993/964 distributor bearings possible solution

[cudabnu]

So I go to change the caps and rotor for my 3.6L coversion, when I get to the secondary rotor, and put it on and start to give it a twist to make sure the rotor is locked down, and it spins nice and freely! A closer look, and sure enought the belt is broken. A quick search on how to rebuild and a new belt and I'm good to go.

Once I get the distributor apart, I find that both secondary bearings are bad which lead to (or helped) the belt to break. Primary is fine and feels smooth.

Of course you cannot just buy the correct bearings. After finding out how much it would cost, I've decided to get a few off the shelf bearings that fit the OD and width. The ID is about .5mm too small.

Here is the possible solution:
I'm having a machine shop turn down the shaft just below the gear for the belt to match the ID pf the new off the shelf bearing. (should only need to take it down about .25mm)

So that is where I am at, just waiting to pick it up and try it out. I will post the results as soon as I get it back together, and hopefully finish a few items on the conversion, with luck Saturday I will know!

If not, I will be in the market for a good used Dizzy!

[lucittm]

Can you elaborate on the bearing number and manufacturer? I have known some bearings in that size range to be for R/C cars or skateboards and they last about 10 minutes under heat and high RPM loading. On the other hand, a good INA or SKF will last the life of the car.

Thanks,
Mark

[cudabnu]

The bearing I'm trying to use is a SKF for a VW alternator. My machinist said he cannot grab the shaft good enough to comfortably turn it, so he is building a jig to hold the bearing and will get or make what he needs to machine out the ID of the bearing to fit the shaft. If he can successfully do it, I'll probably give him a bunch more to do, and start selling them!

[lucittm]

Good idea! Let's see turn down the shaft of a $900 distributor or machine the inside of a $10 bearing, hmmmmmm.

I'll buy one just to have it. SKF = good stuff.

Mark

[cudabnu]

The only problem is holding the bearing from rotating to be able to machine it, then finding the correct size bit to use on the hardened bearing. So i'll have a descent investment into it, but still my cheapest option unless I find a good used dist., but then it's another crapshoot

[briefescape]

I ran into the same problem with the bearings when I got the belt replacement . Al fix it by getting the closest size bearing and fabricating a sleeve . Cost of bearings n material $17 dollars and I have put over 10k kilometers on the car since with no issues with distributor Will try to get Al to chime in with specifics .

Cheers Guy

[Al S]

I used ball brg NSK 6201-08DDU, but there are SKF/NTN/FAG equivalents.
Basically a double rubber sealed 6201 ball brg.
These brgs are the same dimensionally except for the ID wich is 0.5mm dia. larger.
Prepare the brgs in advance by wrapping 0.25mm thick shim stock of appropriate x-y dimension around the shaft, and apply a bit of retaining compound to the ID of the brg so that the shim/sleeve is glued to the ID of the brg.
You will need a blind brg removal tool to remove the olds brgs.
I think the brgs were around $15 ea.

good luck, and have fun!

[dad911]

Originally Posted by cudabnu

The only problem is holding the bearing from rotating to be able to machine it, then finding the correct size bit to use on the hardened bearing. So i'll have a descent investment into it, but still my cheapest option unless I find a good used dist., but then it's another crapshoot

Hardened material would need to be ground.

If you can't find the correct bearing, choose one with a larger ID and machine or buy a bushing to make it fit.

Do you have the dimensions?

try Bearings- SmallParts.com
or Boca Bearings :: Miniature Bearings for Hobby and Industry :: Steel and Ceramic Bearings

[cudabnu]

bearings are 32mm x 10mm x 12.4mm (roughly)

[Traveller]

Originally Posted by cudabnu

bearings are 32mm x 10mm x 12.4mm (roughly)

I take it that is OD, width and ID....in that order.

[cudabnu]

Originally Posted by Traveller

I take it that is OD, width and ID....in that order.

Correct.

[bazar01]

SKF specs for 6201 bearing number.

SKF - Product data

[NoEardGoat]

Any Updates on finding these bearings?

I spoke with the German Bearing Mfg. and they made them specially for Porsche years ago.

12.4mm ID is a son of a *****

[cudabnu]

I had a friend that owns a machine shop custom order a bit, make a holding jig, and machine out a bearing that had the same OD and width, but smaller ID, so far seems to be working good.

[Traveller]

Originally Posted by NoEardGoat

Any Updates on finding these bearings?

The question is, what are these so-called rebuilders of these distributors doing...not installing new bearings as part of an incomplete rebuild or are they modifying a shaft to fit an available bearing?

[cudabnu]

No they are getting the correct bearings, but charging about $150 each, and there are 3 of them the same size, but that is if they need new bearings, otheriwse they just take it apart clean and lube it, new belt, and off you go.

[Traveller]

Originally Posted by cudabnu

No they are getting the correct bearings, but charging about $150 each, and there are 3 of them the same size, but that is if they need new bearings, otherwise they just take it apart clean and lube it, new belt, and off you go.

Sounds like a deal.

I'll be taking my distributor out in the next few weeks for an overhaul at which time I'll finally get to see what shape the bearings are in and what is left of the grease, if any. Those bearings do not see any load or speed.

If I need new bearings, I think I know which ones I will use and modify.

[NoEardGoat]

Originally Posted by cudabnu

I had a friend that owns a machine shop custom order a bit, make a holding jig, and machine out a bearing that had the same OD and width, but smaller ID, so far seems to be working good.

I would like to see a picture and dimensions of this bearing race holding jig. What kind of bit, and how many were used to cut the bearing race, just carbide? Bearings are usually a very hard metal, to say the least.

Interested in renting or selling the jig?

I have come up with 1 other possible alternative that might work.... I have a feeling it isn't or someone would already be doing this.

1. Buy the above mentioned 12.00 mm ID bearing and remove the inner race and replace it with the 12.40 mm Porsche bearing inner race.

Is this even possible without destroying the bearings?

Thoughts, comments?

[NoEardGoat]

Originally Posted by bazar01

SKF specs for 6201 bearing number.

SKF - Product data

I believe the above link is incorrect for bearing use. The above link is for snap ring retained bearings. There is a groove in the outer race for a snap ring. The stock 964 bearing race's I removed from my distributor do not have a snap ring groove.

I believe this would be the correct shielded bearing to machine down .40 mm to work for this dizzy application.
SKF - Product data

From the diagram there appears to be 4.2mm of inner race material before the actual "ball" of the bearing, give or take tolerances.... Only need to remove .40 mm. I cant image this bearing having a heavy load on it where this material removal could become an issue.

[Traveller]

Until I actually see the bearing, I am still uncertain as to what type of bearing is being used in the OEM Porsche distributor; a ball bearing or an angular contact bearing for example.

Having rebuilt mine, the bearings were fine and as a result I did not pop the seals to confirm their type.

I do know that they are loaded by the use of a Belleville (cone) washer which when the clip is installed on the secondary shaft and the rivet that holds the gear on the primary shaft is installed, places a considerable side load on the bearing.

I did take note of dimensions of all the distributor parts...
Distributor

When the time comes and I do need a bearing, I will grind the ID to fit.

There is a someone on RL that rebuilds the distributors and has the bearings at big $$$, but he was unwilling to disclose a source. So much for what forums are about which is why I think business has no place on a forum.