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Not doubting, but wonder why?

jsandidge

jsandidge

Forum Sage
Past Site Supporter
In measuring valve clearances, I did as you guys say. #1 exhaust parallel to the head, pointing forward which also puts #2 exhaust pointing up. Measure both in that position. Similar positions for measuring the others, doing 2 at a time.

If I measure exhaust #1 pointing up, the gap is looser. The same is true for the others that are measured from parallel.

I'm wondering if this method is just for convenience and close enough, or is there something related to the timing? Wouldn't the valves be completely closed at the very bottom of the lobe or should some be completely closed when the lobe is parallel to the head?

I know you guys have logged many miles doing it this way and I don't doubt this is correct. I'm just wanting to understand the reason.
 
By measuring two at a time, you put less pressure on the cams to get a better gap. You probably get more clearance because three valves push against the cam instead of two, when #1 is pointing up.
 
The valve is completely closed as soon as there is no contact between the cam and the shim. I am not an internal combustion engine design engineer but I believe that the designed dwell of the cam lobe would dictate whether or not the clearance should be constant from 90 to 270 deg. On my XJs at least, this is not always true (I havent tested this on the GS yet). I always follow the service manual for valve check procedure. If the manual says 180 deg. for checks that's what I do. Clymer's GS manual says rotate until the cam is perpendicular to the cylinder head surfaces(180 deg.).

This is just one person's opinion and as there are more than a few here who follow the method you are referring to, I assume we would have heard from someone if it did not work well.
 
luvmy40 said:
The valve is completely closed as soon as there is no contact between the cam and the shim. I am not an internal combustion engine design engineer but I believe that the designed dwell of the cam lobe would dictate whether or not the clearance should be constant from 90 to 270 deg. On my XJs at least, this is not always true (I havent tested this on the GS yet). I always follow the service manual for valve check procedure. If the manual says 180 deg. for checks that's what I do. Clymer's GS manual says rotate until the cam is perpendicular to the cylinder head surfaces(180 deg.).

This is just one person's opinion and as there are more than a few here who follow the method you are referring to, I assume we would have heard from someone if it did not work well.
Click to expand...

Most of the guys here use the method I spoke of, which comes from the factory manual. The Clymer manual has a different procedure which is perpendicular to the head for all valves. It seems the factory manual method would give you more clearance for some valves than for the others.
 
That's good to know. I haven't gotten my hands on a Suzuki Factory Service Manual yet so the Clymer's is my only reference for the GS.

Haynes and Yamaha are in agreement on this procedure for the XJ YICS engines. I guess I just assumed(I know, I know!) that Clymer would mirror Suzuki as well.
 
I can't say which way is "better" but with the factory specified way to do it. I believe is to make it faster when working with the flat rate times that are specified for each model and are close enough and mostly within specs. Myself and when the customers complain of excessive noise in that area. I will slowly rotate the engine and find the loosest point the (heel) of each cam lobe and adj. it there. With performance cams that have been degreed I will set each cylinder at T.D.C. and adj. to specs there. Since it is looser and noise is not an issue.
 
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The Suzuki method puts two adjacent valves on the base circle at the same time. Using the 180* method this is not the case; the adjacent valve spring is pushing up on the cam and skewing it within the cam bearing journal clearance. Suzuki designed the engine so I use their method. It's faster too than the 180* method since you don't have to rotate the engine as many times. Of course, do as you like.
 
Several guesses here, Nessism finally hit the proper reason.
icon_thumbsup.gif


When the cam lobes are in the proper positions, there is no deflection on that side of the cam, which give you more-consistent measurements.

And it's quicker. :D

.
 
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