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Leak Down Gauge Search

Bart

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Ok, the normal context of leak down on a 2 stroke chain saw is piston tdc thru spark plug hole for rings, or block carb/exh and check case halves, gaskets and crank seals, impulse line or say tank and carb pressure holding or venting. On a newer 4 mix the valves come into play too. On a car it's intake, exhaust valves, head gasket rings. So normally you have inlet and outlet gauges in psi and you calculate percentage leakage. That's not in the sealed pressure/vacuum maintenance context which is slightly different, but same principle of checking sealing.

My current dilemma is on Briggs small engines the closest thing to a published spec is an unlabelled leak down tester #19413 which I surmise to have a 100 psi full scale inlet dial with target inlet pressure ticked off at about 60% full scale and the outlet gauge looks like 60 psi full scale, but is uncalibrated except for at about 50% full scale it goes from green to red (good/bad). So my question is, does any one have one and know if the 100 psi and 60 psi full scale assumptions are correct? If so, surprisingly Briggs is a-ok with a 50% leaking engine!! Could be, but its a tough one to believe.

thanks

my bad if this is a stretch from directly chainsaw related.
 

Marc-Antoine

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The different engine compartments have nothing as a real airtightness, but only a relative capability of holding the pressure (positive or negative). So you have to put the time in play, because 50% can be very acceptable if the test protocol asks for a long enough duration.
You get a slope with the datas. If it doesn't reach the reference level after a certain amount of seconds/minutes (I don't have a clue about the value), you're good to go.
The other way is to find the time needed to reach the say 50% loss for example.
Either ways, you have to find the value(s) mandated in the test protocol to get a valuable result.
 

Bart

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Thanks Marc, I get where you're coming from. My Mighty Vac is for crankcase, carb and tank testing where you hold vac/pressure for a specified time period My two-gauged leak down tester is meant for situations where it wouldn't hold real steady e.g. a 10% leakage rate spread between intake, exhaust and rings is common in the 4 stroke world. There's a calibrated flow orifice involved in the second tester.
 

sawcollector

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I put this leak down tester, 5910 850 0300, in Service for STIHL back in 2004. It is calibrated for small engines so it doesn't over pressure the engine like an automotive tester would.
See attached for instructions on using it for the STIHL 4-Mix engine as well as how to use it on two-stroke engine when doing a pressure vac test on the crankcase.
 

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Bart

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Maybe I'm a bad reader, but what is the inlet pressure set to the gauge by the regulator? My guess 100 to 150 shop air, tool regulates applied to about 50 psi? Bit smaller orifice in the tool to match smaller cylinder and valve sizes? I can see results dialing as low as 40 psi applied sometimes on mine.
 

sawcollector

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If you are doing a leak down test on a four stroke it doesn't matter what the shop pressure is, just zero the gauge before you hook it up and then read the percent of leakage and locate where with your ear. For a two stroke that is failing the vac pressure test on the crankcase, hook it to the spark plug hole with no air pressure applied, then slowly add pressure until you can hear where it is leaking. Does that answer your question?
 

Bart

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My question really is what psi is your "zero the gauge"? My unit is in psi after the regulator e.g. where you set your testing pressure. The FAA spec most equipment is based on is 80 psi applied and a 60 degree inlet 0.040"dia x 0.250 long calibrated orifice for 5" dia or less bores, although it allows to test as low as at 60 psi applied. The Briggs unit looks like it tests at 60 psi applied. On a calibrated second gauge a reading of 54 psi would be down by 6 psi, 6 psi/60 psi applied = 10% leakage, just using numbered gauges.
 
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