Constant RPM *knock knock knock*

[ReZ]

When cold, at a constant speed, lets say 1st gear, going 10 mph constant, I hear a knocking. Like a valve knock. As the car warms up, this knock seems to dissapear.

Reving and holding 3K rpms it does it too.

Accelerating and Decel, does not make the knock.

Any ideas? I changed the timing belt over 5K ago, and it seemed to pick this knock up around that time. Maybe it's coincidence.

[SoCal Driver]

This is coming from the engine?

Does it sound like a thud or a click?

Right now I would suggest looking at the engine mounts. From below the car try to stick your hand in between the oil pan and the cross member just above the steering rack. If you can just get your finger tips in between them then the engine mounts are shot. Should be over an inch of clearance -- most of your hand to the knuckles should slide in there.

If not engine mounts then you may have a crank or rod bearing going out.

[ReZ]

It's not the motor mounts. I'll double check, but it does not sound like a thud. It has a knock, kinda like a diesel does, but its only momentarily when at constant RPM. I guess the constant RPM would create a harmonic to make this tinny knock. It sounds exactly like a car would when you are stalling it. KNOCK KNOCK KNOCK!!!!!!

The engine runs strong. I drive the canyons daily, and it sees 3-4K RPMS alot. Sometime it gets up there to 5K. But on street driving, I usually stay below 3800 or so...

As I mentioned before, the knocking seems to go away when it's fully warm. And, it only occurs when the 944 is at constant RPM. IE: 3,200.....

Perhaps when the car warms up, the bearing slack dissaprears... I think the crank/rod bearing is a good guess though. How long until she blows up? It's been doing this for 6 months!

Ty

[TheCooler]

Lifters. I got the same problem. Try the ATF trick. Put a quart in before u change ur oil then drive it around for a day then empty her out and put some fresh oil in. See if that fixes it.

Also get car stethoscope and put it on the valve cover and see if its coming from there. Is the sound louder at around 2 rpms in 5th gear when u floor it? Roll down ur windows and listen to it.

[ReZ]

What the hell? ATF? lol

I thought that only worked on rotaries to get rid of carbon build up! LOL!

I'll try it tomorrow @ 2K in 5th gear when cold. Did the ATF work for you? It's not bad to drive it like this is it?

[ReZ]

I'm going to vieotape it so you can hear it tomorrow.

[SoCal Driver]

Originally posted by ReZ
I'm going to vieotape it so you can hear it tomorrow.

Good! I think this is an often overlooked tool for sharing problems here -- audio recording.

Just post/link to the audio part.

[ae1969]

Originally posted by SoCal Driver
Good! I think this is an often overlooked tool for sharing problems here -- audio recording.

Just post/link to the audio part.

That would be a good idea for a website... audio/video components of 944 repair....

...belt whine
...CV clunking... (hate to be the guy hanging over the side of the car)...
...lifter knock....
...how it runs with intake leak ... etc..

It would be a nice diagnostic tool for new guys....

P.S and how long you can run with a rod knock.... augggh fix it before you have to deal with a spun rod....

[serge944]

ATF = auto transmission fluid, right?

i think im having the same problem

[Brando]

it may be a lifter, as my 944 had the same issue. I bought a quart of this wierd lifter-fixer stuff (high-weight gear oil i'm guessing) and it took the noise away after about 20 minutes. ATF should do the trick, that or replacing your lifters.

[serge944]

a mechanic i know recommended diesel fuel instead of ATF, any comments?

[Zero10]

Umm yes, don't.
It just doesn't seem like a good idea.
It is probably much cheaper, but I think it would add to the build-up of tar and such in your oil system.
ATF has many detergents, it should clean up the engine while it's in there.

[ReZ]

Bah. I didn't have time today. I'll see about tomorrow.

[highboost951]

Rez, I agree with the ATF trick but I've got a feeling that your timing belt is too loose, especially if you have 5K miles on it without re-tensioning it. It doesn't really make sense but the belt slaps the side of the timing belt cover until it's warmed up. Take the upper cover off and take a look at the cover and feel the tension of the belt. If you can turn the waterpump pulley by hand, it's too loose.

[highboost951]

BTW: in regards to the rod knock worries, they usually get louder when the engine warms up, not quieter due to the oil thinning.

[FLA944]

1.) Adjust belt tensions

2.) I have had alot of success de-gumming an engine by adding 1 can of "marvel mystery Oil" to the crank and running for 1000 miles then change the oil and use a good synthetic oil and a good oilfilter "mahle".

Rick

[ReZ]

Here is the knock noise in .ASF

If you can't get it to work, update your CODECs. My Panasonic MiniDV automatically coverts to ASF/ASX.


Right click, save as!

http://www.calinetworks.net/rez/944/944 engine nailing.ASF

All input is good. I think I might try the ATF trick you guys keep talking about. You can't miss the nailing. Notice how I constantly hold RPM when it knocks.

[highboost951]

look at your oil pressure!

[highboost951]

how's your oil level?

[ReZ]

Oil pressure gauge does not work. It stopped working over a year ago!

Start flaming me for driving without an oil pressure gauge!

I think it's a loose connection somewhere in the wire. It worked one day this year, then stopped all of a sudden again!

Oil level is fine. I always check my oil at least once a week. I always check it when I fill up with gas. I do lots of driving.

Anyone know where the oil pressure sender is? I don't have a 944 manuel. I've always wanted to know where though. I bet the contact is dirty.

I'm going to check the belt tension. That could be a very valid problem.