Leak down testing?

[mt.sledder]

I've always used a compression tester and had a look at the pistons to determine engine health. Now I'm looking at getting a leak down tester and I've got a few questions.

1. What's the proper procedure for doing a leakdown test on a 2 stroke snowmobile engine to determine proper ring sealing?
2. I Already know how to pressure test the engine to 5-10 psi to look for leaks like crank seals or throttle body boots.
3. How are you holding the clutch to keep the engine from turning over when the piston is at TDC?
4. Amazon has $39 leak down test kits, worth buying or go with a brand like an OTC 5609 kit?
5. Does anyone have a video of doing the complete test?
6. What % leakage past the rings is still except able?

 

[richracer1]

I bought the Longacre Racing Products digital leak down tester with the hose the has the correct threads for the spark plug holes. I finally tested my '16 Axys last week. Their instructionss state to get the engine to operating temp. The air supply must be over 105psi but not to exceed 175psi. Remove the spark plugs. I used a piece of welding rod to check for TDC. Screw the hose into the spark plug hole. Set/zero the gauges to their specs. Close the ball valve then connect the hose to the tester. SLOWLY open the ball valve. Adjust the input (left) gauge to EXACTLY 100 psi. Then the right gauge will give you your leak down reading. The crank did turn a little bit but stopped. The readings I got were 98psi on the PTO cylinder and 98.5 psi on the mag cylinder. They state that the leak down should be somewhere between 3-5% (fresh engine) and 20-30% (very tired engine). While testing, I did rotate the crank a little bit to see what would happen. Where the crank stopped when pressure was supplied was the best reading.

Longacre Racing Digital Leak Down Tester

 

[volcano buster]

I used an old spark plug that I knocked the porcelain out of and a piece of 3/8" all-thread to make a piston stop for the side not being tested. Being that it is a 24 thread/inch pitch, I put a large fender washer on top marked in 1/3's so I could keep track of the reading as I lowered the piston being tested. My theory was, that I wanted to know the leak down as the rings moved away from TDC until they reached the transfer port and the value would drop to zero. Whether it mattered or not, I have that option and this might show a tapering effect in the cylinder allowing the ring gap to expand.

 

[mt.sledder]

I used an old spark plug that I knocked the porcelain out of and a piece of 3/8" all-thread to make a piston stop for the side not being tested. Being that it is a 24 thread/inch pitch, I put a large fender washer on top marked in 1/3's so I could keep track of the reading as I lowered the piston being tested. My theory was, that I wanted to know the leak down as the rings moved away from TDC until they reached the transfer port and the value would drop to zero. Whether it mattered or not, I have that option and this might show a tapering effect in the cylinder allowing the ring gap to expand.

That’s definitely taking a leak down test to the next level.

 

[madmax]

That’s a pretty cool idea for leak down testing.