Type 4 double thrust cam bearing installation

[raygreenwood]

Type 4 double thrust cam bearing install tech

This is for a 1.8L build thread I have running over in the 411/412 forum….but I thought I would post it here in this forum (and link to this in my other thread) because there are many more type 4 engine users here.

So over the last 15 years I have installed maybe 7 sets of double thrust cam bearings in type 4 engines. Not a lot…but enough to know how to do it right and know the ins and outs.

This is the first one I will say I had serious installation issues with. All of them required at least two assembly/disassembly mock-ups to get right…twice… a little thrust face sanding…but usually not necessary.
This one took a whole day and in the process of trouble shooting the issue….wiped out a pair of thrust bearings (mainly because of excessive handling and tweaking).

A couple of things up front in this thread. I am not too interested in the argument over whether the double thrust cam bearing mod is necessary or not. I call them cheap extra insurance toward preventing catastrophic failure in an engine whose case and parts are getting harder to find by the day.

Perfectly willing to discuss it…but if you don’t believe it’s necessary…then just skip all of this!

After this installation episode…I will say…. that I “believe” or at least think…I know why VW decided not to install a double sided thrust bearing. ….AND…it is NOT because it’s not better, safer and “possibly” longer lasting than a single thrust cam bearing.


Bluntly put….it would have been cost prohibitive for the benefits it provided….for these primary reasons.

1. Because this is a split case engine and even with the best machining there are very minor case fit differences to each side of the case even when brand new…and made of relatively flexible metals ….and…. because of the preload that is built into these bearings (more on that issue later)…there will be a fair amount of engine cases that will require excessive amounts of correcting to the bearing and preload to get a perfect fit. This will require excessive assembly time.

For someone..…like a practiced and trained factory technician doing the double thrust bearing install on an engine assembly line, even with the factory tools, jigs and set up procedures.…this could still take over an hour or more to get right on some engine cases….because it may take several assembly/disassembly mock ups…and is not something you would do cheaply enough on an engine assembly line at a factory and get your money back. Time is money.

Again….this is not saying that a double thrust cam bearing is not a better, safer way to go engineering wise but it’s expensive in the time to install aspect AND…..

2. Because within the expected miles/lifespan the factory intended these engines to last…it was unnecessary. They got away without it just fine.
So….it was good enough on a stock engine and would have added cost mainly through man hours per X # of engines.
This is why they didn’t put in the second thrust bearing shell. Not because it’s not better …but because a single thrust was good enough for a limited design lifespan.

Bear in mind….The object of car companies is NOT to make your engine last as long as possible. It’s to make it last long enough to solidify their reputation for mechanical reliability, outlast the warranty period…and last long enough to make you happy with your investment and buy another car.

If I had a serious installation issue with one out seven engine cases….which is 14%....and had very minor…but still time consuming… issues on about half of the other 6…. imagine how much of a drag this would have been when making millions of engines….and 14% took a couple of extra hours to fit. Typically on the other double thrust installs it took me about 2 hours each from start to finish.

All of that said…..here is my narrative of a problematic installation, some observations and some tech tips that can make this easier for others.

Engine Case: EA series type 4 1.8L from a 412.

Camshaft: Web #73

Bearings: Two sets of Mahle 021 198 541 BR. The bearing manufacture date is May 24, 2010

NOTE: I also had four sets on my parts shelf of the same part # made September 9, 2000. These came in handy.

The engine case condition is excellent. The camshaft bores are very round with no damage or wear.

The camshaft also has excellent journal measurements:

All three measured 0.9841” which are just under 25mm (which is .98425”). The minimum diameter spec is 24.99mm which is 0.9838 and the maximum is 25mm.

The bearings: we have heard a lot of opinions regarding main and rod bearing quality these days and even some complaints about cam bearing quality and about issues with Mahle and other manufacturers. Of course most of that is recent build parts.

The bearing sets provided to me for this build are 7+ years old. I compared them and measured them to some of my 2000 build bearings and they look and measure identically and appear to be excellent quality.

NOTE: I will have a small dissection/post mortem of the bearings at the end of this with some measurements and pictures. There are very small some difference in the bearing dimensions from year to year. But…with the right prep…these differences are not a problem.

The camshaft lobes and the edges of the thrust flanges were fully deburred and the thrust faces on the cam were lapped carefully with 2000 grit and then the whole cam was carefully re-cleaned chemically. (See my 1.8L build thread in the 411/412 forum for the deburring process)
https://www.thesamba.com/vw/forum/viewtopic.php?p=8679180#8679180

NOTE: When I do camshaft bearings (double or single thrust) I do them long before final installation/assembly time just like crank bearings. This entails a test fitting, adjustment of end play if necessary, close up the case, check for free play and rotation, disassemble the case, mark the bearings for location, clean and oil them and put them aside either back in the box or in a bag.

This is done as a separate job before assembling the gear on the cam and checking backlash and run-out. I check and set the end play on the bearings in each case half separately first and then check and adjust again once the case is mocked up.

This practice is a good indicator of two things: how close each side of the thrust bearing is manufactured to each other (remember they come from two different bearing sets) and how close the machine work is on both sides of the case.

Bearing Flange OD: 1.1041”

Cam journal ID: 1.1062”

Calculated end play: .0021”…just about perfect.

DISCLAIMER: as we roll along in the photo set…you will notice these bearings getting a little scarred up. When I first encountered a cam rotation issue…I knew these bearings were toast…but I used them through easily about 12 assembly fittings as a sacrificial diagnostic tool to figure out WHY I had the issue. None of these scratches are actually deep enough to feel….but I will not be using them anyway.

Set up:

The left hand (distributor side) of the case was installed horizontally on the engine stand. The bearings were installed with the crush area excess protruding equally on both sides of the bearing with reference to the case edge mating surface.

I am checking that the crush protrusion of each side of the bearing is even (with a plastic razor blade) after pressing them firmly into the case bores.

The cam was placed in the case and the bearings and cam journals were oiled liberally with 0W-40 synthetic motor oil.

The cam was pressed downward lightly to be sure the bearings were seated and then tested for rotation. It was smooth but slightly tight with no pinch spots.

With my finger on the center of the camshaft the shaft was tapped forward about five taps and then rearward. The cam now spins in these bearing halves like glass.

The dial indicator was set up and zero’d.

The end play on this bearing shell set was measured to be .002”. Excellent.

The case half with bearing shells was taken off the stand and put aside and the right hand case half was installed.

The other two halves of the bearing shells from the same set were installed in the center and crank end of the case.

The new thrust shell is marked with a scribe for the tang location so I can line up the punch easier.

The thrust bearing from the second bearing set was installed, a clamp washer installed so the bearing does not rotate in the case when the tang/notch is being punched. A narrow blunt punch was used to “dish in the tang.

This was after the first strike. It took two strikes. Better too soft and needing 2-3 strikes than too hard and warp the bearing.

The new locating notch/tang.


Work gently here. It will almost always create a slight burr on the journal side. This is not a problem. You can use a diamond needle file (best) or standard needle file to “square up” or sharpen up the back side.
I use a Dremel 360 grit rubber Emory wheel that has been dressed to a point to clean up the front notch and make sure any burrs are below journal level.

NOTE: in regard to the worry about using abrasives near these bearings…it’s not a worry if you know how to clean them PROPERLY. I will get to that later. If you are worried about abrasive dust use a Dremel diamond disc wheel that has been lightly broken in on a soft ferrous metal part. It sheds no abrasives. More on this at the end.

NOTE: If you do not trust yourself with a punch….another good way to make this dent is with an old pair of diagonal cutters with the cutting edge blunted. I made the first one this way and the second one with a punch.

The nice thing about this method is that you can control the pressure and depth very well.


The bearing was cleaned chemically and reinstalled in the case.

The camshaft was laid in the oiled bearings, pressed down and rotated. Slightly tight…no pinch spots. The forward and back “TAP” was repeated. The camshaft now spins smooth as glass.

NOTE:…..any time you take any of the bearings out of the case and put them back in…there will be a slight difference in position in the bore and they will feel tighter. Because they have not yet been “crushed” or clamped” they still have a small amount of spring in them.
This changes their angle to the case bore center line by a very subtle amount. Adjusting that fit by tapping at this point…is different that exactly what we are doing to the flange on the thrust bearing. It takes very gentle taps to reset back to flat fit at this point.

The dial indicator was set up and the end play on this bearing shell set was just under .002”…probably .0018”… Excellent.

The other case half bearings were re- checked for position, cleaned, oiled and the left case half was mounted to the right. Tap the case lightly around the parting line to relieve any stresses.

At this point the camshaft still rolls smoothly and lightly.

Insert the six main case bolts. Tighten up finger tight, turn the case vertical and tap along the case parting line top and bottom to relieve stress.
This was the point where the cam tightened up slightly.

It still turned smooth…but is tight…about 2-3X the light rolling force it had.
Repeat the forward and back tap…lightly. The cam loosened up to normal again and rolled smoothly.

Just for a benchmark at this point…the dial indicator was installed and end play was checked again and is at .0024”…so its opened up by .0004”….THIS TELLS US SOMETHING I WILL GET INTO LATER

The case was tightened in an X pattern to 12 ft. lbs. (half the total torque)

NOTE: for what we are doing now….setting the end play….the torque pattern on the six main bolts does not matter that much as long as it starts in the center and works outward in a cross pattern. Once we are sure the bearings are right we will also loosen all of the bolts, install all of the perimeter case nuts and bolts and tighten/torque like we are assembling the engine and recheck rotation and end play again.

This is only about getting the thrust bearings sorted out at this time.

At this point in the process at 12 ft. lbs…. THE CAM LOCKED UP. No rotation…and I was not going to force it.

The case was peened around the parting line top, bottom, front and back. No rotation yet.

The bolts were loosened back to finger tight, the case was peened around the parting line again…..

….and rotation was restored…..but with a slight but even drag….which means SOMETHING has deformed.

I removed the case half to inspect the bearings. The left hand case half bearings (the side that the single thrust bearing normally resides in) all of the bearings “looked” perfect….but there was a “scuff” mark on the flange of the thrust bearing shell…in the center of the arc and at the ends close to where they meet…take note of that.

Yes…its normal to get scuffing of the thrust bearing in the center of the arc…that’s where it wears in normal usage….but not after 10 revolutions.

This picture “looks’ far worse than it actually was. It is just a play of the bright lighting. It’s nearly identical to the right side flange scuff. I should have pulled it out to photograph it the same way.

On the thrust bearing in right side of the case (the one not normally installed by the factory)….the center and flywheel end bearings looked perfect….but there is a scuff mark on the thrust flange similar to the left side….in the middle of the flange arc and right up near the tops of the bearing tips

AND… there was a shiny burnished contact mark next to the inner side flange. Make a big note of this.

Let’s do a test to be sure we think we know what is going on is correct:

Yes….I know it’s a thrust flange issue….but I want to be sure that there are no issues with the other two bearings in the set at this point.

So….

Remove the right side case thrust flange and install the normal half bearing with no flange. Install camshaft, install left hand case half. Finger tighten bolts….cam moves smooth and slick. Torque to 12 ft. lbs. Cam moves smooth and slick.

Tighten to 24 ft lbs. Cam moves slick but has slight constant drag. Tap forward and tap backward to set bearings. Cam rolls like glass. Measure endplay…..00225”-ish….slightly larger…which is explained by the scuffing on the thrust flange.

SO…to this point: it’s definitely a problem with having the second thrust bearing shell mating…in right?

But why?

By their self in each half of the case they fit fine. Yes…I know it’s the bearing crush….but even with that this is not normal

Let’s find out.

Remove bolts, remove left hand case half, remove camshaft. Install both thrust bearing halves and reassemble case without the camshaft.

CAREFUL Inspection through the oil pump hole shows two important things:

1. The deburring/clearance work required to make clearance between the bottom ends of the thrust bearings is not correct. The bearings will and should make “crush” contact along the top and bottom edge along the length of the journal bore on the bearing looking fore and aft….but the flange tips….which have a very slight buckle to them where they turn from the straight barrel of the bearing into the flange….should NOT touch…..in the curved chamfer area between the flange face and the barrel of the bearing.

Notice the wider Vee gap at the top….and where the arrow tips are pointing.
This is the first set I have had that needed clearancing in this area that I can remember.

Why is this an issue?

This is the thrust flange bearing shell from the side before clamping the case and loading the bearing

This is the direction of forces as the bearing is crushed in the case. With a non-flange bearing…these forces just warp the bearing shell harder and more completely into the case bore. BUT…..the flanges being vertical in relation to the thrust compared to the barrel of the bearing shell…CANNOT flex very far in that axis. If something is making contact that causes excessive pressure….the flanges WARP…..OUTWARD toward the thrust faces.

As the bearing shell deforms….the flanges spread OUTWARD toward the thrust surfaces.

This is pure force geometry. This is part of what the “fore and aft” tap corrects. BUT…if the ends of the flanges touch and crush against each other…the flange BUCKLES in TWO directions.

To be more precise…in this top view…you can see that the flanges really only warp outward in the center close to the apex of the arc.

You can see the long term result of this effect looking at the wear pattern on this thrust bearing which has about 90k miles on it. The solver flecks on the thrust face are aluminum…and are from the fact that this engine died violently. This bearing is about 25 years old.

This clearance at the flange ends is a little inadequate…..I am assuming….because these bearing sets were not set up for two flanged bearings to be used together.

Really you only need to reduce the height between the two arrows to keep the two thrust faces from contacting during bearing crush…on that little elbow bend. A little more angle back helps as well.

2. THIS WAS ALSO A BIG TELLTALE that something was wrong: note in this very poor picture how the right side bearing appears to be lifting.

And…the location of this lifted corner….lines up perfectly with the burnished/deformed mark on this thrust bearing shell.
I at first thought I may have deformed the bearing shell during the making of the locating tang.

So….….I pulled out a brand new bearing set…and proceed to fit a new identical bearing (measured within .0001” in flange width and with about .00025” in depth)…and when fitting it to the right hand case half to see if it fit the same as the deformed one………..I SAW THE DAMN LIGHT!

Really…I had to get my brighter lights on it to see it clearly….but I saw something that I had never had a PROBLEM with on any of the other cases I installed double thrust bearings in.

The inside case chamfer on the thrust bearing bore….was VERY SMALL. You can see in these pictures what it does. It does not allow enough room for the radius of the inside of the flange. So when the case is tightened…it deforms the bearing …permanently…and burnishes the surface.

Close in inspection of the left side of the case…..where the thrust flange bearing normally resides shows that its chamfer was slightly better…but also barely adequate. There was a very small burnish mark starting on that bearing too.

I suspect…..that the original German bearings had sharper and more distinct stamping than the Brazilian made Mahle bearings….so this barely adequate chamfer was not an issue during the factory build.

Inspecting two of my other cases found better chamfer on these. The chamfer on my other two cases were easily 0.5mm to 0.7mm wider…..not much….but enough that it was visibly a better chamfer to the naked eye.

The difference in the thrust flange chamfer is very apparent in this picture
So…two spare sets of bearings will come off the parts shelf to steal the thrust bearings from. I got them very cheap on sale years ago…maybe $10 a set…so it no biggie. As I say…collect parts when you can!

Improvements moving forward……

1. I removed the other bearings and…. I increased both case half chamfers by about 50%. With a steady hand, a Dremel and a fine sanding drum, then deburred with a sharp bade at 45 ° and yes they had to go back downstairs to the sink for washing and drying.

2. The two new thrust bearings both had the lower corners of the flanges deburred so they do not touch when the case crushes. These pictures are the old ones I used for practice….but you can see the difference.

The notch was installed in the right hand case flange bearing.
All bearings were cleaned and the whole original process repeated in each case half….bearings in, oiled, camshaft in, spin, tap back and forth….measure end play. The end play on both sets was almost identical to the first set (about .00225”).

Case bolts installed finger tight. Cam still rolls smooth. Case bolts torqued to 12 ft. lbs. Cam rolls smooth but about 3 times tighter. Tap forward and back twice. Cam rolls smooth as glass.

Torque case to 24 ft. lbs. Peen around case, tap forward and back. Cam rolls smooth as glass. Endplay is checked and It is unchanged….right at .0022”
Case bolts loosened. All case bolts and nuts installed and lower center bolt tightened….and all nuts and bolts tightened as if final assembling. Cam rolls smoothly…endplay unchanged.

Success!

The bearing crush issue:

NOTE: I have this suspicion that the bearing crush tolerance…the extra length allowed to the legs of the bearings to force the bearing flat into their bores when the case is mated…..is slightly variable and excessive in some bearing sets.
From inspecting many worn high and moderate miles bearings over the years….it’s clear that just like crank bearings they are slightly egg shaped when installed.

This is not a problem and I am NOT going to second guess the engineers with millions of engines under their belts…but this has IMPACT on the double thrust bearing shells.
The thrust does not just cause distortion in the bearing shell back toward the case bore. It causes lateral distortion/spread of the flange because of how the bearings arc under load….and because this bearing set was not destined to be used with both shells….it is not deburred properly at the ends of the flanges……so be sure you look at this when you put in a double thrust bearing set.

A last little bit of information. A recent comment from Piledriver on the STF noted that double thrust bearings sets are not “bought” they are made. This is quite true.

Meanwhile…you CAN buy double thrust cam bearing sets….but whoever is selling them to you …put those sets together from two sets.

You can buy double thrust type 1 cam bearings from Aircooled.net. I “think” at one time they also sold type 4 double thrust sets.

You can also buy them at the type 4 store for type 4 engines. I have a set of them I got from the type4 store that came in my deluxe cam kit. They will be going into my engine later this year.

Just to compare I pulled them out of the box to look at them.

You know…back in the day…a lot of people gave Jake Raby a ton of shit for his parts prices. But I must say….this double thrust cam bearing set was a freaking bargain at $49.95.

The clearance deburring to the ends was done, the punch mark was done in a special jig (I remember the on-line discussion about this)….and the thrust bearings had an oil groove added in a special machine jig. The measurements were spot on.

Just for reference….on the left the type 4 double thrust set I bought from Jake Raby in my cam kit. $49.95 was a steal! The provided bearings for this build circa 2009 and the back up sets from 2000-ish on my shelf.

Some pictures of what’s in Jake Raby’s double thrust sets. Nice work!
I have no idea how much John puts into his double thrust sets...or if the type 4 store still puts this much into their current stock sets….but if it’s the same it’s a bargain.

At a current price tag for a single thrust set from AC.net…$29.95…and two sets being required…..bringing it to $59.95 a set for parts…..any added deburring etc….would be worth another $30-40 of labor. Bringing the price upwards to about $99…its right in the same neighborhood with the type 4 store current price of $112.

You get what you pay for. My double thrust work is pretty damn good…but for the time versus money perspective (not an issue with me) but for many people…. the risk of having to destroy possibly a bearing set from something like a punch slip during fitting the second shell while doing this yourself….it would be a bargain to buy the set from the type 4 store or AC.net.


Last little bit….abrasives and bearings:

To those swearing one is insane to use ANY abrasive around bearings….just stop it!

First...yes…you should have NO NEED to use large heavy abrasives that can leave “rocks”…..and to me that means nothing below 1500 grit at absolute worst and 2000 to 3000 grit at best….because:

1. The abrasive particle size on P1500 is right at 12-13 microns. The particle size in 2000 grit is right at 10-11 microns.

There are 25.4 microns in .001”….and the most common oil filters only rate 10 microns at about 90% efficiency…which means there is a percentage within that left over 10% that you are passing 20 micron or larger particles into the system…..so there is already grit in your oil larger than these particles. And….the surface profile of your bearings has enough peak to valley to swallow much of the smaller stuff.

https://www.fleetfilter.com/filter/Article--Micron-Ratings-in-Filters.html

But more importantly….

2. Every day…very critical dimension soft metal industrial products (aluminum, brass, bronze etc) are “ground” by abrasives and/or sanded….things like hydraulic cylinders, brake cylinders, air cylinders, ball bearings, roller bearings…etc…..BEFORE they go to plating. They have to be squeaky clean freaking clean to plate.

So keep any abrasive use to the very finest micron size to start with. Then…take a page out of the plating industry book and you will find cleaning things like these bearings is easy.

Understand that…water…and most solvents that are “water thin” in viscosity…have a surface tension that does not allow them to flow into small gouges, grooves or surface profile grinding marks…..that are under about 12 microns in depth and under about 5-6 microns wide. The surface tension just “beads” over those grooves.

Unless….you greatly increase the pressure on the liquid to allow the liquid to “squeeze” into these pores and grooves…and usually in that case the liquid cannot get back out because of the same surface tension….to wash the grit out with it.

Part of this is liquid surface tension and part of it is surface “dyne” level.
The plating industry…and even the dish washing and laundry industry realize that you need to reduce the surface tension of your washing water or chemicals.
They do this by REDUCING THE PH. Reducing the PH of water GREATLY reduces the surface tension and allows it to flow into MUCH smaller grooves and pores.

They use a diluted acid wash.
Too many think they are etching with this acid….NO….they are rinsing with it....AFTER using a caustic for surface etching and reacting.

One “could” get away with a simple vinegar rinse…but you have to heat it up a little because it’s very low solution strength. Or…you can even get away with a common surfactant like “jet dry” for dishwashers. It does the same exact thing….but it may leave some residues that do not do well with oil....but it works.
So…if you have to lap your bearings……use the finest grit paper you can…wash them with a soap and very hot water. Then rinse them in a dilute acid wash for just a minute or two….then rinse again with very hot water. Blow dry with compressed air….and oil them. No grit of a micron size worth worrying about survives this.

Bearing measurements:

As I noted...I think these are about as good of a bearing quality as I was getting 25-30 years ago in the same brand....and teh measurements were very close. There was just a little bit of difference in the sharpness of radius and fold in the cam bearing flange but these are pretty damn close.

Ray

[Busstom]

Nice work, thanks for the heads-up. Can't wait to get home and check my case radii. I'm not running double-thrust, but still...the radius issue remains.

[Jack_O_Trades]

This was a good read, thanks for taking the time to do the write-up

[raygreenwood]

[Mile High Puma]

Thanks for the info. I will be building my short block soon and your test procedures will be used. Is there a way to tell if the bearing crush is correct? If too tight would you be able to see light at the case halves near the bearings? If too loose would you be able to tell as the cam would still spin easily?
_________________
1965 Velvet Green DC

[raygreenwood]

[Jake Raby]

Well, there's what I've been saying for the last 15 years, all laid out... Thats a great write up, Ray.. Its exactly what I see..
_________________
Jake Raby
Raby Engine Development
www.rabyenginedevelopment.com
"I've never given anyone Hell, I just told them the truth and they thought it was Hell"

[raygreenwood]

[69BahamaYellow]

Outstanding write up, Ray! Preparing to double thrust my 1978 2.0 liter, and I would have made a lot of mistakes, had I not seen your post.

I bought 2 sets of Kolbenschmidt cam bearings from eBay for $18 each to make mine, but when I got them, both were part# 85070604, but one set says STD Eh, while the other says STD Cb; hope that won't be a problem. There is a slight difference, but thrust width is identical on both at 1.101"

The thrust flange is not tapered back, nor does it have the leading edge bevel that most other type 4 cam bearings have, so I'm going to remove some metal on the thrust flanges (where the 2 halves meet), since there will likely be distortion from crush. I do like that these bearings have a relief cut at the thrust flange on the case side. That should eliminate the problem you discovered with that inconsistent chamfer on one side of the case...

[raygreenwood]

Ooooh. Those are nice!.....that relief is precisely to get away from the chamfer interference issues. I have thought about putting some relief grooves into some of the Mahle bearings.....but in thinking about it....I would not.

All of these bearings are pressed/stamped into shape. So the skin of then is stressed....especially at the bend between flange and barrel. If the relief grooves are not already there.....putting them in may make it prone to cracking.

I am not 100% sure that the ends of the flanges need to much back angle.....but the bend elbow for sure needs a little. I will post a clearer picture of where I would clearance those. Ray

[69BahamaYellow]

Here are some better pics of the Kolbenschmidt double thrust cam bearing set I made from 2 standard single thrust sets. There are a few extra callouts with the KS bearings that I like (others not so much). In addition to the relief cut on the case side of the thrust bearings, the plain bearings also have a chamfered edge on the case side. I suspect this makes them much more likely to seat squarely in the case during crush.

I made the tang on my thrust bearing with a cold chisel that I ground down to the proper width, clamped a bar across the bearing shell and lightly punched it into the groove of the case, just like Ray did. The picture makes it look like I did the job with a hatchet or something, but the lighting is just making it look bad. I ground my cold chisel to a very sharp edge to make a clean cut on the tang, which I feel is very precise.

One thing that's weird about the KS bearings is that the oil hole chamfer is on the case side of the bearing, not the cam shaft side. These are Brazilian made bearings, so perhaps somebody just accidentally put the chamfer on the wrong side, and nobody noticed. I can't think of any good reason to put the chamfer on the case side (other than eliminating the stress rise from a sharp edge), so I'm just going to attribute this to poor quality control. I believe it's fairly insignificant, so I'll just live with it.

[raygreenwood]

[69BahamaYellow]

[SGKent]

Ray - good write up. That said I think we would need to compare a dozen engines with double thrust vs single thrust to measure the benefit. The reason is this - stock thrust bearings outlive the engine, and all cam cores I have seen have wear in the thrust area after 100,000 miles. I learned from a good friend who is a machinist for 50+ years in the aerospace industry that when working with dissimilar metals, the harder metal often wears faster. Sounds backwards but in general it is not when the cooling medium (oil in this case) picks up small pieces of the harder material. This is because the softer metal picks up debris and it cuts the harder metal. The paper in sand paper is very soft compared to steel, so are the glues on that paper, but some of the abrasives that sit in that glue and soft paper will eat right thru steel. The Babbitt is soft and it picks up steel in the oil. By going double thrust the cutting area is doubled. If more surface area reduces the cutting pressure that may offset. However if the amount of contact area increases and there is no more oil to carry away the heat, then the bearing heat would increase, shortening bearing life. So, since I have no way to measure this and an argument over the science would be moot without the ability to measure it, I think you did a good job. When that engine wears out measure the wear on the bearing, and the cam, then compare it to one that had a single thrust and see if it is more or less. Good job documenting the precision. Not saying the effort was wasted - I don't know because it can be argued either way. I've never been able to find a study on one, and everyone I know with double thrust has been back in their engine for some reason or another before the engine would normally have reached old age.

Here is a science experiment for those not believing the concept. Go get some soft clay used to clean paint. Drop it in some gravel and broken glass. Rub it on something hard and unimportant, see if it leaves scratches. Do not rub it on the car paint because it will scratch right thru it. The same principle is going on with the thrust bearings. By doubling the surface, the amount of area exposed to debris is doubled. In addition the contact area is doubled. It gets its oiling by splash so it is hard to know how much the oil film protects it when the bearing is doubled. One would need to make some engine comparisons at high mileage to see which wore less.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[riverside66]

Thank you for taking the time to write this up Ray!
_________________
1977 Standard Beetle -Sold-
1979 Transporter - "Wheatbread" -Sold-

[raygreenwood]

[lil-jinx]

Great write up, Now to go read up on the rest of your build.
_________________
https://www.thesamba.com/vw/forum/viewtopic.php?t=620186
https://www.thesamba.com/vw/forum/viewtopic.php?t=668799
1974 Bay Westfalia. she likes to be called Ethel.
1968 Dune Buggy
1974 parts bus
A smart man learns from his mistakes,a very smart man learns from other's mistakes.

[SGKent]

[raygreenwood]

[SGKent]

Something else is behind that failure. If a single thrust failure did that, double thrust will only take 1500 miles longer to do the same. What is curious to me is that all the teeth are knocked off. It is hard to visualize a load where each successive tooth would fail on one cycle. I don't deny that failure could have wiped out the cam bearing but I don't believe that is where the failure began. If the engine was being raced then I already said that is the only time I can see benefit of the double thrust. BT the way your shouting is really not up to your normal self.
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