Valve adjustment frequency... Lots of valve questions.

Yamaha recommends adjusting valves every 5,000 miles. I think it was Haynes that mentioned the use of shims as opposed to screws means needing to adjust less often than otherwise would be the case. Elsewhere I read that it also allows higher RPMs and thus performance, and less moving parts is a plus as well.

However, I don't understand a few things. Why don't I ever hear of people needing to adjust valves on modern cars? Don't know about modern motorcycles, but what about them?

I noticed this statement on the Wikipedia article for Four Stroke Engine:

"Valve clearance
Valve clearance refers to the small gap between a valve lifter and a valve stem that ensures that the valve completely closes. On engines with mechanical valve adjustment, excessive clearance causes noise from the valve train. Typically, the clearance must be readjusted each 20,000 miles (32,000 km) with a feeler gauge."

20,000? Is our 5,000 recommendation just kind of an overkill safety thing, is it just an outdated technology, or is there something I'm missing?

----



Separately... I saw a 2 stroke 70's motorcycle here for sale on craigslist that mentioned needing some valve work, but otherwise being fine (banging noise is all the owner knew). At the time, I assumed it was something like our bikes. I found out today that 2 strokes don't have valve trains like 4 strokes, and often (?) just have holes in the wall of the cylinder for intake and exhaust. Is it possible that owner didn't know what he was taking about? What do valve issues on a two stroke mean? (That craigslist ad is here: http://austin.craigslist.org/mcy/2976843379.html)

I love this forum. I'm learning so much.

 

Don't know about cars.

Depending on the motorcycle engine, they could or could not require valve clearance adjustments.

The reason you don't hear about it too much in modern motorcycles is because they can go 20,000 miles before an adjustment, unlike our XJs.

Reasons:
valve design
closer tolerances
modern materials
modern manufacturing techniques

No, 5,000 is not overkill on these engines, just a product of the design.

Usually a "valve job" on a two stroke refers to the power reed valve

 

Believe me when I tell you that cars and trucks both should have their valves checked. It seems more common in some cars that others, and many cars can last a lifetime without adjusting.

In many cases the need to adjust becomes apparent when you hear a ticking similar to an engine tick when the motor isnt getting oil.

I just did my wifes Forester because of valve noise, and it now runs quiet as a kitten. Its the exact same process except that the valve tappets themselves are adjustable. It only took an allen wrench. Automobiles from the 90s, well into the 2000s uses adjustable lifters, but many new vehicles on the road have since converted back to the bucket and shim valves.


A cut and paste about Hydraulic lifters


Hydraulic tappet
From Wikipedia, the free encyclopedia

This article may contain original research. Please improve it by verifying the claims made and adding references. Statements consisting only of original research may be removed. More details may be available on the talk page. (August 2007)

This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (January 2010)
A hydraulic valve lifter, also known as a hydraulic tappet or a hydraulic lash adjuster, is a device for maintaining zero valve clearance in an internal combustion engine. The conventional means of adjusting valve actuation always requires a small clearance to be left between the valve and its rocker or cam follower to allow for thermal expansion and wear. The hydraulic lifter was designed to ensure that the valve train always operates with zero clearance, leading to quieter operation and eliminating the need for periodic adjustment of valve clearance.
The hydraulic lifter consists of a hollow expanding piston situated between the camshaft and valve. It is operated either by a rocker mechanism, or in the case of one or more overhead camshafts, directly by the camshaft. The lifter is filled with engine oil intermittently from an oil gallery via a small drilling. When the engine valve is closed, the lifter is free to fill with oil. When the valve is opening and the lifter is being operated by the camshaft, the oil feed is blocked and the lifter acts just as a solid one would, oil being incompressible.
[edit]History

The first firm to include hydraulic lifters in its design was Pierce-Arrow in the early 1930s. Hydraulic lifters were popular on automobiles designed in the 1980s, but most newer cars have reverted to bucket-and-shim mechanical lifters. Although these do not run as quietly and are not maintenance-free, they are cheaper and rarely need adjustment because the wear caused by operation is spread over a large area.[citation needed]
[edit]Disadvantages

There are a number of potential problems with hydraulic lifters. Frequently, the valvetrain will rattle loudly on startup due to oil draining from the lifters when the vehicle is parked. This is not considered significant provided the noise disappears within a couple of minutes, typically it usually only lasts a second or two. A rattle that does not go away can indicate a blocked oil feed or that one or more of the lifters has collapsed due to wear and is no longer opening its valve fully. The affected lifter should be replaced in the latter situation.
In certain circumstances, a lifter can "pump up" and create negative valve clearance so that its valve cannot close. Typically this occurs in the uppermost speed range of an engine, and limits the engine's performance. Lifter pump-up is serious, as there may be interference of the valve with the piston or, burned valves may result. In all cases it is important to follow the manufacturer's recommendations for oil viscosity and quality.


-Kaya

 

Our Bikes Valve-train does not have "Lifters".

The "Bucket & Shim" Assembly is "Cam Follower"
Non-Hydraulic.
"Solid-type" follower that moves 1:1 with the Cam Lobe.

When an Engine has Solid-type "Lifting", .... HEARING the Valves being Opened and Closed, ... should be considered GOOD NOISE.

The "Ticking" noise is the Valve OPENING and SHUTTING.
Excessive Valve Clearances accentuate the noise.

Adjusting the Clearances to be within Specs reduces the Noise.
Having the Valves ALL at the Same tolerances gives the Plant a very nice running sound.

A "Wide" tolerance is easily detected.
As the Valve clearances become reduced by wear, ... the noise lessens.
Quiet is BAD.

When the Plant is running quietly, ... the Valves begin to not make HARD-FIRM Contact with the Valve Seat.
The TIGHT Condition does not allow the VALVE to Transfer its HEAT to the SEAT.
The Valve will then begin to overheat.

Left undetected and not adjusted, ... the Exhaust Gasses will BURN a Passage OUT.

Hearing Valves ticking-away is Music.
It's when you DON'T hear them you have to worry.

IF, ... you detect an abnormally LOUD Sound emitting from the Valve Train:
Investigate!!!

A LOOSE Valve presents the possibility of the Bucket --> "Throwing" its SHIM.

The resulting damage is of a catastrophic nature.
Could SEIZE the Engine.

 

There are two major things that limit engine RPM:

1) Piston speed
2) Valve float (the inertia in the valve train prevents the valve from closing completely).

Long stroke engines are RPM limited by piston speed. They can afford to have lots of valve train inertia and can tolerate heavy components like hydraulic tappets which automatically maintain proper valve lash. These valve trains get noisy when the tappet becomes clogged with sludge or just wears out.

Short stroke engines that are designed to run high RPMs (like the XJ) need low mass valve trains so the valves close before the piston hits them. They use followers as Rick pointed out and need maintenance.

While 2 cycle engines don't have valves like a 4 cycle, they do have a single valve between the carburetor and crankcase. The purpose of the valve is to let the air/fuel mixture into the crankcase when the piston moves up and then close to prevent it being pushed out when the piston moves back down. That is usually done with a type of check valve called a reed valve. It can also be done with a mechanical valve - generally a rotary valve. Reeds can break and rotary valves do wear out.

 

Back to the original questions:

"Why don't I ever hear of people needing to adjust valves on modern cars?"

-Because with rare exceptions, modern automobiles have automatic, hydraulically-adjusted valves.

kaz answered about modern bikes "The reason you don't hear about it too much in modern motorcycles is because they can go 20,000 miles before an adjustment, unlike our XJs."

The 5000 mile interval is NOT overkill on our bikes; they are from very early in the era of shim-over-bucket design, and if neglected much past that, DO go out of spec. Granted, once an engine has had them adjusted a few times, and has some miles on it, they do tend to "settle down" but they still need to be CHECKED at the specified intervals.

 

I just want to reiterate what BigFitz said about the interval...they aren't being "adjusted" every 5000 miles, they are being "checked." You only adjust the ones that are out of spec. If they all check out, and your gasket/donuts are new, you just button up and ride on. Really no different than any other "inspection" maintenance activity.

The interval might also come from the fact that the first 1-2 intervals will see a SUBSTANTIAL tightening of the valves. I'm restoring a Turbo Seca with 6000 miles on it, and it's clear that the valves were never adjusted, 6 of the 8 were tight by .05-.10 mm. If you (or your PO) skipped this interval, you'll be burning valves when the bike is young.

For a comparison, I bought my 750 seca with 27000 miles, and I've adjusted maybe 2 valves. So there are two data points that illustrate EXACTLY the point members like BigFitz always say about the valves and how they wear.

 

If you don't KNOW the present-day situation of your Valve Clearancnes, ...
Check them!
Write them down on a Note Pad.

IF, ... you have "Out-of-specs" Valves ... Adjust them.
Procrastination, ... Especially concerning TIGHT Valves can wind-up costing you Big Bucks.
A BURNED Valve on one of our Antique XJ-Bikes is RARELY an uncomplicated
"Straight-forward" ... By the Book ... repair job.

The Vast Majority of our Bikes are going to present multiple complications involving highly frustrating detours from any Standard R&R Procedures.

Nearly every single Fastener needing to be undone to Remove the Head poses being Seized.

The Intake & Exhaust Hardware seizures can add HOURS and OUTSOURCED Machine Shop Expenses in a heartbeat.

I've seen guys who never lose their cool, ... have near Nervous Breakdowns struggling with trying to get the Exhaust Pipes off the Bike.

And ounce of Prevention is worth a Ton of Cure.