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Author Topic: Aluminum Engine Component Finishes  (Read 1983 times)
Wayne
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« on: January 01, 2013, 07:03:11 PM »

I thought we might get a thread dedicated to aluminum component finishes and techniques going and hopefully get some good info compiled all in one spot. After hours and hours of searching. reading and looking at pictures I have kind of come to the conclusion that the actual finish comes down to personal taste. It woul dseem that nobody has been able to duplicate Honda's process's thus far??

Riccardo has some NOS components and was kind enough to send me some fairly high quality/resolution pictures. I was a bit surprised at how reflective they are.



















Reflection is very noticeable in this image:



This is the side cover I buffed last year. Cleaned it up, sanded with 1000 grit wet and polished it with a green compound and coated with Eastwood Diamond Clear Coat. Reflection is similar to Riccardo's example:



Here's a side by side:




More from Riccardo:



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Wayne
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« Reply #1 on: January 01, 2013, 07:15:19 PM »

So, after searching and reading and more of the same, it would seem that this is the "holy grail" of finishes for the serious sandcast restorer. Problem being, no one with the exception of perhaps Vic World has figured out how to duplicate it? (the pic came from someone!)



It sure does look pretty! Smiley This is where the water gets muddy. (for me anyway) It would appear that different areas of the bikes do have some stark contrasts when it comes to the aluminum finish. For instance, if 576 did look like the above pic when new, here's what the other side would have looked like. It seems more highly polished than the above image.



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Wayne
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« Reply #2 on: January 01, 2013, 07:26:07 PM »

And now the handy work of others. mark, hope you don't mind me using your images. I know that Mark uses a series of Scotch Pads working his way down to white to achieve the finish he is after. I'm not sure if all of these finished images have the clear coat applied.

This is one of Mark's covers before doing anything with it. First thing was to strip the clear coat:



This is after mark stripped the cover:



Marks cover after he works his magic. Not sure if clear coat is applied or not:



Marks finished rocker cover:



Marks cover compared to a Honda original. Can you tell the difference?:



Marks covers installed. Beautiful!



A set from Riccardo:



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Honda CB750 Sandcast Forum
« Reply #2 on: January 01, 2013, 07:26:07 PM »

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Wayne
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« Reply #3 on: January 01, 2013, 08:34:40 PM »

We can't leave out Andy Morris's ceramic coated covers. I have to admit, this bike and these covers caught my attention the minute I saw them a year or so back. Again, they sure look pretty however as KP pointed out in another thread, the camera doesn't always tell the whole story.





I wonder if he used the same process on hubs, for lowers etc?
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Steve Swan
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« Reply #4 on: January 02, 2013, 01:06:57 AM »

Andy used the ceramic coating on all alum.parts that were polished.

Wayne, great thread !
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vnz00
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« Reply #5 on: January 02, 2013, 03:45:02 AM »

Wayne, nice idea to start this thread.

My thoughts are that no two parts are the same so it is hard to give an exact process.  By that. I mean its down to evaluating the finish applied to the part you have if you want originality.  This to me would rule out ceramic coating.

Some parts have a rough cast finish and some a diecast finish which was much easier to polish. Once the part is cleaned and stripped of grime it becomes easy to interpret what the finish should be.  If the part has Linish marks, but is polished then this is the final finish to achieve.  

If it was rough cast, then polished to remove most of the casting marks, then this is what you aim for.

The polished parts are clear coated, and whatever clearcoat Honda used is unknown. However the surface very rarely shows a peel which is why Rics NOS parts have such a nice reflective surface, despite not being super polished.

Sometimes it is difficult to control polishing when using machines, but it is less time consuming. The polisher may not understand that you are trying to maintain a factory finish, and lose some of the detail the factory left behind.

Ultimately it takes practice to read the surface to replicate its finish, but from what I see of your photos above, you have good examples of the surface finish to achieve.

Here is one of my parts just after clear coating. I do not leave a peel, and work with what level of polishing came from the factory.

Regards,
Steven
« Last Edit: January 02, 2013, 03:53:50 AM by vnz00 » Logged
Wayne
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« Reply #6 on: January 02, 2013, 11:30:01 AM »

Steven
Your work looks great! Nice job! I'm finding it a bit difficult to land on an end result that I'm trying to achieve hence this thread. As you can see from the first pic below, my engine was a bit "weathered" after sitting in a leaky shed for the last 25 years. The only piece that was decently preserved was the rear flange as noted earlier.



I need to land on my final process/finish soon as I want to get the engine all bolted up and back in the frame. The rocker cover is a challenge. Pitting, casting imperfections etc. etc. Question is, how far should I go with this pitting? Some of it looks like it was probable there from day one??



I posted these shots in my restoration thread but though they would be value add for this thread as well. This is my mission cover as removed. Only washed with soap and water.



This is what was revealed after cleaning it up with paint stripper. It was actually pretty nice.



A shot of some of the casting imperfections that were revealed after the clear coat was removed using paint stripper.



In hindsight I should have just cleaned up the degraded areas of this piece,cleaned it up well and shot some clear coat on to see what the end result would look like. That would have given me a bit of a benchmark to work with for the rest of the pieces.

As it stands, the end result is this. I'll keep plugging away at the rocker cover go from there.

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Steve Swan
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« Reply #7 on: January 02, 2013, 11:35:38 AM »

I've seen on different very good condition alum.parts ptiting which appears presetn from day one.
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kp
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« Reply #8 on: January 03, 2013, 06:01:23 AM »

I've had my own polishing system for a fair number of years now and in fact just tossed out 3 burnt out motors which are essentially grinders with polishing components fitted. I've learnt that a polisher motor must have lots and lots of grunt. I have 2 motors set up with various pads from course wide discs to a calico flop. My favourite for alloy is sisal pads and I use different grit polish for different jobs. There are a couple of things I've learnt and that is different pads for different materials ie: chrome, stainless, alloy etc., and different grits for different results. I've never used a scourer pad not because I don't like them but because I know nothing about them. The pads I use are cotton, sisal, calico/linen. Various diameters are used depending on the job. For a tappet cover I would use a 1/2" wide x 2.5" diameter cotton or sisal disc to get into the tight spots. I would use a larger diameter pad on the flat areas. Narrow discs move more easily so a sprocket cover I would use a 1/2 to 1" x 6" diameter disc as this follows curves very nicely. The really tight spots have to be done by hand. A mission cover is relatively easy to do with a 1" or 2" sisal disc using a combination of medium and fine polish
Anyway, I telling this because I've done what Wayne has and that is I've stripped parts of the clear and what's generally underneath to my mind is a highly polished surface. These finishes vary because of the person polishing the part and the materials used to polish. Take the rear sprocket flange Wayne pictured You will notice that some areas are smooth and some are rough from the casting process. The smooth areas to my mind are as a result of polishing (that's an astounding deduction KP  Roll Eyes ) If I had an original casting I could render the rough finish to a smooth result in about a minute using a course high cut polish and sisal disc.Dead f'n easy Grin
A major point to consider is that we have some parts which are cast from nearly pure aluminium whereas some are diecast and contain a lot of zinc and aluminium in combination. Some parts you can polish until the cows come home and they won't come up like original. A good example is the material used to make carb bodies. What you see is what came out of the mould. Same for the cases. The smooth finish on these parts is to my mind not polished. Some chain and mission covers are sandcast and polish up like chrome but the cast type tend to be a little duller unless a different polish is used.
Having done a fair bit of polishing I have found that leaving the finish in a raw state after polishing tends to bling the job up so if I'm not doing a clear coat I tend to employ med/fine grit on sisal discs and this gives that semi gloss finish. If bling is the order of the day then fine grit and red rouge on a large calico flop will make alloy look like chrome. If you use a clear coat on this gloss finish you then tend to get a factory type finish. Each coat takes a little of the dull off. I have also used an alloy cleaner on a highly polished part and that tends to dull off the finish surprisingly. My understanding is that Steven V gets excellent results using grit paper and others such as Mark employ plastic scourer discs and pads. I'm just not experienced with these materials so I've tended to stick with electric discs. The only negative is it's dirty work and the parts get very hot.
Anyway, there are probably others in the club who have more knowledge than I on this subject but I thought I would share some of what I've learnt. Essentially my take is to polish to a 90% gloss and then clear coat the job and I believe this is as close to original as I've seen.
Oh! Another thing is to work with the grain of the material. Fork legs spring to mind which seem to have a grain which I think may be from the factory finishing I canna be sure about any of that though. KP
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Yabba Dabba KP
Wayne
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« Reply #9 on: January 03, 2013, 04:44:07 PM »

Excellent information KP. I have always been very successful over the years at attaining that high polished look on aluminum parts. (that chrome look you discussed) We seem to all be striving for what we think these bikes look like. I would hazard to say that even if one were found in a crate today, the degradation on the clear coat after 43 years would not even be a true reflection of how it left the factory. Anyone have a crate sandcast? I wanna fly in and see it! Wink
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Don R
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« Reply #10 on: August 31, 2015, 11:10:12 PM »

 I don't have one in the crate but I have one and know the guy that built it from the crate. lol.
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ashimotok0
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« Reply #11 on: September 02, 2015, 07:16:49 PM »

I reckon Honda maybe used a chromic acid treatment on the alloy before clear coat and that's why it adheres so well. I know that this is what is done on aircraft alloy because there is (was as most manufacturing sadly gone) a BAe systems  aircraft factory near me and lots of people here worked there and told me that's what was done there to alloy parts. I think Vic World hints at this in the descriptions on photographs he shows of the restorations.
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