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#12481268 - 10/27/17 01:16 PM performing a compression test
joho5 Offline
Extreme Angler

Registered: 07/03/08
Posts: 2823
Loc: Abbott, TX
Can the kill switch just be pulled? vs grounding spark plug wires.

If not, then how do you ground the wires when administering a compression test?

Im thinking that pulling the lanyard thats connected to the kill switch kills the ignition electrical system and that would be sufficient.

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#12481274 - 10/27/17 01:24 PM Re: performing a compression test [Re: joho5]
Muzzlebrake Offline
Extreme Angler

Registered: 12/26/14
Posts: 1605
Loc: Euless
I pull the plugs and then put them back on the wires and let them hang. Never had a problem hurting the ECM this way. Plus you can see it it's getting a spark.
_________________________
From Genesis: "And God promised men that good and obedient wives would be found in all corners of the earth."

Then He made the earth round...and He laughed and laughed and laughed!


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#12481374 - 10/27/17 03:11 PM Re: performing a compression test [Re: joho5]
joho5 Offline
Extreme Angler

Registered: 07/03/08
Posts: 2823
Loc: Abbott, TX
I did this one time a long time ago and the mix of gas that came out of the plug hole was ignited by the spark and sent a huge temporary fire on my carport wall!

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#12481448 - 10/27/17 04:25 PM Re: performing a compression test [Re: joho5]
gary purdy Online   content
TFF Guru

Registered: 05/24/03
Posts: 11195
Loc: Littlefield Tx & Lake A. H. US...
Pull the kill switch, pull all of the sparkplugs and move the control to full throttle then check each cylinder.
_________________________
The world will not be destroyed by those who do evil, but by those who watch them without doing anything. Remember what He has done and remember that He is not done yet!-- GOD IS GOOD

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#12481750 - 10/27/17 09:43 PM Re: performing a compression test [Re: joho5]
Gamblinman Online   content
Extreme Angler

Registered: 11/26/02
Posts: 2936
Loc: Yantis, TX
Engine should be warm, all plugs removed, throttle wide open. That said, a compression test is a preliminary test. To determine actual performance, a leakdown test should be performed.
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Texas Crappie Posse

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#12481865 - 10/28/17 05:04 AM Re: performing a compression test [Re: joho5]
TLW Online   content
Extreme Angler

Registered: 11/16/06
Posts: 2236
Loc: ft worth
gonna be piddlin' with tha motor yourself invest ina remote start button.. you'll be glade ya did.

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#12481926 - 10/28/17 07:33 AM Re: performing a compression test [Re: Gamblinman]
Muzzlebrake Offline
Extreme Angler

Registered: 12/26/14
Posts: 1605
Loc: Euless
Originally Posted By: Gamblinman
Engine should be warm, all plugs removed, throttle wide open. That said, a compression test is a preliminary test. To determine actual performance, a leakdown test should be performed.


On a 4 stroke the leakdown is the most important.
100 psi is applied to a combustion chamber (via the spark plug hole) with both intake and exhaust valves closed. If the cylinder holds 95psi, it will show 5% leakdown on the gauge.

It can tell you if:
Exhaust valve is leaking (most common on these engines, if there is excessive leakage)
Intake Valve is leaking
Piston Rings are leaking

Leakage via a valve can also be caused by carbon buildup on the valve seat, most often on the exhaust valve. This could mean valve guides and seals are excessively worn... but not always.

In general, it can give you a good picture of overall engine health.
It cannot tell you if valve guides are shot, however, if guides are badly worn then the valve will "wobble" resulting in wear to the valve and/or valve seat over time.

A leakdown test on a 2 stroke is much more complicated and will require some special tools and methods but is just as important in determining the engines' health. https://www.duncanracing.com/TechCenter/2stk_presstest.pdf
_________________________
From Genesis: "And God promised men that good and obedient wives would be found in all corners of the earth."

Then He made the earth round...and He laughed and laughed and laughed!


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#12483096 - 10/29/17 09:14 AM Re: performing a compression test [Re: joho5]
gary purdy Online   content
TFF Guru

Registered: 05/24/03
Posts: 11195
Loc: Littlefield Tx & Lake A. H. US...
Where did this post go from asking about a simple compression test to a space rocket launch? roflmao
_________________________
The world will not be destroyed by those who do evil, but by those who watch them without doing anything. Remember what He has done and remember that He is not done yet!-- GOD IS GOOD

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