Is getting Valve Clearances adjusted really important?

valves

#1

Now that I’ve decided to get a new timing belt (that “timing belt–age?” discussion will put the fear of God into you) in my '97 Geo Prizm (aka Toyota Corolla) because it’s got 71k miles (Haynes Repair Manual says replace at 60k), the manual also says (at 60k) “check & adjust the valve clearances.” For a 1997 or earlier model, it says “the procedure requires the use of a special valve lifter tool–it is impossible to perform this task without it.” I can tell from reading the intricate procedure that I’d better have a really experienced mechanic do this. My questons: Why do the valve clearances get “out of specification”? And: Does the fact that I drive my car easy–rarely going above 70 mph–mean that maybe I really don’t need this presumably expensive procedure?


#2

Valve clearances change due to wear. How fast you drive has no effect on the clearance. Personally, I would replace the timing belt and not worry about the clearance unless you hear excessive noise from the valves. If it ain’t broke don’t fix it.

You DO, however, need a new timing belt. 10 years is a long time.


#3

I agree with mcparadise. However if you should have the cam/valve cover off, check the clearances of the valve lifter to the cam base circle. If you find any that is out of tolerance, have a mechanic who has the valve lifter raiser tool and the collection of inserts adjust the clearancex. If you want to be safe make sure that there are no valve lifters with too little clearance because you are risking having the valve held off its seat and burning it. This would be an expensive repair. Having excessive clearance is noisy.


#4

Guess I’m going to have to respectfully disagree with some of the advice you’ve been given. It’s not simply a matter of being noisy; the quiet ones are the ones that really have to worry about.
Valve train lash that is too loose will beat through the hard coating on the lash adjusters, cam followers, or cam lobes over time. This can be expensive to repair.
Valve train lash that is too tight (the TOO quiet part) can burn the valves, valve seats, and in some cases ruin the cylinder head if the situation is bad enough. Not to mention rough running and lack of performance.

Valve clearances get out of spec due to the valve face seating and dishing in over time, wear on the valve seat, and valve stem stretch, the latter of which is generally true of the exhaust valves. Lack of regular oil changes and wear on the valve train can cause excessive looseness.

Whether you do this procedure is up to you. I will only say that I’ve had to perform a number of cylinder head repairs due to neglected or misadjusted valves. In one case, a Subaru, both cylinder heads were bad enough to be unrepairable; and that car only had 7500 miles on it. So much for the DIYer. JMHO anyway.


#5

I have to agree with ok4450. A valve clearance adjustment is inexpensive insurance against future problems, and as ok4450 says, the quiet valves may be the bigger concern. In cars where the camshaft is in the engine block, many cars use hydraulic tappets that presumably kept the valves in perfect adjustment. I always thought that the solid tappets eliminated the occasional problem of clatter on start-up while the lifters pumped up. An occasional valve clearance adjustment was just part of normal maintenance with the solid lifters. As I stated early, the valve adjustment is probably money well spent for your car.


#6

I too have to agree with OK4450. If he hadn’t have said it, I would have. I don’t think the valve lash check is all that expensive, it usually only takes a few minutes, especially if combined with another job, like timing belt replacement. Adjustment on this model, if required, may get a little costly if the cam is directly above the valves, which I think it is on this model.

Know the valve lash specs before you have this done. Consider them as a minimum. If the mechanic says the valve lash is a little too large, I’d let it go, but if its too tight, then it should be adjusted.


#7

I also agree, tight valves are the concern, not loose valves. Don’t feel bad, my car (with mechanical valves) requires adjustment every 15K miles. I would have them checked.


#8

ok4450 has put it as it is. I agree completely. Been there done that and boy did I get burned. The shamefull thing is that I am an aircraft mechanic and out of lazyness, just did not do it.


#9

Oh yeah, well my old Beetle required an adjustment every 3k!

I’d second the “check it yourself and take it in if it needs it” idea. I’m pretty religious about doing valve adjustments, but I’ve never actually seen the valve lash wander on any car except the Beetle.


#10

As others have noted, just check 'em yourself before you panic. A set of feeler gauges is maybe $5 or $6, and at least you’ll know. Besides, a new valve cover gasket will be a really good idea about now anyway. It’s maybe $15 or $20.

If someone else is doing the work, a valve clearance check should be a normal part of a timing belt change, but make sure you ask. Some just reinstall the old valve cover gasket, but I’d insist on a new one.

However, in my experience with this engine and several other Toyota engines, the valve clearances rarely go out of spec. I have a Corolla and a RAV4 in my driveway right now with 170,000 and 180,000 miles, and none of the valves have never needed to be adjusted. I’ve checked them on schedule, but they’ve always been fine. It’s been the same with several other high-mileage Toyotas I’ve encountered.

To make a long story short… on OHC engines, valve clearances can change because of wear on the cam lobes or the valve seat or valve. Wear on the cam lobes causes the clearance to increase, and wear at the valve seat/valve causes clearances to decrease. On the Toyotas I’ve seen, this wear is very slow, or at least in balance – mainly, modern valve seats and cams are incredibly hard durable and modern oils are very good at preventing wear.

If that last paragraph was Greek to you, the upshot is that you must check the valve clearances as scheduled, but the odds are very, very good that you won’t have to change anything. Fortunately, checking the valve clearances is quite simple.


#11

LOL, at one point my old beetle seemed to need an engine replacement every 3000 miles; the #3 exhaust valve had a nasty habit of going through the #3 piston (oil cooler). Fortunately, there was an endless supply of $50 engines back then.

One on my benz valves will occasionally tighten up by .001" or so over 15K miles, but they usually don’t need any adjustment. They still get checked every 15K miles, engines are expensive compared to a couple of hours of labor.


#12

The valve face wears enough to force the stem up, eventually causing the valve to remain open all the time, causing a nice slot to be burned into it. If it’s recommended, have it done.


#13

Whether you should check the valve adjustment or not could not be phrased any better than this.

http://www.americanmemorabilia.com/Auction_Item.asp?auction_id=39729


#14

Checking the valve clearances is part of the timing belt replacement job. Shop around. You can get the whole job done at a reasonable price if you don’t replace the water pump and other belts every time you get a new timing belt. I only replace the water pump, timing belt tensioner, and water pump every other time I have the timing belt replaced (every 2nd timing belt). However, checking the valve clearances with each timing belt replacement is a necessary part of the job. Don’t skip it.


#15

Does the fact that I drive my car easy–rarely going above 70 mph–mean that maybe I really don’t need this presumably expensive procedure?

I would say, probably so. If the engine is running quite with no valve noise, leave it be! I own a 97 GEO Prizm Lsi with the 1.8 engine & 5 spd manual tranny. It has 187+K miles with original timing belt, which I am about to change, and untouched valve clearance. And of course, I’m going to check the valve clearance while I’m in there. But I must say, this car has never gave me any problems what-so-ever and you, nor anyone else for that matter, would ever believe what I have put my 97 GEO Prizm through. I call it “My 1-Ton GEO” because I actually use it for hauling everything from scrap metal to flea-mart items on a regular basis. I have a tow package on it and have actually crossed the scales with 2,100 lbs of scrap metal! And that’s not counting the trailer weight of approx. 900 lbs. I haul, on a regular basis, anywhere from 1,200-1,500 lbs with this car and the engine runs like a Timex. You can hardly hear the motor running with no valve noise what-so-ever. Most of the time I pull with the A/C running and it still acts like there is nothing behind it. You are probably wondering, “why am I pulling this kind of weight with a compact car?”. Well, the answer is simple. My Dodge D-250 gets 10 mpg whereas my GEO gets 38 mpg. Of course, I get that kind of gas mileage because I have a K&N air filter, Iridium spark plugs, and Z-Max additive. Though I only get about 28 mpg while pulling. And the clutch is still original too! You would be amazed at how many people have asked me, “how do you pull all that with that little car?” and I just say, “that’s my 1 Ton Geo”. In short, with only 71k miles, if your engine has no clicking noise, and you have changed the oil regularly, I would leave it be for at least 100,000 miles with no worries. Add Z-Max fuel and oil additive, and I wouldn’t worry about it for 200,000 miles and you will see an increase of at least 6 mpg and more horsepower. Better gas mileage is the key in todays world and Z-Max is the key to longevity of your engine. I am not trying to push z-max or steer you wrong, I’m just telling you my story of my GEO.


#16

And it was the location of that oil cooler that kept killing those valves. It was right above #3 so #3 always ran hot. We generally allow it to run a little loose, to aid cooling.


#17

“If the engine is running quite with no valve noise, leave it be!”

Did you notice a couple of the most respected mechanics on this forum pointed out that a tight valve is a quiet valve?


#18

That’s right. There’s an old saying-- “a tappy engine is a happy engine”. A little bit too loose is better than a little bit too tight.