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| xs650 > > Motorcycle Systems > > Engine > > compression test,hot or cold motor?! |
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compression test,hot or cold motor?!
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smearny
Full Member
Joined: Aug 13, 2009
Posts: 88
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 Posted: September 18, 2009, 2:00 pm Post subject: compression test,hot or cold motor?! |
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| and what to do with the loose sparkplug?! hold it onto mass?!
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xsjohn
Full Member
Joined: Jul 30, 2006
Posts: 5857
Location: North Carolina USSA
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| Posted: September 18, 2009, 3:13 pm Post subject: Re: compression test,hot or cold motor?! |
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Could be carbon that you might could see down a plug hole...small focused light and maybe scratch around with a screwdriver...or maybe someone (PO) lowered the deck.......I got tired of the 150 myself and went to 135 for a smoother ride and all around running......
xsjohn
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xsjohn
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Joined: Jul 30, 2006
Posts: 5857
Location: North Carolina USSA
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| Posted: September 18, 2009, 3:17 pm Post subject: Re: compression test,hot or cold motor?! |
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Couldn't edit the last message for some reason..........
Cranking compression at 150 is pretty much normal.......suppose if you get it running on a warm engine on one cylinder with the guage in the other hole it would go higher.............
xsjohn
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Joseph
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Joined: May 22, 2007
Posts: 767
Location: NY
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| Posted: September 18, 2009, 5:24 pm Post subject: Re: compression test,hot or cold motor?! |
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Just curious, what loose spark plug, and what is "hold it onto mass"?
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Joeymountain
1980sg |
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gordo
650Rider Supporter
Joined: Oct 09, 2008
Posts: 559
Location: CT.U.S.A.
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| Posted: September 18, 2009, 5:39 pm Post subject: Re: compression test,hot or cold motor?! |
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I do believe he's talking about the plug's that are removed for testing the compression. Holding on to mass I interprete as holding it up against the engine A warm engine is the prefered way according to the Society Of Automotive Engineer's, (SAE). A warm engine turn's over easier, & the part's have expanded to 'running' spec.
However, I feel that a 'cold' engine give's a truier reading, getting the result's of the pre-expansion reading's.
If you've got a burnt valve or holed piston, it won't make any difference anyway.
But a warm engine will give better reading's for your ring wear. The oil put into the cylinder's will flow better.
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'80 G, |
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Joseph
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Joined: May 22, 2007
Posts: 767
Location: NY
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| Posted: September 18, 2009, 6:33 pm Post subject: Re: compression test,hot or cold motor?! |
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"I do believe he's talking about the plug's that are removed for testing the compression. Holding on to mass I interprete as holding it up against the engine"
Ok got ya thanks, I was thinking the plugs would be disconected which is what threw me off.. .. when doing a compresion test does it mater if the other plug is in or out? I was thinking both of them would be out.
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Joeymountain
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xsleo
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Joined: Oct 28, 2007
Posts: 1528
Location: Earlville NY
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| Posted: September 18, 2009, 11:31 pm Post subject: Re: compression test,hot or cold motor?! |
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A warmed up engine, both plugs removed, Leave bike turned off, hold throttle and slides full open, Kick over with kick start 3 to five times. This should give you a good reading.
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"You live more in five minutes on a bike than most people do in there whole life"
'75 XS650B with a 79 dual disc front end, rear disk brake, Chrysler reg, Radio Shack rect, LED tail/ brake and turn signals. |
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smearny
Full Member
Joined: Aug 13, 2009
Posts: 88
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| Posted: September 19, 2009, 1:48 am Post subject: Re: compression test,hot or cold motor?! |
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| sorry,that was stupid.i meant with the ignition on,i heard that somewhere...but why?!doesn't make sense,off should be fine as well.
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gordo
650Rider Supporter
Joined: Oct 09, 2008
Posts: 559
Location: CT.U.S.A.
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| Posted: September 19, 2009, 5:29 pm Post subject: Re: compression test,hot or cold motor?! |
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If you leave the key off, you won't have to ground the plug's to the engine, 'cause there's no spark. Like Leo stated, warm engine is best.
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