L81 ticking/knocking noise ??? Help please!
Thread Starter
Intermediate
Joined: Oct 2005
Posts: 42
Likes: 0
From: Saratoga Springs UT
L81 ticking/knocking noise ??? Help please!
I own an 81 corvette, stock L81 engine with 64 000 miles. I have a ticking/knocking noise that follows engine frequency but seems to be 1/2 the crankshaft speed. I can hear it best when I'm under the engine at idle. I used a long screwdriver as stethoscope and the noise can be best heard on the block right by the oil pan under cylinder 3/4 on each side of the oil pan. I can't hear anything around the valve covers…. I’ve already re-adjusted the hydraulic lifters, changed fuel pump and pushrod no effect. All my exhaust manifolds bolts are tight. Can this noise be coming from a bad cam lobe, or collapsed lifter? Or less likely can this noise be coming from a bad or loose connecting rod? Or something else? I’m a little confused at this point. Do any of you have experienced similar noise?
Thanks,
Angel…
Thanks,
Angel…
Race Director
Joined: Jul 2004
Posts: 12,708
Likes: 329
From: Scottsdale Arizona
I had the same anoying tick on my L81 on the driver's side bank. Adjusting didn't help but replacing the rockers did. I replaced mine with roller tip ones but I suspect that it would have solved the problem just as well with a good stamped steel set.
Drifting
Joined: Mar 2006
Posts: 1,369
Likes: 79
From: West Coast
Angel- Like your Vette, is that the original Maroon Mettalic or other? Are you original owner? I am second owner of what once was Maroon/Camel Leather with still original 36,000 miles and mostly all original except for custom Black Show quality paint from original owner. Love the vette and have kept mods to basic Catback Exhaust Flowmasters and Polk Subs/Stereo, Window Tint, etc.. Anyways just thought props were in order and hope you got the Lifters replaced, so far knock on wood no probelsm here except burned out voltage regulator which should be fixed today. Thanks and play hard!
Thread Starter
Intermediate
Joined: Oct 2005
Posts: 42
Likes: 0
From: Saratoga Springs UT
Thanks BACNBLK, the paint job was done by the original owner it's a custom burgundy with tinny little gold flakes in it. It goes perfect with the original tan interior. 
For the ticking/knocking noise, I heard that on these motors, the camshaft is known for the lobes to go bad (flat). I’m thinking that I might as well just upgrade the whole thing with hydraulic roller lifters and camshaft. What would be the best camshaft choice for an L81? I know there are plenty on kit available out there but what would work with the computer and stock heads?
For the ticking/knocking noise, I heard that on these motors, the camshaft is known for the lobes to go bad (flat). I’m thinking that I might as well just upgrade the whole thing with hydraulic roller lifters and camshaft. What would be the best camshaft choice for an L81? I know there are plenty on kit available out there but what would work with the computer and stock heads?
Le Mans Master
Joined: Dec 2006
Posts: 8,837
Likes: 1,028
Thanks BACNBLK, the paint job was done by the original owner it's a custom burgundy with tinny little gold flakes in it. It goes perfect with the original tan interior.
For the ticking/knocking noise, I heard that on these motors, the camshaft is known for the lobes to go bad (flat). I’m thinking that I might as well just upgrade the whole thing with hydraulic roller lifters and camshaft. What would be the best camshaft choice for an L81? I know there are plenty on kit available out there but what would work with the computer and stock heads?
For the ticking/knocking noise, I heard that on these motors, the camshaft is known for the lobes to go bad (flat). I’m thinking that I might as well just upgrade the whole thing with hydraulic roller lifters and camshaft. What would be the best camshaft choice for an L81? I know there are plenty on kit available out there but what would work with the computer and stock heads?
Thread Starter
Intermediate
Joined: Oct 2005
Posts: 42
Likes: 0
From: Saratoga Springs UT
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Instructor
Joined: Apr 2007
Posts: 184
Likes: 1
From: Atlas is shrugging KC, MO area
As far as a computer cam goes, I think they are mainly geared around computer controlled FI. I think the 350 cams would work on the computer/carb cars.
Last edited by 7t3shark; May 6, 2007 at 09:26 PM. Reason: add info
Drifting
Joined: Mar 2006
Posts: 1,369
Likes: 79
From: West Coast
This is one area I have been holding back on. I would love to dump the Carb/Computer/Distributer and go with a nice Cam/Intake/Carb/Distributor combination but everything is so low mileage and running fine (except more ponies would be nice) that I dont want to mess up a good thing. Plus with the above mods maybe best to drop in a nice crate engine or 383 instead: decisions, decisions, decisions...
Thread Starter
Intermediate
Joined: Oct 2005
Posts: 42
Likes: 0
From: Saratoga Springs UT
Decision? Tell me about it… 
I’m struggling to find a cam that would work well with the L81 and don’t have enough knowledge to make a selection. In top of that the computer is limiting the choices but I don’t want to dump it and want to stay street legal. I’ve been in a situation in the past were I bought a vette that had all the emission system gone (cat, smog pump, etc…). It was passing the pollution emission test but not the visual inspection so to register it I needed to spend $1000s to get all the parts back in the car.
Not worth it, I had to sell it. A real nightmare! And the car just sited in the garage for months before someone finally bought it.
The L81 is far from being a race engine but I think if we spend just a little money and upgrade exhaust, camshaft, intake, and maybe the heads we can get pretty good results for half the price of a crate engine… Just enough for crusin’.
I’m thinking upgrading the carb for a TPI system in the future so the computer needs to stay I think
Any of you that have upgraded the cam on an L81 while keeping the computer what was your choice? What about emission? I couldn't find the GM151 anywhere....
Thanks
I’m struggling to find a cam that would work well with the L81 and don’t have enough knowledge to make a selection. In top of that the computer is limiting the choices but I don’t want to dump it and want to stay street legal. I’ve been in a situation in the past were I bought a vette that had all the emission system gone (cat, smog pump, etc…). It was passing the pollution emission test but not the visual inspection so to register it I needed to spend $1000s to get all the parts back in the car.
Not worth it, I had to sell it. A real nightmare! And the car just sited in the garage for months before someone finally bought it. The L81 is far from being a race engine but I think if we spend just a little money and upgrade exhaust, camshaft, intake, and maybe the heads we can get pretty good results for half the price of a crate engine… Just enough for crusin’.
I’m thinking upgrading the carb for a TPI system in the future so the computer needs to stay I think
Any of you that have upgraded the cam on an L81 while keeping the computer what was your choice? What about emission? I couldn't find the GM151 anywhere....
Thanks
Thread Starter
Intermediate
Joined: Oct 2005
Posts: 42
Likes: 0
From: Saratoga Springs UT
I think I found the source of the noise. The oil pump! 
After tearing apart the whole engine to change the cam, (carb, intake manifold, headers, heads, etc...) I didn't see anything wrong except the top of the cylinders and the heads were pretty dirty with a thick layer of sticky oily residue. The cam lobes look very good as well as the lifters. I decided while I'm at it to go ahead and change the oil pan gasket and main rear bearing seal. I removed the oil pan, and then when I started to remove the oil pump bolt, I couldn't feel any resistance on the ratchet like I could have actually loosen if right off with my fingers!!! 
When I was listening for the ticking under the engine, it was coming from the oil pump area.
Do you think that the oil pump being loose can be the source of this ticking? I’ve never heard such a thing as the oil pump getting loose! That would make sense since the oil pump is driven by the distributor so the frequency should be ½ the crank speed right?
After tearing apart the whole engine to change the cam, (carb, intake manifold, headers, heads, etc...) I didn't see anything wrong except the top of the cylinders and the heads were pretty dirty with a thick layer of sticky oily residue. The cam lobes look very good as well as the lifters. I decided while I'm at it to go ahead and change the oil pan gasket and main rear bearing seal. I removed the oil pan, and then when I started to remove the oil pump bolt, I couldn't feel any resistance on the ratchet like I could have actually loosen if right off with my fingers!!! When I was listening for the ticking under the engine, it was coming from the oil pump area.
Do you think that the oil pump being loose can be the source of this ticking? I’ve never heard such a thing as the oil pump getting loose! That would make sense since the oil pump is driven by the distributor so the frequency should be ½ the crank speed right?
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
It could very well have been the problem. Make sure you look for any wear/damage on pump/parts, etc. It might be worth buying a new pump/parts just to be safe. But, if you disassemble it completely and find no distress, it should be OK.
Safety Car
Joined: Dec 2004
Posts: 4,071
Likes: 0
From: San Diego CA
If a cam lobe were going flat the bugger would be backfiring and being an annoying lil SOB.
If/when you decide to replace that cam, the summit 1102, 1103, and 1104 are good cams that will work with the computer. However I strongly recommend spending the extra dough and converting to a roller cam. This no zinc in oil any more thing is getting annoying.
If/when you decide to replace that cam, the summit 1102, 1103, and 1104 are good cams that will work with the computer. However I strongly recommend spending the extra dough and converting to a roller cam. This no zinc in oil any more thing is getting annoying.
Instructor
Joined: Apr 2007
Posts: 184
Likes: 1
From: Atlas is shrugging KC, MO area
[QUOTE=Angel303;1560172620]I’m thinking upgrading the carb for a TPI system in the future so the computer needs to stay I think
QUOTE]
I believe a TPI system uses an entirely different computer than the carb with some electrical components in it.
QUOTE]
I believe a TPI system uses an entirely different computer than the carb with some electrical components in it.
Thread Starter
Intermediate
Joined: Oct 2005
Posts: 42
Likes: 0
From: Saratoga Springs UT
I got a brand new Melling oil pump (M55) and made sure It's tight to the spec: 65 ft/lbs. Hopefully that will take care of the problem.
I think that I'll stick with the carb for a while and spend the money in the exhaust and a nice set of heads before any TPI swap. I thought the computer was the same but apparently not. I'm also installing a comp cam 168H (High energy) that should work well with the carb so I might never swap to TPI, will see......
Thank you all for the info anyways!!! :thumbs
I think that I'll stick with the carb for a while and spend the money in the exhaust and a nice set of heads before any TPI swap. I thought the computer was the same but apparently not. I'm also installing a comp cam 168H (High energy) that should work well with the carb so I might never swap to TPI, will see......
Thank you all for the info anyways!!! :thumbs
Advanced
Joined: Oct 2001
Posts: 65
Likes: 0
From: Moerstraten NL
The only thing you need to watch is that the cam will give enough vacuum. If the vacuum drops to far the ecm thinks your running somewhat higher revs and starts putting fuel in. The ecm will only controll the primairies (first 80%) the last 20% will only be controlled by the carb on its own. Many people are running Comp Cam XE262 and even 268 cams with no problem 
Greetings Peter
Greetings Peter
Burning Brakes
Joined: May 2007
Posts: 1,150
Likes: 14
From: LaMoille Illinois
if it is a sticky lifter pour a can of Seafoam in the cranck case i had one makin that noise in my 454 and used the seafoam and within 15 minutes no more ticking!! great stuff you can get it at menards.
