engine noise? - ZR-1 Net Registry Forums

sdycke · 08-12-2011

Hello. Just got a 91 with 13,000 miles but am not familiar with the LT5 at all. It has a slight engine noise that I wonder if I should be worried about . I know discussing noises in a forum is very difficult but who knows?. Its most noticeable cold and when you slightly crack the throttle. Then it pretty much goes away. It is a very faint, hollow knocking sound. Almost like a loose rod. I cant pinoint it whether its on one side or the other, but does sound more inside the engine. I may try shorting out plugs to see if that affects it. I understand these engines have some chain noise. I will be comparing it to a known good engine at the start of next week so that?s a start. I know these motors are bulletproof and the milage is low but I am finding many little things the previous owner ?forgot to mention?. Any seat-of-the-pants thoughts/diagnosis/opinions would be very welcome. Stan

ittlfly · 08-12-2011

If you are ruling out chain rattle on start up, then it sounds much like ''piston slap''....especially if it goes away on warm up. If so, it's nothing to be overly concerned about, just annoying. I had experienced it in my old 70 LT-1 after a rebuild.
I'm sure others will jump in here though with ideas.

A26B · 08-12-2011

Most likely piston slap if it goes away after warming up. Normal, no worries.

Very unlikely, but to test for rod knock; in 1st gear, at idle, apply brake and slowly release clutch until engine rpm decreases. if it's a rod, the knock will decrease in amplitude or go away completely under the load [not to mention, rod knock does not go away when the engine gets warm.]

gbrtng · 08-12-2011

It's an LT5 - they all sound like that. It will sound like that 200,000 miles from now.

sdycke · 08-12-2011

thanks for your great replies. will try the rod test for sure next time i head out. i'm just a little neurotic cause its only 3 months old and have nothing to go on. i read THOB and engine design/assembly was so crtical, not to mention the nickle balancing trick, I guess I was expecting perfection. piston slap was supposed to happen to the guy with the 01 malubu. and does.

08-12-2011	#1
sdycke Join Date: Jul 2011 Location: grosse isle, manitoba, canada Posts: 52	engine noise? Hello. Just got a 91 with 13,000 miles but am not familiar with the LT5 at all. It has a slight engine noise that I wonder if I should be worried about . I know discussing noises in a forum is very difficult but who knows?. Its most noticeable cold and when you slightly crack the throttle. Then it pretty much goes away. It is a very faint, hollow knocking sound. Almost like a loose rod. I cant pinoint it whether its on one side or the other, but does sound more inside the engine. I may try shorting out plugs to see if that affects it. I understand these engines have some chain noise. I will be comparing it to a known good engine at the start of next week so that?s a start. I know these motors are bulletproof and the milage is low but I am finding many little things the previous owner ?forgot to mention?. Any seat-of-the-pants thoughts/diagnosis/opinions would be very welcome. Stan

08-12-2011	#2
ittlfly Join Date: Jul 2009 Location: Redding Calif Posts: 223	Re: engine noise? If you are ruling out chain rattle on start up, then it sounds much like ''piston slap''....especially if it goes away on warm up. If so, it's nothing to be overly concerned about, just annoying. I had experienced it in my old 70 LT-1 after a rebuild. I'm sure others will jump in here though with ideas. __________________ 1994 ZR-1 # 0102...SOLD

08-12-2011	#3
A26B Join Date: Dec 2003 Location: Arcadia,OK Posts: 3,394	Re: engine noise? Most likely piston slap if it goes away after warming up. Normal, no worries. Very unlikely, but to test for rod knock; in 1st gear, at idle, apply brake and slowly release clutch until engine rpm decreases. if it's a rod, the knock will decrease in amplitude or go away completely under the load [not to mention, rod knock does not go away when the engine gets warm.] __________________ Jerry Downey JERRYS LT5 GASKETS & PARTS http://www.jerrysgaskets.com 1994 *ZR-1, Black/Black, Lingenfelter Aerobody, 416cu in, 3.91 gears, coil-over susp, Brembo brakes, etc. 2016 Black-Red, 3LT-Z51 Auto 8-speed. Last edited by A26B; 08-13-2011 at 09:56 AM.*

08-12-2011	#4
gbrtng Join Date: Feb 2006 Location: San Antonio area Posts: 1,179	Re: engine noise? It's an LT5 - they all sound like that. It will sound like that 200,000 miles from now. __________________ “Buy the best example of what you want, and pay whatever it takes. That way, you cry only once.” ~ Bruce Meyer

08-12-2011	#5
sdycke Join Date: Jul 2011 Location: grosse isle, manitoba, canada Posts: 52	Re: engine noise? thanks for your great replies. will try the rod test for sure next time i head out. i'm just a little neurotic cause its only 3 months old and have nothing to go on. i read THOB and engine design/assembly was so crtical, not to mention the nickle balancing trick, I guess I was expecting perfection. piston slap was supposed to happen to the guy with the 01 malubu. and does.

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