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Main Area => General GS500 Discussion => Topic started by: Krav on May 18, 2015, 05:39:39 AM

Title: Compression question
Post by: Krav on May 18, 2015, 05:39:39 AM
Compression question.

So i did a compression test at cold (i read that cold or hot doesnt matter all that much) And here's the results:
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Right cilinder dry: 90 PSI
Right cilinder wet: 100 PSI
Conclusion right cilinder: Valve's or valveseat worn or broken.
Also possibly head gasket leak, but i don't hear it, so i dont think thats it.
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Left cilinder dry: 90 PSI
Left cilinder wet: 150 PSI
Conclusion left cilinder: Pistonring worn out.
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Im so guttered :S There's no way im going in for a head revision, not after the last time i tried to take out and refit the engine. It was such a hassle.

Got a chance to spot the spark plugs aswell:

Right:
(http://huis-ict.nl/wp-content/uploads/2015/05/20150518_123523-1024x576.jpg)

Left:
(http://huis-ict.nl/wp-content/uploads/2015/05/20150518_123617-1024x576.jpg)



Suggestions regarding this coloration? i'd say it could be a tad richer, but then again, im not completely confident when it comes to spark plug reading.
Title: Re: Compression question
Post by: Big Rich on May 18, 2015, 06:12:14 AM
Wow. What's the spec call for? Around 150 cold on both?

I can't speak for the GS500 in particular, but you may be able to pull the entire top end off (including cylinders) with the engine still in place. Again, I can't speak for the GS500,  but it is usually easier to pull the engine than trying to work everything out of the frame.
Title: Re: Compression question
Post by: gsJack on May 18, 2015, 06:14:44 AM
Did you hold the throttle wide open while checking compression?  Those look like closed throttle values, I checked my compression last year with 100k miles on my 02 and it was much better than that.  Actually about 140 psi in both cylinders before adding oil.

http://gstwins.com/gsboard/index.php?topic=67148.0
Title: Re: Compression question
Post by: gsJack on May 18, 2015, 06:17:07 AM
Right Rich, I pulled my 02 head with engine in frame.
Title: Re: Compression question
Post by: Krav on May 18, 2015, 07:29:06 AM
Throttle closed would give me around 45 psi per cilinder (tested to see how much of a difference it would make.)

Good to know that pulling the head of CAN be done in frame. I was thinking, i can buy a second hand head for 50 euro's and for 50 euro's more, i have a cilinder block. Maybe its worth buying a head and cilinderblock for 100 euro's, and build it on the bench. Make sure everything is tightly fit together, give it a nice paintjob. Make or buy a custom exhaust for it. Take my time, Taking it Slooooooooooooooooooooooooooow :p You knaw what im sayin!

Then again, in a year i'll get my full license, lifting me of the 35KW law. Then ill probably sell the Gs500 to get something with a bit more umpf. So i dont know if it'll be worth it.

Okay, a question. Given the compression i have, would i be missing out on a lot of horsies? This is my first proper motorcycle, so i have no referencepoint as to how fast this bike should go.



Title: Re: Compression question
Post by: Bluesmudge on May 18, 2015, 08:14:24 AM
As you said, I would find a complete head to swap in. Can usually be found for less than $200 if you look long enough. Then just a few bucks more for the gaskets and copper washers. You should probably replace the piston rings as well? Not really my area of expertise but I did swap a 2005 head onto my 2006 GS a few years back. If you fiddle with it, you can do it in the frame.