Products to Compare (max of 3)
Compare These Parts
Talk to the Experts. Call 800.979.0122, 7am-10pm, everyday.
Since 1952
Talk to the Experts. Call 800.979.0122
Shop By
Street Race Truck More... The Toolbox

Engine Cylinder Leak Down Test


Leaking the cylinders should be done on a race engine after every couple of races minimum, or after an engine has been hot. This process is a good preventative maintenance test. We start by removing all the spark plugs. If you also want to check the valve springs, this is a good time to do that; remove the valve covers as well. Once you have the plugs removed, I like to inspect them. This will help indicate how the engine was tuned. You are looking for a nice tan or light brown color on the plugs. If the plugs are wet or dark, the engine was too rich; If plugs are white, the engine is too lean; If plugs are black, it is burning oil.

Now that we have all the plugs out, we are ready to leak the engine. Speedway offers several gauges to perform this task, Longacre Digital Engine Leak Down Tester, Moroso Cyldiner Leak Down Tester, Speedway Dual Gauge Leakdown Tester Tool to name a few. Screw hose into the spark plug hole and snug down. Next, we need to rotate the engine so it is at the top dead center. You can turn the engine by the bolt on the front of the crankshaft. If you have a crank driven water pump, you will need to turn over by the back of the crank or pushing the car if the engine is installed. I will put the end of the hose up to my ear as a rotate engine. Once I can’t hear it pushing air, I stop rotating. This should be top dead center. You can also check at bottom dead center if rocker arms are removed or backed all the way off.

Once the engine is rotated to the top dead center, we can check using our gauge. Once air is applied to the cylinder, if the motor is not at the exact top dead center, it will push the piston down in the cylinder and open a valve; you will need to find the exact top dead center again. Both valves must be closed to get an accurate reading. The smaller the percentage of leakage the better.

Most engine builders want to see less than 10% and engines using gapless rings less than 5%. If an engine has more than 10%, try to determine where it is leaking from: a valve, the rings, or a head gasket. If it is going by a valve, you can remove the rocker and try tapping on the top of the valve stem with a rubber mallet. Sometimes there is just a piece of trash or a valve just didn’t close all the way. Do not hit with a metal hammer or very hard, as this can damage the valve tip. If going by the rings, you can try and squirt a little oil in the cylinder. Sometimes rings will get stuck, and this oil will help. If these suggestions don’t work, consult your engine builder to determine what needs to be done.

Since the engine is at the top dead center, now is a good time to check the valve spring pressure. Speedway offers Valve Spring Pressure Tester, Intercomp Digital Valve Spring Tester and Hydraulic Valve Spring Checker. Place the checker over the rocker and pull down until the valve starts to open. Check to see what the gauge reads. You will want to check with your engine builder as to what the spring pressure should be. This process is good to do after every race. You can easily tell when springs start to lose pressure and need to be replaced or if you have a single spring that has developed an issue.

Once you are done checking the first cylinder, remover the hose from the spark plug hole and move to the next cylinder. Rotate the engine to the next cylinder. I like to go in the firing order. This allows fewer rotations on the engine. Once all eight cylinders have been checked, you can install spark plugs and put valve covers back on. I like to keep notes on how each cylinder leaked and what the spring pressure was for each spring. Keeping notes will help you in determining if your engine is starting to develop an issue if you see changes. Always consult your engine builder with questions on spring pressure and cylinder leakage percentages.

Products Featured in this Article

Related Articles

Cleaning Fuel Injector Nozzels
by Jason Danley - Posted in Tech
Cleaning fuel injector nozzels is a must in your car maintenance regimen. Learn the steps on how to properly disconnect fuel lines and check the barrel valve.
1946 Ford Sedan Delivery-Employee Rides: Jeff Karls
by Jeff Karls - Posted in Tech
Ride along as you read the story of how "Looney Tunes" started and made its way back to the original owner after nearly three decades.
How to Install an Electric Motor Kit for Exhaust Cutouts
by Kevin Webel - Posted in Tech
A guide on removing and installing a new electric motor kit for exhaust cutouts.
Installing a Speedway Motors Wiring Kit - 1967 Chevelle
by Jeff Karls - Posted in Tech
This Chevelle project gets rewired with a Speedway Motors wiring kit. Follow along as Jeff guides you through this application, starting with a good mounting location for the fuse box. Learn more on continuity, grounding and relays.
How to Install an EFI Fuel Tank - 1967 Chevelle
by Jeff Karls - Posted in Street Rod
A step by step on how to install an EFI Fuel Tank kit in a 1967 Chevelle. Learn the benefits of using this kit including expanded fuel capacity and a 24 gallon tank.
Windshield Removal Tool
by Steve Lewis - Posted in Tech
Learn how to use a windshield remover tool to assist with in-depth builds. A step-by-step guide to windshield removal.
Removing Paint on Car Body Panels - 1967 Chevelle
by Jeff Karls - Posted in Tech
Follow along as Jeff demonstrates how to strip paint from the body panels of his 1967 Chevelle using a restorer porter cable tool. Learn how to save time by having the panels acid dipped to remove layers of paint.
How to use a Stud Extractor
by Steve Lewis - Posted in Tech
Learn how simple it is to remove broken or stubborn studs with Titan Tools extractor tool.
Redline Radial Tire Application- 1967 Chevelle
by Jeff Karls - Posted in Tech
Jeff chooses Redline Radial Tires and black powder-coated steel wheels for his 1967 Chevelle. See how he installs the tires with some helpful tips along the way.
Installing a Gear Reduction Mini Starter - 1967 Chevelle
by Jeff Karls - Posted in Tech
To keep this project moving forward, Jeff installs a gear reduction mini starter on his big block. See how to apply the mini starter on 153 or 168 tooth flexplates.