Restoring Type 4 pulley/fan alignment

[raygreenwood]

[raygreenwood]

[williamM]

[orwell84]

This is a really helpful thread. I took my fan apart before I knew any better. I had a broken vane that I repaired with JB weld. That thing will never balance now. Guess it's time for a new one. Luckily I have had no issues with belts but the other issues sound scary...

[raygreenwood]

[raygreenwood]

One version of how to true a type 4 fan pulley:

https://www.thesamba.com/vw/forum/viewtopic.php?p=8681745#8681745

Ray

[SGKent]

Ray - the pulley hub should be sitting on a piece of plate aluminum or steel and lightly greased rather than wood. It would be more stable. Probably lap the hub a couple figure eights too on 500+ and glass.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[raygreenwood]

[raygreenwood]

Steve....so you do not think I was being snooty....here is the geometry in my set up that was missing from my method that allows variation in the surface plate I was working on...to not make any difference.

You will notice that for axles for the 608 bearings.....I did not specify "precision shafts". I listed using a 5/16" bolt.

This was done on purpose.....precisely because there is potential for a small amount of misalignment on MDO board....which is actually quite flat because its CAST in a mold. While it may have surface variation...small low spots created by the grain....it has no high spots....and its softer than the hub.

There is .008" tolerance between shaft/bolt and each bearing. This allows slight misalignment for each bearing to allow the high pressure I imparted to FORCE the bearing and hub face to stay in SQUARE contact....unlike on an inline racing skate.... where these bearings came from....where the shaft tolerance to bearing is about 0.0002" to 0.0003"...a dead fit.

These 608 bearings have the inner face of one side reduced in width by about .010"...as I noted...they are skate bearings (technically 608Z with a seal only on one side). Underneath each bearing is a flat washer that is loose on the bolt with an ID of about 0.335".

Its the bearings having their dead square face...dead square to the dead square face of the hub....that makes this work.

You will notice looking carefully at the red lines...this bolt is not square with the bearing but the bearing is square to the hub. This is what makes it work.

The two methods I used to make sure the hub was riding even with no "helicoptering" that could give errors in reading....were as mentioned in the post....

1. I measured the radial and axial play of the hub at the top fan centering boss and at the seal race with a dial indicator before putting the fan on it.

and the one I did not mention

2. I used a scribe set up on the dial indicator post arm in teh valley of the vee to make a very, light drag scribe line on the valley of the Vee....all the way around and then inspected it for wavering

The scribe....

the scribe in the post mount in action.

The one thing I learned long ago about working on precision fixturing table while working on very precise injection molds and stamping dies.....is that if your working surface or jig plate....is ultra precise.....like the hardened and ground tool steel plates we used for duplicating and laying out parts.....then every single part in the stack up must be exactly equal in tolerance....or you can have an out of square error in setting up.

BUT....BUT....that makes the assumption that every part you work on has straight lines and parallel surfaces. Molds and dies being 3-D curvilinear parts.....trying to force every part to be exact and square to the perfect flat surface insures that you will spend a week trying to set up each mold and never get it right.

Never assume that the table or work surface MUST be the flatness and parallel reference standard.

In the case of this part...when not working on a lathe....the flatness/parallel reference is set by the relationship between the precision bearing faces and the precision face of the hub.

This is actually no different than clamping a block of metal between two precision Gage blocks...on a crooked table....and having the gage blocks mounted on gimbles....and setting the level via an outside point of reference and locking the gage blocks when you get there.

I would submit that the use a of a lathe would be ideal....but also more accurate than you need. You will not get the fan any more perfect than what its capable of due to centerline machining differences in the hub, the aluminum fan and the pulley. Some fans may indeed be nearly perfect...most will not be. Ray

[Busstom]

What would be most fascinating is to see results taken from a hundred or so currently running engines, as they are, measured in situ.

By now, most people are assuming their fan/pulley have been set up near-perfectly to the best attainable concentricity by some appropriately capable individual.

In reality, I'd bet a great many are rotating quite a bit eccentrically, but the data is largely unavailable.

[raygreenwood]

[orwell84]

Is it just me or do other people find that machinists and engine builders unfamiliar with aircooled VW's look at them like old tractor engines? Like because they appear simple that you can just slap them together?

[furgo]

Wow, Ray, thanks so much for taking the time to document this method, with pictures and diagrams.

It's helped me understand what's really involved in truing the fan/pulley assembly. It's also confirmed that this is an operation I don't ever want to do

Just coincidentally, I found another method (V-blocks and crank on a bench) to add to those Ray already mentions in his post:

http://shoptalkforums.com/viewtopic.php?f=1&t=150167

Picture by user captain_kapow at the shoptalkforums

[orwell84]

[Busstom]

[SGKent]

[raygreenwood]

[furgo]

Thanks Ray for the detailed explanation. This thread has brought me a long way from being told not to do something to learning why not and what needs to be done when it happens. I hope it's helped others as well.

I need some more time to digest the info and might have more questions, but here are a couple of quick ones:

[SGKent]

Then inner fan will align with the hub because of how it is made. You want the outer part of the fan carrying the belt running true and not in and out, up and down. You do not want the belt being tightened and loosened every time the pulley turns. It will create vibration and wear if that happens. VW assembled them in a way they ran true. Taking them apart, even if you mark them causes them to be no longer true because of the play in the bolts and holes for the bolts.
_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[furgo]