Leak Down Tester

[Bob Cowan]

I'm trying to chase down a engine problem. Compression was good and consistant.

My next step would be to pull the heads off and inspect everything. That's 10-12 hours of work, and about $250 or so - head gaskets are not cheap.

I wanted to do a leak down test before tearing into the engine. If compression and leak down are good, it's probably not an internal engine problem. Probably.

I looked all over town, and couldn't find a leak down tester. Checked all the parts stores, tool shops, Sears, even harbor freight. Nobody had one sitting on the shelf.

I could order one, and it would get here by tuesday or wednesday, and cost around $125'ish. Being the impatient SOB that I am, I decided to make one. I had to go to Home depot, lowes, and ace hardware to find everything I needed. Cost was about $35, including the #60 drill bit (which only Ace had).

Not my idea, I found the instructions on you-tube. It took longer to shop around and find all the parts than it did to actually build it. It works like a charm. Found out my leak down is 10-15% in all cylinders. Excellent. Within a couple hours I had eliminated a lot of potential problems.



The hose is from my compression gauge, it has a standard air chuck on the end.

Now I can move on to other things.

[CraigS]

Excellent but you forgot the link to utube so we could build one too!!

[dv/dt]

Originally Posted by CraigS

Excellent but you forgot the link to utube so we could build one too!!

I had posted these links a while back, may be the same ones.

Cylinder Leak Down Tester,How To Build - YouTube

Cylinder Leak Down Tester,How To Build - YouTube

Automotive Cylinder Leak Down Test - YouTube

Automotive Cylinder Leak Down Test - YouTube

Cheers, Rod

[Bob Cowan]

Yup, those are the ones I came across. Pretty simple and worth doing if you're having any engine troubles.

I still can't pin point my troubles. I may end up taking the heads off anyway.

[Bob Taylor]

Bob sounds like you and I are a lot alike . I think the impatience is just part of being a "Bob" keep us posted! Bob

[GWL]

Excellent Bob,

I always enjoy reading your posts. Always something new to learn.

George

[CraigS]

Thanks, I saved the links!

[canuck1]

Interesting. I've used a dual gauge leakdown tester before but never really looked closely at how it's put together.

What is the function of the 'damper valve' (the plug he made from JB Weld and then drilled with the #60 bit)?

Sean

[Wade Chamberlain]

Originally Posted by canuck1

Interesting. I've used a dual gauge leakdown tester before but never really looked closely at how it's put together.

What is the function of the 'damper valve' (the plug he made from JB Weld and then drilled with the #60 bit)?

Sean

it's a restriction between the two gauges. You're essentially measuring the pressure drop across the orifice.

[Greg_M]

The damper valve is a restrictor to let a measured amount of air through to the cylinder. The amount of air that leaks and the limited supply from damper makes the gauge drop and read a percent loss or you can calculate it based on 100 psi inlet pressure.

Here's a question for the brain trust. How do you know a #60 hole provides the accurate amount of air reduction for every engine size? Taking two extreme examples, one being a lawn mower with a small displacement and the other being a 502 V8 engine.

A healthy 502 will leak a larger volume of air than the the mower simply because the 502 has a larger piston (ring surface area). Therefore a tight 502 with a true 5% leak might register 10% and a tired lawn mower that's blowing past the rings might also measure 10% with the same tester.

What inlet pressure is optimum? I have a dual gauge Tavia tester and noted a 12% loss at 50 psi and a 5% loss at 100 psi. Some say a higher pressure is better for testing the rings since they seal harder with more cylinder pressure.

Greg

[dv/dt]

Good explaination here:

Leak-down tester - Wikipedia, the free encyclopedia

[Greg_M]

Originally Posted by Greg_M

Here's a question for the brain trust. How do you know a #60 hole provides the accurate amount of air reduction for every engine size? Taking two extreme examples, one being a lawn mower with a small displacement and the other being a 502 V8 engine.

A healthy 502 will leak a larger volume of air than the the mower simply because the 502 has a larger piston (ring surface area). Therefore a tight 502 with a true 5% leak might register 10% and a tired lawn mower that's blowing past the rings might also measure 10% with the same tester.

Greg

DV/DT thanks for the link. It answered my question:

There is no standard regarding the size of the restriction orifice for non-aviation use and that is what leads to differences in readings between leak-down testers generally available from different manufacturers. Most often quoted though is a restriction with a .040in. hole drilled in it.(Some poorly designed units do not include a restriction orifice at all, relying on the internal restriction of the regulator. A very unstable standard.). In addition, large engines and small engines will be measured in exactly the same way (compared to the same orifice) but a small leak in a large engine would be a large leak in a small engine. A locomotive engine which gives a leak-down of 10% on a leak-down tester is virtually perfectly sealed while the same tester giving a 10% reading on a model airplane engine indicates a catastrophic leak. The non standard size of the restriction orifice determines the reading which therefore differs for each design.

So the reading is important as far as variance between cylinders. If the reading is low you can hear where the air is going. It does not prove an absolute diagnosis for ring sealing on every engine unless the builder specifies the damper size.

Greg

[dv/dt]

Yeah, it basically assumes your cylinder will have the equivelent of a 0.040" holes worth of leakage. As long as it is less than this then the pressure should stay at whatever your test pressure is since it can't leave faster than it is coming in. If it is leaking more than that then you'll see a pressure drop. Using 100 psi makes it easy to calculate the percentage.

But it is a relative test so if you tested your motor just after it is broke-in you would have values to compare it to down the road (as long as you use the same tester or at least one with the same orifice size).

Cheers, Rod

[canuck1]

Originally Posted by Wade Chamberlain

it's a restriction between the two gauges. You're essentially measuring the pressure drop across the orifice.

OK, but in a conventional two gauge setup, isn't the orifice between the two gauges? In the video he relied on the gauge at his compressor regulator, then through another regulator and THEN through the orifice and the gauge where the comparative pressure drop is measured.

How would this impact repeatability/accuracy since the air must pass through a number of 'orifices' (regulators) between each of the two gauges?

I feel dirty typing orifices


Sean

[Greg_M]

I didn't watch the video but this is how it should be:


Greg