? about the cylinder pressure

got my motor sitting on the gerage floor while i do a few things to the frame, but today i decided to do a compresson test on the 650 and got around 80 to 90 psi cross the board. I realise that the shims could have a little to do with it being low, but it looking a lot more like rings to me.

Got a feelers guage with .0005 on the smallest blade that will only fit between two cam lobes and shims, so if one of you guys that know a lot more about one of thiese bikes than i do, whats it gonna soak me for a new ring job, or is it even worth it :?:

 

Pour a Tablespoon of Oil in each Spark Plug Hole and take the readings, again, after you Adjust the valves to specs.

You might not need a Ring Job.
You might be able to get-by with Lapping the Valves.

 

If your test was done on a cold engine, you're going to get lower readings. The 120+ PSI at sea level spec is supposed to be for a warm engine. Tight valves, especially if they're not closing all the way, are going to reduce the reading as well, so, as Rick said, definitely adjust the valves and recheck before drawing any conclusions about other needed work.

 

Valve adjustment http://xjbikes.com/Forums/viewtopic/t=14827.html

Valve adjustment Part 2 http://xjbikes.com/Forums/viewtopic/t=29209.html

Valves that tight will most definitely affect your compression readings.

 

streetmaster, before going and doing a ring job, you should get valves back in spec as others have said.

However, I don't think they are answering the real question you have....."How do I measure the clearances when I can't get a 'real' reading for the clearances?"

Here's what you can do.

You'll need either the valve bucket holding tool, or use the zip-tie method...whatever works for you. Then use the tool to remove the first shim. Check the shim number. Replace it with one two or three sizes smaller. NOW remove the tool, turn the cam and RE-MEASURE. You should be able to get a better measurement with feeler gauges. Now, go through the process again, doublechecking what the replacement shim size was, and go up or down sizes depending on what you actually need.

Yes, it will take along time to do that, since you're going to do each shim a couple times over til you get a final corrected clearance, but it will should make all the difference, and hopefully save you a ring job.

The first shim that you put in just needs to be smaller to allow you to get better clearance measurements. Once you have the better measurement THEN you can go to the shim chart to determine what you really need.

Let us know how things go............

Dave Fox