Leak down test???

[Herman Pahls]

I want to do a leak down test on my 07 GSXR 1000.
I have the leak down tester that I use on airplane engines and the adapter to fit the GSXR spark plug threads.
My question is how to hold the crankshaft so the piston stays at top dead center when air pressure is applied.
I could place a socket on thecrankshaft bolt under the cover on the right side of the engine.
On aircraft engines 80 PSI is used and anything over 60 PSI residual pressure is acceptable, but the closer to 80 residual the less leaking past the rings or valves.
Is a leak down test on our road bike engines a good indicator of ring and valve condition as it is on aircraft engines?
Any advice on procedure or validity of this test will be appreciated.
Thanks Herman 541 404 6464 Oregon

[924RACR]

I did mine last fall, don't seem to recall having to go to any heroics to hold the engine in place - maybe a socket and breaker bar on the crank, at worst. OTOH, mine is still a stock motor, so doesn't spin so wonderfully freely; my ITB car, with a fully built motor, will move across the garage very easily in-gear with air pressure... LOL

I would expect a leakdown would still be valid useful info, but am looking forward to replies from those in the know...

[kea]

When we perform a leak-down test on an engine, while on the compression stroke, we position the piston of that cylinder at TDC.
If you are the least bit before or after TDC, than the crank will rotate.
For all the automotive based engines I've done, we mark the flywheel or flywheel ring gear for TDC. I don't know what you have on a M/C engine to duplicate that.

[924RACR]

Herman probably already knows this, but for the record... on the GSXR, there's a scribe mark and a notch to line up under the access cover on the front of the crank. For convenience's sake, I also put a mark 180-out with a paint pen for the "off" cylinders...

[Daryl DeArman]

If it's at TDC it will stay there. If it's not at TDC it will move...as far as holding it---those pistons may seem tiny relative to an aircraft engine however they still have about 10 square inches of surface area. Even 80psi would be 800pounds on the piston, not sure you are holding that with a breaker bar.

Interesting observation about ring sealing at higher psi. I've always, perhaps incorrectly, used 100psi as the input pressure and consider a healthy engine something in the less than 5% range. 25% leakage would be way past the TBO for a race engine in my opinion.

[Ivinsea]

It is easy to hold the crank with a breaker bar or better yet a T handle.

I had 2% to 3% leakdown @ 100PSI with my 07/08 GSXR.

[Albatross]

When doing a leak down, I have all the plugs pulled, place the gear box in fourth gear and wedge a 1 x 4 approx 23" long between the brake peddle and the back of the frame holding my engine gauges for each and subsequent reading. Removing the 1 x 4 each time to rotate to the next piston in the firing order and re-inserting... Yes, the piston must be on the up stroke at TDC or at the 180 degree mark for the off pistons. I have the LR wheel jacked a few inches off the ground to rotate the engine/flywheel to the next cylinder and rotate slowly enough to sneak up on the 000/180 degree marks. The elevated wheel remains elevated throughout the process. Had an airplane, flew for a living, don't know why FAA chose 80 psi. I set the input air at 100 psi and read the result (loss) on the leak down meter. A no brainer. Listen to the losses through the carb, exhaust and breather. Rings will leak a little, intake should be relatively quiet (carb) and exhaust valve which takes the beating generally leaks the most -hopefully very little. Not familiar with the idiosyncrasies of your engine type. GL

[brownslane]

FAA choose 80 psi as the engine is designed to function at altitude, and lower air density. Lower air density equals lower cylinder pressures.

At least that is my story and I'm gonna stick with it!
Tom

[Jon Jeffords]

Had an airplane, flew for a living, don't know why FAA chose 80 psi.

Being in the engine business, the story I heard is that ALL shops have compressors that will provide at least 80 psi under flow to the meter. Shops with 100 psi capacity are less common.

[Herman Pahls]

Thanks for all the responces.
I removed all the plugs and placed a 3/16 metal rod on top of the piston and turned the engine to TDC by watching the rod.
You will know immediately if you have the wrong TDC when applying the air pressure.
I found that the piston would stay at TDC but if it is the least bit off the air pressure will turn over the engine.
The idea that 80 PSI was chosen versus 100 PSI makes sense in my case since the compressor I was using struggles to get to 100.
I was shocked how lttle leak there was on my GSXR 1000 compared to aircraft engines.
Herman

[Albatross]

Herman, sounds like you have mastered the process. Would you care to share the numerical percentage leak down results or lbs loss for each cylinder with 80 psi input.

[brownslane]

Herman, the aircraft engine may have more leak down if it is air cooled and not near operating temps. Not to mention how many hours it had.

[starkejt]

I would not expect a piston aircraft engine, even brand new and warmed up, to have leak down numbers anywhere close to a sport bike engine.