Compression tester

Been working away an a 2n lately, and along with working on the snowmobiles, decided it's time to get one. Figured I've got a good collection of tools thanks to Daleinwv and Brad Gyde, so I'll get a compression tester. I see a couple for around $20-$30. Friend has the harbor freight one. Junk. According to it no engine in the world has above 60 PSI. So anybody had any experience with the cheaper ones? And if so which would you recommend? I see them at Sears, Walmart, and Autozone.

I got one at O'Reilly's years ago and it has been good and the cost was not all that bad. I would stay away from auto clone and go to O'Reilly's or Napa for one at either one the warranty is likely to be life time

Send me an email. I have several extra ones that I will give some one that uses one.

Just a thought ? Wonder if the one you saw was reading in BAR instead of PSI ?

Working on snowmobiles? Tell you what. I've got five of them, all vintage 1970s. They are for sale and I will throw in a compression tester for free if you buy them. Email me at [email protected]
Loko

That crossed my mind a couple times. So went out and checked again. Nope. Been using the flexible hose though, and in the reviews, some guys say that their flexible hose gave low readings and the solid tube worked. I'll have to try that later today.

Sears

If you are looking to invest some money, might be interested in a "cylinder leak down tester". A little more money, about $80, and require compressed air to operate, but will be much more useful for diagnosing a problem than a simple compression test. This will actually tell you where the leakage is.

[color=blue:73ccd16d2d] According to it no engine in the world has above 60 PSI.[/color:73ccd16d2d]

Did you have throttle plate wide open when doing test? If you can't get air in you can't compress it.

The problem with that is the needing a compressor part.

I had seen those, and wondered about them. Didn't realize they require a compressor. Doesn't matter, my Dad has a 8 gal HF one that's been getting some use lately. Is it still in general a screw in and get the compression just get more then find out how much compression it has?

Yes, it screws in the plug hole, then puts air in the cylinder. It calculates the percentage of leakage wit 0% being ideal (that will never happen though).

The best part is you can then listen for the leak, out the intake or exhaust, it's valves. Out the crankcase it's rings/piston. Out the radiator it's head/head gasket/cracked liner.

The down side, you have to make sure the valves are fully closed as it will try to turn the crank to BDC and the ex valve will begin opening. You have to lock the crank or back off the valve adjustment. Also be sure it comes with the adapter you will need. Some of the older engines used the large plugs.

Yep, throttle open all the way. 60 PSI.

I bought one at Farm/Fleet about 45 years ago, has 2 tips and it expands the tip as soon as the eng. starts to crank, just push it in, no screwing involved. I always hooked up a remote start button under the hood and could check the comp. by myself in about 10 minutes or less, worked slick.

I have several compression testers. As a kid I bought a Gilbert Davis Instrument, (still use it) with a very short, angled metal tube attached to the gage. At the end of the metal tube is a tapered rubber cork which is pushed into the spark plug hole to obtain the reading. The rubber cork works good on lower compression engines however, it is prone to leak at high compression levels. Also, it requires one person to hold it in the plug hole and some times one to crank the engine.

My Snap-On tester has fittings that screw into the spark plug hole and uses snap connectors to attach the hose/gage. This arrangement insures a leak proof seal against high compression pressure and leaves you free to crank the engine.

I have a fancy schmancie K-D tester with a starter switch attached and self expanding rubber fittings at the end of long hoses that go into the spark plug holes. The expanding rubber plugs can leak and some times are hard to remove from the plug hole. The long hoses allow use in hard to reach places and the starter switch is a nice feature.

Since the volume of the compression tester gage, hose and fittings adds to the trapped volume at TDC it can reduce the measured compression pressure. To correct for this a check valve is typically used within the fitting that goes into the spark plug hole. As the engine is cranked the reading will increase as this volume is filled. Once the reading is taken the pressure trapped in the gage is released by opening the check valve.

In short the pressure gage can be checked against another gage however, the other fittings are what makes for a good compression tester.

You're not the only one with the harbor freight compression tester issue. Bought 2 of em at Christmas time for my 2 cousins that help me bale straw in the summer (chose the hf ones because it was the only one I found with the small adaptors that their dirt bikes use.. Never have I saw a spark plug with that small threads!) anyhow, neither of those register right.. Traded them in for new ones, but haven't heard if the replacements work right or not.

The compression tester I have is a Actron brand, I believe. I don't recall where I bought it anymore, but I bought it when I got my first truck (20 years ago). I'm sure there's nicer ones, but has worked for me on the many trucks, tractors, snowmobiles, and quads I've played with. I believe it's fairly accurate, and must be decent quality if it's lasted this long.

Brad

Replace the Schrader valve core with one for a compression tester. A standard tire valve core will give you very low readings. Learned the hard way.
Check with your automotive parts supplier.

Sent ya an email.