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New (to me!) '77 CB400F - US model
mattsz:
I'm at a bit of a standstill waiting for a few parts... I finally got the electric start up and running so I decided to cross my fingers, hold my breath, and do a compression test. Should have done it a lot sooner, although I don't know if it would have mattered. My results are most disappointing...
I tried it with all the plugs out, to go easy on the motor and battery - all four read only in the 72 - 78 psi range. That's right, 100 psi less than they should be. Next I tried it with all the plugs installed - excepting the cylinder being tested, of course - and found no change. I added a little oil, against ring leakage, which bought them up just a few points. I tried loosing all the tappets, against valve leaks due to bad adjustment, which brought them up to the 91 - 95 psi range... better, but still nowhere close. I pulled the head cover and tried re-torquing the head, against a leaky head gasket due to a loose head (all the head nuts were tight except for the two "pillar nuts," which moved a little bit), but this made no change. While I had the cover off, I checked the cam timing, just in case - the marks on the sprocket are just where they should be with the "T" mark on the spark advancer aligned with the matching mark...
To rule out a faulty compression tester, I tried a borrowed one, which matched mine's readings. I also hooked my tester up to my air compressor, and found it's readings within 5 psi of the compressor's regulator gauge.
Things aren't looking too good for our hero...
Bryanj:
Its not been run for so long get it going and see what happens
mattsz:
--- Quote from: Bryanj on June 01, 2020, 05:58:28 PM ---Its not been run for so long get it going and see what happens
--- End quote ---
It's been about 2 years.
I was going to ask whether it was a good idea to try it first, before "writing it off" and opening up the engine...
Bryanj:
As you can take the top off in the frame i would try and get it to run, probably bolting on the absolute minimum
K2-K6:
I'm with trying to start it too, give the little guy a chance ;D
First it may be worth spinning it with plugs out and wd40 down the bores to help if there's any long term oil gumminess in the rings.
If it runs, let it warm a bit, plugs out, carbs open and retest for compression then. See what you've got as it'll tell you one way or the other if it stays low as to further decisions.
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