Calling all leak down detector experts

[Reinman]

I’m new to using this - so did my first test. Found an old B&S lawn mower, hooked up leak detector, set to TDC, put in 70lbs of air. Here is what I got.

25lbs out
Feel air coming out of muffler - not a lot
Feel air coming out of carb - a little more.

Any diagnosis?

 

[Rivets]

Did you make sure the crankshaft did not move when you did the test?

 

[Reinman]

Did you make sure the crankshaft did not move when you did the test?

yes - it wasn’t moving

 

[Rivets]

Good, couple more questions. What did the gage say was the leak down percentage? I like to put a 100 lbs of pressure if I can then see if I’m in the green range. Any leakage passed the valves is not good. Did you have the crankcase open, oil cap off, could you hear air coming out the this opening. A leak down test will tell you how well the cylinder is sealed and if there are leaks, where are they coming from.

 

[StarTech]

This why I like my low pressure leak down tester. If you don't lock down the flywheel on the high pressure version you actual get hurt by the spinning flywheel. Also with low pressure version you can disable the OHV valve train and test other parts of the piston stroke in cylinder instead just the TDC. Places like middle of the stroke and BDC.

My low pressure leak down tester actually operates at 12 psi which you hold and move the piston though out the stroke.

Also on many engines and especially Briggs you need to be 1/4" down pass TDC compression on the piston position. This so the ACR doesn't interfere by having a valve cracked open.

 

[Reinman]

Good, couple more questions. What did the gage say was the leak down percentage? I like to put a 100 lbs of pressure if I can then see if I’m in the green range. Any leakage passed the valves is not good. Did you have the crankcase open, oil cap off, could you hear air coming out the this opening. A leak down test will tell you how well the cylinder is sealed and if there are leaks, where are they coming from

Good, couple more questions. What did the gage say was the leak down percentage? I like to put a 100 lbs of pressure if I can then see if I’m in the green range. Any leakage passed the valves is not good. Did you have the crankcase open, oil cap off, could you hear air coming out the this opening. A leak down test will tell you how well the cylinder is sealed and if there are leaks, where are they coming from.

Sorry - just saw this, for some reason I am not getting notified on activity on my account. I have a OTC 5609. Crank case wasn’t open, oil cap off. Air seems to be leaking out of the Carb tube. Like I said 70lbs (which is what I was told never to do over) in and 25lbs out.