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How to adjust engine valve clearances.
Modern efficient motors need the valve clearance to be spot on and this is crucial to their operation. A wide valve clearance will make an audible ticking sound if it is wrongly set by even a few thousandths of an inch. If you can hear it, it is doing damage.
A valve clearance that is too small will lead to serious internal damage of the motor in time. If a valve clearance is too tight the motor will lose power when warmed up to operating temperature and start to misfire.
I still see mechanics today who have no idea how to adjust tappets or replace shims. I wonder how they got certification, but sadly this is not unusual.
With racing motors you need to allow a wider clearance to ensure the extreme heat does not result in zero clearance under extreme conditions, but it is only a couple of thousandths of an inch because the metallurgy is so damn good these days that the metal does not grow more than an almost immeasurably small amount even when fully stressed.
Accurate valve clearance is crucial for peak engine performance, yet many auto mechanics are not skilled enough to make the adjustment as well as it is done in the factory that assembled the motor new.
The clearances are set in sequence with the position of the camshaft/s so that the widest setting is read when the camshaft lobe is in the correct position.
The way to achieve this is to rotate the motor until it is in the prescribed position for each valve adjustment to be made.
These days cars motorcycles and trucks have different camshaft configurations, with the twin overhead camshaft motors making a comeback due to their generally better fuel consumption.
The valve timing on newer multi cam motors is often variable and the camshafts often belt driven instead of being solely chain drive. Valve timing is easy as always, you just need to align the marks on the cam wheel to those on the block, however to do the adjustment to the rocker arm or to change the shims although simple enough requires feel, experience and patience.
It has been my experience that very few mechanics get valve clearances close enough to factory specs because they lack engineering knowledge and feel.
Newer motors if assembled so well at the factory they do not require valve clearance adjustment until they have done at least 50,000 miles.
Often engine wear and other problems are caused by mechanics who lack the knowledge to make accurate adjustments during scheduled service.
The valve gear on Honda motors is so good, that when I bought my first Honda car I made sure they did not do the tappet adjustment when due in service as it was perfect and I knew from experience it was unlikely the dealership would set them and lock them down with the same method used in the factory.
On many older models I replace the lock nut and adjuster when I re-set the valve clearances. If there is any sign of wear on the working surface of the adjuster or shim, I know the clearance will not be close enough or remain accurate without replacing with a new one.
If you look in the manual you will see a recommended tension for the adjuster lock nut. I use a special very small accurate tension wrench used on motorcycles to bed them down.
Here is the technique I taught to my mechanics.
- Clean all mating surfaces to ensure there will be no particles on any of the mating parts such as the locknut flat surface where it meets the rocker shaft.
- Ensure the thread in the rocker arm is completely free of friction by screwing the adjuster in by hand.
- Make sure the lock nut screws on the adjuster shaft by hand without any binding.
- Put a good quality feeler gauge of the correct thickness between the valve stem and the adjuster.
- Screw the adjuster in until it binds tight and you can't pull it out.
- Now bring the adjuster back out till you can pull the feeler gauge out with a slight binding.
- hold it in place by putting a spanner or key spanner on the shaft of the adjuster as you tighten the nut firmly but lightly.
It should still bind very slightly.
- Now put the tension wrench on it and tension to the recommended setting.
If you follow these instructions, the feeler gauge will now slide in readily and have a little less binding after the tensioning to specs which will change the setting to make it about one or two thousandth of an inch wider as the locknut pulls the thread to lock the tappet adjustment shaft against the female thread wall of the rocker arm.
Engine cooling, fuel consumption, power output, valve stem and guide wear all rely on valve tolerances being accurately set.
Hone your skills and ensure you do the job properly.
Comments
I think that these days a valve adjustment is beyond most DIY-ers skill level. I know it's beyond what I would tackle but it does point out the importance of choosing a mechanic based on his knowledge, not by his charge per hour.
When my vehicle was new I always had the dealer do all maintenance to be sure that the guarantee would not be violated. The work was often done by "mechanics" who whose skill level was not up to their excuse-making ability.
I soon returned to my regular mechanic - who had the education/know how and facilities to do proper work.
I don't know about Australia, but in the U.S., the teen gearheads who used to hang out at the local garage, are pretty much gone.
Good informative Hub though.
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Great comment Hugh. I know it is getting so most DIY mechanics don't do tappet adjustments much anymore, it is too hard to find the damn motor under all that plastic and plumbing!
I really wrote this for motor mechanics, as my experience is that most do not get it right.
earnestshub, there's something to be said for a Hubber's mentioning his own area of expertise in forums other than the ones in that area. I saw one of your posts and thought I'd come read this Hub. If the question below is too long and "weird", and not something that could be answered easily here, I understand. It was your mention of Honda that brought on my question.
Here's what I know is most likely an ignorant question, but one of my kids has a well preserved early 90's Honda Accord. For the most part, it runs fine. It has a weird, almost whirring, hum (kind of "high-ish pitched") to it, that brings to mind something similar to the sound used in old movies when "flying saucers" landed. Whenever mechanics have been asked about it, they've all said, "It's just what they (old Honda's) sound like." Well, it isn't, because there are still a lot of them around; and none of them I've heard go by me sounds like this one. It doesn't sound like any of the "classic, engine-problem, sounds" I, or anyone else in the family, has ever heard.
So, my question is: Might need for this adjustment be what's making something like that, and is this the kind of thing mechanics working on old cars would just ignore? OR, is it the kind of thing that, if left long enough, would cause enough problems that it couldn't be ignored (and would end up making the person with an "oldie" car have to get a new one (if he wasn't someone who could do the adjustment by himself, and it would just be too complex a thing to be worth spending on an oldie?) I know nobody can diagnose weird (and not at all even ominous sounding) over the Internet, but it's hard to believe this sound isn't some problem LOL and mechanics all have said it's not a problem. In other words, is this something mechanics might miss?
The other part of the question (and this is, I know, the most ignorant part) is: If there's the chance this is at the root of that sound, and if a person wouldn't tackle this adjustment himself; how big of a deal would it be for a mechanic to do the adjustment (labor/hours-wise) if someone asked a mechanic to check this out and see if it could be the cause of such a sound? My thinking is that this particular sound cannot possibly be heading anywhere good. LOL I'm not asking if you can identify the sound - only whether an adjustment to the valve clearance could be an overlooked cause of it (particularly, maybe, because the car is so old, and mechanics just think some stuff isn't worth looking into).
I suppose I could have asked the question in fewer words: How would a person with an old Honda Accord (or any car) know if this is something to, maybe, point a mechanic toward?
- Author
Hi Lisa. Nothing wrong with your question, and I still keep a 1984 Honda with The same Civic motor as yours.
Any noises such as the one you describe simply should not be there.
My old Honda hasn't any strange sounds, and the motor is well known for being mechanically quiet.
I am way less than surprised that the mechanic can't find it.
Yesterday my son bought my Honda back after using it for the last 2 years to run to Uni.
It was idling rough and cutting out at the traffic lights. A thin rubber vacuum tube was leaking. My son had it to a mechanic on his side of town who claimed it needed 2k spent on the motor. It took all of 2 minutes to fix it!
Now, to the noise in your car.
The sound you hear is not likely to be the motor itself.
The sound could be.
A. The water pump needs replacing. Cheap to buy and fit, should cost under 200 dollars to replace.
B. A vacuum hose leak as I mentioned above.
C. An alternator bearing. Replace the whole alternator, they are cheap after market and should not exceed $120 to replace and takes about 15 minutes to fix.
D. Fan belt slipping. Simply adjust the belt tension or replace the belt, also cheap, probably under $20 for the belt, and minutes to change.
I don't know if you have skype, but if you want to contact me direct I will talk it through with you and I bet we can locate the noise. I also wrote a hub on identifying weird sounds in motor cars which I will find and provide the link if you would like to work it out for yourself.
Whatever you do, don't get rid of the Honda unless it is worn right out and ratty.
Very informative article, Earnest. Unlike when I was a teenager, there aren't many of what we referred to as "shade tree" mechanics around these days. My nephew recently replaced the battery in his truck and installed it incorrectly, swapping the positive and negative terminals in the process
He ended up having a tow truck haul it 30 miles to where he bought it just to find out his problem. 8 years of college and didn't know how to replace a battery. Sad!
But there are still those of us who aren't afraid of getting our hand dirty. LOL! Rated up, of course!
Earnest, thank you. I'm going to copy that list for my son. Thank you for the offer of help; but because the car is my son's, the only thing I really know about it is that it has had the strange "flying saucer" noise since he got it two years ago. (It almost sounds like a loud version of those old musical tops that kids used to have). This car sounds like no other car I've ever heard. (LOL) I just know the mechanics' remarks, "That's just how it sounds," can't possibly be right. Again, thanks. I'm going to pass the list to him. Somehow, that alternator bearing possibility is kind of uppermost in my mind (based on what I know he has had already had fixed in the past). Again, thanks.
Wow what you are describing is what we used to simply call "feel" don't see much of that around these days!
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Thanks for stopping by agvulpes, You have a good feel for engineering yourself.
I guess I hope to instil a sense of what really destroys motors.
Bad mechanics.
So to all mechanics I say Ya gotta have luv! ............and "feel" the tolerances grasshopper!
This should be very interesting for my son. He is trying to learn as much as possible to repair his own car. So far he hasn't done to badly. In England too the garages are hopeless in their service but know how to charge sky high prices.
- Author
Thank you my friend hello, it is the engineering knowledge that is most important when setting engine tolerances.
Fine tolerances are the stuff of good results in the workshop.
You thought I was joking about my valves? How am I going to do it myself in a mini van - no access unless I take the whole thing apart.
By the way, you didn't show up. I love you mate!
Are you off task? What about my sticky valve or whatever? What can I do? This thing ain't no straight 6 Ford. Those were the days. You could rebuild 'em without taking 'em out of the chasis! All you needed was a screw driver, a wrench set and a pair of vise-grips.
- Author
ask me here and I will give some help. What is it and what is wrong?
Not sure. one of the cylinders is "missing". I bet I can clear it up by adjusting the valves. It is a "dodge" town and country. Hard to access. I am lousy mechanic! Need bullets.
I put the serpentine belt back on by myself. I wrapped painter's tape around the pulleys to get the size for the new belt. I am scared of the valves though.
- Author
First thing to do is check the compression of the cylinders.
A sure way to know if the misfiring is caused by any valve leak, or piston/piston ring wear.
Cylinders should read within a few PSI of each other, any wide variance indicates wear or leaks.
Okay, now I have something to do. Thanks. I'll get the guy at the parts store hook me up with his equipment. They are good about that these days . . . as long as you end up buying parts. Like you said, you need to have a feel for it. I am feeling my way along the wall here.
- Author
WD you could also do a simple ignition check to ensure all cylinders are receiving spark.
It could be as simple as a faulty spark plug or lead.
Good one, thanks. I learned this as a bellhop. Don't take a new TV to the room before checking to see if the "faulty" one is plugged in.
I've been thinking about this valve clearance thing. It may be a big problem in the repair industry around here.
- Author
WD you can buy a compression tester for under $30 and while you have the spark plugs out you can check ignition at the plug.
Frankly it is unlikely to be a valve clearance problem unless they were set wrong during a full service.
If you can give me enough background and information I can work it out from here.
Thanks so much for the help! Listen, I think mechanics around here aren't that good at setting things like valve clearance. You have to go to a really good dealership. I think American cars traditionally have more leeway on things like that (which might not be a bad thing). The people who set valve clearances as tight as you are working in NASCAR.
- Author
Many American cars have hydraulic valve lifters too. They are fine unless the engine is run low on oil, or badly serviced in which case they will block up and cause valve problems.
As I said, with a compression tester and the plugs out you can check ignition and engine condition. If you need to know how to do the test yourself, just let me know.
- Author
Many American cars have hydraulic valve lifters too. They are fine unless the engine is run low on oil, or badly serviced in which case they will block up and cause valve problems.
As I said, with a compression tester and the plugs out you can check ignition and engine condition. If you need to know how to do the test yourself, just let me know.
I agree, most of the good mechanical engineers get job offers from the pointy end of the industry.
I was paying a grand a week for my best mechanics way back in the 1970s
The part store guy is good. If I catch him on a slow day, he'll let me do it in the parking lot. Work on my car that is. He likes to help and beat the man. You know about that.
- Author
Good. Glad to know your man has some integrity. I hope you get it sorted.
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I'm good to go now, thanks, brother. New wires.
By the way, the Aussie Rules punter for LSU (Louisiana State) Kicked a 70+ yard punt to get his team out of trouble on their own end and win the game. The Alabama receiver watched helplessly as the ball sailed over his head. If you don't know, that is South East Conference football (their religion). No touchdowns in this smash mouth dual - all field goals. It was more of a mixed martial arts match than a football game. The last man standing won.
Lisa HW, I'm almost sure your car has (had) a timing belt that was installed (replaced) too tight. Many 'shadetree' mechanics don't know that a tensioning procedure should NOT be followed, regardless of what the AutoZone repair manual says. I can't tell you how many older Hondas I've heard making that ridiculous-funny 'whirring' sound under the hood. The other bad part is this will also shrink the life of the timing belt. Again, this is spot on with this Hub's author's well spoken point on (lack of) mechanic competancy.
Not sure which Genny you're talking about but the 2.0T is HIGHLY tubnale GReddy Performance Parts has paired up with Hyundai to begin manufacturing new products for the Hyundai Genesis Coupe that has been raising eyebrows. Expect the new high performance parts to be launched at the 2009 SEMA Show on the GReddy X-Gen Street Genesis Coupe. The production tuning kit will include all the parts needed for the Hyundai Genesis 2.0T engine. The GReddy Total Tune-Up package will be a blend of performance, handling, and braking improvements. Hyundai plans to market the car as a reliable street performance vehicle with a powerful driving experience. At first they plan to increase the numbers to 350 hp and 320 ft lbs of torque, but after the SEMA Show further plans are to push nearly 500 horsepower. …The V6 will also has tuning potential but the 4 cyl has a good head start.While it's true that doing it yourself will void the warranty Hyundai did have the tuner crowd in mind when making the Genesis. You may want to wait until more aftermarket stuff, like GReddy, comes out so you could have more stuff to choose from. Warranty issues may not come into play if you get stuff sponsored by Hyundai like GReddy.
Tire valve caps are the final seal again potential faliure in the valve of the valve stem. A good tire valve cap will come with high quality rubber seal that push against the circumferential 'ring' of the valve stem and thereby help to contain the air should the valve fail or not containing the air very well. You observation of your tire (the one with the missing cap) losing air confirms that this could be a possibility.Of course, the other possibility is that your tire is having a slow leak go to any petrol station, and it could be rectified at a minimal cost.Note: Even if the valve is perfectly good, if the tire go over a bump or pot hole, it is still susceptible to lost of air due to the additional pressure asserted during the hit.
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