I don't have an immediate need (knock on wood), but am always tool shopping. What make/model compression, and/or leak down tester(s) do folks recommend? Post your choice, and why.

Thanks in Advance!

 

I purchased mine years ago through the eastwood catalog. As things are, its probably not the same one offered now. I briefly searched and found they run from 30-75 bucks and even a bit more nowadays. I can't comment on brands, but if it has a hard case for storage, I'd consider that a bonus. Also, I'd shy away from Harbor freight stuff.

 

I couldn't find my old Milton tester and bought one from Harbor Freight because I needed something in a hurry. It was cheap and works OK. Fortunately I've since found the good one.

Of course, that's usually the fastest way for me to find a lost tool. No sooner do I step into the shop with the new one, but the old one pretty much falls from the sky and lands at my feet. Frequently, that happens as soon as I hit ENTER on the web page to buy the new one.

 

For a compression tester, I've been using a Snap-on MT 308 JB. It has two 18mm and six 14mm adapters. The gauge goes to 250 PSI. I like the versatility; it fits everything I have. I also like the length of hoses; they help with those cylinders in the back near the firewall that are more difficult to reach. I've never checked the gauge calibration, but it seems reasonable. The biggest problem I had with it was that the clasp on the case broke off. I made a big rubber band from an inner tube to re-rig it.


Snap-on MT 308 JB case with home made rubber band



Snap-on MT 308 JB

 

1. Yeah, I like the Snappy compression testers. I have two. Also a couple of Actron or some other import jobs. Once I assured that they all read the same when compared against each other, I screw 'em into every other cylinder in the firing order, test four cylinders at a time. Then, test the other four. The Snappys I bought intentionally, the Actrons or whatever they are, were part of a big eBay lot that I bought for some of the other items, the compression testers were a bonus. The trick with compression testers is to verify that the gauges are accurate and repeatable. I built a Tee that I connect to my "shop" compressed air system.



Then I connect the compression testers to the tee using the "M" "Industrial Interchange" coupler plugs. If both gauges read the same, and the same as the gauge on my regulator, I'm reasonably sure that they're all accurate.




2. Leakdown testers vary so widely that the tester used has as much influence on the gauge readings as the actual leakdown of the cylinder. There are NO legal regulations, or "industry standards" for the performance of an automotive leakdown tester; so there a huge range from "total junk" to "very nice"; and the indicated results vary greatly...

...HOWEVER, the Federal Aviation Administration (FAA) has set two design standards for aircraft cylinder leakdown testers; and the one for 5" or smaller cylinder bores works just fine with automotive engines. Continental/Teledyne demands yet another improvement, the "Master Orifice". In short, it's a way to verify the calibration of the leakdown tester by using it on a known, calibrated "test leak". The "Master Orifice" can be built-into the tester, or made as a separate item.

My first leakdown tester--which I used for over twenty years--is a Snap-On MT324. Single-gauge unit, the gauge is calibrated in percent leakage. The thing seemed exceptionally sensitive up to the point where I took it apart and cleaned-out the internal orifice; now it's nicely consistent with the tool I'm actually going to recommend:

The Aircraft Tool Supply (ATS) dual-gauge leakdown tester with Master Orifice, for engines with 5" or smaller bore size. This is an FAA-compatible, Continental/Teledyne compatible tool. It normally ships with an 18mm spark plug adapter; I told them I wanted a 14mm (standard automotive) adapter instead. I got it on Amazon years ago. The quick-coupler is a standard "Industrial Interchange" (Milton "M") so it'll work with most quick-coupled compression tester hoses if you remove the valve core from the compression tester hose. The similar tool on Amazon now comes with a molded plastic case, and a long-reach adapter. It might be that ATS will sell the bare tool + stubby spark-plug adapter, like I bought; and for less money than what's listed:


Mine:

 

Oh, yeah. If your cylinder leakdown tester doesn't have a "Master Orifice", you can make one and just keep it handy so that you can test the tester before each engine you use it on. I'm told that a Holley main jet of a certain size works well for the actual orifice you build into the "Master Orifice" unit. I forget which size main jet.

If you don't have a master orifice, you MUST MUST MUST use your leakdown tester on at least one "known-good" engine of approximately the same bore diameter as the one you really want to test. Because the internal orifices vary with the brand and model of leakdown tester, the results can be all over the map. Test the same engine with five different leakdown testers, get five different results. You need to know how YOUR tester reacts to "good" engines before you can be sure what a "bad" indication looks like.

Some guys say that--for example--20% leakage is acceptable for a "grandma" car, 10% is acceptable for a high-performance car, and 5% is acceptable for a race car. Holy crap, my old Snap On MT324 would show 40 or 50 percent leakage on engines that ran perfectly fine. I used to regularly see 80% leakage on "151 Iron Duke" engines; although they were pretty lazy and low-powered. That Snap-On tester just showed high leakage on EVERYTHING. If I paid attention to the magazines, I'd have considered every engine I ever tested to be failed. No, that particular tester was just very sensitive, and I had to "get used to it".

 

Thanks, guys. I really appreciate the additional information regarding usage, accuracy, etc. These points are exactly what I need to know before I spend good money on a device that is likely to outlast me, and wind up in one of my kids' tool boxes. Joe, what are your thoughts on the HF unit?

 

I question the accuracy, but it's fine for a cylinder-to-cylinder comparison or if you are trying to locate the source of a leak (ie, listening for leakage from the radiator or crankcase to find a blown head gasket).

 

Thank you.