Compression numbers, 650 seca

Finally got around to doing valve shims. Finished that without issue, valves now all in spec. While I was at it I figured it would be a good time to check compression as I had not done that yet. Keep in mind this was done with tank off, carbs off, valve cover sitting loose on top of motor, all plugs out, engine dead cold. Not standard operating procedure I know...
Initially got:
#1 - 80 #2 - 110 #3- 40 #4 - 110.
1 and 3 obviously not good... I decided to let bike sit a few min and try again, thinking "well, it's been sitting minimum 5 yrs... Stuck rings maybe?"

On 2nd go round...
#1 - 90 to 100 or so #2- 110 #3 - 90 #4 - 110.
Better.. but still..
Thoughts?

 

Stuck rings. Try again after she's been run in for a while. I think you'll find good numbers on all 4.

 

That's sort of what I figured. Awesome, thanks. Will Continue with teardown/rebuild.
Just didn't want to dive in and start ordering all sorts of parts with a crap engine.

 

Put about a teaspoon of ATF in each cylinder , spin it over a few times with the TCI unhooked. Leave sit for a few days. I would fire it up and go for a long ride and re-Test

 

Still a ways to go before she's rideable. Otherwise yes I'd definitely do that.

 

Guess it wouldn't hurt to give it the ATF treatment and see if that helps.

 

Shouldn't a compression test be done at wide open throttle (WOT)? You need air to compress and if the throttle plates were closed or almost closed on various cylinders you would get low and uneven cranking pressure.

 

That low on #3 could also be a bent valve.

In diagnosing a similar problem previously, I took the air nozzle from my compressor and fed air into #3 (that was the low compression one on my bike as well) through the spark plug hole, with 3 at TDC for compression/power (i.e valves closed). The air rushing back through the carburetor and into the air box was quite easy to hear.

 

Bit tricky with '..carbs off..'

 

another thing to consider that if you are using a similar tester to this

Clarke CHT692 2 Piece Compression Tester Kit
from Machine Mart
2 Piece Compression Tester Kit. This 2 piece compression tester kit is ideal for use with most petrol engines. Featuring a dual calibrated gauge reading, 150mm straight push-on ...more »2 Piece Compression Tester Kit. This 2 piece compression tester kit is ideal for use with most petrol engines. Featuring a dual calibrated gauge reading, 150mm straight push-on connector, 320mm flexible hose and 2 adaptor sizes.« less
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then unless there is a shrader type valve in the end that screws into the plug ole, then you are increasing the size of the combustion chamber, by way of the rubber pipe, so compression numbers will be on the low side a little.
all be it , they should be uniform across all cylinders
stu

 

I was working with a friend back in the "70s" on an old Chevy six that had sat for a while. While in the Navy, he had run the motor pool
at the base on Key West. He said to first spoon or spray some "croil" (n0t wd-40) into each plug hole, turn the engine over a few
times and let it sit overnight. then run it till warm. Let it cool down (important) and spoon some ATF into each plug hole. Put the plugs
back in and start it, run till full operating temp. Revving the engine occasionally. The ATF was burning the carbon in the combustion chambers.
You could see chunks of it flying out of the tail pipe with the smoke. I gained about 20 lbs on the low cylinders. I'm going to try this on an xj650
parts bike I picked up last week.

 

Your Navy friend was referring to Kroil http://www.kanolabs.com/
It, PB Blaster, and the 50/50 mix of acetone and Atf are the three best penetrating oils around.