PeterK

Took my car to work this morning and it was fairly cool ~50 degrees.
When I turned on the starter and the engine started to turn I could heard pretty loud periodic slapping/clapping/knocking sound that went away once the engine fired out.

I've started the engine when it was warn and it sounded normal. What do you think it might be? Should I be concerned?


[Modified by PeterK, 1:11 PM 10/22/2003]

johnC5

First thought: perhaps it's starter related. Piston slap generally continues until the piston metal expands (heats up). However, piston slap is affected by the firing pulse and engine timing, so it's still a possibility.

If it's not starter or piston slap, it could be oil pressure related.

Marginally collapsed lifter: pumps up quickly once oil pressure stabilizes.
Dropped rocker needle bearings: excess clearance until lifter pumps up.
Spun bearing: stops making noise once higher oil pressure is reached.

Valve noise: I don't have a good explanation for valve noise during startup only (bent valve, worn valve guide, damaged seat, valve-spring?).

What year and how many miles?

Does the sound always happen at start up?

Can you record and post the noise?

xlr8nflorida

I'm pretty sure the Z06 motor is bulletproof like the LT5.

I would have it checked out though, it ain't sounding good :smash:


[Modified by xlr8nflorida, 6:09 PM 10/19/2003]

Mr. Jones

sounds like you are describing piston slap, pretty common and not a problem.
a loose fitted piston that tightens up the tolerences with a little temp. in the motor. there are some good explanations on site that describe piston/connecting rod design in the LS1 that cause this noise. try a search

PeterK

Hmm, that doesn't sound good at all.
The car is only 7 month old and has about 5K on it.

I was thinking about taking it to a dealership, but you can only reproduce this problem on a very cold morning. This noise stops as soon as the engine fires up.
The car runs strong and has no codes.

I was thinking that it might be starter - but it doesn't happen when temperature is above 60.

dubya

So, does this problem happen every cold morning. If it does it doesn't sound good. If not it could be an isolated incident with detonation. One of your injectors may have leaked too much fuel into a cyliner. PS, also check your air filter.

PeterK

Yep, happened this morning too. Sounds like if it is cold - it happens.

xlr8nflorida

Bring it to the dealer. Its a new car :mad

johnC5

You might want to Videotape / record the noise before the dealer visit. You can then discuss it with the service manager before leaving the car overnight for a cold startup test.

PeterK

Well, I called my dealer and they said it is nothing that I should really worry about.
I'm gonna try to record this sound with a lap-top and a suspended microphone.

xlr8nflorida

Hey Pete bud -- I know we like to razz one another but do yourself a favor

Bring it to a dealer and get documentation that you brought it in for repair and let a mechanic thoroughly look at it.

Some guy is going to just say don't worry about it? I wouldn't let that mechanic work on my car anymore.

Recording the sound and letting a forum member listen to it won't help you.
You need documentation from dealer in case anything happens down the road.

Any good mechanic would say bring it in and let me take a look at it.
How can he tell you it is not a problem without physically looking at the motor and hearing it? :rolleyes:


[Modified by xlr8nflorida, 3:48 PM 10/20/2003]

PeterK

These are all very good points. The reason I want to record is so I can swing by the dealer and see what they think of this sound.

PeterK

Well, tried to record it this eve, started the engine and heard nothing out of the ordinary. The temperatures are in 90s, so I'll try it in the morning.

pwrshhftd

I have the same exact problem. One dealer said it was normal. The car is at Tom Jumper in Atlanta right now. Maybe David F. can figure it out. I have heard piston slap all my life. Lots of tractors and old worn out farm vehicles but this sounds like a hard knock. It can be heard with the windows up and until the car has reached about 200 degrees oil temp. It can be heard from about 100 yards away outside the car. It does it the worst at low rpms cold and under slight throttle. It seems to be worst when you short shift or do the 1-4 skip shift, anythging that loads the motor at low rpm and cold oil conditions.
I am not happy to say the least.

xlr8nflorida

Don't tell them your name on the forum is powershiftd -- it might void your warranty :lol:

PeterK

Well, I've gotten the sounds. Just need to find a way to host them.

PeterK

Here they are: http://forums.corvetteforum.com/zerothread?id=676472

johnC5

Recordings sound like the noise is from the starter solenoid. Perhaps weak electrical system (battery, contacts, etc.). Engine sounds great.