Honda HR17, HR173, HR194, HR195PXA, HR195PDA JOB AID LEAK DOWN TEST

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INTRODUCTION

JOB AID

LEAK DOWN TEST

A piston engine is just another pump. It makes sense that excess leakage can render it pretty useless.That’s why checking compression is such a basic step in determining the health of an engine.

Rather than relying on the engine to build up pressure (compression test), a cylinder leakage tester uses compressed air to pressurize the cylinder with the piston at TDC (top dead center) on the compression stroke and various other positions. By performing a cylinder “leak down” test, you can closely pinpoint the area of the leak and the amount it is leaking in the problem cylinder.

By regulating the pressure going into the cylinder, then measuring the pressure being held in the cylinder, you can determine how much leakage exists and where the leak is coming from.

There are a number of tool suppliers that make single and dual gauge leakage testers with all the fittings and adapters and instructions. The Motion Pro single gauge leak-down tester is available from the Tool and Equipment Program (see below). Get one, and it will pay for itself in reduced diagnostic time and accurate estimates on service work and trade-ins. It’s the best way to get inside an engine (before actually getting inside the engine) and find out how well it’s performing.

Points to observe when conducting a cylinder leakage test:

• Always wear eye protection; you're working with compressed air.

• If possible, check the engine when it’s warm. The results will more accurately indicate actual operation if the engine is warm, but be sure to wear gloves to prevent burns.

• Be sure the valves are correctly adjusted.

• Follow the instructions that come with the tester.

LEAK DOWN TESTER, MTP-08-0126

Commercially Available Tool

Description Model Number

Leak Down Tester MTP-08-0126

There are two convenient ways to order: online or by toll-free phone.

• To order online, go to the iN: SERVICE>Tools>Tool and Equipment Program>Online Catalog, and then search by model number.

• To order by phone, call 1-888-424-6857. Customer service representatives are available from 7:30 AM until 7:00 PM CT, Monday through Friday.

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PROCEDURE

The GCV160 engine is shown throughout. The procedure is similar for all 4-stroke engines.

1. Remove the spark plug, and screw the threaded flexible hose into the spark plug hole.

2. Remove the recoil starter.

3. Remove the valve cover.

4. While observing the valves, rotate the crankshaft to position the piston at TDC on the compression stroke.

5. Remove the exhaust and intake valve rocker arms (GC/GCV types).

On GX/GXV engines, remove the intake and exhaust valve push rods.

The leak down test can be done on any type of 4-stroke engine. Have a plan on how to conduct a leak down test on your engine.

SPARK PLUG

VALVE COVER 6 x 12 mm

EXHAUST ROCKER ARM

FLANGE BOLT

FLEXIBLE HOSE

EXHAUST ROCKER SHAFT

INTAKE ROCKER ARM

INTAKE ROCKER SHAFT

6. Secure the crankshaft at TDC on the compression stroke with a breaker bar or long wrench.

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7. Make sure that the air supply is regulated to 60 psi before connecting to the leak down tester.

8. Connect the leak down tester to your air supply.

REGULATOR ADJUSTMENT

9. Turn the regulator until the gauge is reading 0%.

10.Connect the gauge to the threaded flexible hose and observe the gauge.

B CAUTION

When the cylinder is pressurized, the pressure will try to turn the crankshaft; this could cause the wrench on the end of the crankshaft to be thrown off, causing injury.

Make sure the wrench is securely braced before pressurizing the cylinder.

TO AIR SUPPLY

Turn regulator adjustment until the gauge reads 0%.

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11.If the leakage is excessive, listen or look for the area of the leak.

% LEAKAGE CONDITION

0 Remove the valve core from your adapter hose 2 ~ 6 New/perfect to very good 7 ~ 9 Good, well broken in

10 ~ 15 Acceptable, some power loss, minor oil consumption 16 ~ 20 Worn, low power output, probably running poorly, and using oil

Greater than 20 Needs repair

• If an intake valve is leaking, you will hear air coming from the carburetor or air box.

• If an exhaust valve is leaking, you will hear air coming from the exhaust pipe/muffler.

• If there is leakage past the rings, you will hear air in the crankcase through the oil filler opening. If you have a head gasket leak on a single cylinder engine, you will hear the leak at the head gasket area, or you will

see bubbles if you spray the area with soapy water.

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WORN CYLINDER TEST

Perform this test if you have a reasonably low leak percentage (10 ~ 15%) with the piston at TDC and air is coming from the oil filler opening, indicating worn piston rings.

1. Disconnect the leak down tester from the threaded flexible hose.

2. Rotate the crankshaft to 90º after TDC.

TO AIR SUPPLY

REGULATOR ADJUSTMENT

3. Readjust the regulator until the gauge is reading 0%. Make sure that the air supply is regulated to 60 psi before

connecting to the leak down tester.

4. Connect the gauge to the threaded flexible hose and perform another leak down test.

Turn regulator adjustment until the gauge reads 0%.

5. Compare this reading to the reading obtained with the piston at TDC.

• This checks the wear at the maximum side-thrust position of the piston — where you’re most likely to see wear on

an older engine.

• This also gives an indication of scoring on the cylinder wall. This may cause the rings to loose their seal with the

cylinder wall, causing a increase in leakage.

Remember to securely hold the breaker bar or wrench you’re turning the crankshaft with, since you’ll be at the maximum torque position of crankshaft rotation.

B CAUTION

When the cylinder is pressurized, the pressure will try to turn the crankshaft; this could cause the wrench on the end of the crankshaft to be thrown off, causing injury.

Make sure the wrench is securely braced before pressurizing the cylinder.

6. Disconnect the leak down tester.

7. Rotate the crankshaft so the piston is at BDC (bottom dead center).

8. Perform steps 1 ~ 5 again, and compare this reading with those obtained with the piston at TDC and 90º after TDC. If the leakage increases even more, this indicates that the cylinder is out-of-round, tapered, or scored allowing

leakage past the rings.

TDC

90º AFTER TDC

BDC

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SOFT CARBON REMOVAL

Occasionally, an engine can develop a build-up of soft carbon from running rich, such as when the air cleaner becomes restricted. If you are testing an engine and it has low compression and the leak down test tells you the valves are leaking, it may be something as simple as a little carbon on a valve seat. Before performing an expensive engine tear-down, try this easy way to determine if the problem is soft carbon.

1. Rotate the crankshaft so the piston is at BDC.

2. Reconnect the leak down tester to pressurize the cylinder.

B CAUTION

When the cylinder is pressurized, the pressure will try to turn the crankshaft; this could cause the wrench on the end of the crankshaft to be thrown off, causing injury.

Make sure the wrench is securely braced before pressurizing the cylinder.

3. Use a plastic hammer to lightly tap the top of the valve stems.

NOTICE

Hitting the rocker arm too hard may cause the valve to strike the piston crown. Use light taps only.

4. Check leak down again to see if there is any improvement in the leakage percent. If the engine leak down is acceptable, reassemble the engine.

5. Disconnect the leak down tester.

6. Rotate the crankshaft so that the piston is at TDC of the compression stroke.

7. Install the rocker arms.

8. Install the spark plug.

9. Install a new valve cover (GC/GCV types) using Hondabond HT sealant.

• New Valve Cover (P/N 12310-Z0J-000)

• Hondabond HT Sealant (P/N 08718-0004)

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Honda HR17, HR173, HR194, HR195PXA, HR195PDA JOB AID LEAK DOWN TEST

Specifications and Main Features

Frequently Asked Questions

User Manual