Cleaning magnesium?? - turning into the black paint debate

So what does everyone use to clean type 1 cases and gear boxes??
I've been soaking an old gear box with kero for a week, then for a day with degreaser before pressure cleaning. All the junk is off, but it still looks dirty. Even scrubbing with a stiff brush doesn't seem to do the job.
I have seen some acid based aluminium cleaners, but are they a little violent for magnesium, and will the remove baked in dirt??
Thanks,
Andy

[Edited on 25-3-2003 by Baja Wes]

I found bead blasting was the only sure way. But it will tarnish quickly. You can use a good quality clear coat over the top if you wish.

That's about all I've ever done - degrease and clean. No one can see a polished gearbox on a daily driver anyway!

If everything is clean, try just using a rotary wire brush in a drill. It should whisk away whatever is clinging to the metal, and make the casting come up rather shinier. At least until it reoxidises again and goes grey. But it will be clean!

Thanks Folks.
Might just give it a good scrub and re-clean, then leave it at that!!
:thumb

theres not need to polish the inside of the engine or gearbox... only remove the sharp dags n casting lines so they dont break off and damage yr engine.

Blasting should only be done on the outside of the engine as glass grit and or oxide will imbed in the surface of the case and drop out again under heat thus contamination your new engine or gearbox

Cleaning the outside can be done with emery paper and or a emery buff on a drill if you want it shiny.

bead blast then paint with a good quality heat resistant paint like POR-15. It will stick like sh%t to a blanket and will clean easy in the future with a pressure kero gun.

I've always been reluctant to paint any GB or case. Wouldn't it reduce it's cooling effect??
Andy

Recent comments posted to this list make it clear some subscribers are not aware of the benefits of painting their engine. The basic reason for doing so is preservation. When fitted with a full-flow oil filtration system the VW flat fours can deliver 150,000 miles or more of service before the lower end requires overhaul. Indeed, when fitted with hydraulic cam followers, stainless steel valves and other modern innovations such as electronic ignition, it's not uncommon for a properly assembled engine to deliver 100,000 miles of service without requiring any form of repair.
A light coat of flat black paint on the magnesium-alloy crankcase not only protects it from corrosion, it enhances the heat-flow characteristics of the surface. The cast iron cylinders benefit even more, although they are more difficult to paint. The trick is to get the paint right down into the bottom of the fins. To do so calls for the use of a suitable brush, made by cutting off half the bristles from a small (1/2") paint brush; not an artists brush, the regular sort does fine. You must use a brush instead of spray because by the time you've sprayed enough paint to reach the bottom, you've flooded the upper part of the fins and made an unholy mess. So start with the brush, take your time and give your new jugs at least a day to dry before handling them.

High time engines, especially those operated in cold climates where corrosive substances are used for snow removal, are often found to have virtually no fins at all when the engine is torn down for rebuild. Ions of the corrosive material, common rock salt in most cases, attach readily to unprotected cast iron, and once attached are impossible to remove without boiling with a 'getter.' This means that once the corrosive ion finds a home on your cast iron cylinders, the corrosive action will continue year round, thanks to water vapor in the air.

Rusty or corroded metal makes a fine heat insulator, as every weldor knows. A few ounces of paint judiciously applied prior to assembling your engine is not only the mark of an experienced mechanic, it is one of those tricks so simple it is often overlooked. But in the long term it means greater service life and lower operating costs.

And before you succumb to conventional wisdom, drop by any airport and examine the engines that inspired the original Volkswagen engineers. Aircraft engines are painted as a matter of course, although such niceties were ignored with the VW in the interest of economy. The original idea was to replace rather than overhaul the engine, and to replace it fairly often -- typically, at something less than 100,000 km (56,000 miles). Alas, this option is no longer practical in todays economic climate.


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Copyright © 1995 Robert S. Hoover

This is from the main man as far as VW's are concerned. I have always paimted my cases and gearbox's with no ill effects. Wes is the man to confirm this though as he did a large project on this, perhaps you could check it out @ www.offroadvw.net

Mmmmm,,,,, I thought it was a little risky making a comment like that!!! I've seen many an argument over paint/no paint and cooling, raidient heat, conductive heat, the theory of cool, turbulent air, laminar air etc, not to mention your comments on corrosion etc, etc, etc....
I'm sure most people have their own opinions, as I do, and it's probably best to keep it that way (for me anyway) as I am the first to admit I have never sat down in a lab to do exhaustive controlled tests to prove my opinions.
Thanks for all the great suggestions,
and Keep un Dubin'
:thumb
(555bug, no dis-respect to you, just trying to avoid another never ending debate 🙂 )

Didn't Wes do some testing on this and the results ar on his web page?

I will now try to end the never ending debate. But someone told me
"Arguing on the internet is like running in the special olympics, even if you win your still retarded".

Painting your cylinders will ever so slightly reduce the cooling effect. This is because of a couple of reasons being that the paint acts as insulation and also smooths the rough casting which reduces turbulence and decreases heat transfer. The small increase in radiation heat transfer from the emissivity of the black compared to the cast iron is neglible.

However painting your case and gearbox is quite different. The case and gearbox is not subject to the same cyclonic winds as the cylinders / heads. You will not be able to notice any difference in painting your case or gearbox. I recommend painting gearboxes as the best way to make them look decent.

trust me on the cylinders, I was retarded enough to measure it

"Arguing on the internet is like running in the special olympics, even if you win your still retarded".

LMAO!
Love that!
HEHEHEHEHE!

Hey Wes, thanks for the great info!!
That looks like something I'd do 😀

I had a quick sqizz through your web page (traced back from the pics), but found no mention of the test. I was hoping to find a few details of how you performed your test. Would make some interesting reading.

:beer

And like tassie, love the quote, how true!

if you go to my website, then go to tech articles you will see it.

here's a link for the lazy people
http://www.offroadvw.net/tech/wes/black.html

I never finished writing it, but it's still worth reading.

Thanks Wes, so did you pass you thesis?

got a 7 out of 7 :bounce

I was happy since it was worth 48 credit points (a whole semester) :thumb

Boy, I should have done that for my Thesis, would have been much more fun!
Probably would have gotten a better mark also!!
:thumb

so there you go, I was correct in stating that you can paint your box and case + I wone a gold medal 🙂

using plane engines as an example is not a good idea, aircraft engines don't have any problems with cooling. In fact with some small old piston engine aircraft you have to be careful you don't shut the throttle too quick in decent, because the front of the engine cools real quick and causes the engine to crack. That piece of advice came from a friend with his pilots licence and his dad has a plane that is prone to this problem.

Also, many people will see emissivities published, and say wow look at the high emissivity of that surface or the low emissivity of that other surface. Be careful at what your looking at, for any colour / surface the emissivity changes for various frequencies of radiation. A lot of the data published is the UV / solar type radiation from the sun (insanely high temps). This wavelength typically gives whites a low emissivity, and black a high emissivity. You will notice this effect if you wear a black or white shirt in the sun, the black one will absorb the heat and be very hot.

But this is a completely different wavelength to heat energy (low temps). With normal heat radiation white and black emissivities are extremely close. This means that if you paint your engine parts black or white it won't make a sh*t of difference to how much heat it radiates. Some people have even been silly enough to say that you should paint things white if you want to keep the heat in.

And some people critise other people for having coloured fan shrouds, because they think they should be black to radiate heat. This is also crap because for heat the emissivity of the various colours is very close to black, plus your tinware doesn't get hot enough to radiate much anyway. Painting a shroud black will just make it get hotter if it sees the sun.

OK, I admit I studied Applied Physics at uni... but I'll try not to get too technical:

Any paint is likely to impede energy loss in the form of heat - the paint is a kind of plastic, which acts as an insulator. However, a number of studies have been done; some of which actually showed a lower thermal resistance (meaning better heat loss,) with the use of some black paints. The recommended procedure for heatsinks (used to dissipate heat in electrical and mechanical situations: eg the fins on a cylinder,) is anodising (where a dye is applied to the metal electrolytically,) and this has been shown to be almost universally effective.

As for an engine case - even the original designers didn't consider this a vital part of engine cooling, and many have painted their cases and been very happy. There is always the problem of paint entering the engine (or coating machined surfaces; eg barrel mating surface,) however. I would not, however, recommend colouring cylinders or heads (or even pushrod tubes) by any other methods than anodising or metal plating.

And, yes, I do not believe the colour of tinware would have any significant effect on engine operation (except how hard the driver pushes the accelerator.) I use black because I like the "Stock Look."

P.S. The generator (or alternator) also needs to lose quite a bit of heat - painting it will reduce it's efficiency, but probably won't kill it.

P.P.S. If you want a show-standard car, but intend to drive it, try chrome barrels, black anodised heads, and use your imagination on the rest!

[Edited on 25-3-2003 by 70AutoStik]

you paint the case after the engine is assembled, that way you don't get paint in machined surfaces.

The generator and alternator are air cooled and will not suffer from painting.

chrome barrels? are you mental? :o chrome will trap the heat in the barrels, and significantly reduce the turbulence and have negative effects on the boundary layer formation around the fins. This will really reduce heat transfer of the barrels. Never ever chrome your barrels.

Chrome tin ware is ok because it is not directly transferring heat.

ahh thats better...feel that tension 🙂 I thought Wes would like this one...a bit vlose to home. You see Wes was beaten as a child and locked in a small box that was painted black, he noticed that this did not aid him as he frequently became dehydrated. In later life Wes set out to prove his fledgling thoughts in the lab (which was cool with plenty of fresh water) HAHAHA just shiting you Wes...hurry up back to Brisvagas

I was just bored last night so I figured I would rabble on a bit 🙂

But then I went to urbandictionary.com and looked up phrases like "pearl necklace" and ended up giggling the rest of the night 🙂

Boy, and all I wanted to do was get some crap off my GB. Once it's back under the beetle it will probably never see light of day again (unless I don't fix it right).

Anyway, if your that bored and love an argument, check out some of the US VW sites, it's an argument that has been beat out plenty of times! :P:P:P:P:P

Hey Wes, should I now start to rip appart your test procedure 😀
Richard

Wes, the barrels and heads are cooled primarily by conducted, not radiated heat. Any metal plating will have little to no effect on their cooling (the greatest harm that could be caused would be if such plating were too thick - smoothing the fin surface.)

no Peter, the heads and cylinders are not cooled by conduction, and I have already said radiation plays a very small part and that's why black paint doesn't have the effect people think it might.

The heads and cylinders are cooled by forced convection. The relationship between the air velocity and the heat transfer coefficient are greatly influenced by surface roughness. A smooth surface will encourage laminar flow around the fins, and hence a large boundary layer. This could be considered to be an insulating pocket of air around the fins.
A rough surface will encourage a turbulent flow regime results in a higher heat tranfer rate for a given cooling air speed.


So basically rough surface has two advantages over a smooth one;
(1) - it radiates heat better (smooth ones reflect it)
(2) - it creates more air turbulence and therefore transfers heat better.

What about the "reverse swing" theory, where rougher surface = faster air flow.

No. 🙂

It is all about bondary layers and laminar/turbulent flow regimes. It would be too difficult to explain it in detail on an internet forum.

The best research on the subject has been compiled into one book by the ex cheif engineer at Tatra. The book is called "air cooled engine" (I think), written be Julius Mackerle (will have to check the spelling). QUT in Brisbane have a copy.

Bugger that Wes. Send ‘em a few Thermodynamics and Fluid Dynamics texts and they can figure it out for them selves. Then we’ll have a debate and a half.
And we’ll all still believe what we believed before anyway!!

From the QUT library search:

Author Mackerle, Julius, 1909-.
Title Air-cooled automotive engines.
Published London : Griffin, 1972.
Edition 2nd revised and enlarged ed. / [authorised English translation from the Czech by K. Caslavsky, edited by Keith S. Alderton].
Uniform titl Vzduchem chlazene vozidlove motory. English
Description 518 p. : illus ; 23 cm.
ISBN 0852642059 : 8.00
Note Previous ed. in Czech has title: Vzduchem chlazene vozidlove motory.
Bibliography Bibliography: p. [507]-511.
Staff use 629.2/504
Subject Automobiles -- Motors -- Cooling.

It's a good read, all 518p 🙂

Although I'm a newcomer to VWs I've spent quite a few years playing with air cooled motorcycles. In the days when air cooling (free air rather than forced of course) reigned supreme, even on the highest output four stroke engines and hyper stressed two stroke screamers, manufacturers applied a variety of finishes to their engines from satin black, through dull, lacquered alloy to polished alloy. Some engines received different finishes depending of the style of bike they were fitted in whilst remaining identical from an engineering point of view. I can't think of a single case of a bike engine dying as a direct result of general overheating (as opposed to holing a piston due to lean mixture or similar).

Even before I became aware of the great VW paint/no paint debate I'd started to suspect that, as long as an engine is in good nick and not severely abused, with an intact cooling system the differences wouldn't be great.

Would I paint my engine? Yep, but that's because I grew up where road salt will dissolve magnesium alloy before your very eyes and old habits die hard.

Wes, I had a friend who had the fins of his 45 chromed, with black-anodised heads (Harleys are air-cooled, too; remember) and it looked fantastic and ran well (the rocker covers were re-chromed, too.) I think he later painted the primary cover gloss red - this is more than 20 years ago!

Yes, "forced convection" is the correct engineering term, but think about it - the heat is still conducted to the air. Chrome plating is so thin it makes bugger all difference to the texture of the surface - even "triple chrome." I, personally, don't like painted cases- but I love things looking really "mechanical." A painted case (if done right) should work OK, but paint on the cooling fins of the cylinders or heads (possibly the sump) is likely to cause problems. But try not to be such a fresh engineering graduate - plating or anodising the cooling areas is not likely to cause any great problems.

I will add as a postscript that there are paints that can be used in such areas, but as inferior products also make such claims, I won't recommend any.

Exactly what I'm saying, paint colour has very little effect. Although I have never seen a factory motorcycle with chrome plated fins before, and don't think it would be a good idea.

Motorcycles also use a much wider fin spacing to suit the much lower cooling air speeds.

I live in QLD so have never experienced the problems of severe corrosion of the cylinders, but from a corrosion point of view I think paint would be a good idea.

Autostik, a harley is not a good example, as it is a very understressed motor. They make hardly any power for their capacity and as such are not prone to any cooling problems.

I would hardly call myself a fresh graduate, I think 4 yrs of eng industry experience is plenty, especially with it being so specialized in the field of stress analysis and heat transfer / thermodynamics. But there are plenty of much more experience people than me that will still tell you that chrome plating your cylinders would be a very silly thing to do. In fact I think the cheif engineer at Tatra would have told you that.

I never said I had anything against the painting / anodising idea. I said and showed from my results that it made very little difference either way.

[Edited on 27-3-2003 by Baja Wes]

I have ridden a bike in a coastal area and the corrosion on cast iron fins doesn't build up to the point of causing a problem as fast as some will have you believe. If you are restoring an old bike from a coastal area (that happens to be healthy enough to be worth it,) simple sand-blasting gets 'em back to original condition pretty quick.

I should add the qualifier to my last post that I'm talking about Japanese engines in the main. I can think of cases among various accquaintances running late 60s and 70s Triumphs and the like (whose engine designs were getting pretty marginal for the power outputs they were being asked to produce) who polished and/or chromed their crankcases and subsequently found that their oil boiled when running hard. However, these were engines that were so overstressed that they needed all the help they could get. I still maintain that anything not already on the limit would barely notice a difference.

Yeah; actually the trumps you are talking about are exactly where anodising and artificially roughing surfaces became popular in the auto industry - personally I think the fins just weren't big enough (but they were/are still wonderful to ride.)

[I should add that the Bonnie had no in-built oil cooling, so after-market finned tranny covers actually made a significant difference - for those who don't know, many bikes share the oil between the engine and tranny.]

[Edited on 29-3-2003 by 70AutoStik]

Thanks Wes, I, glad all that painting I did on My engine and gearbox... doesn't have to come off... LOL....!! I have found that VW Engines corrode very badly, even in the country, laying out in the open.... No Salt etc.. Just Corrosion....

Baja Wes wrote:you paint the case after the engine is assembled, that way you don't get paint in machined surfaces.

The generator and alternator are air cooled and will not suffer from painting.
chrome barrels? are you mental? :o chrome will trap the heat in the barrels, and significantly reduce the turbulence and have negative effects on the boundary layer formation around the fins. This will really reduce heat transfer of the barrels. Never ever chrome your barrels.

Chrome tin ware is ok because it is not directly transferring heat.

:o:thumb:thumb:thumb:thumb:thumb :bounce:bounce:bounce:bounce

I take my baja on the beach, and if you have clean bare magnesium there it gets really attacked. So painting cases and gearboxes is very smart if you plan beach driving. I haven't noticed the cylinders get too bad. They get a light layer of rust but then doesn't corrode any further.

My bike actually has a dry sump design and uses the steel frame to store the oil. My dipstick is in the top of the frame just under the handlebars.