Factory Pro Valve clearances

[lamoun]

Saw this today. Factory has a table giving  intake 0.005" - 0.006" and exhaust 0.007" - 0.008".  Suzuki recommends 0.001" - 0.003"

Has anyone tried those values?
What's the logic behind them?

http://www.factorypro.com/Prod_Pages/prods10.html

[joshr08]

well the inch to mm = .03-.08 mm and on the exhaust side i would say they are saying run them a little tighter when valves are closed to not loose anything on the power but if you run them all between .03 and .08 youll keep your exhaust valves a little cooler.  but thats just my guess

[gsJack]

Based on my 150k miles of GS500 experience I've decided to keep my exhaust valve clearances greater than the Suzuki .001-.003" clearance spec.  The GS engine is well known for eating exhaust valves, they receed into the seats reducing clearances.  I put 80k miles on my 97 GS and one exhaust valve was down to the 2.15 mm minimum shim thickness.  It had run at a tight .001" clearance for many thousands of miles before it began receeding and required constant changes to thinner shims after that.  The other exhaust valve stayed at greater clearances and only required one shim change during the 80k miles.

Here's my log of valve checks and shim changes on both bikes for the 150k miles so far:

http://img.photobucket.com/albums/v443/jcp8832/valveclearances.jpg

My 02 GS with one exhaust valve on the tight side began requiring similar shim changes on that valve at about 30k miles while the other exhaust valve with more clearance hasn't had a shim change yet.  On the second shim change at approx 40k miles I bumped the clearance up to .005" and it hasn't required another shim change since and has over 70k miles on it now.  

I'll keep the exhaust valve clearances at .003-.005" now and expect this 02 GS to go 100k miles without further shim changes.  Time will tell.  Intake valves didn't required any shim changes on the 97 GS and while I changed one intake shim on the 02 GS I changed it back next time and it's running on the original intake valve shims now at over 70k miles.

I have no idea where Factory Pro came up with their valve specs but I agree with the idea of running looser exhaust valves to give the valves more seat time for cooling but see no reason to change intake specs.  Both my 97 and 02 GSs were/are stock and will remain so.

[lamoun]

I understand your reasoning, (and your tests gsJack).

But what about factory says? "Valve clearance greatly affects idle and off-idle"

[gsJack]

I understand your reasoning, (and your tests gsJack).

But what about factory says? "Valve clearance greatly affects idle and off-idle"

Yes valve clearances can affect idle if you have a tight valve, that can be an indication you have a tight valve.  If you have a rough idle after startup and it smooths out as it warms up it's likely a tight valve.  The valve clearances increase greatly as an overhead cam air cooled engine warms up.  The aluminum head expands more than the steel valves do so the camshaft is lifted away from the valves as the engine warms.  I experienced this on my 97 GS when I had a tight exhaust valve but after warmup there was no loss of performance I could notice, only the long term damage from an overheated exhaust valve.

Some claim better performance with closer valve clearances because it gives longer and greater valve open time but I never noticed that small if any difference.  The only consideration in leaving the clearances looser besides the possibility of more valve noise would be the slightly greater chance of throwing a shim.  If your racing and running close to the 11k redline and even over it at times it might be a consideration but since a stock GS gives it's best performance at 7-9k rpm I just limit my stock GSs to a 9-9.5k rpm redline.