Topic: Valve adjustment question

[cmills83]

I just dug my CB750 out of storage, I had the engine rebuild professionally on this bike and it ran perfect a year ago.  Anyway, I go to start it and it has some top end noise so I cut it and wanted to run through everything.  I bought this bike years ago, the frame is a '75 f the bottom end is a '77f and the head/carbs are a '74(?)k.

Im following the valve adjustment instructions here (http://www.sohc4.net/cb550-faq/indexphp/tappet-adjustment-procedure) but am getting a little confused.  It says to turn the crank so the #1 cyl is at tdc, adjust the O valves.  Ok no problem, then spin the crank 360 degrees should move the #4 cyl to tdc and adjust the X valves.  But I noticed that cyl #2 and #3 are tdc, not #4 after spinning the crank 360 degrees.

Can someone explain what Im doing wrong here, am I just being a dummy?  Couldn't I just wait for each valve to close, go to the nearest tdc and check the clearance from that point?

[flatlander]

that x/o procedure that the manual describes, can be a bit confusing.
try this method which goes in firing order of the cylinders 1-2-4-3 (not my write-up):

First take out the sparkplugs so the engine will be safe to rotate using the 23mm nut under the points cover(-do not use this nut to rotate the engine with the plugs in as it is actually only as strong as the 10mm (M6) bolt holding it on!).
 In this case (adjusters have all been backed out) temporarily tighten the adjusters on the two #4 cylinders valves to eliminate all play.

Rotate the engine until you see the T / F 1.4 marking through the inspection hole in the points plate, now whilst closely watching #4's tappets (look into the two closest adjusting holes) rock the engine back and forth either side of the 1.4 timing mark (~10 o'clock to 2 o'clock) - If you are not seeing the tappets move rotate the engine one full turn back to where you see the 1.4 again and repeat - what you need to see is the exhaust tappet coming up just as the inlet tappet is going down for #4 - this indicates that #1 cylinder is on compression stroke so you can go ahead and adjust #1's tappets.

Rotate the engine half a turn only till the T 2.3 timing mark lines up and adjust #2's tappets

Rotate the engine half a turn only till the T 1.4 timing mark lines up and adjust  "4's tappets

Rotate the engine half a turn only till the T 2.3 timing mark lines up and adjust  "3's tappets

I would normally double check that cyl 3 tappets were rocking before adjusting cyl 2 and that cyl 1 tappets were rocking before adjusting cyl 4 and that cyl 2 tappets were rocking before checking cyl 3, but not really necessary (I got into the habbit of doing that because the Honda's firing order of 1-2-4-3 used to confuse the hell out of me when I was under the assumption it would be the more common 1-3-4-2!)

[rotortiller]

It says to turn the crank so the #1 cyl is at tdc, adjust the O valves.  Ok no problem, then spin the crank 360 degrees should move the #4 cyl to tdc and adjust the X valves.

 

Exactly how it's done. 1 and 4 pistons are at TDC at the same time. One of the two outer cylinders will be at compression and one will not. You adjust the two valves on compression on the outer cylinder and also the intake on an inner cylinder and the exhaust on the other inner cylinder.
Rotate 360 degrees and do the remaining valves.  2 and 3 cannot be at TDC with the 1/4-T mark lined up.

edit: Kawasaki and Honda use the same method with this type of engine configuration as do cars.

[cmills83]

Seems odd that the bike would need valves adjusted if it just sat. I would certainly look towards oil and lubrication if you have not already. Maybe cam tension too.

Yeah just sort of running through everything.  Changed the oil, un-tightened and re-tightened the cam chain tensioner, ran through the valve adjustment inspecting things as I go.

[Redline it]

put your finger over number 4 spark plug hole, key off, and push the kickstarter down slowly, when you feel pressure building then number 4 is coming up on compression stroke. the next one is 3 then 1 and 2, that way you won't be guessing or counting turns after putting the cam cover on or checking valves. oh and it works great as a compression check as well. not sure if it works on the 750s or not, but all my compression checks with gauges show results in the 70s or 90s. so instead of using gauges put the same finger over a hole and if it goes pfffsst and blows your finger off, call it 150. learned that on this site.

[pjlogue]

When you get your valves adjusted check your cam chain tensioner adjustment.  If the bike was running OK when you put it up a year ago it should not need any adjustments.  If, during storage you had humidity or condensation in the engine from short runs you may have a sticking valve that is holding up and not seating fully.  This would give you excess valve clearance and top end noise. 

-P.

[Bodi]

That chart is confusing but it saves a few steps from doing it one cylinder at a time, where you confirm a cylinder is at TDC compression so intake and exhaust valves are both fully closed and you adjust them. Turn 360 and do the other one of the pair (1-4 or 2-3), then repeat for the other pair. There's no hurry so using the chart isn't necessary. Basically that way adjusts the intake valves on exhaust stroke and exhaust valves on intake stroke, reducing the number of crankshaft turns.
It is much safer to use the alternator rotor or its bolt to turn the engine by hand, it's pretty easy to break the advancer bolt. Plugs out for sure.

[rotortiller]

This might explain how it would be impossible to be at TDC of either 1 or 4 then rotate the crankshaft 360 and be at TDC on 2 or 3. You must have rotated the crank 180 degrees instead.

[754]

I pull the tapped cover, turn the crank to 1.2 or 1.4 mark . Find the cylinder that HAS BOTH rockers loose, check with feeler gauge adjust if needed. Then turn 360 degrees and do the other of the pair.
 Then turn 180 and repeat same procedure.

 So we're the valves out of spec, when you checked them ?

[cmills83]

thanks for all the feedback, as pointed out I think I was not paying attention to the 1.4 and 2.3 marks.  Looks good now

[cmills83]

Seemed like 1 valve was slightly out of spec but not much.  I was thinking there was a sticking valve since the bike was sitting covered outside.  Everything seems to be moving ok and I put a little bit of marvel mystery oil up around the valves.  Waiting for the battery to charge to try starting again