valve lifters/valve clearance adjustment

valve lifters, in the most basic of terms, are little "buckets" that sit between the camshaft and the valve that lifts the valve up when needed in time with the rest of the engine.

here are a sampling of them:


toyota has used a series of valve lifters over the years, the first generation look like so:








note how the bucket has a shim on top of it that lifts out. this is what is used to adjust valve clearance. many different sized shims are available to adjust to a proper clearance. shims can be replaced easily by removing it from the top of the bucket.

the second generation, we don't have any buckets to give you an example. but here is a shim.


now on to the new generation, as on the prius. there are 16 of these suckers in a prius engine.




look mom, no shim! this is what makes valve clearance adjustment a serious PITA... you have to remove the whole bucket, not just the shim from the top. and to get the bucket out, you need to take the camshaft out. and to take the cam out, you have to remove the sprocket. and to remove the sprocket, you have to get the timing chain off it.... get the drift

then all 16 buckets need to be replaced with ones that have different thicknesses.

so for those of you concerned about valve adjustment- 60k is pretty early to do this and theoretically your valves shouldn't be out of adjustment yet. 100k or more is more reasonable... basically if there's a reason to go in there. as in, if your valve cover gasket starts to leak and it needs replacing anyway. around 100k is where you might start to see evidence of your seals degrading with use, so if you're having something replaced this isn't unreasonable to do at that point.

to adjust this, you do need to break that seal. and breaking engine seals unnecessarily, unless in the hands of a known competent engine gasket person, is a bad bad idea.

Is it far to say then, leave it alone till the engine acts up? Is there away to otherwise check to see if the valves are out of adjustment, like compression check or something or checking compression with compressed air like they do on little airplanes and see if air hisses out of exhaust or the intake?

I remember reading all about buckets and shims in a repair manual for my motorcycle, then opening up the engine to find screw-type adjusters. They were very fidgety and took several tries to get just right with only two hands, but it was much easier than taking half the engine apart. Dual overhead cams, four valves per cylinder, and 11,000 rpm was way cool for 1981.

compression test won't tell you if your valves are out of adjustment, it will tell you if one is sticking. but it won't tell you if that's because of clearance or because they're not getting proper lifting.

so there's no way short of going in there to check the valve clearance.

valve clearance doesn't typically tighten- it gets more slack. you'd start to hear a valve lifter tick in the top end before you noticed performance issues as far as the engine 'acting up' goes.

there's actually a special tool for those screw-type adjusters now, hyo, but just the mention of said adjusters got quite the reaction out of DH

<div class='quotetop'>QUOTE(galaxee @ Oct 22 2007, 10:37 PM) [snapback]529113[/snapback]</div>

We have screw type adjusters on our boat's diesel engine. The special tools for that are a large flat-blade screw driver and an a big crescent wrench. It's very delicate.

Tom

Never adjusted the valves on the Camry and I'm guessing the Prius will be the same.

Thanks for the pictures though galaxee.

I had the last model of Subaru with the pushrod engine. It used a special tool, with two handles. One had a hex that loosened the lock nut, the other had a hex that did the adjustment. And yes, it was very fidgety. I eventually learned the angle that compensated for the screw movement when you tightened the lock nut.

If there is a problem with the valve seat moving in the head material the valve will tighten. Otherwise, it will loosen. In my experience, -most- of the time these things don't need to be adjusted over the life of an engine. Particularly for a 5000 RPM engine. But I guess we'll see. The manufacturers always provide a lot of effort to make sure they stay in adjustment, and a lot of effort to make sure the dealers know how to do so. Even so, the anti-Prius (2001 Pathfinder with 3.5L VQ engine) never needed this service. You can usually tell it's needed if it gets noisy (so called "tappit noise"), or seems to "miss" (tight valve).

Some of the high reving motorcycle engines (and the Ford SHO engine) would have a tendency to "spit out" the shims when over-reved! Not nice!

One hopes that in these engines, valve and seat wear will compensate
for bucket and cam wear. If they both happen at roughly the same
rate the whole valve will gradually sit a little higher than it used
to, but all the relative clearances will still be the same!
.
_H*

Whatever happened to hydraulic valve tappets?

<div class='quotetop'>QUOTE(apriusfan @ Oct 25 2007, 01:45 PM) [snapback]530338[/snapback]</div>

They tend to float at high speeds.

Tom

<div class='quotetop'>QUOTE(apriusfan @ Oct 25 2007, 01:45 PM) [snapback]530338[/snapback]</div>

gm sucks. thanks for your question

<div class='quotetop'>QUOTE(qbee42 @ Oct 25 2007, 01:25 PM) [snapback]530423[/snapback]</div>

When did 5,000 rpm become high speed? There are any number of manufacturers that use hydraulic tappets in engines that pull into the 6,500 rpm territory. North of 7,000, I can understand would require non-hydraulic tappets, but 5,000????

<div class='quotetop'>QUOTE(galaxee @ Oct 25 2007, 04:45 PM) [snapback]530494[/snapback]</div>

Way more than GM are using hydraulic valve tappets.

Where would you put said hydraulic lifters? They are for pushrod engines and go deep in the block. The Prus uses a -modern- overhead cam engine. All valve gear is in the head. I'm not aware of any overhead cam engine that uses hydraulic lifters, GM included. Other than the F1 engines, but they are pneumatic valves, I believe. And I don't think they have cams. You need the range of automatic adjustment hydraulic lifters afford when you have pushrods, due to the large expansion changes as well as the wear of the valve gear. You only need a very small amount of adjustment with overhead valves directly driven from an overhead cam. Perhaps some version of variable valve timing might use some kind of hydraulic component. But this gets expensive very fast.

Please list the engines that run up at 6500 RPM with hydraulic lifters. I know the Corvette engines use solid lifters, both with the pushrod engines and the overhead cam engines. All truck engines are limited to lower RPM. All NASCAR engines run solid lifters.

<div class='quotetop'>QUOTE(apriusfan @ Oct 25 2007, 09:45 PM) [snapback]530530[/snapback]</div>

I don't recall anyone saying 5,000 rpm was high speed. The original question was "Whatever happened to hydraulic valve tappets?", not "Why doesn't the Prius use hydraulic valve tappets?"

The answer is that most modern engine designs have gone with overhead cams to allow for better control of the valves at high speed. The Prius engine uses this configuration because it is part of the same family of engines produced by Toyota for other vehicles. There is economy in standardization of a design even if all of the features are not used in every application.

Tom

<div class='quotetop'>QUOTE(David Beale @ Oct 26 2007, 08:47 AM) [snapback]530713[/snapback]</div>

Well, the C5 Corvette with the LS1 & LS6 engines use hydraulic tappets. Same for the C6's LS3 & LS7 engines (the LS7 has a redline of 7,000 rpm, as well). Volvos have used hydraulic tappets going back to the 1995 850 Turbo (I know because if I didn't drive the 1995 850 Turbo that I used to own for a period of 2 weeks or longer, there would be a clicking sound for about the first 30 seconds after the engine was started). The dealer's shop foreman said the sound was the hydraulic tappets getting re-oiled. Continuing on with the list, there are some BMWs that come to mind: X5 with 4.8 liter engine, E61 545 are two that immediately occur. Mercedes also features hydraulic tappets as well. If you want an exhaustive list, I would invite you to research the subject.

NASCAR engines are racing engines and I presume they run over 6,500 RPM, so they don't count.

Lots of ohc engines have used hydraulic tappets. 1980's Camrys and 1990's Maximas are two. Toyota says to just check Prius every 60K, which should not be hard to do, and should be done. I wonder though how the engine is turned to do this.

<div class='quotetop'>QUOTE(Mr.Vanvandenburg @ Oct 26 2007, 04:59 PM) [snapback]530937[/snapback]</div>

So do I (wonder how the engine manages to go 60,000 miles before checking/setting valve clearance). I wonder if perhaps this isn't a preventive maintenance item at say, 30,000 miles? The primary argument against a preventive check at 30,000 miles seems to be difficulty of sealing things back up after checking (and adjusting if necessary) the clearance.

<div class='quotetop'>QUOTE(Mr.Vanvandenburg @ Oct 26 2007, 07:59 PM) [snapback]530937[/snapback]</div>

ummm.... the first generation i pictured above came out of the head of our 1988 camry. unless you're referring to the 83-86 which are extremely rare today, which may or may not contain above mentioned tappets. suffice to say the 4-cyl in that one was pretty unsophisticated.

no, this job isn't easy. hence my use of the term "serious PITA." especially if one is burdened with such things as timing chains. even with a timing BELT, it's still a PITA. there aren't a whole lot of times that camshaft removal can be considered easy.

are you referring to the crankshaft bolt to turn the engine?

no!!! it does not need to be done at 60k, and the mere suggestion of busting the valve cover seal out to do this at 30k reeks "useless waste of time and money." toyota knows how to design engines that don't f themselves up. the ENTIRE POINT of my post was to tell people it does not need to be done at 60k.

the primary difficulty is the job itself. maybe i under-emphasized how hard this job is by using the term "serious PITA" and over-emphasized the incidence of leaky seals after factory ones are broken.

just because they're not hydraulic and self-adjusting does not indicate they NEED to be adjusted. we've run yota engines to 250k and beyond, still running, NEVER a single valve adjustment. the cylinders wore out before the valves went out of adjustment on our 88 camry...

are you a mechanic? how many valve clearance adjustments have you sold and why? you are likely the only one. the ONLY time a valve clearance adjustment is really a good idea is if you're going to be in there anyway. the only times DH has adjusted valve clearance is when he was rebuilding an engine from the bottom up.

-------------------

[deep breath]
general message to all:
really, people need to chill out about this kind of stuff. i know there are a bunch of folks among us who are extreme perfectionists and think that every possible thing that can be done should be done as frequently as possible, but seriously. but let's refer back to rule #1: if it ain't broke don't fix it. just drive the car. it will be fine. seriously.

<div class='quotetop'>QUOTE(galaxee @ Oct 26 2007, 08:40 PM) [snapback]530999[/snapback]</div>

In a prior lifetime, I have indeed adjusted valve clearance on cars I owned. I have a complete set of the adjusting disks along with the special tools to depress the cup/bucket and remove the previous disk and insert the new disk used to set the clearance on a 1978 Diesel Rabbit. That car would need between 1 - 4 (out of a total of 8) clearances adjusted every 15,000 miles. Later cars i have owned were equipped with hydraulic tappets, which was why I made my original post.

The 83-86 Camry had hydraulic lifters, I had an 85 which I bought new. If I remember right, the block was cast iron, 2 liters, there was the Al cylinder head and another separate Al casting on top of the head that held the OHC. Simple it was not. I changed the timing belt myself twice, not easy at all. I didn't know checking valve stem clearances would be so tough, unless the valve cover is hard to remove. I was just pointing out there are various OHC engines that use hydraulic lifters.

I never looked at the Prius engine enough to see if it had an accessible crank bolt. Of course if it does, it can be turned by hand. Or can it? I hope I never have to try.