Building an AutoStick Engine

[Bookwus]

Hiya All,

Admittedly, there is not a great deal of difference in the building of an AutoStick engine as compared to its manual cousin.  Still, there are some differences.  Now, there are any number of references for the building of a Volkswagen air-cooled engine but none (that I have found) detail the specific put-together of an engine intended for use with an AutoStick.  To that end (and since I have to assemble an engine for my Bug anyway) I am going to do this step-by-step thread on AS engine building.

I will add an entry for each session I spend with the engine.  Hopefully, that will be each evening.  I'll take lots of pictures to help illustrate any points I might be trying to make.  We'll go all the way from parts preparation to breaking in the new engine.  I am not promising that this will be a smooth process and handled in a time-efficient manner.  Quite the contrary, it has been my experience that something usually goes wrong and requires redoing, even in well planned and prepped projects.  And it has also been my experience that predicting those mistakes or hang-ups is next to impossible, so you'll just be along for the ride on this rebuild, bumps and all.

And to give you some context...........this engine will be a relatively stock 1600 single port.  This was the engine that was originally installed in my 1970 Bug.  However, I will be using a post 1970 case (an "AE" series case) because it is a dual relief case with 10 mm oil passages.  Additionally, I'll be installing a doghouse fanshroud for more efficient cooling.  I have already started some facets of this rebuild (machine shop work and reconditioning engine tin, for example) but I'll catch you up on those steps.  I'll also outline any tools you might need besides those tools one might commonly find in any garage.  I'll do my best to give you prices for parts and services.

Should you have comments on this step-by-step engine build, don't hesitate to chime in.  If there is one thing I do know, it's that I don't have all the answers or a corner on the best techniques.  If you know a better way, let's hear about it.

Tomorrow we'll talk tools and supplies for an engine build.

[Bookwus]

Hiya All,

In order to get a VW engine together you will need a few special tools besides the usual wrenches, sockets, and screwdrivers usually found out in the garage.  You can substitute for some of these tools, others you just gotta have.  I'll try to alert you to those you'll definitely need as we go along.  You'll also need some supplies and there is actually quite a wide range of products to choose from.  I'll show you what I use for the most part.

One item you will definitely need is a tool for measuring the endplay of the crankshaft as it sits in the case.  As well as rotating round and round, the crankshaft can actually move in a forward and backward direction.  The amount of this movement is referred to as endplay.  Volkswagen has set endplay tolerance at between .003 and .006.  Yet when most engines are assembled the endplay is usually measured out between .035 and .040.  To bring that endplay into the range of tolerance shims must be added (we'll go through that procedure later).  And to properly add shims the endplay has to be measured.  Here's a tool that helps with this important chore......



One may also use a dial indicator but the tool above when used in conjunction with a set of feeler guages has proven accurate and reliable.  It also has the advantage of being cheap - about $5.00

You'll also need a way to keep the flexplate from rotating when you tighten/loosen the gland nut.  While one can use the old VW mechanic's trick of stuffing a length of rope in one of the cylinders, a more conventional method is using a set of four flexplate clamps. 



These clamps are attached to the flexplate loosely with the flexplate bolts.  The flexplate is then rotated so that the clamps align with the bolt holes in the crankcase for engine mounting.  The mounting bolts are put in place and tightened down.  And then the flexplate bolts are tightened down.  This will freeze the flexplate in place.  However, be sure to use at least three of these clamps when removing or installing the gland nut.  Anything less than that and you risk warping the flexplate.  These were homemade from scrap.

And for the gland nut you'll need a 36 mm socket.  Gotta have it!  There is no other way to get the gland nut off or on.  And definitely go for a 3/4 drive.  These gland nuts take between 260 and 300 ft/lbs of torque.  That amount of torque will break a 1/2 drive.  Take a look at the sockets, breaker bar, and cheater (4 feet of cast iron pipe)




By the way, the other socket in the picture above is a 30 mm for the main pulley nut.  You may be able to remove that main pulley nut with a crescent wrench, but I like using the socket.  All of my 3/4 drive sockets are from Harbor Freight.  The entire set of sockets (19 mm - 50 mm), wratchet, and breaker cost $42.95

When you assemble the clutch components you will need a clutch pilot in order to center the clutch disc.  I got a plastic pilot from my local FLAPS for a couple of bucks.



You will also need a ring compressor in order to slide the cylinder over the piston assembly.  VW ring compressors are pretty simple and straightforward affairs.  Basically, it is just a sprung steel band which is compressed with a pair of pliers.  Cheap at $5.00.  But be careful because VW ring compressors come in two sizes.  One for pistons up to 87 mm and one for pistons over 90 mm.  Make sure you buy what is appropriate for your build.



Here's a handy little item to have............



This a digital scale which will weigh up to 600 grams.  This is great to weigh pistons.  And it can also be used with this....



This is a homemade jig for weighing the small end of the connecting rods.  Weighing the connecting rods and the pistons will enable you to "mix and match" rods and pistons in order to equalize the weight of the rotating mass.  More on that later.  The scale cost $16.00.

This wrench/driver....



was made to remove and install the nut which holds the oil filler assembly to the generator stand.  It's quite handy and I can actually get some torque on the nut by slipping a Phillips screwdriver through the holes in the handle end.

During actual assembly I use this engine stand from Harbor Freight.......



Now this stand does not have the regular VW attachment arms which allow one to also work on the clutch and flywheel.  However it does a nice job of holding the case in a good working position and I can rotate that case as needed.  Cost was $37.00.

Of course I have to have some way of getting the engine up to the stand.  Since I have no helpers and I am on my own I had to rig up some basic machines to help me with moving "dead weight" around.  For that I fabbed an A-frame and set up that A-frame with a come-along.  Take a look...........



Now this picture has a busy background, so here's a better shot of the come-along I use to raise and lower engines....



And at the end of the come-along I use this harness to attach to the engine.



And here is what it looks like in use.....



Of course for removing and installing the engine a good floor jack is necessary.  Many folks have been using ATV jacks for this purpose.  Although I have an ATV jack (you may have noticed the motorcycle in the pictures above) I find that a floor jack is much more convenient for me.  My 3 tonner from Sears cost $59.00 when I bought it (a long time ago!) and it came with a set of jackstands also.  The jackstands are super important.  Don't use any substitutes for a good set of jackstands.



If any other tools come up during this engine build, I'll try to remember to pause and describe them.

[volkenstein]

Mike,
      That's a legendary rod balancer! Ditto for the gramme scales!

I haven't had much luck with oil breather gland nuts and have gone for the doctor. A 1 inch internal pipe wrench resides in my tool box now.

Regards
Sean

[Bookwus]

Hiya Sean,

Thanks!

I was at my local machine shop and the owner was giving me a tour.  We spent some time looking at and playing with the rod balancer.  While I was doing that I thought I could make one of these from scrap lumber, so I decided to give it a try.  I built it so that the rod sits level on top of the digital scale when the scale is placed on the jig's platform.  I get little or no variance between separate weighings of the same rod.  I always weigh each rod at least three times and then average out the weights (if needed).  While this may not be as accurate as a commercial model, I reckon that it will give me reliable data for pairing up connecting rods to pistons.  And that's what I'm after.

Good idea about the internal wrench for the oil filler nut.  I hadn't thought of that!

[volkenstein]

Mike,
      The only warning with using the pipe wrench is to make certain the rotating claw is contacting the gland nut 100%. It will rip the alloy to pieces if it's positioned incorrectly.

Back to normal programming .

Regards
Sean

[Bookwus]

Hiya All,

There are some expendable supplies needed when assembling an engine.  And before we get into them, please understand that the supplies I have listed are those that I have chosen to use.  There are many other choices out there in the market.  Perhaps others will chime in with their particular selections..............

You are definitely going to need a sealing compound when you mate the case halves together.  One product is almost universally mentioned as the standard for comparison.  It has been around for years and has given excellent service in all applications.  That's why I use Permatex 3H, usually referred to as Permatex Aviation for sealing the mated surfaces of the case halves.



I use Curil for the "add-ons" like the generator stand, fuel pump assembly, and oil pump.  It's a little less "gooey" that Permatex and a little neater to apply.  I have also heard (and I'm not vouching for the truth of this) that Curil was the sealant used in the factory while assembling engines.  Whatever..............I have found both of these products to be outstanding.

I also use two lubricants in the actual assembly of the engine.  Many folks use lubrication compounds especially designed for engine assembly like.......



I use a combination of STP and 30 weight oil.  I mix STP and 30 weight in a 60/40 solution in my oil can.  It makes for easy lubrication and this stuff stays where it's put, but can be smeared around.  It's cheap (compared to the assembly lube above) and I like to goop it on liberally.



And I also use White Lithium Grease.  This stuff is especially nice to use on cam lobes and lifter faces where you need a little extra protection until the oil arrives.



And about shop towels.................  Generally speaking I use cloth towels for me!  I wipe may hands and clean myself off with cloth towels.  But I try not to use them on the parts that are going into the engine.  That's simply because most cloth towels will leave lint or threads behind and I want to keep the inside of that engine as clean as possible.  So, when it comes to wiping up in the engine I use a lint-free paper towel.  While they are less likely to leave anything behind, one still has to be a bit careful.  They will tear and some chemicals will dissolve them to an extent.



Next up:  Cleaning and weighing.

[Bookwus]

Hiya All,

Cleanliness is the name of the game when it comes to engine building.  You cannot get the engine parts too clean.  And rebuilding an engine with dirt or other contaminants is asking for trouble.  So, by all means take the time (and it will take plenty of time!) to get your parts clean.  Interestingly, I'm not just referring to parts you are planning to re-use.  This goes for brand new parts also.

Now on this particular rebuild I've opted to buy a new set of pistons and jugs.  Although I could have re-ringed the old pistons and had the cylinders honed I'm impressed that a new set of cylinders and pistons costs only $160.  That comes down to $20 per cylinder and $20 per piston (plus wrist pins and clips).  A pretty good deal, if you ask me.  I bought a set of Mahle pistons and jugs...............



I've had pretty good luck with this product.  The original factory specs from VW were that all pistons (and that includes wrist pins and clips) should vary by no more than 5 grams.  I've not had any set exceed that amount.  With each set you get the following times 4............



But, as I mentioned before, these parts have to be cleaned before installation.  There's even a warning on the box cautioning the user to clean the parts.  That's because the factory applies a preservative (I've been told that it's cosmoline) to keep the parts from corroding.  That preservative has to be cleaned off.  To do that you'll need mineral spirits, soft bristle brushes, hot water and dishwashing soap.



Using a small bucket, pour in a gallon of mineral spirits.  Brush both cylinder and piston (no need to remove the rings).  You'll notice the preservative come off and you'll see it at the bottom of the bucket.  At $11 a gallon, I filter the used mineral spirits and reuse them.  Give both the cylinder and the piston a good scrubbing.  From there it's on to the hot water and soap.



Again it's the scrubbing routine.  This time you want to be sure that all the mineral spirits are gone.  Use plenty of soap and make sure your water is as hot as you can stand it.  Rinse with clear hot water and dry.  Just like doing the dishes.  However, make sure that you wipe some oil (I use the STP/oil mix) on the inside of the cylinders.  You don't have to use a lot of oil, but enough to give the inside of the cylinder a thin even coat.

When I clean pistons and cylinders I do one set at a time.  This allows me to dry and oil everything in a timely manner and I keep the piston and the cylinder together.

But other parts need to be cleaned also.  I probably spend more time on the case than any other single part.  It has to be clean inside and there are many nooks and crannies in which dirt can and does hide.  Now this case.....



may not look sparkling clean, but believe me it is clean.  The magnesium alloy Volkswagen used in their cases tends to grow gray as it oxidizes over the years.  This particular case is 37 years old.  Try thinking of a mechanical device or casting that looks this good after 37 years of heavy use.  This case was cleaned chemically and mechanically five separate times.  Twice by me, then into the machine shop and their cleaning process, and then again twice by me.  Before I took it into the machine shop I cleaned off the grime with a putty knife (oh yeah, it was that bad).  Then I sprayed it with aerosol brake cleaner to remove the grease.  It then went down to the local self-serve car wash for a dose of degreaser and spraying.  After I got back from the machine shop and their chemical dip bath I went after the interior surfaces with a Dremel and tip brush.  I was careful not to touch and mating or bearing surfaces with the brush.  They must remain pristine.  I then soaked the insides of the case halves with a Kafko product, Oil Eater.  Following all that I washed the case halves in hot water and soap.  They were left to dry under 500 watt Hologen shop lights.

I even went so far as to remove the oil pickup tube so i could clean the case in that area.........



And don't forget to make sure that the small oil passages are clean.....



This is a shot of the oil return passage just under the forward cam bearing.  And notice that the groove for the cam plug is nice and clean.  The details really do make the job!

Finally do not forget to thoroughly clean all threads in the case studs.....



When you go to button up the case each nut will have a torque requirement.  If the threads are dirty or rusty you'll never be able to get the required torque - and that is very important in VW engine construction.  So, take the time now to clean (a wire brush attachment on a drill works great) and chase the threads on all these studs.

[hercdriver]

Fantastic thread Mike. Keep it up!

[LA Irish]

I'm starting mine next week so this has given me some addtional motavation to keep pace and finish my project (1776).

Thanks for the great pics and tool suggestions!

Bob

[Bookwus]

Hiya Guys,

Thanks!

I have had to take a short break.  Real world problems have intervened and I need to deal with them right now. 

However, I should be getting back to the build in just a couple of days. 

[Bookwus]

Hiya All,

OK..........back to engine building..............

Once you have the cylinder and pistons all washed out in both mineral spirits and hot soapy water, followed a good rinse in clear hot water you need to do one thing for sure and maybe another.  You'll decide on what's best for you.

After you pull the cylinders out of the hot rinse of water you want to make sure thay are dry as you can get them in the cylinder bore.  If you have never experienced the natural phenomena of "flash rust" you definitely don't want to start now.  To that end, once you have the cylinder insides nice and dry coat the insides with a this layer of oil.  I use the STP/oil mixture.  This will prevent any rust from forming on the inside cylinder walls.  It sure wouldn't hurt to put a little oil on the piston rings either.

I also elect to treat the outer surface of the cylinders.  I give them at least two light coats of high temperature flat black paint.



The paint serves two purposes.  It helps to seal the surface against rust and it also helps to promote more efficient cooling of the cylinders themselves.  Now there are those out there in VWLand who will dispute this saying that it's not necessary.  And I will admit that you can certainly build an engine without painting the cylinders.  But I do think that rust prevention and more efficient cooling are worth the time this step takes.

With the pistons now dry it is time to weigh them.  Before we get into that however, a word or two about this process.  Many folks do not pay any attention to this step.  They take the parts out of the box and assemble them into an engine as it were.  But it is definitely a good idea to to try and balance the rotating mass of the engine as much as is feasible.  This will produce a smoother running, longer lasting engine.  You can have this done much more precisely at your machine shop.  They call their service dynamic balancing and it's pretty high tech.  The machine shop will take your rotating mass (crank, flywheel, rods, clutch pressure plate) and balance it as a unit.  Were you building a high performance engine this is certainly a service you'd want to check out.

So, how to weigh a piston?  I place my digital scale on my connecting rod weighing platform (it's easy to level) and place the piston, wrist pin, and wrist pin clips (2) on the scale.  



I weigh each piston assembly three times.  Now, truth be told, with a good digital scale there is little to no difference between the weighings.  But I do this just to be on the safe side of the equation.  Notice in this following picture...........



I am noting each piston weighing.  I am about to weigh Piston B for the third time.  By the way, I label each one of the pistons A, B, C, or D.  That help to keep things organized (their respective cylinders are alphaed likewise) and will help when we get to weighing connecting rods.

Once all the data has been noted I calculate the average weight for each piston......



and then figure out the range of the weight.  I've listed the pistons at the bottom of the page in order from heaviest to lightest.  Looks like I have a range of 3.4 grams in these pistons.  Factory specs say all them should be within 5 grams, so it looks like I'm doing just fine at this stage of the game.

Now we move on to weighing the connecting rods.........



Actually, "weighing the connecting rods" is a bit of a misnomer, at least in this case.  A full service machine shop will weigh both ends of the connecting rod for you.  I am only set up to weigh the "small end" of the connecting rods.  But even the folks at the machine shop will tell you that the small end, the end that is thrown by the crank, is the important one to weigh.  

Now, weighing the small end of the connecting rod will produce more varied results with each individual weighing than we experienced with the pistons.  That's due to a number of factors, exact placement on the jig being the big reason for variation.  This makes multiple weighings and averaging the weights very important.  And with the connecting rods when I list them in order (I number each one of the connecting rods) at the bottom of the page I do it in lightest to heaviest order.  Just the opposite of listing the pistons.

This gives me the information I need to match up the heaviest piston with the lightest connecting rod and vice versa.  Take a look at how this works on paper........



As you can see, by matching the lightest with the heaviest I did pretty well.  The first two pistons/rods are almost identical in weight.  However, my problem is going to be the last piston/rod assembly.  To get all the piston/rod assemblies dead equal I will have to lighten each of the first three assemblies by the amount listed at the bottom of the page.  The figure in the parentheses is the amount I'd have to lighten each one to get everything within one gram.  And that's VERY acceptable.

So, tomorrow we'll look at lightening those assemblies.
 

[volkenstein]

Mike,
      A scrap piece of beautifully sawn 3/4" dowel, a longer screw that'll pass through the dowel and your Conrod Big End piece there and Bob's your fathers brother!! Just a thought for later down the track.....


Regards
Sean

[Bookwus]

Hiya Sean,

That's the ticket!  I'll give that a shot.  Great idea.

[Bookwus]

Hiya All,

Down to balancing the rod and piston assemblies.  After this we start to put the beast together.

Given you understand that a rotational mass operates most smoothly when all its components are in balance, you can understand that it is best that all piston and rod assemblies weigh the same or very nearly the same.  For our purposes in this assembly, as I mentioned before, we are not weighing the entire connecting rod, just the "thrown" small end of each rod.  Certainly if you are building a performance engine a more thorough weighing of the rods is indicated and, as has been mentioned, the dynamic balancing a machine shop can offer should be investigated.

Inasmuch as this engine will be an almost completely stock setup the balancing we are doing will go a long ways toward making the rotational mass a happy one.  And when that rotational mass is fairly well balanced it is much easier on the bearings and the case journals.  Less wear, less heat, more mileage out of the build.

However, getting the piston and rod assemblies to just about the same weight can be a bit of tricky endeavor.  Ideally, we would want to take the weight off the component furthest out on the "throw"  That, of course, would be the piston.  The main problem is that the piston is cast from aluminum and very lightweight.  I'm not comfortable taking any more than 2.5 grams out of the piston.  That's a bunch of lightweight aluminum.  When I have removed about 2.5 grams I turn to taking weight off the connecting rod.  

There are problems with removing weight from the connecting rod.  One, VW rods do not really have weight pads which can be ground away to remove weight.  Two, remember that the small end weight of the connecting rod is an average.  It will be difficult to tell EXACTLY how much weight has been removed.  Three, the connecting rod is not at the end of the "throw" and while it's less desireable to remove weight at this point, it is often necessary.

So, how does one remove the weight from the piston?  I use a Dremel type rotary device with a variety of bits.  The overriding caution in taking off material is Never take much from any one spot and try to balance what you do remove   Let's start off by looking at where to remove material from the piston........



Take a look at the arrows.  The bigger they are, the more material can be removed.  The red arrow indicates the spot of the factory weight pad on the wrist pin boss.  This weight pad is minicule and about the most weight you could you remove here would be about .3 grams.  The yellow arrow indicates the sides of the wrist pin boss.  These can be shaved down somewhat, but be sure to shave each side of each boss equally.  Expect about .5 grams from these areas.  The blue arrow is pointing at the skirt of the piston.  When I remove material here I try to bevel the skirt wall inward.  Doing each side (remember the balance) it's good for about .2 grams.  

Before we go on with weight removal, a word about organization.  Be sure that you remove a little and then weigh the piston.  Typically, I'll weigh the piston twenty or thirty times during the weight removal process.  I definitely do not want to be in the position of removing too much material.  And I can get a pretty good idea of how much weight I'm removing while I'm actually working by doing these constant weighings.  

The meat of the removal will be in the piston floor surround.  I use a technique called dimpling.  With a drill bit attached to the Dremel I push hard enough to engage the steel drill bit into the aluminum piston.  Once the drill bit starts to grab, I pull it out.  Think of the dimples on a golf ball........that's the idea here.  By going all around the inner diameter of the piston you can expect to remove about 1.5 grams.

Is it possible to remove more material?  Absolutely.  Some may suggest other areas (such as the flat floor of the piston) but I tend to be a little conservative at this stage of the game.  Once I get to the 2.5 grams removed, I want to look elsewhere for weight.  And that means the rods.

While many connecting rods from other makes do have weight removal pads, VW merely has a generous seam at the small end of their rods.  This seam can be ground down with an angle grinder.  



Again, one needs to proceed with caution, removing just a bit of material and then weighing the rod.  Also going in small steps helps greatly to keep the accumlated heat from friction from doing anything bad to the rod itself.  Small baby steps here.  But, since the rod is steel, the weight does come off pretty fast.

Oh and one last item to check out...........you can play mix and match with the wrist pins.  To be honest, wrist pins do not vary that much in weight.  However you might be able redistribute them to pick up or lose .2 or .3 grams here and there.  Don't bother with the wrist pin clips.  They are uniformly 1 gram apiece.  I did switch wrist pins in the example below.

I thought I'd give you the before and after for the Piston A/Rod 2 assembly.  Here's how it looks...

                  Old Weight                                                New Weight

          Piston A .................444.8                                       Piston A ...............442.4
          Rod 2 ....................186.2                                       Rod 2....................184.0
          Wrist Pin ................111.6                                       Wrist Pin ...............111.3
          Clips ......................   2.0                                       Clips ....................    2.0

          Total .....................744.6                                       Total ....................739.7

If you'll recall, I wanted to remove 4.4 grams from Piston A/Rod 2 to get down to 740.2 (the weight of the lightest piston/rod assembly)  I actually went past that just a bit, but inasmuch as there will always be some variance in the weight of the connecting rod small end, I'm not too concerned about the present difference.  Besides I could always go back and reswitch the wrist pins and that would make the result closer yet.

If you cannot get all four of your piston/rod assemblies really close (within one gram) think about doing this...............  use the two heaviest piston/rod assemblies across the crank from each other.  They will work to counterbalance each other (but definitely do try to get those two close to each other in weight) and lessen the stress on the bearings.  Do the same with the lighter pair of pistons.  

[Bookwus]

Hiya All,

Let's take a look at the heart of the engine, the crankshaft.  Here's a typical VW crankshaft.....



These cranks are really over-engineered.  They might be what you'd term "Super Heavy-Duty".  With such a robust build these cranks can be used over and over again.  But before you use that old crank of yours, you HAVE to take it to your local machine shop.  Actually, you need to take it in for a variety of reasons (which we'll get to) but the most important reason is to have it reground.  The shiny sections of the crank above are contact surfaces with bearings.  As such they have to be smooth.  Regrinding those surfaces assures that the surface is smooth and that it will play nicely with a new set of bearings.  Even a crank that has seen very limited use needs to be reground before it is used in another engine.

Then too, the techs at the machine shop can check the crank for any sort of defect.  They can even straighten out a crank that has been bent along its axis, provided that the bend is a small one.  There is no way I'd do a rebuild without first having the machine shop inspect and grind the crank.  That's just good common sense.

But there are things you can do also.  Let's take a look at the rear end of the crank above and explore a little of its geography.........



A key to the picture above....

1.  Main Pulley Nut
2.  Main Pulley Nut Washer
3.  Oil Slinger
4.  Rear Main Bearing
5.  Distributor Drive Gear
6.  Camshaft Drive Gear
7.  Main Bearing

Now all of these parts above can be removed from the crank.  Numbers 1 and 2 come out simply by unscrewing the Main Pulley Nut.  Numbers 3 and 4 come out after removing a woodruff key which is located just to the rear of the oil slinger and just out of sight in this picture.  Oh, and note the orientation of the oil slinger.  That will come in handy later.  Numbers 5 and 6 can be removed with the even application of heat.  And in the reverse process of assembly of this section, all of this can be done by you.  Most folks just let the machine shop remove these gears when they take the crank in for regrinding.  Once they have been removed, the main bearing simply slides off the crank.

And let's take a look at how the crank is oriented in the case and matched up with its piston/rod assemblies by cylinder number.



Imagining that the front of the engine is at the top of the picture, we find the flexplate.  By the way those components inside the case are in white, those outside the case are in yellow.  The labeling actually gives you a pretty good idea of how the crank is set up.  Notice that Cylinders 3 and 1 are out at full throw while Cylinders 4 and 2 are all the way in.  This also gives you a good visual reminder as to why it was important to balance those piston/rod assemblies.

Next time, we'll assign each piston/rod assembly to a cylinder position and begin the assembly of the rotating mass.