What do you call "good" leak down test results?

[outboardnut]

Finally got a leak down tester! Been using compression for years, now I'm moving on up to doing both.

I've been testing at 50 PSI but am thinking about getting a different gauge so I can test at a lower number to make holding the motor while testing easier. Some of my motors are testing around 10% leak and some are around 15%. One motor that is a suspected problem child is up around 35% leak.

Where do you draw the line and say "this is bad"? What PSI's do you like to test at?

 

[tashasdaddy]

Re: What do you call "good" leak down test results?

leak downs are not really great on 2 strokes. you have to get the piston in the perfect position. the lower unit is the best thing to use it on.

 

[rodbolt]

Re: What do you call "good" leak down test results?

I prefer a leakdown test over a compression test any day of the week.
industry standard for 2 strokes is about 10% max,four strokes about 15% but it depends on where the leakage is.
2 strokes can be a beast to set the piston correctly.
I have made a few tools for various models that will hold the flywheel in place.
on two strokes i dont reccomend trying to hold the flywheel with a breaker bar,it may break your jaw.
dont ask.
a leak down test simply measures the ability of the cylinder to seal.
inject a known air pressure,measure the amount of make up air needed to maintain the known air pressure in the cylinder and convert it into a percentage.
my tester is calibrated in PSI and the second guage in percent.
industry standard is 100 PSI input and monitor how much makeup air is required to maintain 100 PSI in said cylinder.

 

[outboardnut]

Re: What do you call "good" leak down test results?

I'm not really having trouble with piston postion.
I experimented around with a breaker bar on the crankshaft nut, and as long as I'm past the ports, they seal up and I can get a reading. I can turn it and it will fluctuate a little but I can get a pretty good idea. The reading really isn't changing much up and down the cylinder unless you are in the ports.

I'm running at 50 pounds and it seems like to much, the motors can get lively with the air on the pistons.