Valve Adjustment Methods and Pros/Cons

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Any gearheads here want to talk specifics about valvetrain design?

I am trying to get a understanding of the various ways that valvetrains are designed for adjustment, and the pros/cons of each type. A lot of this is coming from my experience with motorcycles where valve checks/adjusts are common maintenance. Can't say I have ever needed to do any valve work on any cars/trucks I have owned.

1. Locking screw type - I was exposed to this method on an old Honda dirt bike with a single cylinder engine. The cylinder head has "port holes" where you can access the valve clearance adjusters, which consist of a threaded post and some locking nuts. Dead easy to do (if access isn't a problem), but very imprecise.. You would adjust the post for length, and then when you tightened the lock nut, the clearance would change just slightly. I would imagine this design only works for fairly "agricultural" applications at low RPMs.

2. Shim over bucket - This was the first type of valve adjustment I did and it was surprisingly easy. Still requires removal of the valve cover and you have to be careful once inside there, but the shims are easy to access and swap out. I did a little reading and it seems the drawback of this method is increased weight due to the size of the shim and it doesn't seem well suited for high-rpm applications.

3. Shim under bucket - This is my current challenge. Both of my bikes use this method and I don't look forward to removing the camshafts just to change the shims. The shims are tiny, though, so that helps to decrease weight in that area.

I know that cars are using some more advanced methods for adjustment (some automatic).. Can anyone talk about these?
 
Number 1 is the way Honda uses in their K and F series engines, which can easily rev over 8-9k rpms. If you have valve adjustment screwdriver, it is easy to do. It literally takes less than an hour to check all valves.

#2, I have never dealt with it. No idea.

Number 3 is PITA to adjust, and this is my current challenge either (1zz-fe Toyota engine). I don't want to remove the timing chain/tensioner/cams. I am just going to keep it as is until the engine stops working lol.

In my opinion, locking screw type with rocker arms is the most convenient way, and the easiest to adjust.
 
My '75 Civic, '81, '85 and '88 Accords used #1 method.
I found it to be one of the more satisfying maintenance jobs.
Checked the clearance on my Matrix (#3) at 60K miles and one intake is at the loose limit of spec.
I think I can hear it tick, but it's not worth the trouble to change.
 
Originally Posted By: circuitsmith
My '75 Civic, '81, '85 and '88 Accords used #1 method. ...
So did all my previous cars (2 with pushrods, one OHC) listed below. Old-timers used to adjust them with the engine idling.
 
I have the #1 type locking screw on my BMW motorcycle and find no problem at all setting them accurately, easily to within .001"

I done #2 shim over bucket on a Z900 and it was also easy enough.

#3 does sound a real PITA but bear in mind both #2 and #3 will normally need doing very rarely and adjustment should not be needed at every annual service.
 
Its all been pretty much covered but the automatic ones you refer to are also known as hydraulic lifter or lash adjuster, they were also used in the Honda CB Seven Fifty.
There is another type that hasn't been mentioned and is the easiest of all adjustable ones and that is the wedge screw in the bucket like those used on Porsche 924 engines, Insert the feeler and turn the screw with an Allen key until its correct. It takes all of a few seconds per valve once the lobe is in the correct position.
 
#1 isn't so bad. I put a feeler gauge in (it's coated in oil as are my hands and tools at this point) and adjust the tolerance, lock the locknut, and gently yank the feeler out. Then I confirm by reinserting and looking for slight drag.

However hokey this sounds, the engines I've done it on started out way out (and all over the place over/ under) and purr when done, so it seems good within my tolerances. OM617 Merc diesels love and need this.
 
Originally Posted By: CR94
[quote=circuitsmith Old-timers used to adjust them with the engine idling.


Still got some mangled feeler gauges from doing that...only with pushrod engines, there is too much oil flying around with ohc.

Easiest to adjust are eccentric shafts. Matchless/AJS twins, and some early BMW cars. Not common, but very nice.
 
I've only had experience with 1 & 2 - 1 was a friend's Honda. Wasn't too bad, but if I had the factory SST or the Snap-On/Lisle adjusting tool it would have gone faster. 2 was my old car and my parent's Sienna. Checking the clearances isn't too bad. It's taking the shims out with the lifter bucket depressor and wedge to press down the lifter bucket while you take the shim out that's a pain. Toyota switched over to SUB lifters or even solid lifters, both need the cams to be pulled - supposedly a Suzuki/Yamaha shim will work on the 1UZ/3UZ SUB setups. You need to buy new lifters in some cases.
 
Method #1 is what MG engines require. I use a feeler gauge between the rocker and the top of the valve to set the micro-adjust screw and then tighten the locknut. I do 15 thousandths and adjust until the gauge is "sticky."

Granted it's a 4 cylinder and the valve cover takes all of 30 seconds to remove or reinstall. Still, I can set the valves in about 10 minutes-the rule of 9s is your friend on a 4 cylinder.
 
The only thing except single-cylinder small equipment engines I've ever worked on that wasn't hydraulic/zero lash idea is my '72 Honda 175 twin with the screw/nut + porthole setup. It takes some experimentation to get the feel of, but after doing it about twice (and being a machinist with more idea of what .002" feels/looks like) I feel comfortable in doing it somewhat quickly. Basically, snug it onto the feeler, tighten jam nut, wiggle it - if you can feel it just barely move but can't actually hear it rock back and forth, it's real close.
 
We used to do 650 Triumphs by feel/sound. Inlets were 1 1/2 thou - 2 thou you could hear and feel, 1 thou the rocker was loose, but you couldn't hear or feel anything, 1 1/2 you could hear but not feel. Exhausts were 4 thou, 1/4 turn was 5 thou, so not quite a 1/4 turn.
 
Originally Posted By: CR94
Originally Posted By: circuitsmith
My '75 Civic, '81, '85 and '88 Accords used #1 method. ...
So did all my previous cars (2 with pushrods, one OHC) listed below. Old-timers used to adjust them with the engine idling.
first time I saw valves adjusted was a running slant6
 
Originally Posted By: Chris142
Originally Posted By: CR94
Originally Posted By: circuitsmith
My '75 Civic, '81, '85 and '88 Accords used #1 method. ...
So did all my previous cars (2 with pushrods, one OHC) listed below. Old-timers used to adjust them with the engine idling.
first time I saw valves adjusted was a running slant6


My MG mechanic(who also does a lot of old American stuff) has a Pontiac-branded tool that has a wrench for the jamnut and an integrated screwdriver/clutch. The idea is that you turn the handle a quarter turn or however far to loosen the jamnut then use the knob on top(attached to the screwdriver blade) to turn the adjusting screw until the rocker stops ticking. Then, you just turn the handle back to tighten the jamnut and go on to the bottom. "B" engines splash very little oil on the top(you don't really get appreciable splash until you get to high RPMs).

That aside, I don't like "zero lash" on B series engines-I've had more than one person who knows these things inside describe the sound of a properly adjusted one as being "like a sewing machine." Aside from have more valve train noise than we're accustomed to on other engines, I sort of like it.
 
The 2.5L DOHC turbo flat four engine in my Subaru requires camshaft removal, and lifter replacement (no shims) to adjust valve lash. A giant PITA. The job can be done with the engine in place, but it is much easier if the engine is pulled.

Subaru claims the valve lash does not require adjusting over the life of the engine, and checking of valve lash is not required in the maintenance schedule. But there are plenty of online reports from Subaru owners of burnt exhaust valves.
 
Last edited:
Originally Posted By: Reddy45
Any gearheads here want to talk specifics about valvetrain design?

I am trying to get a understanding of the various ways that valvetrains are designed for adjustment, and the pros/cons of each type. A lot of this is coming from my experience with motorcycles where valve checks/adjusts are common maintenance. Can't say I have ever needed to do any valve work on any cars/trucks I have owned.

1. Locking screw type - I was exposed to this method on an old Honda dirt bike with a single cylinder engine. The cylinder head has "port holes" where you can access the valve clearance adjusters, which consist of a threaded post and some locking nuts. Dead easy to do (if access isn't a problem), but very imprecise.. You would adjust the post for length, and then when you tightened the lock nut, the clearance would change just slightly. I would imagine this design only works for fairly "agricultural" applications at low RPMs.

2. Shim over bucket - This was the first type of valve adjustment I did and it was surprisingly easy. Still requires removal of the valve cover and you have to be careful once inside there, but the shims are easy to access and swap out. I did a little reading and it seems the drawback of this method is increased weight due to the size of the shim and it doesn't seem well suited for high-rpm applications.

3. Shim under bucket - This is my current challenge. Both of my bikes use this method and I don't look forward to removing the camshafts just to change the shims. The shims are tiny, though, so that helps to decrease weight in that area.

I know that cars are using some more advanced methods for adjustment (some automatic).. Can anyone talk about these?


I have experience with #3 on the old Alfa Twinspark engine: 8 valve but twin cam. Dead easy to do, you removed the camshaft caps of 1 cam, then rolled the cam under the chain towards the spark plugs and had easy access. Put everything back and do the other cam. The chain tensioner was fixed, to tighten the tensioner you undid the locking bolt and pulled the car forwards while in gear, then tightened the locking bolt. Once every 100k miles sufficed.
 
"Valve adjustment while the engine is still running"
You guys are pulling my chain, right?
 
Last edited:
Originally Posted By: Vikas
"Valve adjustment while the engine is still running"
You guys are pulling my chain, right?


Not the least bit. It's honestly not a huge deal on pushrod engines with solid lifters. As I mentioned, there are special tools to do it, but you can also do it with a wrench and screwdriver just like you do with the engine stopped.

At idle, the valves aren't moving very fast nor is the motion that great. The only downside is that some engines will sling oil all over the place.
 
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