R.B.

Question for the 951 gurus:

Yesterday morning a friend of mine heard a metallic rattle coming from my car. We tried to reproduce it but couldn't. Through out the day I noticed the rattle getting more severe. Though it was an exhaust thing. Got home, parked her and open the door to listen. Around 2-3K rpm it would start. A jacked up the car and checked heat shields and exhaust part. No rattle. I had my wife start and rev the car and noticed it was coming from higher up in the engine. Popped the hood. The rattle sounds more like a hard knock coming from somewhere under the intake manifold.
Engine still runs fine other than this loud knock.
I checked the cam and balance belts and they look fine. I am guessing but could the balance shaft make this kind of noise? Any other ideas?

Thanks,
R.B.

Perry 951

Is it a thud, knock, or tick?

Thud= rod, bad bearing, valve if higher pitched, bad news
Knock= rod, piston slap, bad news
Tick= lifters, springs, injectors, not really a big deal

Danno

Most likely not balance shaft since those spin. You would get a whining sound if something went wrong with them (never does). Sounds more like a collapsed lifter. If it's just gummed up, you can run with 1qt ATF in your oil for about 1000miles gently) to see if that flushes it out. Some people have used the Rislone stuff with success. If none of these don't cure it, most likely the cam housing has to come off for a closer inspection. Good luck!

R.B.

Good question considering I thought it was a rattle. I am going to go with the knock because as the rpm goes up the knocking is louder. It also seems that something has gotten progressively more loose through out the day. The car still ran very strong the whole time and there isn't any noise at idle. If (please let it not be so) it was a valve, piston, rod etc. Would the engine still run strong and be quiet at idle?

R.B.

Perry 951

Lifters can be quiet at some RPM ranges and loud as hell at others. Try the Rislone or ATF. It won't hurt. If it is still knocking, then more inspection is needed. Rod knock is very noticable and is a THUD! Let us know. A good automotive stethascope could be a good investment here.

R.B.

Thanks guys for the suggestion. I'll give it a shot. As far as stethescope goes, I tried the old screwdriver to ear trick but the noise was so solid that no matter where I listened it seemed loud.

R.B.

BigPorscheGuy39

Maybe come at this from a different angle: So what sounds are the precursor sounds to other really bad things happening?

superjet.1

sounds like the #2 rod going it makes little noise under idle but when under a small load or under boost can be very load.the noise will travel up the rod and sound as if its near the head area.I hope this is not the case.Jack up the car and listen with stethoscope on the pan have the wife rev it slowly then have her rev it in short guick bursts.If you hear it clacking call for help and get your wallet ready.

Dal Heger

What is your oil pressure doing? If it's a rod bearing then it would be most noticable when the engine is cold and the oil pressure would be lower than normal. When hot the oil pressure would fall very low (below 1bar potentially).

It would also fail rather quickly after you start to hear the knock (within a few miles).

Easy way to check is to drain the oil. Check for pieces of metal from the bearing(s).

If it's just a tapping then it's most likely a bad lifter.

Good luck!

Dal.

R.B.

Can anyone tell me why the lifter would collapse? I would think that during driving there should be plenty of oil pressure keeping it filled. Also would thinner/thicker oil help with the problem? Why is ATF fluid going to help?

I did not get a chance to try the fluid last night it seems old man winter had other ideas (15 cm snow)

Additional note: There isn't even a hint of noise at idle so I am hoping that discounts the rod bearing failure. But when I let some oil out to add the ATF I will check for metal particles.

R.B.

Danno

Well the lifter have these little orifices to let the oil in and out. They can easily get clogged by slugde in the oil. The idea behind the ATF and Rislone is to dissolve these clogged passages. May or may not work, but it's at least worth a try.

R.B.

Another question: just in case it isn't the lifter maybe a broken valve spring which could kill the motor, how would I recognize a collapse lifter once I take the valve cover off?

R.B.

Danno

Take a broom handle or something similar and push down on the center of the lifter. It should be solid. If it gives or squirts out oil and collapses, it's defective. Compare all of them, they should all be similar in feel. The oddball one is probably the one that's bad.

Pitstop

R.B.-
My 951 makes the same noise. Between 2k-3k the noise is there but anything else nothing. At first I thought it was a rod knock but I have put a few hundred miles on the car with no negative effects. I have tried the spark plug wire trick in trying to isolate the cylinder, but no matter what the noise is still there. My oil pressure is good also. I am going to remove the cam cover first and check the lifters before I drop the pan, much easier. Good luck.
Pete

Dal Heger

In my experience these lifters tend to last a long time, but not indefinitely. My 951 has over 155K miles on it and only had one lifter replaced. The rest are fine. When I start it now I sometimes hear a little tick but it goes away after a few minutes of running as the weak lifter pumps up.
In my S2 a couple of lifters started to make noise this last summer. I changed to synthetic oil and they quieted down until recently. I recently changed the oil and (mobil 1 15/50) and the one lifter that was the weakest now starts to tick (loudly) at about 3000 rpm. I'm going to bite the bullet and get it replaced (actually all of them while I'm at it and all the valve springs - they tend to wear out and break after a while - this car has about 145K miles on it). I can't wait until the car is quiet again. My pride can't take the sounds that the car makes now. The only solice I get driving it is that over 4000 rpm the intake/exhaust sounds tend to drown out the valve ticking!

Good luck!

Dal.
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