HLAs Revisited

[yel-low]

There isn’t anything I hate more than doing something twice! This is a classic example.

A little over a year ago I tore my current engine apart to freshen it up. Along the process I replaced all the HLAs (or attempted to). In itself the process is uber simple. Just pull them out and drop in new ones. Getting to them is another story. You have to remove the intake manifold, timing belt, valve covers, camshafts, cam bearings, distributor… and the list goes on.

What I realized was that in my 1995 L the intake and exhaust HLAs were NOT the same size. Every year afterwards used the same diameter HLA for both intake and exhaust side. I bought a set for the later years from another member on here a while ago not knowing this.

I was forced to reuse my old intake side HLAs. I “attempted” to clean them as much as I could from reading various tid-bits of info on the net. I just want to make a note that the factory service manual has no note about cleaning or fixing these little buggers. If not in spec, all it says to do is replace them. You will learn why in this article.

I did the squeeze and flush technique, solvent bath, running kerosene through the engine and all the other snake oil gimmicks that claim to clean out your engine. NONE OF THEM WORKED!!

Let’s start with the basics:
Q: What the **** is an HLA?
A: Hydraulic Lash Adjuster

Q: Why do we need them?
A: In Mazda’s attempt to make an uber luxury quite ride they employed this simple yet genius method of constantly adjusting valve lash on the fly. What you get is no cam to valve stem slap noise associated with fixed rocker arms or shims and presumably a zero maintenance valve train.

Q: How does it work?
A: The HLA is simply a one way check valve that allows the adjuster to lengthen but not compress with oil pressure. Oil flows in, separates the two pistons, and your valve lash is automatically adjusted. There is NO two way oil flow. What goes in STAYS in. (unless they are severely worn and the two pistons no longer seal)

[yel-low]

Here is a simple break down of how it works. (This is not my artwork)



What happens is that oil flows through the passages in your head and through the tiny orifice on the side of the HLA. Coincidentally, I always try to line up this hole with the one in the head to allow for more of an unimpeded flow. It could just be in my head and have negligible benefits but that’s what I do.

After the first chamber if filled with oil (blue line); oil then flows into the smaller piston via a small circular depression formed in the HLA body.

Here is a picture of the depression and smaller piston seat.



Oil then flows up through the steel ball check valve into the third piston thereby separating them. There is a small spring that ensures that the two pistons do not bottom out on each other.

Here is a picture of the smaller piston and the check valve.

[yel-low]

This is a picture from the other end where the ball is clearly visible.



This is a picture of how it all fits together.


As you can see.. when oil flows into the HLA there really isn’t any way for it to flow out. If in the worst case scenario your HLA is so badly worn that the smaller two pistons do not seal well you may get some sort of “leaking” (red area in first pic). This “leaking” is not nearly enough room or has a sufficient flow rate to clean out the carbon buildup and sludge what WILL accumulate in the chambers.

To give you and idea of what I am talking about this is an old HLA from my exhaust side that I pulled and had soaking in solvent for over a year now.





There is some nasty crud and carbon sludge built up all around the check valve preventing any flow through it. This is exactly what leads to the squishy HLA syndrome and the terrible “diesel” like knock. You engine will suffer shorter valve lift and loss of power (although slight) when your HLAs do not perform well.

Thank god these are non-interference engines because if an HLA comes to total failure, who knows what damage, could have occurred... but then again.. total HLA failure could also mean your valves would just barely open.

Well….. so your asking what is the point of all this rambling??

[yel-low]

Here goes:

It’s amazing how much noise these things can make. They are often underestimated and I can’t tell you the number of times I’ve heard people confuse the noise with rod knock. Even my trusty dealer even once diagnosed a perfectly fine engine with a few bad HLAs as rod knock and suggested I buy another car. YES! My dealer.. my beloved Mazda dealer with factory trained techs, super fancy testing equipment, and cool Mazda jumpsuits, even confused the noise from a simple $8-15 part with engine devastating rod knock.

I have to admit. I have snatched up quite a few Millenias from people who were told the same by their dealer for GREAT prices. The noise is very scary and the labor involved is certainly not worth it if your car has many miles on it or is from the earlier years. If you don’t do the work yourself then it quite possibly may be in your best interest to junk the car or part it out.

I wouldn’t consider the job a simple shade tree mechanic job either. The timing belt, cams, intake manifold, vacuum hoses and plenty of electrical connectors have to be removed and replaced with precision. Botch any one of these and you’re in a world of hate trying to de-bug your car and left wondering why that **** CEL light won’t go off… but don’t let me discourage you. If you know your way around an engine and have plenty of tools around jump right in.

The cleaning process:

When I first starting working with these engines I didn’t know much about them. I just kind of dived in and learned about the Mazda specific components from trial and error. I was too shy and didn’t want to risk having to tear an engine apart twice if I botched something so I was pretty conservative in the past. I tried my best in cleaning out the HLAs with all the info I read on the net about flushing and additives. NOTHING WORKED.

Being totally frustrated this time around when one of my HLAs decided to crap out I decided to explore them some more. What I found out was that they are fairly easily disassembled and cleaned with minimal effort and they can be reused!

I start by pulling on the larger piston with pliers. A sharp crisp pull with moderate pressure is all that is needed to disassemble the entire HLA. The pistons are held together with some simple c-clips that you should take care not to crimp or damage but other than that its pretty simple.

[yel-low]

I start with them all disassembled.



I then dip one by one in an ultrasonic bath with some very nasty solvent in it.


That solution was initially clear but after just about 3-4 of them this is what was extracted from the HLA crevices.

One thing I also did was dip each check valve in the solution with one of the pipettes from those carb cleaner aerosol cans jammed into it. This allowed the ball to be elevated and allowed the seat of the ball to be cleaned. The pipettes are the perfect size to fit into the tiny hole and stay in place.



I hope this little write-up demystifies HLAs and the noise associated with one that has failed a bit more.

[yel-low]

Just as a side note. When you do reassemble it is VERY important to submerge all the pieces in the best quality oil you can find. Assemble them submerged and make sure you get all the air bubbles out. I STRONGLY suggest staying away from mineral oil to refill these. The mineral oil will deposit all the tar and petroleum by-products in the HLAs when the oil starts to coke and you will be left with this same problem down the line. The HLAs get very hot because they are in constant contact with the valve stems and the valve stems get the brut force of the combustion heat.

My problem was certainly the fault of the previous owner(s) using inferior grades of oil. I have always used synthetic oil and periodically used very nasty harsh engine flushes. As you can see.. the flushes had zero affect on my HLAs. Once bad stuff is in there.. its there to stay.

[Xedosman]

Great writeup! I suggest this is moved to the technical guides section.

[Goliat6288]

i concur.

[milly00]

Randy what are you up to? You building a millenia race car? I think I'm gonna see a new youtube video here in a year or so with a millenia 5 speed with a roll cage in it blowing flames out the back running 10 seconds. I know whatever your up to it's gonna be bad ass.

[yel-low]

Can we get this in the tech section?
Redundant info but I'm sure its useful to whomever ventures into an engine tear down.