Topic: CB350 twin...nasty sounds!

[quietlikeachurch]

A friend of mine recently bought a '70 CB350 twin that had a distinct lower-end knock coming from the left side.  He picked up a spare engine for beans and we switched 'em out, only to find that the second engine has a slight top-end click on the RIGHT side.  We replaced the plugs (B8ES), checked valve adjustment (it was perfect) and reset the camchain tensioner (the plunger is not seized) and the noise was still there.  Then we looked for anything loose that might have been clicking (including possible exhaust leaks) and found nothing.  We even loosened the valve cover to check the cam timing (it might click if the camchain jumped a tooth, right?), and the cam sprocket mark is pointing straight up at LT on the alternator, just like the original engine.  So unless both engines have bum cam-timing, what could be causing the click-noise?  My only other idea is a broken ring, but the engine runs great and doesn't smoke at all.  I know SOHC/4 750s pretty well...this is my first time working on any other model.  Help!!!

-Ian

[quietlikeachurch]

Oh yeah...the carbs are balanced fairly well and the ignition timing is spot-on according to my strobe light.  Also, the head is getting plenty of oil on both sides based on the view through the valve-inspection holes, and the engine is filled with new Honda brand 10-40.

-Ian

[bwaller]

I have seen worn piston pins and or also big end rod bearings cause a knock like you describe on the first engine especially when you just blip the throttle off idle. As far as a top-end click with the second engine, my quess would be cam/rocker wear from a previous low oil pressure situation. I've also seen them run a long time like this.

[byidesign]

Do you have any idea, as to how many miles actually on the
   engine's?
      also how crappy is the centrifugal oil filter,
       if let go{filter} without cleaning it
        and it gets full,it craps up the oil journal holes especially the head,
        restricted oil=noise,even if you see a puddle in there....
       you might want to check if thats full
         if so ,clean the cam lube holes in the head out.
           they will be partially plugged.
                     Hope it helps
                            Bruce
 

[quietlikeachurch]

The original engine has almost 13K on it, and all the cover screws are scarred...there are some stripped screws as well, making it look like someone was inside it.  We're going to tear that one apart and rebuild it anyway.  The second engine has 7K on it (supposedly)...the plugged oil passage sounds good.  I'll see if we can pull the head tomorrow.

Thanks
-Ian