As the title asks, is the standard fan for a type IV engine made of aluminum or magnesium ? Trying to figure out how I'm gonna restore mine - mine currently has speckles like the mag. (fan) Housing - which I'm considering spraying with gray POR-15, along with the transmission. But I'm not sure if the "weight" of the paint would create issues on the fan itself (balance issues). thx.


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The fan is aluminum. over time they will form some white rust similar to magnesium if it is dry — which seems rare as engines like to leak a little and it ends up in the fan. Whatever you do, don't remove the steel pulley ring as it's balanced at the factory, and I don't know how you'd get it back on exactly the same.

I'm not a fan of painting aluminum or magnesium parts. I like how they look raw. I blast and then rub them with a coat of motor oil and I've found it to not spot up with any oxidation in the years I've been doing it.

Ok Aluminum then, thanks!

As for removing the pulley ring.. well Ooops, I already did! Actually I did consider this before pulling it all apart, then after looking at it long enough decided that couldn't be the case. My thought was along the lines of.. 'well, none of it looks machined and hey, there's only 3 choices in how it goes back together.' Too impatient to go check, I guess . It's been a while since I took it apart but I thought I'd made a note on how it went back together (marks to line up or something), but no.. can't find any such thing.


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Send it out for dynamic balancing. Can be balanced 1st as a component, and then again as part of the crank / flywheel assembly.

If you're not going to to that, get a new one that is balanced.

As I recall there are weights that are sort of swaged into the steel pulley. I've heard arguments that there are only 3 ways it can go, but I think the slop in the screw holes play into it. They mount the pulley to the fan, then run it on a balancer that tells where to put the weights, kind of like a tire balancer machine does. — that's my theory anyway.



Do you know where to go to get this done?

I have a pulley that I separated years ago before I was wise to know not to. I ran it after and the motor actually felt lumpy/off-balance. I want to use that fan as it has the timing marks in the right spot. I have another fan that's balanced but it's from a bus and the 2nd timing mark is in a slightly different spot.

Here's a pic of my bus fan (haven't refinished it yet) — from a Bus CB case
Click to view attachment

This fan has the same timing mark positions as the unbalanced fan I have. I'm saving this for a different motor, but I have another that is the same, both from EA motors. I think it should be the proper one for a W engine I want to build.
Click to view attachment

Sorry for slight thread sabotage

Ya that is FUD Any competent machine shop can balance them. youll notice there are weights already pinched into th outside ring.

No, I'm more than interested in all that can be garnered on the subject now


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I had to look up FUD — I think "Fear Uncertainty Doubt"? Like a marketing tactic... I guess I should say don't separate them unless you have a plan to get it rebalanced.

I'm going to take a drive up to Brothers Machining up in Ontario pretty soon with my case and crank and rods. I will bring the unbalanced fan and ask them if they can do it for me. I'll ask if they balance it with the crank as an assembly, too. I just have never had it done before. I think a lot of people think you can just take it off, and put it back on and run it no problem where I've found that isn't the case.

I'd generally agree if we are talking about High Performance Automotive Machine Shops. If they don't do it themselves, they will have a shop they sub the dynamic balance work out to.

When I was in college I used to balance building HVAC fans as part of my job with the university facilities engineering department. It really is amazing how much force a tiny balance mass can have if the fan is spinning at high RPM's. In the case of building fans, high speed was only about 3500 rpm vs. the fan on a T4 engine is spinning at 5500 rpm or so.

It wouldn't have to be off much to create some noticeable imbalance at 5500 rpm.

Well... I took mine apart to paint the ring and clean the fan, but not before making sure TDC was notched on the ring (it already was) to know which way it went back on. Put it back together, but didn't notice much slop in how the ring went on. Not saying there wasn't any, but I was looking for it.

Took it to a machine shop (there aren't many to choose from here). Guy says he didn't have a rig to balance stuff and sends me to a place the next town over. It's one of those places that is harder than hell to find even when you know you are right there. Go in and the guy says he can balance it, but it would be 6 months minimum before he can get to it. Then he starts asking questions. "What's it off of?" "Why do you think it is out of balance." I explain the remove and replace to clean it up. "Was it balanced before you took it apart? Yes, as far as I know. "Did you put it back on the same way it came off?" Yes. "I wouldn't worry about it." I took his advice to not worry about it, but wondered if he'd have been able to balance it in less time than the conversation we had just had.

I've driven 6K miles with it now and as far as I can tell, the engine is balanced and silky smooth. Far smoother than this car before the rebuild, or any of the other 914s I've owned. @Superhawk996 drove it but was probably too busy bitching about the slop in my steering rack to notice any engine vibration.

I'm not claiming I did the right thing. Just telling the story.

Clean it up and run it. Is there damage? Why do you think it needs to be balanced. Back in the '70's I was a dynamic balance tech for 6 years and got pretty good at it. To balance just the fan would require fabricating a hub.

Unless the all of the rotating parts are being checked for balance, I would skip balancing just the fan.

As long as it goes back together with the same indexing as it came apart it would be fine. I don't think the slop in the bolt holes would be enough to throw it off to a noticeable extent.

As I understood the original post, the original index position is unknown. I don't have a part in front of me but if I recall correctly there were 4 bolts that hold the stamped pulley to the aluminum impeller. That could lead to weight being 90 deg., 180 deg., or 270 degrees out of phase from where it is supposed to be. 180 deg., especially would be a big deal since it would make what ever inherent imbalance it started with 2x worse rather than counteracting it as it's supposed to.

@bbrock
I'm awaiting a post on the rack adjustment . . . I did look at the service manual -- rack to pinion clearance is adjusted via shims. I really did appreciate the drive -- car is marvelous. Sorry if I pointed it out and now it's driving your crazy? That wasn't my intent

See, I'm thinking something pointed me to 'not worrying about it' during disassembly but again, it was a while ago so..


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Fan is balanced for a reason. Agree that if the whole assembly is dynamically balanced from fan to crank to flywheel, it can be offset as an assembly.

In production, each rotating part is balanced to a component spec such that the assembly tolerance will fall within an acceptable range without the need to do dynamic balance on the assembly line.

When building high performance engines, dynamic balance of the assembly is the commonly accepted practice. Whether or not a VW T4 engine can ever be considered high performance . . . . we'll leave that for another day

Re reading your earlier post regarding the fan/v-belt pulley assembly, I would send the rotating parts out for balance. I would bet the factory balanced the fan/pulley when assembled. Seeing you dis assembled this and perhaps failed to index the parts, they should be checked for balance. I would not invest the time/$$ with fabricating a hub, just have everything balanced as an assembly.

Back to your original post, clean and forget. Paint or other treatment is unnecessary.

Yep. I revisited the factory manual after your visit and found the same thing. It seems the older 911 racks had the adjustment bolt you were talking about. The thing is that I went through their procedure when I refurbished the rack and I wasn't able to detect any play. If I'm under there doing something else and can check/adjust without dropping the rack, I might revisit. Otherwise I'll leave it alone so you have something to pick on the next time you drive it.


Oh yes, every time I drive the car now I wiggle the wheel and then say to myself, "he's full of shit..."

@Superhawk996
@bbrock

Having restored several fans i found that the problem is getting the ring centered. They rub on the fan housing if not perfectly centered. One way to center the ring is bolt it to a crank placed on half of an engine case. Set up a dial indicator and check for run out.

Bruce

So.. if I find that the v-belt ring is indeed index’d to the fan itself - I will mate them up that way. If not, it’s off to the machine shop it goes for balancing.

Bruce - Any reason (once the correct balance is obtained on the fan/v-belt ring), you couldn’t fine tuning the assembly (not to interfere with the housing) by installing it after the housing is already installed? ..So, install, rotate the assembly, loosen the 4 bolts on the perimeter of the v-belt ring, adjust and rotate again to check, & repeat.. ? @bdstone914


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You could do that but it would require several attempts. Maybe if the the bolts were just snug and you could adjust the ring until it did not rub. There is also a little play in the four studs that hold the fan housing to the case.

I was thinking about trying to get the even gap with the housing by using 4 flexible shims .. like foam rods or rubber hose shoved in for the gap 'til the bolts can be torqued.

Anything not to do it right!


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That's the spirit!

I was thinking, could static balance be used to find the correct position the ring should be on the fan if the original position is lost?

Do you mean, like, stick a level and horizontal pipe thru it, and spin it? I'd thought of that but was too embarrassed to bring it up


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If you need one that hasn't been disassembled, I have a few laying around here.

Clay

Ha! I have no shame, so I've got your back. I don't think you even have to spin for static balance. Hopefully the spin balancing gurus will correct if my logic is flawed, but I'm assuming that an object that is dynamically balanced would also be statically balanced but not necessarily the other way round. So if you disassemble a fan that we assume was dynamically balanced, reassembly the pulley ring in the position that restores static balance would put it very close to dynamic balance again. Okay experts, do your worst.

Brent is correct. Static balance is a subset of dynamic balance. Since you only have 4 possible orientations, finding the static balance point would probably be enough to put the weighted pulley back on the impeller in the proper orientation to regain the dynamic balance.

@bdstone914 -- great note on the importance of getting the radial run-out of the pulley minimized.

However, spinning the fan impeller on a pipe though the center is probably going to have too much friction to get a reliable static balance. Maybe since there are only 4 possible orientations . . . . maybe not depending on the friction. If you can repeatedly get the same static orientation, you're probably OK.

A truing & balance stand like those used for balancing motorcycle wheels would be closer to what you want. Fan would get centered on cones. Shaft spins on bearing rollers. That will give you a reliable static balance. I built one of these out of scrap metal a long time ago. Comes in handy for anything related to static balance as long as it will fit on the stand. Looking at the price of this . . . . I should have just bought one given the hours of machine work it took me to build mine even though mine is way more robust than this cheap Amazon version.

https://www.amazon.com/VIVOHOME-Motorcycle-...0NsaWNrPXRydWU=

Completely disagree. A static balance is completed at 0 rpm, a dynamic balance is completed at generally 1,000 - 2,000 rpms. How fast is your engine running?

There is very little comparison between the two. A static balance does not differentiate between planes (inner vs outer).

Assemble the fan/pulley, attach it to a crank and spin it up

Hmm, in theory couldn't one go to the extent of balancing a complete assembly to include fan/ring, crank, and flywheel.. only to have the thing foul the housing? I mean, obviously nothing of the fan/ring gets "shaved" , just sayin' & thinking out loud I guess.

..and honestly, this idea of high performance engine balancing is probably beyond my immediate needs (fingers crossed).. which is just to get the engine (2056) back together and running while not being a vibrating monster is what I'm gonna focus on at this point. Great points and info that will come in handy though. I will be breaking the engine down at some point to switch out the cam (current a Carb cam presumably) for FI, and add flat top pistons. So hopefully I can hold out 'til then for the dynamic balancing. Thanks y'all.


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I don't completely disagree.

Statics act generaly in two planes axial and lateral. So the static balance is in relationship to the center of the fan and the dynamic balance is how it reacts while in motion around the axis of it or when it is spinning.

Normally the center steel ring is the heaviest part so if that is screwed up or bent....will screw up the dynamics when it is spinning. If you've ever watched anyone balance a tire....you'll see them check the static balance first before they balance the tire and rim assembly.

I've seen fans on Type Iv's come apart becuase to dynamically balance it someone drilled out the ring and at high RPM the outer rim cam apart and the fan basically implodes like a spinning washing machine with wet blankets in one spot.

I saw this happen on the Frank's 1.7 914-4 Ginther car at Rennsport. Course this little 1.7 was spinning at near 10k!

Edit. Dynamics was my toughest course in college and the reason I went towards civil engineering. It's all about the relationships, ask my Ex wife....no better yet don't.

OK so here is why finding the static balance point (assuming a zero friction pivot) will end up fixing the fan.

To achieve dynamic balance:
Click to view attachment

Static balancing sets the sum of forces (F) = 0 (in one plane)
Dynamic balancing sets the sum of the moments (M) = 0 (in the 2nd plane)
Pay particular attention to figure 12-2 in the attached link at the bottom.

As 914_teener notes: when a wheel/tire assembly is dynamically balanced the very 1st step is to do a static balance. This reduces the amount of mass that will be required to achieve dynamic balance. This is standard practice. You can't have a dynamic balance condition without satisfying static balance (sum of forces F = 0) simultaneously with having the sum of the moments=0 at the same time to achieve dynamic balance.

So since we started with a fan that was dynamically balanced at the factory, it will have at least one but sometimes multiple weights staked into the pulley ring. If these haven't moved angular position relative to each other, there is only one position on the impeller that should allow everything to come into static balance of the hub and impeller assembly. That static balance is a subset of the original dynamic balance from the factory.

Knowing that we can't have a dynamic balance condition without static forces, F=0, if we can restore static balance AND knowing that none of the weights on the pulley have moved relative to one another there is a very high likelihood that we will put the pulley back where it came from. Furthermore, if we take Bdstone914's advice and make sure the pulley is running zero radial run-out, it is even more likely that the pulley will be put back exactly where it came from.

Further increasing the chance of success is the fact that the pulley can only go on in one of four distinct orientations.

Here is a good summary of balancing as well as the link to diagram 12-2
http://eng.sut.ac.th/me/box/2_54/425306/Balancing.pdf

I'm holding to my guns

To consider any part of a modern engine to receive a static balance is just wrong.

Had the OP not removed the pulley from the fan, he would probably be ok.

Send the assembly out for a good spin balance (2 plane)

Thanks for the link Phil, I was a near master at this stuff 50 years ago

Just to be clear about what is being proposed, it isn't to do a static balance. Nothing is to be adjusted.

What is proposed is to find out where the pulley and impeller achieve static balance as an assembly as it left the factory. It can only go together one of four ways.

One of those four (180 degrees out) will be clearly wrong since the pulley weights will be 180 degrees out from where they ought to have been when it was originally balanced. This will not static balance since the balance weights on the pulley are now adding to what ever imbalance was in the impeller.

One of the four will be right (0 degrees) -- it will static balance as it left the factory. Since the weights have not moved from factory position, it will be dynamically balanced to the same extent as it left the factory assuming it had zero radial run-out when it left the factory.

The other two (90 degrees and 270 degrees out) are up for grabs. If the weights are very small, it might be hard to tell in these positions if we've returned the assembly back to the same static balance the assembly had when it left the factory. If the weights are large, static balance won't be achieved in either of these positions.

Overall - I'm with you. It would be better to send it out and have the whole fan, crank, and flywheel/pressure plate dynamically balanced but that doesn't seem to be on the table.

This was more of the thought excercise to figure out how to return the pulley/impeller assembly to the same condition that it left the factory in. Of course, we are ASSUMING all fasteners weigh the same and can have their positions intermixed without ill effect. The chance of returning all fasteners to exactly the same position as it left the factory are about as good as winning the Lotto.

Back to one of my earlier comments . . . considering a VW T4 engine to be modern or high performance is a stretch of the imagination.

anyone know what these weights look like exactly? I can not recall seeing anything that looked like a weight on the ring.


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Just little pieces of steel rod crimped into the flange of the ring.

I had a look at the fan that I separated, thinking there would be a filed mark where #1 tdc was. It's been about 15 years it's been laying around now, and I can't remember if I had put it back in the same orientation as it was originally. Somehow the filed marks seem to correspond to nothing. Possibly I had the distributor like 90 degrees out or something. I used to do dumber stuff than I do now even

I checked the 4 fans that I have here and the weights are all in different places so I think there's no way to tell at this point. I guess I hope the machine shop can figure it out/that they know how to/have the tools/knowledge to dynamically balance it. It's never been the prettiest fan, always had weird marks in it, but it's not missing any teeth. The one that I got with this motor I'm building had 3 teeth missing.

Click to view attachment

Very possible the fan/pulley you have does not require weights, IF you can orient the parts as originally assembled. Look for any telltale paint marks, ... in an attempt to get things back to where they were when it left the factory

Been doing a little reading over on thesamba and the general consensus is that the mark on the ring lines up to the general area of the dowl/peg in the hub of the fan. So that standardizes it in a way. Then they like using a simply made jig to line things up and bolt back together. I’m going with this approach as a first step.

I have a few laying around, a couple with broken fins which I will not use. Let me have a peek and perhaps there may be an end to this.

Can you post a pic?