Valve clearance

Not to beat a dead horse, but i need to ask. Ok, taking big fitz advise and checking clearances. Now i am wondering about the min. and max. clearance values. Would it be better to be on the max. end of the scale or lower? Also when i checked them (3 times)I went by the first (metric) feeler that sliped under. Is this correct? This is why i am asking what end of the spectrum is the safest.

 

Valves get tighter over time (meaning, they like to burrow into the valve seat), so if anything you'd want to stay near the larger gap side of the in-spec range.

Although getting them exactly where you want is tricky. Better to just get them in spec and check them every 5K miles.

 

good question, i don't know the answer really, but this is just the way that i would figure it; Having more gap would be better as long as its in spec as since they get tighter over time, it would mean that you would have more time before they would need to be swapped out again.

but once again, thats not true maintenance advice, but purely mechanical theory.

 

If a reading is borderline, fit the next shim down.

 

Ok, andrew is thinking the way i am and wizard you would also be on the same page with us i think. I was not sure if the shim wore faster (or at all) than the seat.

 

And i will just get them in spec. no matter where they fall and re-check in 5,000mi. Was just curious. Thank you all for the help.

 

Here are the measurements if anyone is interested.
#1 I=.08 X=.10
#2 I=.10 X=.15
#3 I=.07 X=.15
#4 I=.06 X=.09
All with mm. gauge

 

+1 to the advice above-If you go out of spec on either end (tight is dangerous) you create bad valve timing and sealing issues.

Your new measurements should be:

#1 I=.08 (d1size to .13) X=.10 (d2size to .20)
#2 I=.10 (d1size to .15) X=.15 (d1size to .20)
#3 I=.07 (d1size to .13) X=.15 (d1size to .20)
#4 I=.06 (d1size to .11) X=.09 (d2size to .19)

so if you had on #4 say a 265 on the exhaust, go to 255 and if you had a 265 on the intake, go to 260.

Since it's so easy to check the clearances-once you get them re-shimmed I would check them again right after the first time you get the motor warm and under load. I say this because after I did mine all the clearances went out the exact amount of the new shim, but I checked after about 10 miles and two had changed and went tighter. I realize this isn't suppose to happen-but it did. And you will want to watch your #4 intake since it will be right at the tight spec.

Everyone knows a tight valve can kill an engine, but I think it gets overlooked that out of spec valves mean less power, efficiency, and make it virtually impossible to get your running synch to come out right.

 

Thanks MM! Thats how i figured it. Now i feel confident to place my order.

 

The shims don't really wear at all.

 

Hey, MM: since when is 7+5=13? (Intake 3.)

One shim and one shim alone puts any given valve within the specified range. Intentionally setting them out of spec hoping they'll "come in" is NOT a good idea. Yes, you will often end up with one or two that are IN spec, but "right on the edge." That's fine, you know to have their next size shim ready for when they do get out of spec; but until that happens, leave them there.

I've got one intake valve in my '81 that's been at .11mm for about 9000 miles and it refuses to get any tighter; I'm leaving it alone until it does.

 

In an alternate universe that Pythagorean never survived infancy in.

Basic math dangit! My bad bigfitz your are correct it should be .12 not .13.

who told him to put them out of spec?

 

Andy and Wiz both hinted at it.

 

Appears to be true on my '82 XJ650J. At 26K miles all 8 shims showed no wear at all on the upper surface.

 

Any wear will be apparent on the underside; they rotate within the bucket and often wear the markings off. However, shim wear IS minimal; the valve train wears by the valves pounding themselves into the head, which is why they tighten up, not loosen.

 

Actually , proper valve clearance is a plus , to tight results in loss of compression , valve doen't close , to lose results in short valve duration , loss of fuel air mixture ! I would say to get it as close to center of the [min / max] numbers as possible .

 

Too tight leads to hanging open a whisker when the head and exhaust valve stem heat-expand, which leads to a warped or tuliped valve, which leads to anger, which leads to the Dark Side !

 

IN spec is IN spec, no matter where in the specified range you are;

because

ONLY ONE SIZE SHIM WILL PUT ANY GIVEN VALVE IN SPEC.

You cannot "fine tune" where within the specified range you end up unless you start grinding shims which is NOT a good idea for a number of reasons.

 

Had mine made here at the local machine shop , cut to my specs , and picked up the same day . Sure beats the wait having them shipped .

 

Really? And then they case-hardened them, like the factory?

The hardening is why it's not a good idea to grind factory shims. It's also why they wear very little, ever. I would be greatly concerned about the longevity of "local machine shop produced" shims.