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Author Topic: Comp checking elec ign - JimRillieR65LS 10/30/06  (Read 575 times)

Offline Justin B.

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Comp checking elec ign - JimRillieR65LS 10/30/06
« on: November 18, 2006, 10:12:12 PM »
JimRillieR65LS Posted: Mon Oct 30, 2006 7:53 am    Post subject: Compression checking with electronic Ignition version R65


found my left exhaust valve so tight it didn't seem to close.
I had a look because the R65L wouldn't idle below 2000 RPM, just one of the many things I checked (last valve adjustment about 50000 kM ago.)
Reset, and it seems to run fine again, but I would like to run a compression test to see how one cylinder versus the other now reads. Should I disconnect the ignition can before attempting this. It sems I read somewhere (Duane maybe) that the Hall effect transistor in the can may be damaged if plugs are not grounded, and grounding them while also trying to test compression with ony two hands......well, you get the idea.


Jim Rillie
R65LS - manufacturing date Oct 1981

airhead Posted: Mon Oct 30, 2006 9:06 am    Post subject:

It's not the Hall Effect transistor that is at risk, but the ECU. Simply cranking for a comp test shouldn't do any harm, but it's still good practice to disable the ECU or short the plugs. You could unplug the beancan, but you would have to disconnect the battery as a safety thing for removing the timing cover, then re-connect for the test. Don't forget the plug/socket is secured with a thin bail clip, remove this before trying to pull the plug arrangement apart or something will break. It would be simpler to wire or bungee strap the plugs to the heads.
Thought about a leak down test? Much better as you get more and truer info as there are less variables involved. If you still want the comp test, make sure the battery is fully charged, crack open fully the throttle and carb slides as well, or better still, pull the carbs off the heads. Only give it around 4 or 5 pulses for the reading.

justinbowser Posted: Mon Oct 30, 2006 9:36 am    Post subject:

However many "pulses" you give it, make sure you do it exactly the same on both sides. Your exact reading is not as important as the variance from side-to-side. If you have a large variance you will likely never be able to get a ghood smooth tune out of it but it will still run. I ran my '81 R100 for the first year I had it with 65/125 compression (burned exhaust valve), got 40+ mpg, but no way the idle was ever gonna be smooth...

JimRillieR65LS Posted: Mon Oct 30, 2006 12:09 pm    Post subject:

Thanks, Gents

Just the kind of info I needed.


Emiller Posted: Mon Oct 30, 2006 12:23 pm    Post subject:

I bought some metal clamps, like alligator clamps but bigger, at an electronics store.

I connected a big one to a smaller one. The big one clamps around the threads of a spark plug very securely, whilst the other one clamps to a cylinder fin. I made two of these tools. So I remove both spark plugs and use my clamps to ground the spark plugs and whirl the motor away. Good for testing for spark at the plug too.

suecanada Posted: Wed Nov 01, 2006 10:15 am    Post subject:

Exactly the info I need as well. Thanks for asking Jim. My LS had a closed left side exhaust valve as well!! I had read some warnings in my Haynes manual but couldn't remember what it said to do about the electronic ignition before a compression test so I didn't do one when I was with my older brother John and he was willing to do one for me. So we left it not checked for fear of damaging something. My exhaust valve had closed down in 5000 miles, so it bears checking again next springtime.

Now I know.
« Last Edit: November 18, 2006, 10:12:49 PM by admin »
Justin B.

2004 BMW R1150RT
1981 R100RT - Summer bike, NEKKID!!!