scottzr1

i am new to this forum and have spent a lot of time reading all of the past posts. i have really enjoyed everyone's perspective and have gained a wealth of info from each post.i have a 91 zr1 50k in super condition.this past week i noticed at low rpm what seems to be an engine knock,as the rpms increase i do not hear it or the sound of the motor drowns it out.there is one zr1 trained mechanic in my area,but he does not have an opening until next week.can anyone give me their take on this, because i fear the worst.

90 Corvette ZR-1

Bad gas, chain slap, bad injector(s). Anyone else? BTW where are you from?

scottzr1

i am from montgomery

FU

You may want to contact Mike Ebert from Slidell La. He go's under the name MrCrowley here on the board.

1990 QUASAR BLUE

Flywheel going bad?

scottzr1

i appreciate eveyone's input. i have been referred to south georgia corvette by some corvette friends in that area. thoughts?

FU

Maybe. Maybe a bad injector , coil , wire or plug.

SGC or Mike E. both are very good and both are pretty close to you. Good Luck.

8388

Does the sound change with engine temperature ?

scottzr1

i do not know if the sound changes with temperature. the first time i actually heard was at initial start up and i shut the car down immediately and have not run it since.

DDSLT5

Ten bucks says it is cam chain tensioner rattle.

8388

Also, a little bit of piston rattle is normal when cold. The sound does tone down a bit when the engine warms up, but it's still noticable if you have your ear tuned to it.

bad-zr1

Watch your oil pressure gauge the next time you start it and see if the noise quits as soon as the gauge goes up off of 0. If so it should be the cam chain tensioner and should not be a problem.

8388

Another thing that can sound like a knock is an exhaust leak at the manifold.

Rkreigh

if the engine has good oil pressure and it goes away when you rev it

check flywheel

the dual mass knock like crazy when they go bad and it's fairly common

sgc

or mike ebert at ees

can definitely help you out. bot are close to you

ZR1991

I agree with Rkreigh, it is likely the dual mass flywheel. Do yourself a big favor and assume it is (in otherwords, prove it isn't), before you even consider doing anything to the motor. And in many instances, if the idle is rough (sometimes not even enough that is feels rough to you), the uneveness of the rotation will make the dual mass knock like hell. Sounds just like a rod knock. Mine does it on startup occassionally, but when I shut off the engine (clutch engaged in neutral), it always gives me a knock or two as the engine stops rotating. Scare the hell out of you until you understand it!

I would be pretty sure that's it until proven otherwise.

Hope this encourages you some.

Regards,

Dandy97

I vote bad flywheel dampners.

Bans25

I second the flywheel...

Bring her up to 7k and see if all holds together

RatRacer

I had a exhaust heat shield that used to make a huge racket at lower rpm. Expect something simple first.

scottzr1

i appreciate the input from everyone. i talked to the mechanic today and he is going to start tomorrow looking for the problem. when i started giving him the run down on the things i wanted him to check first he laughed because he knew i had direction from an outside source. thanks again

ZR1991

And keep in mind, scott, that though the flywheel knock varies a bit from car to car (assuming that is it), it is likely that the knock is not "wrong". It is a predictable and understood characteristic of the design. As I said, mine gives me a good knock on shut off once in a while, or on rough idle, but if I shut down with the chutch pushed in, it is quiet. I just don't bother to, now that I understand it. Mine hasn't changed in 55,000 miles. it's just fine.

Good luck.