TheSamba.com :: View topic - Engine case corrosion repair. Advice to keep OG 40HP case.

Thu Oct 07, 2021 10:17 pm

40hp case. Want to keep the case number so looking for advise on repairing and stopping corrosion in the oil sump. Working to clean the case up from 60 years of grime.

Corrosion is light to moderate with a few spots rather deep but not through. Not sure how aggressive magnesium rote really is.

1. Is there a way to stop or neutralize the corrosion after you grind out all that you can?

2. Is it advisable to fill the voids once done? I tend to think no.

3. Are there any coatings you can use to seal the sump? Like what you do for gas a tank?

Image below is after sanding and light grinding out of corrosion. Looks worse than it is.

Fri Oct 08, 2021 4:05 am

Good work with cleaning out and grinding down the corrosion nibs. I cannot speak from experience, though I have a 1500 cc "H" case that was a freebie which had a bit less corrosion on the inside of the sump area. At the time I also wondered what would be some alternatives. If anything.

I think any method to fully or partially fill the pits would be dependant on the heat rating of the product. Years ago Eastwood Company offered a product called "Gliptone" for painting the inside of an engine case. It was in a small can and you brushed it onto the chemically cleaned engine block. The smooth paint finish was supposed to promote engine oil running down to the sump area easier. I looked at their site and that product name is no longer offered. Search of Summit Racing also had no hits.

You mentioned gas tank sealer... here, you'd need to check the product's safety sheet for its sustained heat ratings. I looked up MasterSeries CT's sheet for the moisture-cured urethane silver paint, and it does have a rating for 350 F which is higher than the engine oil inside a VW case. You'd really only need a small amount to dab into each crater with a brush and smooth out any roughness on the crater walls. Probably not needed to fill the crater. http://masterseriesct.com/page8.html

Would POR-15 epoxy putty be suitable to press into and fill the craters?

Is JB-Weld a similar material, since once hardened it is solvent resistant? With both of those putties/epoxies, the heat resistance and the constant cycling of hot to cold would be a long-term concern. If any of the chunks loosen and break off, they could be whipped up from the oil splash to contact a bearing...

Fri Oct 08, 2021 7:03 am

Understand....this is not like "tree rot". Its not a disease. Its corrosion. Its electrolytic....and therefore electrochemical. Rust is the same.

There are too many myths floating around regarding rust and corrosion.

You do not need to cut away rusted or corroded metal.....unless you plan to paint it and the surface is too irregular to either sand, grit/bead blast or chemically neutralize....or if you need to weld it or have welded too close to it changing the temper.

This is not because rust is a cancer that will grow....its because a rough rusted surface will entrain oxygen and moisture....against bare metal. THOSE are the seeds of the cancer.

The only other time to literally "cut out" metal....is when you are removing metal where a crack has propagated....OR.....when it is a high tensile area and you have acid treated or base treated the metal and cannot neutralize and re-anneal it.

The example being.....if you acid treated or electro plated bolts, studs and hardware better than SAE grade 5....they must have a post plating neutralization and bake or they WILL develop hydrogen embrittlement. Likewise if you acid wash rusted things that are high tensile like springs and suspension components.

Aluminum and magnesium are somewhat the same way.

Those cases rot away like that because oil ....with combustion residue in it....has been left for YEARS....and had moisture in it along with gaining moisture through condensation cycles.

With time.....the oil begins to break down. The combustion residue has sulfur in it. That sulfur with water breaks down into dilute sulfuric acid......THAT is what eats your magnesium case like that.

To your questions:

First....the only grinding you need to do is if you want it smoother. Actually removing all of the powdery corrosion residue (which is called white rust)....is typically done with a light acid ....a specific acid.

1. You need to first etch it with a redox reaction to get rid of the existing corrosion then neutralize it. Personally.....with the correct acids required....I would simply take your case to a plating shop that does aircraft parts and have it prepped for plating or Alodine coating....even though you may not want to do either of those.

This uses either chromic or nitric acid to "react" all of the existing corrosion down to bare metal. Then they rinse it and then use a caustic ...which magnesium is more resistant to than aluminum....like sodium hydroxide....just a quick dip....to neutralize all of the acid and electrochemically activate teh surface for plating.

Yes...you can do a good enough version of this at home but need to be careful and specific. If you need some help I can answer some questions.

2. There is n need to fill the pits unless it is on a mating surface or has a hole you need to seal.

The object is to kill and clean the surface and then simply keep it full of oil and do not let it get into an acidic condition again.

Yes...a serious epoxy putty will work fine if you need to fill something but there is no guarantee it will not crack off in the future.

3. Coatings. Really there is no need for coatings.....on the inside of the case. Keep it oiled and acid free. Change your oil and dont let it sit around for years without running.

But...on the outside.....the magnesium engine cases on aircraft, the fan housings on type 4 engines and Porsche engine housings....are "Alodine" coated". This is an electrolytic coating...it ranges from gold/brown to tan/greenish......and can only be applied after the same chain of treatments I listed above.

It is actually a "passivating" layer. Its a chromate coating...just like you see on zinc chromate. It has to be applied by someone who knows what they are doing.

Within less than a minute after acid etching, rinsing, caustic neutralization, caustic activation and rinse....it is applied as a chromate top coat. This forms a SACRIFICIAL barrier that keeps oxygen away from magnesium for years....so that the magnesium does not start forming its natural patina....which is actually corrosion in a uniform layer.

So the object is that with an "Alodine" coated engine case....you will have years where the Alodine coating is slowing changing colors and getting lighter as it oxidizes away. This keeps teh magnesium underneath from starting to oxidize. Its only purpose is to extend the time by years before the magnesium starts to oxidize....and first gets that darker color and then gets that powdery residue on it...which is white rust....and then starts to oxidize further.

There is a guy in the Porsche forum that has reasonable Alodine services. It will probably cost $300-400 to do an engine case.

But....for a magnesium engine case for a VW.....just keep it oiled inside. It keeps the oxygen away from the metal so it does not oxidize.

The other coating that Rome mentioned.....is "Glyptal". It comes in several names but Glyptal is the original brand and has been around for about 100 years.

It is the red or green ceramic looking paint that you see inside of very old 1920's aircraft engines and oil field and marine engine crankcases. It lasts for ages.

It comes under several names.....Glyptal, Glyptic, Glyptone etc. It is an Alkyd/epoxy enamel...and also needs specific cleaning and surface activation for aluminum and magnesium. And....those for aluminum and magnesium are a "silicone epoxy". These only come in a few colors....and most have to be baked on.

https://www.electro-wind.com/glyptal-s-1300-white-...ubstrates.

Here is the Glyptal website....fantastic products....but call them and tell them what you want to do and aske them which product you need. Ray

Fri Oct 08, 2021 7:07 am

Disclaimer - I have never used this, but seems popular with guys restoring early Harley motors.

https://www.eastwood.com/glyptal-red-brush-on-1-qt.html

Fri Oct 08, 2021 10:23 am

Thank you to the input. Greatly appreciate not being blown off and so many threads say to just get a new case.

Fri Oct 08, 2021 12:38 pm

Glyptol is a superb coating.....but understand....coatings of any kind will not stick to magnesium long term unless the metal is chemically etched FIRST to remove the magnesium oxide patina coating .....which is harder than the metal itself. This is important if you want to paint or coat something that is a magnesium alloy....like painting the outside of a case or a type 4 engine shroud.

In those two examples....sure you can do less than is chemically required....paint the OUTSIDE of the parts....any maybe get q few years of good looking parts before it starts peeling.

The question here....is why would you NEED......to coat the INSIDE of the case? As long as the corrosion that has already happened is not producing a hole or leak (and that leaves a question of patching not coating).....or has not weakened the case structurally.......all you really need to do is remove/dissolve any crusty corrosion....knock off any small brittle metal points that could break off and get into the oil.....and just neutralize/stop the corrosion that is still growing.....and then just fill it up with oil and drive it. Keep clean oil in it and run it on a regular basis.....and it will not corrode anymore.

The risk of coating the INSIDE of the case even with something like Glyptol......is that unless you get the surface etched and activated PERFECTLY.....the coating will eventually,start sloughing off and into your oil. Ray

Fri Oct 08, 2021 12:54 pm

Question here....is why would you NEED......to coat the INSIDE of the case?

Old race engine building trick, helps oil drain back to bottom faster.

Fri Oct 08, 2021 3:18 pm

Thanks for the explanations, ray; and the correction- yes, Glyptal, not Gliptone as I first wrote. I wondered why I was getting search results for a polish instead of that paint.

My thought with the Glyptal would be to only paint the corrosion craters to cover the sides and bottom, not to fill them; nor to paint just along the flat bottom sump surface on the inside.

Fri Oct 08, 2021 4:48 pm

Again thank you guys.

I will NOT be painting the inside of my case with this new knowledge. No point IMO.

The plan is to clean the case at this point with Sodium Hydroxide and as long as i do not break through any of the corroded areas leave the case be.

If the worse happens then i am sure i will be looking for further advise or a new case.

Fri Oct 08, 2021 4:53 pm

Zundfolge1432 wrote: Question here....is why would you NEED......to coat the INSIDE of the case?

Old race engine building trick, helps oil drain back to bottom faster.

Oh for sure! That is a good REASON to coat the inside of the case.....and is actually WHY Glyptal was developed.

It was originally used in the early 20th century on splash oiled cast iron engines whose inside surfaces were rough as the surface of the moon!

Was used for the same reason on one lung oil field equipment and still is.

Agree.....great reason......but my point was more in the range of NEED.....on this application.

I think better oil return drainage is good for any engine. The problem with situation and virtualy any magnesium based engine.....is that you will have to have a chemically perfect prpcess to make SURE it has good adhesion to the case.

You cannot afford to have a coating that you cannot inspect on a regular basis....cracking, chipping and sheeting off into your oil. Thats a very likely process on magnesium. A good deal less so on an engine that is aluminum. They make a specific product just for aluminum. It works better because aluminum is slower to start its oxidizing and oxide patina process.

But magnesium is VERY quick to start the oxidization process.

In fact....the process required for PAINTING or powdercoating aircraft magnesium parts is to first go through the chemical etch and activation process described earlier.....then neutralize......then rinse in DI water.....and keep it submerged away from free oxygen ...and go straight into an Alodine or Bonderite chromate surface coating bath....which prevents free oxygen from ever contacting the magnesium. Then force air dry .....then straight into painting or powdercoating.

The chromate coating is an oxygen sealer and IS the primer for the paint or coating.

Ray

Sat Oct 09, 2021 1:03 pm

Alodine 5200 is for magnesium, the more common 1201 is for aluminum & will not be effective on mag. I have also used Stitts magnesium prep... it has a name but I can't think of it right now. it is available at places that sell aircraft paint. the old version had chromic acid in it but I don't think they do that anymore. there are a number of formulas for "chrome pickle" solutions that will neutralize corrosion with chromic acid. there are others that use nitric acid.

once cleaned up, I would epoxy the holes with liquid 2 part, not the stick stuff. that way it can soak in better

Glyptol is some heinous paint.... sticks like dog doo to the picknik blanket. I've tried to strip it from the inside of old aircraft engines a couple times & its hard to do... even with the chemicals we had back then

Sat Oct 09, 2021 1:24 pm

dogmeat wrote: Alodine 5200 is for magnesium, the more common 1201 is for aluminum & will not be effective on mag. I have also used Stitts magnesium prep... it has a name but I can't think of it right now. it is available at places that sell aircraft paint. the old version had chromic acid in it but I don't think they do that anymore. there are a number of formulas for "chrome pickle" solutions that will neutralize corrosion with chromic acid. there are others that use nitric acid.

once cleaned up, I would epoxy the holes with liquid 2 part, not the stick stuff. that way it can soak in better

Glyptol is some heinous paint.... sticks like dog doo to the picknik blanket. I've tried to strip it from the inside of old aircraft engines a couple times & its hard to do... even with the chemicals we had back then

For sure.....Glyptol is damned ugly, fine stuff. I still see it being used (mostly in oil field industry videos).....regularly....when rebuilding pump jack gear boxes. I "think" they just sand blast it off.

They still use chromates....but typically its chrome 3 and not the hideous and nearly gone and illegal.....and deadly.....chrome 6 (hexavalent chrome).

There are also some non chromate pickels and passivating agents.....but they can have a shorter life.

Yes....5200 for magnesium.....but its still back to the problem at,hand. If he were just Alodine coating....no problem. Still has to be done rigjt but one can do that with care and planning at home. And if its not perfecyly and proffesionally done.....and it comes off.....inside the crankcase.....Alodine by itself causes no problems.

Its any coating on top of the Alodine that will cause the issues.....if the Alodine is not perfectly applied.

Even Glyptol will not stick to magnesium if the chain of events leading up to coating is not perfect.

The magnesium has to be kept oxygen and oxide free to have a surface that can be bonded to with confidence. This is actually one of the main things that Alodine and Bonderite coatings on magnesium are used for. They provide the oxygen sealing to prevent magnesium oxide from forming.....before painting or coating.

If it were the outside of the case we were worried about.....sure.....Alodine it....then coat with whatever you want. But inside the case.....there is no need. It stays full of oil and oily.....and that alone prevents further corrosion as lomg as you do not let it sit for years not running and heat cycling.

Ray

Tue Jul 25, 2023 8:22 am

would you guys risk an unknown bore condition case with this corrosion? Price is pretty low.

Thanks

Heck, maybe it's paint?!?!? I hate being ignorant on an interest.

Tue Jul 25, 2023 8:28 am

found "Center main spread" written on case. Would that mean the #2 main bearing cradle has warped enough that it has a gap??

Tue Jul 25, 2023 8:31 am

I see no corrosion.

Bolt the two halves together and shine a light from the rear, while looking in through the crank opening. The #3 saddle will show light at the seam if it is separated badly.

Tue Jul 25, 2023 12:01 pm

Once you scrub it down, just put a coat of Gibbs on it a couple times a year or WD40 a little more often. Either will keep the white fuzz away

Tue Jul 25, 2023 1:32 pm

matthew henricks wrote: 40hp case. Want to keep the case number so looking for advise on repairing and stopping corrosion in the oil sump. Working to clean the case up from 60 years of grime.

Corrosion is light to moderate with a few spots rather deep but not through. Not sure how aggressive magnesium rote really is.

1. Is there a way to stop or neutralize the corrosion after you grind out all that you can?

2. Is it advisable to fill the voids once done? I tend to think no.

3. Are there any coatings you can use to seal the sump? Like what you do for gas a tank?

Image below is after sanding and light grinding out of corrosion. Looks worse than it is.

Have a look into 'Keronite' coatings...whether the process involved is applicable or financially viable I wouldn't like to say, but certain industries use this particular process for preventing corrosion in alloys prone to acidic or galvanic corrosion, such as magnesium. Send an email to [email protected]. see if there product is suitable. Would be a rewarding job if so...Good Luck

Wed Jul 26, 2023 6:52 am

VW_Jimbo wrote: Bolt the two halves together and shine a light from the rear, while looking in through the crank opening. The #3 saddle will show light at the seam if it is separated badly.

Had a machinist who frequents here often tell me to get the case as "Cores are drying up and to get all you can." as well as that a line bore would work on the case even if it has separated webs/saddles"?!? WTF?

I'm conn-fused

Wed Jul 26, 2023 6:53 am

VW_Jimbo wrote: Bolt the two halves together and shine a light from the rear, while looking in through the crank opening. The #3 saddle will show light at the seam if it is separated badly.

Had a machinist who frequents here often tell me to get the case as "Cores are drying up and to get all you can." as well as that a line bore would work on the case even if it has separated webs/saddles"?!? WTF?

I'm conn-fused