Topic: I'm burning out my feeler guage , '72 cb750 valve clearance adjusting..

[Hondawggie]

I followed the manual (specifically, pages 42 and 43 of the fsm I downloaded from the 'Manuals' section of the SOHC site, filename "Honda CB750 SOHC K0-K8 F1-F3 Shop Manual.pdf") -- I finished my valve tappet clearance check/adustment today after some distractions the past 2 days.

Nearly all the clearances required either reducing the clearance, generally on the exhaust side it was reducing from .1mm to .08mm.  Most of the intake tappets needed to be reduced from about .075mm to .05mm.

Only bit of strangeness was the intake and exhaust on #4 were *less* than the .05mm and .08mm called for -- the #4 intake was about .038mm and the exhaust was about .05mm.  I opened up those gaps to the required .05mm and .08mm respectively.

Now here's a question as I broke my feeler gauge tonight.  I could not get my feeler gauge to slide in under the #3 exhaust tappet, I tried different angles of attack, from the front/horizontal/try to slide it in NOPE, from the sides, insert the leaf to either side kind of deep then as I pulled the leaf out try to slide it under NOPE, bent the tip of the feeler gauge leaf upward to try another angle of attack NOPE.

I broke the tip off one of the leaves doing the bending-the-tip-upward try.

I REMOVED THE THREADED ADJUSTER SCREW COMPLETELY and could not get a leaf under there -- despite the fact that I could move the tappet up and down with what felt like 3/16" of gap or more.  Still couldn't find an angle of attack to get the leaf under it!

I finally put a curve along the entire length of the feeler gauge leaf, identical to the curve you find on a tape measure.  I was able to get the leaf under there 1 or 2 times out of 50 tries.

My procedure was *exactly* as on pg. 43:

"Line up the 1,4 'T' timing mark and check valves on #1 in & ex, #2 ex, #3 in.  Then rotate the crankshaft 360 degrees and check the valves not checked in the first step."


I even used a permanent ink marker and watched it go completely around just *one time* to achieve the 360 degree rotation of the crankshaft, lined up the 'T' mark on 1,4 again after the 360 rotation and did the other valves.

So I'm wondering --- in assembly of a '72 cb750 motor, is there a way to assemble the tappets/valves/whatever to cause this kind of difficulty in doing a measurement?

ALSO - does Honda sell a special type of feeler gauge for checking tappet clearances on these 750 sohc motors?

When this 'cant get the leaf underneath the tappet' started, I thought I noticed that the tappet for #3 exhaust, the one giving me grief -- the head of the tappet where the adjuster screws in -- that part of the #3 tappet looked TALLER than the #4 exhaust tappet.  Then again I was p.o.-d and was looking for something to explain the difficulty.

[bikebitzofvt]

Automotive or generic feeler gauges tend to have very wide blades that can be tough to use in motorcycle applications.  I use a set of Motion Pro "go - no go" gauges.  They have a rigid steel body and small, very flexible sections of gauge.  They will easily bend to 90 degrees without breaking and are small enough to fit in tight openings like our bikes have.  Hopefully the attached picture will load so you can see what I'm referencing...  if not, here's a link to their website:  http://www.motionpro.com/motorcycle/partno/08-0392

Do you own a micrometer?  The built in clutch on a micrometer is very handy for learning the proper drag on the blade.

Your referenced measurements all sound fairly normal.  It's tough to tell if they were properly adjusted last time - it's a good idea to track them so you can see what's happening with your engine. 

Good luck!
Tom

[Rio_CB750]

I used this method after a similar experience that you are describing:

http://www.salocal.com/sohc/tech/vlvadj/vlv.htm

[Toxic]

If you are planning on keeping the bike for awhile ... get those feeler guages.  They make a huge difference.  I paid $5 each from Z1 enterprises.

Also the adjustment tool that holds the locking nut while you turn the screw is worthwhile as well.

[Hondawggie]

Okay, I read the procedure fpcb750er and in the text, it mentions 'bevels' -- I'm wondering if the bevels on the #3 exhaust valve tip are somehow munged making it hard to get the feeler gauge leaf started.

The MotionPro feeler gauge looks promising -- I thank you for that and will buy a set of those.  Last night I was messing around with that one valve (#3 exhaust) for WAY too long for adjusting one valve.  Those MotionPro feeler gauges look *excellent*, thanks for your suggestion.