hallo,

I have a 1988 Olds Custom Cruiser with the 307 Olds V8.
In my car I hear a light rattle noise while driving. It is a similar noise like a old timing chain, but the timing chain was replaced 20k miles ago. But it is strange, this rattle can be heard only while driving when the engine is warm, not at cold engine, not at idle, not in P or N.
Does anyone have an idea where the noise could comes from?
Is it possible that the AIR check valves makes such a weird noise?


Best regards
Munzel

 

Are you sure it isn't spark knock? Does it mainly make the sound when the engine is under heavy load (for instance trying to climb a hill at low RPM)?

 

I am sure that it isn't spark knock. I had spark knock because of clogged EGR Passages and this sounds a little bit quieter and also at higher frequency.

The rattle noise is under any load. One thing I have to remark: in idle (in D) and not driving a slow ticking noise can be heard. Maybe it has the same source like the rattle.

 

Olds engines have aluminum rocker arm towers that are known for wear at higher mileage. They will start out as a light "tick" and get louder with more wear. Another thing that can be a constant noise is the fuel pump. They are made to ride on the cam drive and have constant tension to keep it in contact. As they wear they also can get just a touch of play and not keep constant tension. Also causing the same type of noise just in a different location.

 

Clue: Which metal expands greater, proportionate to temperature increase? Steel or aluminum?

 

It could be a lot of things. If the sound appears to be coming from the driver's side of the engine, check the EFE flapper in the outlet of the driver side exhaust manifold. When cold this is held closed. As the engine warms up, a thermal vacuum switch operates the vacuum diaphragm that opens the flapper. If the spring is loose, the flapper will rattle when open. I've had this problem on several Olds 307s.

 

It can also break loose completely from the shaft basically letting it spin on the shaft. But that would be a LOT of noise.

Just remember when it's IN the engine or on it metal sounds can transfer.

 

If that were the case, it would also make noise ALL the time, not just when warm.

 

Well like I said that would be a LOT of noise. Also the thinner metal flapper is going to get (and stay) hotter faster than the shaft so it will expand at a faster pace. Thus it's possible it would not move so much if at all when cooler.

Take a piece of old broom handle and cut it appx 3 ft long. Put it on the engine closest to where the noise seems to be and stick your ear on it. Not exactly a stethoscope but it does work. Very helpful pinpointing sounds.

 

I use a steel prybar, more dense, of course, so the sound transmits better. Check the rockers, check the fuel pump and check around the flexplate and starter (which means you need to jack it up).

 

Which end of that bar ends up getting stuck in your ear, then? Didn't your mother teach you not to insert anything into your ear which is sharper than your elbow? Or was she into pranks?
I use a sort of stethescope intentially manufactured for picking up analog sound. In fact, I bought it in the States and it's a German-made Hazet. Back when I bought it, the $ traded at 1 for 3 German Marks. So, it was dirt cheap, back then. If it doesn't root out the annoying sound, nothing will:

 

Was simply talking about what the man may have "on hand". Of course this would be the way to go but I will warn you if you have any ear problems like I do this will NOT go well. I cannot use one of these with my right ear prob and need to use my left.

 

First things first, WHERE in the car is the sound? And can you make the sound? That was always a fun game to play at the shop, get the customer to make the sound and try to guess what it is. My buddy would say "wait, wait, wait, can you make the sound without making that terrible face?" Wonder why we never got much done?

 

Another advantage of working in a factory, driving an 18-wheeler, tuning and riding motorcycles and old cars......................... huh?
It's also handy when the wife has honey-do jobs while I'm at the computer. ........ huh?

All of my cars and tools like the chain saw are much quieter now days.


I'm still guessing the exhaust heat flapper.

 

Try contracting the "honey-do" wife on the chainsaw and see what happens, Sir: