Generation III Internal Engine 1997-2006 LS1 | LS6
Sponsored by:
Sponsored by:

my first leak down test..

Old Sep 6, 2016 | 06:40 PM
  #1  
brett14's Avatar
Thread Starter
Teching In
iTrader: (3)
 
Joined: Nov 2014
Posts: 20
Likes: 0
Default my first leak down test..

whatsup guys picked up a lm7 for 500$ supposedly had 80k miles on it. def doesnt look like it. anyway i wanted to do some test before i start doing anything to it so i dont waste my time.

mind you this engine has been sitting 2+ years on an engine stand.

this is my first time doing a leak down test. i had the intake manifold off.
i ran through all the cylinder

1- 25%
2- 25%
3- 45% heard air leaking the intake port.
4- 25%
5- 25%
6-25%
7-40% again heard air leaking from intake port
8-25%

than i did it again and nearly all of them were 40% + all leaking from intake port

i dont know much about internals but it seems like the valve stem maybe pushed up?

im also not 100% sure if i had the cylinders at TDC i just kept turning the crank until air stopped coming out of the exhaust.

insight please
Reply
Old Sep 6, 2016 | 07:02 PM
  #2  
farmington's Avatar
TECH Fanatic
iTrader: (14)
 
Joined: Jun 2010
Posts: 1,807
Likes: 13
From: Little River SC
Default

If the piston isn't at direct top center the air pressure will push the piston down giving bad readings.
Reply
Old Sep 6, 2016 | 07:29 PM
  #3  
NowhereFast's Avatar
Staging Lane
 
Joined: Apr 2015
Posts: 68
Likes: 0
From: Long Island
Default

Since it's on a stand, why not pull the valve covers and make sure both valves are closed before screwing with it? I find it hard to believe EVERY intake valve is bent.
Reply
Old Sep 6, 2016 | 09:51 PM
  #4  
brett14's Avatar
Thread Starter
Teching In
iTrader: (3)
 
Joined: Nov 2014
Posts: 20
Likes: 0
Default

can you give me advise on how to make sure each cylinder is at TDC. i heard of the screw driver one but the spark plugs are on the side so it cant really push the screw driver up.

yeah thats a good idea i can take the cover off and play with the valves
Reply
Old Sep 9, 2016 | 10:21 AM
  #5  
farmington's Avatar
TECH Fanatic
iTrader: (14)
 
Joined: Jun 2010
Posts: 1,807
Likes: 13
From: Little River SC
Default

make a mark on the balancer at tdc, and every 90 degrees. follow the firing order.
Reply
Old Sep 9, 2016 | 11:13 AM
  #6  
LFX1stGenF's Avatar
Registered User
 
Joined: Sep 2016
Posts: 7
Likes: 0
Default

Whoa! The same thing has happened to me. I purchased an LM7 from an 04 Silverado and it only had 139k miles! How did the bullsh*** alarms not go off? Okay, this is Texas, the only way you can get around anywhere is if you get on the highway so this translates to roughly 65miles/day. 65miles per day multiplied by 365 multiplied by the age of the vehicle (12yrs) = 284,700miles.

Well.. It turns out that at its last recorded oil change the vehicle had 299,5XX miles and then in March of this year the title was transferred and somehow the miles went down to 139k. :-)

F*** Me right? :-)
Reply


Thread Tools
Search this Thread

All times are GMT -5. The time now is 05:56 AM.

story-0
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph

Slideshow: A modern Camaro transformed into a retro icon, this limited-run "Bandit" build blends nostalgia with brute force in a way few revivals manage.

By Verdad Gallardo | 2026-04-21 13:57:02


VIEW MORE
story-1
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked

Slideshow: Cadillac didn't just crash the high-performance luxury vehicle party, it showed up loud, supercharged, and occasionally a little unhinged...

By Pouria Savadkouei | 2026-04-16 10:05:15


VIEW MORE
story-2
Top 10 Most Powerful Chevy Trucks Ever Made!

Slideshow: Top ten most powerful Chevy trucks ever made

By | 2026-03-25 09:22:26


VIEW MORE
story-3
Hennessey's New Supercharged Silverado ZR2 Has 700 HP

Slideshow: Hennessey has turned the Silverado ZR2 into a 700-hp off-road monster with supercharged V8 power and a limited production run.

By Verdad Gallardo | 2026-03-24 18:57:52


VIEW MORE
story-4
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes

Slideshow: A one-off sports car that looks like a vintage Italian exotic-but hides a C6 Corvette underneath-just sold for the price of a new mid-engine Corvette.

By Verdad Gallardo | 2026-03-23 18:53:41


VIEW MORE
story-5
Awesome K5 Blazer Restomod Comes With C7 Corvette Power

Slideshow: A heavily reworked 1972 K5 Blazer swaps its off-road roots for a low-slung street-focused build with modern V8 power.

By Verdad Gallardo | 2026-03-09 18:08:45


VIEW MORE
story-6
10 Camaros You Should Never Buy

Slideshow: There are thousands of used Camaros on the market but we think you should avoid these 10

By | 2026-02-17 17:09:30


VIEW MORE
story-7
10 LS Engine Myths That Refuse to Die

Slideshows: Which one of these myths do you believe?

By Verdad Gallardo | 2026-01-28 18:10:11


VIEW MORE
story-8
Five Reasons the Camaro Was the Most Pivotal Player in the Pony Car Wars 2.0

The world was a better place when it was still around.

By Brett Foote | 2026-01-23 09:20:37


VIEW MORE
story-9
10 Reasons the LS7 Is GM's Most Extreme Naturally Aspirated V8 Engine Ever

Slideshow: The 7.0-liter LS7 was designed for absolute cutting-edge performance.

By Verdad Gallardo | 2026-01-07 18:36:00


VIEW MORE