Theory behind valve adjustment?

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Originally Posted By: HTSS_TR
Originally Posted By: Trav
The only thing setting valves out of spec will do is create noise. On the one i just did all the exhaust were tight and most of the intakes were loose.
I set the intakes on the tight end and the exhaust on the loose end of the spec. Valve seat recession can be ongoing or it can come to a stop but you wont know that until you have checked them a few times down the road.

The non VCM is easier to do than the VCM engine to do the job on. These engines should have been equipped with hydraulic adjusters, Honda just went cheap on it anywhere the eye cant see like the rest of this vehicle.

I think most engines in vehicles manufactured in America are engineered here too. I think Honda engineers in Japan are under less pressure to cut cost than engineers here.

Looking at under the hood of 2014 Accord I can see many items are not very high quality as 1991 Accord made in Japan.
My mom had a couple of Accuras . Unimpressive as can be.
 
Originally Posted By: DBMaster
My 89 Accord had the lash adjustments as a 15K mile service. I used to let it go to 20K or more. They were rarely off by much and I found that a go-no-go gauge set made the adjustment process easier. In keeping with what Trav mentioned above the required adjustment became nearly non-existent after about 200K. I thought that Honda used such a valve train because it was presumably higher performance than a hydraulic valve train. All I know is that A20A3 Honda 2.0L was one durable engine.


Thats true but Honda uses hydraulic lash adjusters on the old CB Seven Fifty motorcycle which has a red line of 9K and are perfectly quiet and reliable in over 21 years of service so they know how to do this.

Not many V6 engines in a mini van will ever see 9K RPM. What this is IMHO is creating a large service bill that includes the timing belt, valve adjustment, brakes, plugs, coolant, etc at the 100K mark.
 
Design it once, milk the design for years. Kinda risky to change something once proven. And it would seem customers did not care--they keep buying these engines rather than something else.
 
Thanks Trav for pointing out that mfgrs will allow a few bones for the stealership in the form of valve adjustments, etc.

Chrysler puts cheapo copper plugs in their Hemis yet they do not require them at all. Many more examples out there.

And note what Trav said about seat recession. It is not always linear, and I have seen it virtually stop in some engines even with ridiculous miles...
 
Originally Posted By: Clevy
Originally Posted By: zach1900
There has to be a reason Nissan and Toyota used non hydraulic valves for so long. Even the modern at the time Nissan V6 used solid lifters. I think my Camry has them too. My 2001 Sentra had solid lists and i didn't touch them ever. 250,000 miles.


That doesn't mean it was running optimally.
250000 miles is no big feat. If that means something significant on a toyota then I'll stick to my mod/ls/hemi engines thanks.
Heck my brothers o8 ram has over 300k on the odo now. Never had anything but oil changes. Is that something special.
Yippee toyota.
Yipee my 99 Camry with 330,000 MILES.
 
I prefer adjustable valvetrains. I've owned too many engines with hydraulic cam followers that created enough noise to drive me nuts. One of them as recent as a 2007 model 3.8L pushrod V-6 engine. Problem with these is you can't adjust the noise away. You either live with the noise or tear the engine down to replace a bad lifter. Not my idea of a good design, personally.

If the price of a quiet-running engine is spending 3 hours under the hood every 8-10 years or so, I'm in!
 
Originally Posted By: zach1900
How would one even attempt to adjust hydraulic lashers? !


If adjustable tighten till you can't turn the pushrods with your fingers . Than 1/2 a turn more.
 
Did the Fit's valves just a few minutes ago. True to what Vikas found out about other Honda engines, the intake valves were mostly fine while the exhaust valves were almost all on the tight side. The exhaust valves got set to 0.012", or the loose end of the specification.
 
Suppose exhaust valve clearance have gone to zero. What would happen to the engine vacuum at idle? Would vacuum increase, decrease or stay the same? And why?
 
Zero exhaust valve clearance, or at least exhaust valves hanging open, would probably show up as decreased vacuum, as the engine can draw air through the partially-open exhaust valve. I imagine this would have to be fairly severe for this to happen, though.
 
Originally Posted By: eddy21
Originally Posted By: zach1900
How would one even attempt to adjust hydraulic lashers? !


If adjustable tighten till you can't turn the pushrods with your fingers . Than 1/2 a turn more.


I was taught to spin the pushrod while tightening the rocker down until you felt drag on the pushrod, then 1/2-3/4 of a turn.
 
Originally Posted By: Hokiefyd
Zero exhaust valve clearance, or at least exhaust valves hanging open, would probably show up as decreased vacuum, as the engine can draw air through the partially-open exhaust valve. I imagine this would have to be fairly severe for this to happen, though.
Wouldn't too lose valves also cause the same decreased vacuum?
 
Originally Posted By: Vikas
Wouldn't too lose valves also cause the same decreased vacuum?


If valve lash is loose, the valves will seat fully due to the springs, so vacuum will be OK. However the cam/lifter/roller/rocker mechanism might get battered.
 
Originally Posted By: Vikas
Originally Posted By: Hokiefyd
Zero exhaust valve clearance, or at least exhaust valves hanging open, would probably show up as decreased vacuum, as the engine can draw air through the partially-open exhaust valve. I imagine this would have to be fairly severe for this to happen, though.
Wouldn't too lose valves also cause the same decreased vacuum?


No, they would have to be REALLY loose.

The "lash" is taken up as the bucket/rocker/lifter (depending on valvetrain layout) catches the first bit of the ramp on the lobe. You'll often see duration for a cam expressed in two different numbers, seat to seat and from @0.050. The 2nd number will always be a lot shorter as this is from where the ramp on the lobe has been engaged vs from the flat before it.

If the lash is too loose the valve will open a touch later due to the opening event occurring slightly later on the ramp but the overall profile will be basically the same; duration would be a touch shorter but nothing significant. Overall lift would also be slightly reduced but again, not significantly.

However, with a valve hanging open (exhaust valve usually as the seat erodes) you'll have reduced compression, power stroke bleed-off, exhaust ingestion and this may present as a poorer running engine, loss of power and if bad enough, cause misfires. This can cause permanent damage like a burned valve as well, if not caught.

Think of a loose scenario like a slightly less precise; a more worn-in engine. The cam is the same, the profile is the same, you might lose a little seat to seat duration and you might lose a touch of lift but otherwise the engine is going to run the same. Think of the tight valve as a serious mechanical issue that can cause poor running and valve failure if not caught. The issues potentially caused by a hanging valve, as already described (and beyond), are significant and can cause permanent damage, even failure.

Because of the serious differences between the symptoms of the two presentations here the impact on vacuum would be far more prevalent on the tight exhaust valve than on a loose intake valve, particularly if we are talking a valve tight enough to be held open.
 
Originally Posted By: HangFire
Originally Posted By: Vikas
Wouldn't too lose valves also cause the same decreased vacuum?


If valve lash is loose, the valves will seat fully due to the springs, so vacuum will be OK. However the cam/lifter/roller/rocker mechanism might get battered.


Yes, and will make a bit of noise. However the "loose" specs are generally relatively generous. Things would have to be REALLY lose for damage to occur as once the spring is taken up and the valve is on the seat the force acting on the lifter/rocker/lobe interface is quite small. There will be oil film present to absorb shock and flutter shouldn't be significant unless there's a lot of clearance.
 
Thanks Overkill! Very nice and detailed explanation.

Given all that, I am inclined to leave the valve clearance as it is because

- No valve train noise
- great idle vacuum readings
- no complaints about engine power

I think I can safely ignore the dire warning about have to do the check/adjustment based upon the mileage/age.
 
Some cam companies state the lash ramp on their lobe specs.
For example if the lash ramp is .012" multiply that times
your rocker ratio and subtract about .004" for a maximum
lash setting cold.

If you are going to play with lash settings as a fine tuning
aid, do it on the intake side.

If your power increases with a tighter lash, retard the cam
a couple of crank degrees and install the next bigger rocker
ratio on the intake side first.

A word of caution when playing with lash settings;
With a tighter lash, the lifter will be higher up on the lobe
when it contacts the next transition or lift rate and the
lifter could edge into an aggressive race lobe.

The solution for the old Chevys, is a large core cam with the .875" Ford lifter.
But, those two changes "grows" the duration a few degrees.

Just for fun with everything else the same.....

A 332 stroker' Cleveland with 1.8 intake and 1.7 exhaust rockers, will
take a lot less cam than a 332 small block Chev with 1.5 rockers all
around and it's smaller base circle cam core.
 
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If I end having to do the valve adjustment, I am now ready to tackle it. Possibility is very remote but one can never have enough tools!

Homemade Color coded intake(green) and exhaust(red) filler gauges and corresponding matching NOGO filler gauges:-
P1070119 by sontakke, on Flickr

Homemade special tool to adjust valve; assembled using passthrough 10mm GearWrecnh socket, extension, locking pliers and screwdriver; Version A, regular height:-
P1070120 by sontakke, on Flickr

Homemade special tool to adjust valve Version b stubby height:-
P1070121 by sontakke, on Flickr
 
This is a bit off-topic, but could tight exhaust-valves cause excessive engine vibration at cold idle?
 
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