660 COMPRESSION TEST. - Yamaha Raptor Forum

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Old 03-14-2007, 06:13 AM   #1 (permalink)
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Default 660 COMPRESSION TEST.

This may be a silly question, but I will ask it anyway. I have problems with a 660 raptor. I did a compression test and only got 80psi. I thought about it later. ( after I had pulled it apart) How can I get an accurate compression test if the decompression mechanism on the camshaft is releasing the compression when cranking the engine. Or does the decompression pin retract under cranking revolution speed?
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Old 03-14-2007, 01:14 PM   #2 (permalink)
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Default Re: 660 COMPRESSION TEST.

the pin does not retract under cranking speeds (that's what its there for) but it does retract at running speeds.

chances are your battery will not spin the motor over with the decomp defeated but to do it, loosen the left(as you sit on the bike) exhaust valve adjuster, just back it out until it is flush with the rocker arm (on the bottom of the rocker arm) and tighten the nut back down. You need to remove the slides from the carbs to get a good reading too.
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Old 03-14-2007, 06:11 PM   #3 (permalink)
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Default Re: 660 COMPRESSION TEST.

I've always been told I should be getting around 130psi with the decomp in.
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Old 03-14-2007, 07:45 PM   #4 (permalink)
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Default Re: 660 COMPRESSION TEST.

Quote:
Originally Posted by Maddog56
I've always been told I should be getting around 130psi with the decomp in.
thats the right number alright
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Old 10-07-2011, 05:32 PM   #5 (permalink)
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I to got 80psi jwhat would be casing it to blow one header off and spiting out oil to?
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Old 10-07-2011, 05:32 PM   #6 (permalink)
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I to got 80psi what would be causing it to blow one header off and spiting out oil to?
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Old 10-07-2011, 11:12 PM   #7 (permalink)
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The header shouldn't be a factor, the exhaust valves should be sealing up on the compression stroke. But if it's "blowing oil" from somewhere that could certainly be a problem. Check your valve lash again and look for signs of a leaking valve stem seal or worn valve seats.
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Old 10-07-2011, 11:24 PM   #8 (permalink)
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80 psi with the decomp operating is about the minimum at which the engine will start and run - you likely have problems. Have you added a teaspoon of oil to the cylinder to see if compression goes up? If it does, this is an indicator of worn rings or cylinder wall.
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Old 10-08-2011, 08:02 AM   #9 (permalink)
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Try adjsuting the valves first and then retry the compression test, maybe you have tight valve clearance...........
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Old 10-08-2011, 10:09 PM   #10 (permalink)
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The oil is coming out of my crankshaft cover. i know i looked
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