View Full Version : Good compression and leak down tester

03-27-2017, 04:12 PM
Hey guys.

I have (three actually) compression testers. I trust none of them. One is at least as old as me, and the hose is shot. That's an easy fix but 50+ year old lubricants in a gauge does not enhance accuracy...

But the point is I'd like to find one (or I'll make it if I have to) that holds max pressure- in other words, one with a one-way valve so if you stop cranking with any valve partially open (which is pretty easy to do) you won't loose your reading. Unless you have a helper to crank and you stare at the gauge old school ones are not practical to me at least.

I also want a leakdown tester, which I don't currently own. Any suggestions for a good quality (that means accurate to each other gauges) anyone can suggest? Similarly, I'd like to have an isolator valve for the compressed air input. Once the (closed) cylinder is filled, you read on the second guage to determine pressure drop. Testing at 100PSI is the easiest way, because dropping to 80PSI tells you you are at 80%. No math really. I could modify a cheaper one too but I don't want to go too cheap as at that point I might as well make the whole thing from scratch.

Looking at Snap-On (because I'm a third-generation fan-boy) but I don't think those do what I want either... And the "read" gauge is color coded rather than pressure. It does have hash marks for pressure but why bother? Plus it is $200+ and looks much like $40 ones on Amazon...

I may end up making them from scratch if I can't find what I want if anyone is interested. In that case I can get crazy with calibratable precision gauges if you want. I've found 0-200 PSI gauges with 3-2-3% accuracy for ~$20 each with a metal case. So that's 2% at mid scale (100PSI) and 3% at zero and 200PSI. 10:1 compression would be about 150PSI so I may need to go higher on pressure. For the leak down tester, you just need two gauges that behave similarly. So if you dead-end the cylinder connection and add pressure, both gauges should read the same thing. You don't actually need absolute pressure in that case, just comparative pressure.

For the compression tester, you do need accuracy. Also a bar scale as well as PSI is useful because 10 bar equates to 10:1 compression. Again, no math to deal with.

1% full scale gauges are hundreds of dollars each...

Sorry to bore you guys... But any input/suggestions welcomed.

03-27-2017, 07:24 PM
I have 2 compression testers, one at work and one at home. Both are Autozone specials and work well. They do have a check valve that will hold the reading until you release the pressure manually. I can't chime in on a leakdown tester, as I've never needed one. If a cylinder has low compression, I generally just put a air hold in it and listen for where the air is coming from. Just my $.02.


03-28-2017, 12:58 AM
Yeah I think that is the easy answer.

I'm going to check my compression gauges and find one I can trust. Replace the hoses and go from there.

I'll probably end up making an over-engineered tester for myself at some point out of all the bits.