Strange engine noise - ZR-1 Net Registry Forums

SharkPilot · 05-10-2011

I need some advice from the more experienced people(than me) here. This is going to be a bit long winded but I'm trying to be thorough.
On two occasions my engine has made a rattling sound. The first time was about five weeks ago and it started just as I was merging onto the freeway. It has the rhythm of a valve or lifter and the engine had a miss for just a few seconds then returned to running normally, except for the rattle. The nature of the rattle changed a bit and then it quit. It was so brief I even wondered if it was my car or not, except for the momentary misfire.
After that I removed all eight plugs, thinking something may have gone through the engine. All eight looked perfect and the engine continued to run great.
Five weeks and about 750 miles go by and yesterday it happened again. I exited the freeway and heard a rattle. The engine misfired a couple of times and when stopping at a signal was rough and the idle dropped down to 300-400 rpm. I feathered the throttle and it came back to normal and acted fine the rest of the way to Mom's house, about 1/4 mile. Once there I opened the hood and listened to each bank. The noise seemed to be coming from each side evenly. The idle was perfectly smooth and even the exhaust at the rear sounded totally normal.
The car sat for six hours and started fine to go home. The rattle was still there and I noticed that the nature of the sound varied with engine load. It sounded harsher under light acceleration. I was only going 15-25 mph through the neighborhood. When I turned out on to the road the noise altered again and then disappeared entirely. The engine ran perfectly for the 12 miles home and also ran great today.
I was thinking a valve lifter until I noticed how the nature of the rattle varies with engine load. When coming to a stop, when the clutch is depressed just before rolling to a complete stop it almost went away only to return when the engine got to idle speed.
I do have a rather noisy flywheel that rattles on just about every shutdown. I run Mobil1 oil (10W-30) and change it every 4-5000 miles. The car has about 55,000 miles on the stock engine.
This is more than a bit $cary and I wonder if anyone else has experienced this with their engines? Does anyone have any idea about what I could be checking for?
Thanks for the help,
SharkPilot

05-10-2011	#1
SharkPilot Join Date: Aug 2005 Location: Anaheim, California Posts: 105	Strange engine noise I need some advice from the more experienced people(than me) here. This is going to be a bit long winded but I'm trying to be thorough. On two occasions my engine has made a rattling sound. The first time was about five weeks ago and it started just as I was merging onto the freeway. It has the rhythm of a valve or lifter and the engine had a miss for just a few seconds then returned to running normally, except for the rattle. The nature of the rattle changed a bit and then it quit. It was so brief I even wondered if it was my car or not, except for the momentary misfire. After that I removed all eight plugs, thinking something may have gone through the engine. All eight looked perfect and the engine continued to run great. Five weeks and about 750 miles go by and yesterday it happened again. I exited the freeway and heard a rattle. The engine misfired a couple of times and when stopping at a signal was rough and the idle dropped down to 300-400 rpm. I feathered the throttle and it came back to normal and acted fine the rest of the way to Mom's house, about 1/4 mile. Once there I opened the hood and listened to each bank. The noise seemed to be coming from each side evenly. The idle was perfectly smooth and even the exhaust at the rear sounded totally normal. The car sat for six hours and started fine to go home. The rattle was still there and I noticed that the nature of the sound varied with engine load. It sounded harsher under light acceleration. I was only going 15-25 mph through the neighborhood. When I turned out on to the road the noise altered again and then disappeared entirely. The engine ran perfectly for the 12 miles home and also ran great today. I was thinking a valve lifter until I noticed how the nature of the rattle varies with engine load. When coming to a stop, when the clutch is depressed just before rolling to a complete stop it almost went away only to return when the engine got to idle speed. I do have a rather noisy flywheel that rattles on just about every shutdown. I run Mobil1 oil (10W-30) and change it every 4-5000 miles. The car has about 55,000 miles on the stock engine. This is more than a bit $cary and I wonder if anyone else has experienced this with their engines? Does anyone have any idea about what I could be checking for? Thanks for the help, SharkPilot __________________ [CENTER][SIGPIC][/SIGPIC] 1991 ZR-1 #1135 Red/Red with both tops. Stock except for an open topped K&N filter.[/CENTER]