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Anyone know where to get a compression tester?

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Does anyone know where to get a middle of the line compression tester, the kind that actually screws into the cilinder?

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I got mine at Advance Auto Parts which is associated with O'Briens and Kragens. I don't know if they're the same company or not, but they're somehow connected.

$40 IIRC, buy the one with the extra spark-plug adapters, you never know if you're gonna need it.

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$29 at advance auto. Comes with adapters....

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If it's for a 2 stroke, all the above responces are perfect. If it's for a 4 stroke with automatic decompression, then you need a leakdown tester.

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it is for a four stroke, whats a leakdown tester? and are they also available at these auto part stores? I should have specified.

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Harbor Freight, two models available depending on how many plug adapters you need..

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A leak down tester requires you to set your motor at bottom dead center, then with compressed air you pressurize the compression chamber and it measures the leak. If you have excessive leak, you can track it down by listening for the hiss.

Harbour freight has on here http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94190

But you will need to buy the proper spark plug adapter from motion pro.

10mm adapter : http://www.motionpro.com/motorcycle/partno/08-126X/

12mm adapter: http://www.motionpro.com/motorcycle/partno/08-126Y/

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A leak down tester requires you to set your motor at bottom dead center, then with compressed air you pressurize the compression chamber and it measures the leak. If you have excessive leak, you can track it down by listening for the hiss.

Harbour freight has on here http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=94190

But you will need to buy the proper spark plug adapter from motion pro.

10mm adapter : http://www.motionpro.com/motorcycle/partno/08-126X/

12mm adapter: http://www.motionpro.com/motorcycle/partno/08-126Y/

I looked at that leakdown tester and have a question. It says the operating levels are 0-100 psi. Aren't most bikes supposed to normally operate with over 100 psi? Won't this affect the reading if it is not pumped up to roughly what the cylinder is supposed to hold?

Has anyone had luck with harbor freight stuff? I have heard mixed things about their products.

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I think the reason they use 100 psi is because it makes it easy to get a percentage of leakage rather than trying to calculate the percentage lost at say 176 psi. Not to mention my compressor only goes up to 125 so thats not much more.

As far as HF stuff is concerned. I do buy stuff there but my compression tester is Actron (what you can pick up at autozone and sears). I am sure the HF brand wont be as accurate as a snap-on but it gives you a general idea.

Now for my question. What I have always wondered is with a 4 stroke and a decompression release, can you unhook that release and do a regular compression test? will it harm anything by disconnecting the decompression release?

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No, the pressure fed to the cylinder doesn't need to match the compression reading since you're looking to see how much and where the air escapes.

Harbor Freight isn't that great for precision instruments IMHO. Great if you need a clamp or a hammer, pieces where precision isn't all that important.

I'm not sure why you were instructed to get a leak down tester instead of a compression tester, a CT will work just fine on a automatic decompression bike, either A: disconnect the auto decomp or B: kick harder so it goes through several cycles with full compression. If it's a manual decompresser, just don't use it when you're testing.

CT and leak down testers each have a good area of use, chances are for your average shade tree mechanic, a CT is all you really need.

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The reason why I recommended a leak down tester is because with a modern 4 stroke you need to jimmy rig the auto decompression open with something that most likely will fall off and eff something up within the cam chain area. And secondly, 99% of the time, with a 4 stroke you don't need to test for max compression, usually the reason why people are testing for compression is to see why there isn't any, aka a valve stuck open, which only a leak down tester will show. You could probably go hundreds upon hundreds of hours on a 4 stroke before you'll see a major loss of compression from the piston which is the only time in my opinion that a compression tester would be useful.

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