Valve clearance

[jphish]

OK - My very questionable mechanical genius being temporarily on hold - why do the valve clearances get tighter as they wear ? Seems counterintuitive to me... but my recent Girly :?:  experience tells me different. They do. I'm sure there is a simple explanation - just escapes me at the moment. anyone...?

[JetdocX]

The valves beat themselves into the cylinder heads due to steep cam profiles.  Acceleration and deceleration.  It's a bitch.

[jphish]

Ah Ha... Thus the valve stems move closer to the cam lobes / spacers. Got it, thanks jetdocx. j

[TigerTrax]

I just had my valves adjusted....
I was told they were very loose ( I checked them at 24K and they were
in-spec on the tight side.....

So the valves were adjusted ... now I have a serious drop in MPG...
high 30's - low 40's..... from mid-high 40's.

I need to have them checked again for certain...  
I'm being told 'valves won't effect mpg'.... I'm thinking 'Oh Contrer'...
If valves were 'loose' that would be lower mileage' than if valves were tight.....
Any ideas beyond that?

I have until April to correct this.... so far  'I'm thinkin'....

[Bixxer Bob]

So your tech has made them worse?  It was just explained above that the valves tighten up not loosen off as the mileage climbs.  You tech is snowing you with old logic that applied when valves had tappets.  If they were loose someone made them that way, they wouldn't be loose from the factory.

I'm not sure about the fuel consumption. but gut feeling is it wouldn't make any difference.  I'll have to ponder on that.  Carbs or FI?

[JetdocX]

I'll bet you breakfast that your tech got the cam chain timing off.  That will definitely cause your symptoms.

[NKL]

It will have an effect on fuel consumption as it will on power, valve clearance effects valve timing, may be small but it will have an effect.

[Bixxer Bob]

It will have an effect on fuel consumption as it will on power, valve clearance effects valve timing, may be small but it will have an effect.

That's why I asked carbs or FI. If FI the ECU will meter the fuel through the injectors to suit the throttle posn and depression level in the airbox.  Since the valves opening less will lower the depression, the fuel will be less also so the mean effect is same fuel consumption but less power for a given throttle position.  BUT the throttle will be open more as he tries to get the same response so fuel consumption will be worse as a result.

I haven't thought through the effect on carbs as I assumed Mustang would chip in there.

[TigerTrax]

The Tiger is an '06 FI... not beat at all.

HE did the same work on my buddies '05 w/o probs or issues.

Come to think of it.... he removed the cams.  

jetdox . .  you may be right.

[Colonel Nikolai]

Removing the cams scares the crap out of me. In 12,000 miles I will need to replace the cam chain on the Sprint. I'm very afraid.

[jphish]

Yeah - I always worry about a "runaway" shim making its way into the engine. Can ruin a perfectly good morning. Being organized, methodical & not in a hurry, is the key I think. All 3 difficult, for my ADD ways. Good mechanical 'joss' to ya Col'. j

[Colonel Nikolai]

Yeah - I always worry about a "runaway" shim making its way into the engine.

After splutching a good dollop of oil on them and putting them in, I always turn the cam once by hand over the shim before moving on. They make a little "snap" when they seat. Helps my peace of mind on that front.

Good mechanical 'joss' to ya Col'. j

Backatcha, jphish.