It's Not the Valvetrain... What Else?

**Sizzlenut** · 04-20-2007, 08:54 AM

This is on a stock 01 LS1:
I was at the road course at the end of last season doing some hot laps. I got a little too ambitious and bounced off the 6800 limiter a couple times on a straight. A puff of smoke came out of the exhaust and it lacked a little bit of power so I did a cool down lap and headed in. The idle isn't normal- it seems there is a rythmic more powerful puff of exhaust every rotation of the crank. Also the car bounces at idle now that clears up over idle RPMs. Since then, I've driven the car about 30 miles and nothing's changed. The oil pressure is fine, so I assumed I had broken something in the valvetrain, but after taking it apart, I discovered that everything still looks brand new and checks out okay. I'm thinking maybe the cam or main bearings, but they should have gotten worse in the 30 miles, right? Having the heads off, I also check to see if any pistons were loose- (conrod, piston pin worn) and they are all still tight with no play. The cylinder walls look good so the rings should be in good shape. When I drained the oil, there was some fine particles on the drain plug that felt like that fine grey graphite lube. Does anyone have any suggestions or thoughts? Also, if you spin a bearing, how long do you have before it gets really chewed? A couple miles? More? Thanks, Andrej.

**Street Lethal** · 04-20-2007, 09:36 AM

You definitely overlooked something in the valvetrain. A spun cam bearing will cause a consistent "howling" noise, while a spun main bearing will eventually knock (light or loud depending on thickness of oil). Also, you stated that your oil pressure is fine, whereas a spun cam bearing slowly but surely actually robs you of pressure...

You might have inadvertently killed one of your lifters. Are the pushrods all even, did you check for any bends...?

**2001hawk** · 04-20-2007, 01:35 PM

X2 on the valvetrain since you say it was at the rev limiter on a straight. If it was in a turn then you might have sucked a little air into the oil pickup tube and then it would be possible to spin a bearing. It would have to be seriously low on oil to do it on a straight.

**Sizzlenut** · 04-20-2007, 01:48 PM

Thanks for the input guys,
I automatically thought it was the pushrods to begin with, so I bought some Manley hardened pushrods and replaced the old ones, checking to make sure they were in good shape when I took the stockers out. There was no wear and none were bent. The lifters I removed yesterday and show very little wear. I put the heads upside-down and put water in the chamber to see if any water would leak through and in 5 hrs it's still the same. No pistons show any signs of hitting a valve and the valves seal. I'm going to check the cam bearings tomorrow.

**Street Lethal** · 04-20-2007, 02:01 PM

Originally Posted by Sizzlenut

The lifters I removed yesterday and show very little wear...

Did you check them though...?

Originally Posted by Sizzlenut

I'm going to check the cam bearings tomorrow...

Although I would recommend for everyone to check their cam bearings once in awhile, this is not your particular problem....

"it seems there is a rythmic more powerful puff of exhaust every rotation of the crank. Also the car bounces at idle now that clears up over idle RPMs"....

This is clearly not due to a cam bearing. It's either in your valvetrain (lifters, rockers, springs, pushrods, or even the cam lobe itself), or in your ignition (broken spark plug, shot coil pack, etc.)....

**Sizzlenut** · 04-20-2007, 02:11 PM

I checked the rollers on the lifters by rotating them and feeling if the needle bearings still roll smooth and if there is any play in them. What else is there to check on the lifters other than that and if there is any wear where the pushrods sit? Is there any chance I damaged a valve guide? If I bent a valve, is there any chance it would still seal in its seat?

**Street Lethal** · 04-20-2007, 02:27 PM

Originally Posted by Sizzlenut

Is there any chance I damaged a valve guide? If I bent a valve, is there any chance it would still seal in its seat?

A bent valve stem will not allow for a proper seal. But I doubt you bent a valve, unless your PTV clearence has been altered in a very big way (in reference to an aftermarket camshaft)....

When the engine is at idle, do you hear anything (knocking, clanking, etc.) with your head being under the hood (regarding a possible bearing)?

If not, then your concern of a stumble/smoke upon a full crankshaft rotation is obviously somewhere in one of the combustion chambers. One of the valves timing can be off, or a valve is simply not opening (due to a loose/broken valvetrain component), or your intake charge isn't properly being burned (failing ignition)....

**Sizzlenut** · 04-20-2007, 02:52 PM

There has always been a noise coming from under the hood and it's gotten a little worse after the incident at the track, but it may also be that I'm more aware of it. I've put quite a few abusive miles on the engine and nothing got worse. It's hard to describe and I've tried to diagnose it and have it diagnosed for a while. It gets worse when I don't use 91 or 93 octane. It sounds like something is loose. If you rev it a little bit as the revs drop back to idle, it sounds a little like a rattle and sounds like it's coming from the middle of the engine, not the valvetrain. You could also hear it once in a while at WOT but louder.
The smoke was a one time thing, I haven't seen it again since. My initial thought was that one of my exhaust valves was opening too late, hence the accelerated exhaust puff and slight loss of power.
I'm still at a loss of what is going on here.
Ever hear of the magnetic pickup on the camshaft for the ignition timing getting broken?
Camshaft getting pulled tomorrow.

**Sizzlenut** · 04-21-2007, 10:06 AM

I think I might have found the problem. The timing chain seemed to be too loose. I tested about 3/16" deflection. Is this enough to throw my timing out of whack enough to get the wrong valve timing and cause my problems?
What is a standard amount of deflection?
The cam still looks perfect and the cam bearings appear okay as well.

**VYSSKiwi** · 02-01-2008, 04:15 PM

Hi,Iv got a simular problem.car has been running weard for a while.After a we upgraded camshalft i drove about 1 KM then a wheeerrrring noise started.no one has been able to put a finger on this.finaly got sick of it and pulled the engine down.the cam chain is a bit slack and the cam bearings have a copper colour showing through.Did you change your cam chain and did it make a differance?What was your end resolt?cheers