Ryobi 990r

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Old 01-12-07, 08:00 PM
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Ryobi 990r

Hello all & Cheese: I have another 990r in the shop and can't remember what the compression should be? It's been over a year since I worked on one? Thx, Ron
 
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Old 01-12-07, 09:58 PM
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Hi Ron!

I never have stuck a guage on one, so I can't say from experience. I judge compression a different way...but I think somewhere around 80-90 psi should be good on a sharp pull of the rope.
 
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Old 01-13-07, 12:16 AM
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Cheese is the method you normally use a bleed or leak down test?
 
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Old 01-14-07, 01:10 AM
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The method I use is pretty low-tech...and I think a person needs to be quite familiar with small engines to be able to do it...but I slowly pull the rope and basically just feel and listen to the compression. It's fairly easy to tell (for me anyway) when one has sufficient compression, or when one doesn't. If it feels borderline, I pull the muffler and inspect the cylinder and piston. The sound of one that is good usually has more of a plop plop plop sound when it turns, and the rope has a sharp resistance going through the compression cycle. One with low compression has more of a fluf fluf fluf sound and no sharp increase of tension on the rope, but more of a gradual increase, with less resistance to overcome.

I don't think I'll ever be asked to write about compression testing in any textbooks, haha! But hey, it works for me without fail.

I do own a couple of compression guages, but I almost never use them. Usually if I do, it's on an engine with more than one cylinder. I also do perform leakdown tests to determine the source of compression problems on 4 strokes(listening to where the air is going).
 
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Old 01-14-07, 01:47 AM
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Excellent description! I know exactly what you have just said! I can detect the same things. Why I've never put two and two together and trusted my judgement is beyond me. This helps greatly because it gives me "Assurance" that what I think I can feel & hear is "Probably" correct. I think I'll ask a friend of mine to pull a couple of 2 cycles that are good and two that are bad and just go through the proceedure to see if I can actually feel it & hear it...I bet I can. As always, I really appreciate the help.
 
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