7 replies to this topic

[sinister]

Leakdown Test:

To perform a leakdown, start by taking off the oil cap off. Then you bring the cylinder to top dead center (TDC). Hook up the leakdown attachment to an air compressor and screw it in the spark plug hole. Turn the compressor on and bring the cylinder pressure to the factory spec. (Consult your Helms manual for this number.) The attachment allows air into the cylinder and brings it to the factory pressure. You then listen for air coming out of the manifolds. If you hear air hissing out of either manifold or the muffler you have bad valve seals. If you hear air hissing out of the oil cap or breather valve (if the oil cap is still on the motor), then chance are your rings are bad.

Information Source: www.hondaswap.com

[ferret]

nice...didn't know that one. Thanks.

[david kriedeman]

When doing a cylinder leakage test you WILL need to have your rocker gear inactive.
On engines where the rocker arms are not removable EG: OVERHEAD CAMSHAFT DESIGN ENGINES normally you will have to remove the CAMSHAFTS.
You need to disable the valve train as when you put the compressed air into the engine the crankshaft ALMOST ALWAYS MOVES.
When this moves so does the timing belt or chain which inturn moves the CAMSHAFTS.
You can be misled into believing you have avalve or valve seat issue due to tell tale air hissing out of the inlet or exhaust.
THIS IS NOT RELAVANT IF CHECKING FOR CYLINDER SEALING ISSUES.
HOWEVER with the valve train disabled it ELIMINATES the air leakage past valves which could be confusing when fault finding.
NEVER REMOVE JUST THE TIMING BELT or CHAIN to do a LEAKAGE TEST as there will be a number of valves off their seats.
If your engine is not of what we refer to as a "FREE RUNNING DESIGN"
YOU WILL BEND VALVES.
FREE RUNNING MEANS THAT EVEN IF A VALVE IS FULLY OPEN YOU CAN TURN THE CRANKSHAFT 720 degs. and none of the pistons will touch the valves.
NOT ALOT OF ENGINES ARE FREE RUNNERS.
DONT RISK IT.
REMOVE THE CAMSHAFTS.
MAKE SURE YOU KNOW HOW TO DO THIS PROPERLY.
MAKE SURE YOU KNOW HOW TO SET UP YOUR VALVE TIMING AND TIMING BELT POSSITIONS CORRECTLY ON REASSEMBALLY.
DO NOT ATTEMPT THIS UNLESS YOU HAVE GOOD SOUND MECHANICAL KNOWLEDGE IN THIS AREA.
IT COULD END UP BEING A VERY EXPENSIVE EXERCISE IF YOU GET IT WRONG,BENT VALVES ETC.
OR YOU COULD END UP WITH A VERY DOUGHY DOG OF AN ENGINE IF YOU HAVE THE VAVE TIMING OUT,
1 TOOTH OUT ON YOUR VALVE TIMING IS ENOUGH TO MAKE YOUR ENGINES DRIVABILITY SUFFER BIG TIME
ALWAYS START YOUR ENGINE DIAGNOSIS WITH A COMPRESSION TEST FIRST.
"""ANY ENGINE """ EXCEPT for a diesel, REQUIRES A MINIMUM of 100PSI COMPRESSION PRESSURE to have half a chance of having the air fuel mixture combust.
Most engines these days in good condition should have around 160 - 175 psi on a compression test.
If i test an engine and it has less than say 140psi, i then do a wet test.
A wet test means removing the compression tester from the suffering cyl. putting a small amount of engine oil down the sparkplug hole and retesting.
The oil helps seal the rings better.
If the final figure is still unexceptable, i then procede to a leakage test.

[xdclevo]

david kriedeman, on Jul 9 2006, 02:48 PM, said:

If your engine is not of what we refer to as a "FREE RUNNING DESIGN"
YOU WILL BEND VALVES.
FREE RUNNING MEANS THAT EVEN IF A VALVE IS FULLY OPEN YOU CAN TURN THE CRANKSHAFT 720 degs. and none of the pistons will touch the valves.
NOT ALOT OF ENGINES ARE FREE RUNNERS.

Also known as either "interference" or non interference. You will know which one you have if you break a cam belt. You will either cry (interference), or just replace the belt with some grumbling (non interference)

Edited by xdclevo, 09 July 2006 - 07:43 PM.

[tonyma61]

That is some very usefull info. It will come in handy at one stage or another.

Cheers...
Tony...

[R32 GT-R]

If your engine is not of what we refer to as a "FREE RUNNING DESIGN"
YOU WILL BEND VALVES.
FREE RUNNING MEANS THAT EVEN IF A VALVE IS FULLY OPEN YOU CAN TURN THE CRANKSHAFT 720 degs. and none of the pistons will touch the valves.
NOT ALOT OF ENGINES ARE FREE RUNNERS.

Also known as either "interference" or non interference. You will know which one you have if you break a cam belt. You will either cry (interference), or just replace the belt with some grumbling (non interference)

i got some interferance going on.

[The Don]

When doing a cylinder leakage test you WILL need to have your rocker gear inactive.
On engines where the rocker arms are not removable EG: OVERHEAD CAMSHAFT DESIGN ENGINES normally you will have to remove the CAMSHAFTS.
You need to disable the valve train as when you put the compressed air into the engine the crankshaft ALMOST ALWAYS MOVES.
When this moves so does the timing belt or chain which inturn moves the CAMSHAFTS.
You can be misled into believing you have avalve or valve seat issue due to tell tale air hissing out of the inlet or exhaust.
THIS IS NOT RELAVANT IF CHECKING FOR CYLINDER SEALING ISSUES.
HOWEVER with the valve train disabled it ELIMINATES the air leakage past valves which could be confusing when fault finding.
NEVER REMOVE JUST THE TIMING BELT or CHAIN to do a LEAKAGE TEST as there will be a number of valves off their seats.
If your engine is not of what we refer to as a "FREE RUNNING DESIGN"
YOU WILL BEND VALVES.
FREE RUNNING MEANS THAT EVEN IF A VALVE IS FULLY OPEN YOU CAN TURN THE CRANKSHAFT 720 degs. and none of the pistons will touch the valves.
NOT ALOT OF ENGINES ARE FREE RUNNERS.
DONT RISK IT.
REMOVE THE CAMSHAFTS.
MAKE SURE YOU KNOW HOW TO DO THIS PROPERLY.
MAKE SURE YOU KNOW HOW TO SET UP YOUR VALVE TIMING AND TIMING BELT POSSITIONS CORRECTLY ON REASSEMBALLY.
DO NOT ATTEMPT THIS UNLESS YOU HAVE GOOD SOUND MECHANICAL KNOWLEDGE IN THIS AREA.
IT COULD END UP BEING A VERY EXPENSIVE EXERCISE IF YOU GET IT WRONG,BENT VALVES ETC.
OR YOU COULD END UP WITH A VERY DOUGHY DOG OF AN ENGINE IF YOU HAVE THE VAVE TIMING OUT,
1 TOOTH OUT ON YOUR VALVE TIMING IS ENOUGH TO MAKE YOUR ENGINES DRIVABILITY SUFFER BIG TIME
ALWAYS START YOUR ENGINE DIAGNOSIS WITH A COMPRESSION TEST FIRST.
"""ANY ENGINE """ EXCEPT for a diesel, REQUIRES A MINIMUM of 100PSI COMPRESSION PRESSURE to have half a chance of having the air fuel mixture combust.
Most engines these days in good condition should have around 160 - 175 psi on a compression test.
If i test an engine and it has less than say 140psi, i then do a wet test.
A wet test means removing the compression tester from the suffering cyl. putting a small amount of engine oil down the sparkplug hole and retesting.
The oil helps seal the rings better.
If the final figure is still unexceptable, i then procede to a leakage test.

do you still tune cars?

[sinister]

Dave no longer comes on here.... hard to get a hold of unless you know him but yes he does.