Honda CB750 Sandcast

The Restoration Shop => Chrome - Anodizing and Other Metal Finish Procedures => Topic started by: markb on August 02, 2015, 03:37:00 pm

Title: I know this is backwards but is there a good way to dull aluminum (carb bowls)?
Post by: markb on August 02, 2015, 03:37:00 pm

My carb bowls came out shinier than I think they should be.  Does anyone know of a way (like a chemical dip or wipe) that would turn polished aluminum to a dull grey finish?

Title: Re: I know this is backwards but is there a good way to dull aluminum?
Post by: Bowswell on August 02, 2015, 04:59:44 pm

Sandblast with bicarbonate de soute....cow brand

Title: Re: I know this is backwards but is there a good way to dull aluminum?
Post by: Steve Swan on August 02, 2015, 08:38:29 pm

were your bowls polished by someone or unmolested ?

reason i ask, some unmolested bowls i've seen are astonishingly bright.

Title: Re: I know this is backwards but is there a good way to dull aluminum?
Post by: DW69K0 on August 03, 2015, 05:29:46 am

I agree with Steve, I have seen unmolested carb bowls that are very polished. IMHO, I think the earlier Sandy's had a might brighten surface finish on engine cases and other polished areas, as production picked up less time was spend on the polishing.
DW

Title: Re: I know this is backwards but is there a good way to dull aluminum?
Post by: 4pots1969 on August 03, 2015, 06:32:35 am

Mark, here are pictures of a ramp of Carburetors K0 new never installed on a motorcycle...
I think that it can guide you to determine good appearance... ;)
I agree also that the bowls have a different appearance compared to the top..

Title: Re: I know this is backwards but is there a good way to dull aluminum?
Post by: markb on August 03, 2015, 12:40:09 pm

Quote from: Steve Swan on August 02, 2015, 08:38:29 pm

were your bowls polished by someone or unmolested ?

They were polished by the guy who rebuilt them, a well renowned expert who knew exactly what he was working on.  I had them rebuilt in an effort to expedite the assembly and since I'm not much of a carb expert.

Quote from: 4pots1969 on August 03, 2015, 06:32:35 am

Mark, here are pictures of a ramp of Carburetors K0 new never installed on a motorcycle...

Thanks for the great pictures.  Maybe mine are OK then.  I will post a pic of mine.

Thanks all for the comments.
Mark

Title: Re: I know this is backwards but is there a good way to dull aluminum?
Post by: markb on August 03, 2015, 07:12:32 pm

Here’s my carbs.  Opinions?
(http://cb750sandcastonly.com/coppermine/albums/userpics/10002/DSC01690.JPG)

(http://cb750sandcastonly.com/coppermine/albums/userpics/10002/DSC01691.JPG)

(http://cb750sandcastonly.com/coppermine/albums/userpics/10002/DSC01692.JPG)

Title: Re: I know this is backwards but is there a good way to dull aluminum?
Post by: Sam on August 03, 2015, 10:30:14 pm

My vote is to keep them like they are. Looks correct to me.

Title: Re: I know this is backwards but is there a good way to dull aluminum?
Post by: DW69K0 on August 04, 2015, 04:41:37 am

I agree with Ujeni, leave them as they are, there should have enough shine on them to reflect distorted images but not be mirror like. They look correct and will oxidize with time.
DW

Title: Re: I know this is backwards but is there a good way to dull aluminum?
Post by: 4pots1969 on August 04, 2015, 06:03:18 am

Mark, time normal ca might be correct... But given the level of quality that you bring this restoration... for me, sincerely I think that this is not good...
I see that the carbs are reassembled... Are they finished?
Gerard

Title: Re: I know this is backwards but is there a good way to dull aluminum?
Post by: Steve Swan on August 04, 2015, 08:32:28 am

how were carb bodies cleaned ?  the photos make them look overly flat.  the #4 from backside appears to have a bit of a sheen.  the #1 from side looks overly flat.

in my ultrasonic, i use Branson us cleaning solution which suspends debris in solution.  generally, the carb bodies come out with at least a bit of a iridescent sheen (as usually seen on unmolested carbs.)  the last set i recently did (76F1) came out flat, but not as flat looking as what your set looks, Mark.  after they come out of u.s. unit, i wash them with a plastic bristle brush and hot soapy water.

ps - why do the nuts fixing your choke arms not look bzp ?  the rest of your small parts attached to bodies look fresh bzp.  and what i can see, 2 bowl drain screws appears raw brass ?  gosh.  sure don't want to sound like i'm nitpicking.... >:(  surely not my intent.....

Title: Re: I know this is backwards but is there a good way to dull aluminum?
Post by: markb on August 04, 2015, 12:37:08 pm

Gerard,
What does "time normal ca" mean?  Are you asking if I'm done with them?  I don't know yet.

Steve,
These carbs were in terrible shape, worst I've seen.  I had to try to save them because of the horizontal vents.  I believe the bodies were ultrasonically cleaned but I don't know what in.  I will check into it.  The difference in the sheen isn't as noticeable in person.  What would "brighten" them up?

The reason the nuts don't look zinc is they are covered with a soft coating presumably to keep them from loosening.  I intend to remove it.  I think I will replace the drain screws too.  I also have new adjusting nuts (5mm to match the cable) for the tops.

Don't worry about nitpicking.  The reason I posted was to get honest feedback.  So thank you all.

Title: Re: I know this is backwards but is there a good way to dull aluminum?
Post by: 4pots1969 on August 04, 2015, 04:32:04 pm

The translated translator of the times a bit a side "in normal times" it mean: for motorcycle in its own juice not restored... Here is a picture of the restored carbs of Big Boss... But perhaps are new ones?

Title: Re: I know this is backwards but is there a good way to dull aluminum?
Post by: markb on August 04, 2015, 04:58:28 pm

Those look nice but I wonder if they are too bright.  The more I look at mine I think they are a least a bit dark/dull but I might let them go for now.  I sure would like to have this project together and do a test run yet this season.

Title: Re: I know this is backwards but is there a good way to dull aluminum (carb bowls)?
Post by: Steve Swan on August 04, 2015, 10:37:12 pm

Mark, i wish i knew what would brighten carb bodies.  i have no experience with soda blasting as someone previously mentioned trying it.  would be nice to have a darkened body to try soda blasting on, then run through ultrasonic.  i am goingto guess the heat in u;trasonic sol'n helps bring out the iridescent surface sheen. 

Title: Re: I know this is backwards but is there a good way to dull aluminum (carb bowls)?
Post by: DW69K0 on August 05, 2015, 05:14:13 am

I think everyone is over thinking the situation and process. I run an investment casting foundry. When an Aluminum casting is pulled from a mold it is process through a shot blast process to remove any she'll and de-burr the casting. The surface finish is not shiny, but just fresh aluminum. IMHO, the surface finish of an ultrasonic clean carb looks the most like a fresh cast surface, any more prep is over doing the work an original casting would have received.
The carb float bowls are a different story, the early bodies were definitely finished to have a high luster, but not shiny and should look different from the carb bodies. Later production changed and Honda did not invest the time (money) in finishing the bowls.
Mark- I think your bodies are close to the correct surface finish, but an ultrasonic cleaning would improve the appearance of your restoration. The choke arm seems overly shiny to me.
Respectfully,
Duane

Title: Re: I know this is backwards but is there a good way to dull aluminum (carb bowls)?
Post by: markb on August 05, 2015, 08:22:36 am

I found out the carb bodies were cleaned with xylene.  Could that have darkened them?  

My final drive flange (where the rear sprocket mounts) was dull and yellowed in the areas where I couldn't get at it to polish.  I used diluted phosphoric acid on those areas and it cleaned and brightened it really nice.  I had the carbs for 1553 rebuilt at the same time as 97 and they look exactly the same.  I think I will do a little test on those.

BTW, the choke arm is zinc plated as well as the rest of the choke linkage.  Were they originally zinc? 

Title: Re: I know this is backwards but is there a good way to dull aluminum (carb bowls)?
Post by: 4pots1969 on August 05, 2015, 12:40:43 pm

Yes, they are zinc plated... But it is funny because me is the only thing that I found rather successful...
As what, a person has the other notices are different, and it is interesting.. ;)

Title: Re: I know this is backwards but is there a good way to dull aluminum (carb bowls)?
Post by: Sam on August 05, 2015, 12:42:45 pm

Quote from: markb on August 05, 2015, 08:22:36 am

BTW, the choke arm is zinc plated as well as the rest of the choke linkage.  Were they originally zinc? 

Every sandcast I own has blue/clear zinced choke arms and linkage.