Refinishing (not rebuilding) Carbs

[FirstYearDeek]

Just got back from the holiday season break with 3 whole days before I go back to work... not quite ready to tear into these carbs, but all the linkages and associated mess needed freshening, so I decided to give the Powderbuythepound Ultimate Chrome powder a second chance.

Here's some of the parts (all that will be chrome) before:


And here they are coated:


And a closeup of the bellcrank. (Beautiful!)


How awesome will THOSE look in front of flat black carbs and plenum? I'm so happy with these pieces, it's taking all I have not to chrome the carbs in this stuff!

-Deek

[JBz]

loookin good. JB

[Whiskerfish]

Those look Great for a Home job!!!

[sunnbobb]

wow, ultimate chrome is right!

[FirstYearDeek]

I was really shocked when I pulled these pieces out. If you remember, I wasn't too happy with the rear master cylinder I did... I think I put it on too thin for that piece. The powder is slightly transparent and the master is such a dark piece, I think it just wasn't opaque enough to block the finish underneath.

The choke pieces came out nice too... I'm noticing something odd that I need to test at some point. Wherever I put tape and there is an exposed edge, the powder is dull or missing close to the adhesive.

I think the powder is there to begin with. I inspect the pieces with a high-power LED flashlight before they go in the oven. It's easy to see where powder might be missing and I didn't see any missing before it went in the oven.

The cable stay, for instance, couldn't be coated in the fork area because the bell crank post clearance is very tight; I ran a piece of tape on that inside profile all around. Once the part was cured, the coating is missing or just dull (hard to tell) all around that inside edge.

For this reason, I didn't tape off the cable tie-ins on the bell crank. I'll use a small round file to remove the coating instead.

-Deek

[FirstYearDeek]

Today I made some observations and measurements of the carburetor that Mike sent me (thanks!) before testing it in the oven.

Basically, I'm looking at every plug, port or plastic part that could be affected by the heating.

On the float side or outlet, I was mostly concerned with the fuel jet:


On the air circuit side, a few plugs and one very important piece where the CV slide lug is staked to the carb body:


On the fuel circuit side, more plugs... the one at the bottom in the center actually isn't a plug:


The intake side has one plug and the brass nozzle:


Here's my biggest concern; the CV slide lug. It's the only non-metallic part on the carb and is also impossible to remove/replace without destroying it.


I tested the plugs and whatnot by applying pressure to see if they were free to move, or were solid in their place. Of course they were all solid.

The normal procedure for most powders is heat to flow-out temps (450 deg F in this case) for around 10 minutes, then lower to cure temp (400 deg F in this case) for 20 minutes. To make sure the carb would hold up to the heat, I baked this carb for 30 minutes at 450 degrees to represent a worst-case scenario.

I'm happy to report that after subjecting the carburetor to this test, there were no obvious failures. All plugs remained flush and are solid. The plastic CV slide lug didn't melt as I had feared. It did, however turn black! I suspect oil and/or gasoline saturated the piece and that is what changed its appearance when heating; the piece itself is not brittle or stiff. (you can see the nick in the piece where I tested it...)


So it looks like I'll be able to powder-coat them after all. In fact, I've already done the float bowls and the air cut-off valve...





Tomorrow I'm going to try to get all four carbs and the central plenum coated. When Randakk's kit gets here next week, the fun will begin.

Oh, also the CV needles I got from the bag o' parts are correct for the 755A. SCORE!

-Deek

[rdgrnr]

It looks like they will look great when done
I am a little curious though...Will the extra material added from coating affect the mechanical operation of the carbs?

[LikeMike64]

Today I made some observations and measurements of the carburetor that Mike sent me (thanks!) before testing it in the oven.
-Deek

Glad to help!
I love the way those bowls and linkages look.
Keep us posted on your progress.

[FirstYearDeek]

It looks like they will look great when done
I am a little curious though...Will the extra material added from coating affect the mechanical operation of the carbs?

Good question.

I'm plugging any orifices with silicone plugs and taping over the big openings... I actually made (not danced) a little jig to hang the carb in such a way that allows me to spin it around and let gravity help with the nooks and crannies.



The jig works fine, the carbs are holding up fine, but there are some SERIOUS outgassing issues that I need to remedy before I go any further.

I've had occasional problems with a too-thick coating of the black wrinkle causing bubbling of the finish, conversely a too-thin coating shows as a glossy spot. So when I did this carb, I thought "crap, too thick"



So I put it aside and thought about doing one in chrome; I got the exact same bubbling in the exact same places as the previous carb. So now I'm thinking I didn't prep well.



I have three more unuseable carb bodies to play with; I'll get it eventually but I'm going to have to pull out all the stops including a pre-heat step that I haven't done previously.

-Deek

P.S. These shots are from my wife's new Kodak Z128S... Bad camera. Don't buy.

[sunnbobb]

Keep at it! You will get them perfect!

[FirstYearDeek]

Thanks for the vote of confidence, sunny... as it happens, I finally got it right this morning.

I was suspicious about the oven early on; the thermostat I use agreed with the oven's thermostat so I knew the temperature was right, but the finish appeared to have outgass-related bubbling (see above) all over it. As I noted before, it was in the same spot each time and a member here (Mike) suggested that it might be that those areas were thinner, and got hot quicker.

I did some asking around and found that the heating elements in all ovens have a seriously strong infrared component to their output, causing hot spots if the part is too close.

So I put the test carb back in the oven, preheated it to 400 and took measurements (with my IR gun) every so often. The part seemed to come up to temperature within a few minutes, and the oven does overshoot a bit (maybe 10 degrees) but comes back down very quickly. But then I noticed a pattern... whenever the heating element was on, or had just turned off, there were parts of the carb that were over 430 degrees!

Mike had suggested using tin foil to cover the element so there wasn't as much radiant heat reaching the part. I took his advice and re-tested. Regardless of the state of the element, the part stayed exactly 400 degrees (+/- 2 degrees or so)

So I coated one of my carbs and...



Ha ha!! NO BUBBLES! It turns out the defects weren't outgassing after all, but over-heating. (I shudder to think how hot the part got while the oven was set at 450 during flow out... I'm not using that powder anymore so it won't be a problem in the future, but MAN... hot...)

So it looks like I'm on a roll until I pull the part out... see, I had to re-fill the gun mid-way through coating and I THOUGHT I grabbed the black wrinkle...



Nope. Grabbed the mirror black.

So I'll have to strip this one and get some more wrinkle powder, but I can finally move on with my pictorial... Yay.

-Deek

[millerdog]

I was reading this post, and noticed you said there were steel needles in the carbs when you got em. If you have any problems with it running after you get it all back together, check out you'r needle jets. The steel needles have been known to wear these needle tubes out. They are not steel I don,t think. They are probably titainium. In any case, it can cause a problem. Just something to keep in mind. I had it happen to me in about 5000 miles. It wasn't a wing, but the mechanics are the same.

[FirstYearDeek]

Thanks for the tip! I was surprised to see those, because all I've seen till now have been brass. Assuming I can find all four, I'll be replacing them with some original brass ones.

-Deek

[JRK5892]

hey man they where just not prepped right, you have to soda blast carbs to coat them


also the ultimate chrome must have a clear on it or it has 0 chemical resistance

[McLeod]

Wow totally sweet. I'm just now getting to this thread. The powder coated glossy carburetors with the chrome and polished alum. look awesome! More pictures please! Where's the finished product all put together?