Worn alternator fan key what to do

sanandreas · 10-09-2021, 09:07 PM

Hello.
I have 1978 911 sc 3.0. Odd noise from around alternator fan assembly. I found the key on fan where shims go on is worn. Can this be fixed or do I need a replacement fan?

Some one suggested JB weld but never used it. Could this be spot welded to add some metal and then filed down to shape?

aigel · aigel's Garage

JB weld is a good suggestion here IMHO. Build it back and then file it down to the correct shape. This isn't something that will fail catastrophically.

If you would have it fixed by a machine shop, I bet the better fix over welding (isn't it magnesium?) would be to cut it down on a lathe, sleeve it and then machine the key back into it. If you need to bring it to a shop, I bet you can get a decent used fan for the cost of doing that machine work.

I haven't followed the parts prices though - when I had my SC a good used fan would have been maybe $100 and may have needed a good cleaning and powder coating.

Dpmulvan · 10-10-2021, 06:48 AM

It’s not magnesium, drill out rivets, build it up with some tig beads, put it on a lathe and turn it down. You should be able to find a new or used center as well.

eastbay · 10-10-2021, 06:48 AM

Just put a new center on your fan. If you don't think you can do it yourself there a few guys on this forum who restore fans and should be able to help you.

Dan J · 10-10-2021, 07:02 AM

Replace the center or the whole fan. JB weld won't last there

sanandreas · 10-11-2021, 02:09 AM

Thanks people.
amazing what you can learn in 24 hours. Some quick responses.
1. The centre hub is metal and you can buy replacement ones on ebay with the rivets for around $150 US.

https://www.ebay.com.au/itm/380162189084?_trkparms=amclksrc%3DITM%26aid%3D1110 006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20200 818142055%26meid%3D8cf1fa8ce3df4be991417a4264a6691 f%26pid%3D101113%26rk%3D1%26rkt%3D12%26sd%3D403014 381472%26itm%3D380162189084%26pmt%3D0%26noa%3D1%26 pg%3D2563228%26algv%3DDefaultOrganicWeb&_trksid=p2563228.c101113.m2108
2. You can buy these rivets separately too:

https://www.ebay.com/itm/133878903592
3. I have see pics of some people who have used allen key counter sunk bolts as replacement for the rivets. Anyone know what type to use? the rivet is 5mm wide and the combined thickness of hub and fan is 10mm.
4. And here is a nice video of someone who actually building the collar up:
https://www.youtube.com/watch?v=RGHSfE6ubEI

My issue is not being able to weld, and not having a snap press to crush the rivets. Thats why I would like the counter sunk allen key bolts.

yelcab1 · 10-11-2021, 06:25 AM

Cool TIG welding video. I gotta get me a tig welder. Too bad for all of us that Partsheaven is no longer around. Wonder where Al is at this point.

I had the exact issue. The local welding shop charged $50 to weld the thing up. My machinist next door neighbor (who since moved) machined it down to size for a 6-pack. And back in business I was.

scottb · 10-11-2021, 04:03 PM

Quote:

Originally Posted by sanandreas

My issue is not being able to weld, and not having a snap press to crush the rivets. Thats why I would like the counter sunk allen key bolts.

Do you live near a machine shop that can handle the rivets for you?

sanandreas · 05-28-2022, 08:28 PM

Revisiting this project. So I have found the hub I want to buy:
https://www.**************/products/d1a-s137-142n-111623

What I would like to find out has anyone used countersunk screws / bolts with lock nuts instead of the rivets?

Here are the rivet replacements:

https://www.ebay.com/itm/133878903592

There are a couple of threads talking about it but no mention of a successful allen-head bolt size.

Someone reported supertec uses the allen-head / hex bolts from the below picture but I cant find anything listed on their website.

Discseven · Discseven's Garage

Tested drilling out the old rivets and heading down the stainless Allen route. Didn't keep record of what size this hardware is.

Went with these "nuts" to minimize rotating mass. Not sure what they're called. Never went further than "test."

.

scottb · 05-30-2022, 07:54 AM

Quote:

Originally Posted by Discseven

Went with these "nuts" to minimize rotating mass. Not sure what they're called. Never went further than "test."

.

Are you using Loctite to prevent the nuts from loosening?

Discseven · Discseven's Garage

Quote:

Originally Posted by scottb

Are you using Loctite to prevent the nuts from loosening?

Were I to actually do this, definitely would lock them.

As a "test," I was looking to see how a hand drill would work here and if counter sink bit on hand would make for a suitable finish. My bit left a slight gap between the hub and Allen when the Allen was flush to the hub. Gap would stand out more were the hub not rotting. With "screw-nut" applied, I recall having to open the hole in the fan.

.

Discseven · Discseven's Garage

...is called "through hole slotted book binding screw." Am now recalling math done on the increasing weight of a lock nut rotating around the radius a fan hub. Was interesting enough to avoid going that route---too long ago to remember what the figures were. My lock nut comments here are given with no offense to "SanA." Having done the math, using no more metal than was necessary was the path explored. Even the Allens arrived at were no longer than necessary to engage a few threads in the through hole post screws.