Machine work on SU for roller bearings

[AK260]

On 5/26/2024 at 2:37 AM, Captain Obvious said:

Thinking about this a little... Most of those drawn cup needle roller bearings are available in a configuration where one side is closed off. Totally blind. If one finds that the vacuum leak past the bearings is objectionable, they could use that closed end variety on the outboard ends of the carbs.

That would completely eliminate two of the four potential leak locations.  

You know chap, I’ve been having the same thought for sometime now on the cup bearings - this is the type of thing I was considering …

 

https://signetid.co.uk/metric-bk-series-needle-roller-bearing-closed-end/

 

That way who cares if the shaft wears inside it! 😉

Edited May 29 by AK260

[Captain Obvious]

7 hours ago, Jeff Berk said:

At first I thought CO was joking, but after reading the zclub thread, I'm not too sure.

Haha! I was serious about the intent. The joke part is the value of that mod on our (mostly stock) Z cars.  

[Captain Obvious]

5 hours ago, AK260 said:

 this is the type of thing I was considering …

Yup. That's the closed end version I was referring to. Using those on the outboard ends of the carbs would eliminate two of the four leaks:

[AK260]

I think it’s key to get a good dollop of high temp grease in there before re-assembling the carbs. With no airflow through it, the bearings should stay lubricated for our lifetime!!

Edited May 30 by AK260

[zKars]

On 5/27/2024 at 7:09 PM, Captain Obvious said:

I don't know about your side of the border, but on the US side, I'd get 'em from McMaster.

Here's the through version with seals on both sides https://www.mcmaster.com/5905K586/

 

McMaster will ship to me, they do it all the time. I just have to be registered as a business. They won’t ship internationally without that check box being ticked. 

Thanks!

[zKars]

Not sure if this has been discussed above (to lazy to read every word (but not too lazy to type endlessly here…)) but is the usual “leak” caused by bearing wear or shaft wear or both? Just replacing the bearing is fine, but how are we building the shafts back up to 10mm? Or is the fact that the new bearing have seals now, that these seals now rub on what’s left of the shaft, and maybe at the very edge of where the old bushing touched it which might be still mostly 10mm,  effectively sealing it? 

Which begs the question, are new shafts and butterflies available anymore? 

Edited May 30 by zKars

[Captain Obvious]

I'm no carb expert, but on the ones I've messed with the wear appeared to be on the shaft. the chrome plating had been worn through, and once that happens, it exposes the (even softer) brass underneath, and things spiral quickly from there.

billgtp posted a pic of one of his shafts, and it might be a trick of the camera, but I think I can see the brass color peeking out at both ends. Between the bearings and the marker lines?

As for availability of new, I have no idea. Certainly any well tooled machine shop could make them, but at what cost?

 

[AK260]

So as @Captain Obvious says, when I took apart thee  set of worn carbs that I’m modifying (eventually!!) I found that worn “collar” was 9.5mm and the wear on the bush was about 0.4mm.

The wear on both ends was 180° with 90° being the most worn but interestingly the wear was 90° offset rotational from one end to the other!

 

The chap in Birmingham (UK) is remaking new shafts. I can only assume Ztherapy do the same.

Butterflies don’t really wear appreciably. But I’m happy to be corrected.

I’m potentially going to get a buddy to CNC some new stainless steel shafts for me, but they will be “modified for flow versions”, not stock.

 

Happy to measure / share stock dimensions if any good to anyone wishing to CAD them and make some..

Edited May 31 by AK260
Goddam autocorrect

[billgtp]

He did tell me if I want new shafts he will make them out of stainless steel. But it was me that said no. I would like to see what the carbs do with just the new bearings.

If I have a problem I will have him make shafts. He is not charging me a thing for doing this.

[Captain Obvious]

Hardened and polished throttle shafts paired with bearings would be best. Those bearings are designed to run against a pretty high quality surface finish.

For example, the versions offered by McMaster recommend a surface finish of Ra = 8 microinches

Where...    

That said... Even without hardening, new stainless shafts with a good polished finish will be worlds better than worn soft brass.

[AK260]

45 minutes ago, Captain Obvious said:

Hardened and polished throttle shafts paired with bearings would be best. Those bearings are designed to run against a pretty high quality surface finish.

For example, the versions offered by McMaster recommend a surface finish of Ra = 8 microinches

Where...    

That said... Even without hardening, new stainless shafts with a good polished finish will be worlds better than worn soft brass.

Captain, you never disappoint!

@billgtp - it would be very interesting to see how the worn shaft does with new bearings. Are the seals rubber? Do the rotate with the bearings? If not, is it worth adding some high temp silicone grease to them to help them?

[Captain Obvious]

Haha! I try!   

So as scary looking as that integral equation is, it is basically means "average". As in "Roughness average". And to make matters simpler, I think a surface finish of Ra at 8 u-in can be achieved with something around 400 grit sandpaper*. The typical (and best) means for achieving the appropriate surface finish would be by grinding the shafts and again... A well tooled machine shop should have that capability.

* Note that I did see some indication that the UK numbering system for sanding paper grit is different than the US, so be aware of that.