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Thread: Compression tester

  1. #1

    Default Compression tester

    I'm going to buy a compression tester and was curious about opinions on the $30 range. A buddy of mine has the Napa unit and it seems pretty good. I also see Home Depot has a Lisle brand tester for the same amount. Does it really matter?
    2020 TE300i

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  3. #2

    Default Re: Compression tester

    I don't think so I still use my 40 year old Craftsman.
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  4. #3
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    Default Re: Compression tester

    I'd trust a Lisle brand tool, and most Napa brand stuff. Sound like good choices.
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    Default Re: Compression tester

    I agree with the above. I have an old Craftsman gage, but use a Snap-On hose with the proper spark plug thread. I have no way to test accuracy, but believe it to be consistent. I use to compare differences in compression from previous readings on my 2 stroke or differences between cylinders on my street bike or lawn mower.

  6. #5

    Default Re: Compression tester

    I went through this a few years back and picked up a very low cost ($25) no name China made compression tester and it was worthless providing readings that were not close to ballpark. A mechanic friend of mine recommended OTC brand at a $90 price point and it works much better.
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  7. #6

    Default Re: Compression tester

    Quote Originally Posted by nycresearchrat View Post
    I went through this a few years back and picked up a very low cost ($25) no name China made compression tester and it was worthless providing readings that were not close to ballpark. A mechanic friend of mine recommended OTC brand at a $90 price point and it works much better.
    Had a similar experience.

    Accurate readings normaly require quality brand tools.
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  8. #7

    Default Re: Compression tester

    I purchased a cheap and nasty compression tester tool recently, I tested the gauge using an air compressor and it matches up quite well with the gauge on the compressor, the problem that I've got is that the 'one way valve' that holds the pressure that the gauge reads is up near the gauge and there is about 20 inches of tube that leads from the sparkplug hole adaptor to the gauge, all this extra volume is 'added' to the combustion chamber volume which effectively lowers the compression ratio.

    My crappy gauge reads 130 PSI when cranking my engine on the starter motor with the throttle wide open. There is no way the pressure is this low because I know that the piston/rings and bore are all in very good condition. I have a leak down tester, I might give that a go. I might try to modify the compression tester too.

    EDIT....

    Just been out to take a closer look at my compression tester, in fact the one way valve was about half way down the rubber tube at the point where two tubes join together, I managed to eliminate half of the tube so that the one way valve is much closer to the engine, I now get a reading of 160 PSI so it just shows that simple things can make a big difference!

    160 is still a bit low but I have a brand new piston and rings in the engine with only a couple of hours on the clock, hopefully they just need bedding in. I have also done a bit of work on the head, I closed up the squish gap but maybe a took a bit too much material out of the combustion chamber, I can sort it out on my lathe if the PSI figure remains low.
    Last edited by Sidecarbod; 05-23-2020 at 09:32 AM.

  9. #8

    Default Re: Compression tester

    Had the same issue. You need one with the valve (looks lkke the valve core inside a schrader valve on tubes) at the end of the hose that goes into the spark plug. Ideally the part of the hose that threads into the head is the same length as your spark plug but i think that just changes a couple of psi.

    Cheap $30 ones gave me a reading of 90psi.... Gave up and got an OTC anf got a reading of 210psi...

    Fitted the cheap gauge to the hoses from the OTC kit (modding might be required) and it read 210+- psi as well.

  10. #9

    Default Re: Compression tester

    I looked at the OTC compression testers and see that it comes with Schrader type valves. Do they trap the air in the combustion chamber at the fitting? How is that more accurate than the other types? The Napa tester is made by Innova which gets good ratings. So does the Lisle brand. It doesn't appear that these are cheap Chinese brands. Educate me why I shouldn't buy one of these.
    2020 TE300i

  11. #10

    Default Re: Compression tester

    One thing to note on 4 strokes are they have a built in decomp and rarely should go over 115 psi, mine was 150 and was told by DJH I adjusted the valves wrong readjusted and had 115. Just in case any 4t people are posting.
    present bikes
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    2006 KTM 400 EXC
    1999 Kawasaki Concours
    1983 Husqvarna 250WR
    1968 Honda CT90 trail 90
    1971 Suzuki RV90
    1964 Honda CT200 Trail 90
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