Theory behind valve adjustment?

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Please correct my understanding.

If the intake valve are too lose, it means they open too late and close too early and thus does NOT take in full charge and thus making engine sluggish.

If the exhaust valve are too right, that means they open too early and close too late, it means exhaust gases escape through the exhaust valve reducing the effective compression and also making the exhaust port too hot and possibly burning them.

Something interesting which was noted by my shop. He had seen quite a few MDX and Pilot with random misfire codes tracked to needing valve adjustment but never had any Odyssey with similar issues. This is all empirical but I am wondering if there is some theoretical basis to it. The engines are very much similar but I wonder if the compression ratio and cam profile etc are somewhat different in these two applications.
 
There's more to it.

If the valves are loose, the cam hits the follower too hard, adding noise and wear.

If the valves are too tight, they might not cool enough and burn.

misfire codes are generated when oxygen is found in the exhaust gas. too much valve overlap could cause this maybe?
 
A modern engine should never need a valve adjustment if they have hydraulic lifters.

The last engine I did a valve adjustment on was an OM617 which has solid lifters. But that motor is old school even by 80's Mercedes standards.


Typically as valves wear they could get tight, which is why Honda probably says to check them at 120k or something like that. But to be honest I have not read a Honda manual that was built in this century. 99.999% of owners never have them checked anyway.

I can't imagine a modern car requiring anything like that.

The valves would have to be way out to cause a misfire code like that. Did your mechanic check the timing? Maybe the timing belts are old and one of the cam's slipped a bit?
 
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DIL's 99 CRV burnt a #4 exhaust valve at 100k. She was putting my son through law school at the time . so I loaned them a spare BMW and I set to on my first valve job in 30 yrs. My son, bought the parts and I replaced the valves in #4 only and I went a tad wide when I set the lash.Valve seat recession tends to tighten the lash. This is how valves wear. Running wide on the exhaust valves might waste a little power but they won't burn.
 
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.
 
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.
 
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.

Actually the Nissan had 250,000k miles. Yipee for Nissan. I guess.
 
Quote:
A modern engine should never need a valve adjustment if they have hydraulic lifters.
Good point. The Honda 3.5L V6 does Not have hydraulic lifters. And does need valve adjustment. My exhaust valves were mostly tight at 105K. Some Honda manuals for these say adjust if noisy. This is not accurate as too tight exhaust valves are not noisy. As said above, too tight is bad. Arts Automotive recommends V6 adjust 105K. Old CRV much more frequently. http://classic.artsautomotive.com/HondaV6ValveAdjustment.htm
 
Not having HLA's means you can run lighter springs, which generally last longer before they allow valve float. These components are also simpler, so they are cheaper to manufacture.

Most of the domestic marques migrated from pushrod engines into the OHC scene. In the pushrod sector hydraulic lifters were basically an essential item; nobody wanted to be popping their valve covers to adjust a solid valvetrain. So when they migrated to OHC, the natural progression was to retain that system. That's likely why the Modular uses little HLA's and roller followers.

This of course isn't a rule of any sort. I know Ford used cam-over-bucket (non-hydraulic) in the Focus. But that was a European car..... My BMW is also cam-over-bucket, most of them are, with hydraulic lash adjusters as part of the bucket assembly. But it does seem that the Japanese marques, like the Euro marques, didn't ever get much into the the pushrod scene and so the adoption of HLA's is hit and miss and may only be in certainly applications if at all.
 
Found this on the web regarding Honda/Acura J series V6 motor; at least it makes sense to me. In terms of the MAP reading, I am assuming he is at sea level. I do not know if MAP readings are automatically compensated if at the elevation or not.
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Alldata book time for the valve adjustment is 3 or 3.2 hours. With cost of the valve cover gaskets and spark plug seals $450-$500 seems normal dealership cost. Normally Honda V6 engines do not get "loose" valves like the 4 cylinders. Normally the intake valves hardly need any adustment, and the exhaust valves are "tight". The valve seat gets pushed deeper into the head, and it decreases the exhaust valve clearance. If this gets bad enough it will cause a rough running engine, misfire, decreased gas mileage, and sometimes the engine will stall at idle. This problem is the worst in 01-06 MDX and 00-03 TL's. You can get a rough estimate on how "tight" or "loose" your valves are by looking at Map voltage with a scan tool. The map voltage gives a rough indication of valve lash by telling you how much vacuum the engine has at idle. You are looking for a voltage between .88 volts and .95 volts ( no load idle ). If it is under .88 volts the valves might be "loose" ( too much vacuum ). If it is over .95 volts the exaust valve might be "tight" ( not enought vacuum ). If you attempt an adjustment yourself, adjust the exhaust valve on the very loose side. I use .22mm for the intake and .33mm for the exhaust. The specs are .20 - .24 intake and .28 - .32 exhaust. I find with .22 intake and .33 exhaust it will land your map voltage at .88 - .90 ( perfect ).
 
Honda Fits are hit or miss with needing valve adjustments. I adjusted the valves at 30k. Most of them were fine while a few needed adjustment. It's getting a day in the garage soon, so I may have to add that to the to-do list.
 
Originally Posted By: hattaresguy
A modern engine should never need a valve adjustment if they have hydraulic lifters.

The last engine I did a valve adjustment on was an OM617 which has solid lifters. But that motor is old school even by 80's Mercedes standards.

Typically as valves wear they could get tight, which is why Honda probably says to check them at 120k or something like that. But to be honest I have not read a Honda manual that was built in this century. 99.999% of owners never have them checked anyway.

I can't imagine a modern car requiring anything like that.

The valves would have to be way out to cause a misfire code like that. Did your mechanic check the timing? Maybe the timing belts are old and one of the cam's slipped a bit?

None of my cars had the valve cover removed for anything. My mechanic told me modern engines with hydraulic lifters don't need valve adjustment.

I had misfire code couple months ago with my E430, probably because of bad gas. I used 2 bottles Techron in 2 consecutive fill ups and changed ATF, the misfire code is gone the engine and transmission are smooth now.
 
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.
 
Line by line....

If the intake lash is wider than specified, the cam will
act a few degrees smaller.
In other words, more bottom end and less top end power.
The engine may idle better because of the slight reduction
in overlap. Intake vacuum may increase.
Due to the later intake valve opening point, port velocity may also increase.

Increasing the lash on the exhaust side does much the same.
It also prevents the valve from being held open when and if
enough heat is generated to grow the valve beyond the lash setting.

Highly loaded valve trains flex, cams wind-up and
let-go, so actual valve timing will be like a game of
horse shoes, where close counts.
 
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 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.
 
I don't buy cars with cam belts or non hydraulic valve trains. when you get paid for the work it is a great way to get paid, but other wise it is a waste of my time.
 
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