Valve lash vs. cam lobe position

Noticed my Chilton's manual says to put the cam lobe opposite the bucket (when measuring lash) and the Kaw manual says to line up the "Ex" mark on the exhaust cam and the "T" on the intake cam with the head. When I measure with the cam lobes in both of these rotation settings, the lash difference on some valves are up to .05mm. Which way is right? The valve lash spec on the Z650 is .08 to .18mm so one valve measures .15 when lobe is opposite bucket and .20 when using the "ex" or "t" cam alignment. Is it safest to measure the minimum clearance as to not end up down the road with .00 lash on some point of the cam rotation?

I would trust a Kaw manual over a Chilton anyday. The Kaw manual says to do it like that so you only have to roll the motor over to TDC twice.

They tell you to find TDC compression on #1, then check #1 Int & Ex., #2 Ex and #3 Int (could be the other way around) Then roll the motor over one full turn and that's TDC compression stroke on #4 cylinder, check remaining valves.

That works, but if you don't mind spinning the motor over a lot, just get each cam lobe pointing directly away from its bucket and check clearance one at a time.

Line up the timing marks. That should be the most accurate way.

The "valve-lash" is just that! The greatest clearance between the highest point (wrong! see later posting) on the cam-lobe and the flat surface of the bucket. It is this clearance that should be measured and adjusted to spec.

There has been another posting on this or similar topic, just recently, where Nads.Com mentions the ramping, cam lifting and valve timing. However, I believe on standard cams, the above method is correct.

RegardZ.

Post edited by: Garn, at: 2005/12/16 13:07

This is interesting.

Just thinking so take this in the form of a postulate, not fact

Off the lobe, that cams circumference should be constant radius and the clearance should not vary. If it does, then it's not round which is pretty unlikely or it's shifting in the bearings. So if you've got a big difference in clearance when an adjacent lobe is 'on the spring' or a lobe at the other end of the cam is 'on the spring' then your cam is moving around in the bearings.

The cam is gonna move around anyway, but there is a spec for how much is tolerable. Perhaps measuring the lash in a few different spots would indicate whether or not it's time to measure the bearing clearance.

What do you think?

-Duck

Duck, you just brought me back to reality. It's that lowest diameter (commonly called the PCD) that I should be measuring the clearance between, hope I haven't confused anyone.

As you say, that diameter would be pretty constant on a standard cam. Hence, there would be a reasonable tolerance with regarding the measuring position, once the lobe is pointing away from the bucket.

Regardz

For most cams bikes like the inline DOHC fours the base circle is comsistent around the back of the cams - so it shouldn't make any difference if the cam lobe is not perfectly 180 degreeds away from the bucket. One cavaet on this, some early 'performance' cams were reground stock cams where the back of the base circle was ground to remove metal rather than the lobe being built up.

There are some bikes where cam position when measuring clearance is critical. An example is the Honda CB450 twin from the late 60's and early 70's - a pain in the butt to check and setup...

Post edited by: jeff.saunders, at: 2005/12/16 07:57

If I could jump in, I will be doing my valve adjusting soon, so this is a timely thread. But I'm still not sure what to use...

So to figure out the new shim size, is it best to look for the smallest cam clearance, or the largest... ?

I'm leaning toward using the smallest:huh:

Kent, If this thread did confuse you, nothing will!

Turn the lobe of the cam where the lash it to be checked 180 degrees away from the bucket. This is the point where there is the GREATEST clearance already. Check it there and use it to calculate your shim size.

Hey Jeff

What about my new 78 hawk hondamatic?
Manual sould be here next week.

Any tips/tricks?

81 CB650 here too since we last spoke.
Good compression but knocking seemingly from right side tranny when using 'stick to ear' locator.
First thought was clutch but it seems much too solid a knock for that so I'm gonna drop the pan and see if anything jumps out. Knock goes away with higher rev around 1500 to 2000 and decrease ever so slightly in intensity when clutch is pulled in or it's put in gear on the center stand.

I fear it may be loose rod cap so won't run until I have a look.

-Bob in Atlanta AKA Duck

I panicked the first time I checked my valve clearance, too.
The manual said to line up the mark on the cam chain sprocket with the surface of the the cylinder head. But when I did that, the cam lobes were not pointing directly away from the shim bucket. But the gap was about 0.003", all around.
When I rotated the shaft to get the lobes 180 degrees from the shims, then I had no gap.
I went with the manual's instructions. Don't know why the lobes aren't 180 away from the shims when the mark lines up, but they're not.

I can't see the darn marks on the sprockets anyway... hehe