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[C2] 3890490 GM Intake questions

Old 12-04-2018, 06:17 PM
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R66
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Default 3890490 GM Intake questions

I am swapping the intake on the 68RS to an Eldebrock C3B as I want to use the 3890490 GM intake on R66.

I found they are both the same height within 1/8 - 4 1/8 vs 4-1/4. It surprised me that the 3890490 was also used in Chevelles and Camaros and other 350 hp performance cars as well as Corvette.

I found the date on the bottom side 12/7/65 which is just before the build date of R66. Bit of luck.

I have a couple of questions on the 3890490 GM intake:
  • I assume all of these intakes even for corvettes had the coil mounting bosses?
  • On the #2 runner it has a Q stamped? Was this factory?
  • The date is cast on the bottom with RD . CM under it. What is RD . CM?
  • Also cast on the bottom is 123345678 with a series of hash marks and a square 0 between the second and third hash marks. Is that normal and significant?
Tried cleaning both with diesel fuel, then soap and water. Tried brake cleaner and spray carb cleaner that helped a little, but not satisfied with the results. I have some caustic carb cleaner I am going to try next. Any other recommendations?

GM and Eldebrock C3B

GM

Date


Winters


Thanks

Ron

Last edited by R66; 12-04-2018 at 06:31 PM.
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Old 12-04-2018, 06:53 PM
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Hi Ron,
According to the Corvette by the Numbers guide, the 3890490 intake was used extensively as a service replacement with one of its major change (from the previous iteration) being a carburetor pad design change. It was said to be used in 1966 and 1967 in the Corvette for the 327/350hp motor. The large "W" is the Winters logo (who produced the manifold for GM) and I am not sure about the number string or the RD.CM. I'm sure that someone else will know.

I have found lacquer thinner (buy a gallon at Home Depot or Lowes) to be excellent in cleaning an aluminum intake manifold. It takes everything off including any old paint.

Good Luck. C.J.
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Old 12-04-2018, 11:07 PM
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Thanks CJ,
Right now using lacquer thinner is not on the list as I have an open flame heater in the garage - Ka Boom. And you know it is cold outside, ya, I've become a wimp.
I have tried foaming mag wheel cleaner and caustic carb cleaner with little success. Thinking I may have to immerse them in something for a few hours and then return to scrubbing.
Thought about the wife's dish washer, but don't want to die yet.

Ron

Last edited by R66; 12-04-2018 at 11:08 PM.
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Old 12-05-2018, 08:22 AM
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If you use the dishwasher, don’t turn on the drying cycle! The heat will turn it black. Ask me how I know...
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Old 12-05-2018, 08:53 AM
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Try wheel cleaner.
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Old 12-07-2018, 02:15 AM
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GearheadJoe
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Regarding your question about cleaning an aluminum intake, I completely agree with people who say that sand blasting an aluminum intake is a bad idea, particularly if coarse media is used. I have seen many intakes whose surface texture was ruined by sandblasting.

HOWEVER, my preferred method for cleaning an aluminum intake is to blast it with *glass beads*, which are far more gentle than sand on the surface texture of the aluminum. While all glass beads are quite gentle compared to sand, the most gentle glass bead media has a very small bead size that is referred to as something like "300 sieve" to indicate the bead size. It's only a slight exaggeration to say that this media is just a few notches up from talcum powder.

The photo below was taken to highlight a particular feature of an intake that I was working on, but the photo happens to clearly show how the surface texture of the as-cast aluminum has been fully retained after glass beading. I have been very pleased with the results I get when using the smallest available glass beads. This particular intake had only received a "first pass" glass beading, but I can assure you that a second pass would make the intake look brand new. I have done this many times on other intakes and the results are always very nice.

The glass bead media is about $60 for a 5-gallon container, so it's a lot more expensive than sand, but the results are excellent. When I get home tomorrow I can check to see the exact size of beads that I use. I think the supplier is Ballotini.


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Old 12-07-2018, 10:14 AM
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Thanks Gentlemen,

Going shopping today for materials. I have tried a cheap wheel cleaner with no success. Tried test spots of white vinegar, bleach, and cream of tarter. Little success. I have learned that muriatic acid will clean, but also pit aluminum. Looking to try coil clean (potassium hydroxide) and Eagle 1 wheel cleaner, Aluminum Navel Jelly, and Alumina prep. All are acid based and should be used outside, but in IL right now it is below freezing. Cast Blast paint may be the fastest answer, but I hate to paint intakes due to the heat passages always burn the paint.
Glass bead blasting would appear to be desirable if I had a blast cabinet, might have to get one.

Ron
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Old 12-07-2018, 11:33 AM
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Ron, I haven't used it in a while, but have you tried any of the Oven Cleaners on it? I've used it Easy-Off in years past and it does a good job of removing crud. Not sure if it will remove paint, but I know it will discolor it (paint) if left on too long.

We would get the engine good and warm, drive to a car wash, spray down the engine good with the Easy-Off and let it set for a few minutes. Then wash it off with the soapy water of the car wash. Most of the dirt and crud would be gone.

At this point we would break out a can of CRC 556 and spray the distributor cap and wires, fire it up and head home.

One other option is many machine shops have a cabinet with high pressure heated water nozzles and a turntable that you could set blocks and other items on that they use to clean gear before machining. I can't imagine it would cost too much to have them use it on your intake.

Good luck... GUSTO
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Old 12-07-2018, 11:49 AM
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Would a local machine shop bead blast and tank it for you?
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Old 12-07-2018, 02:29 PM
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Originally Posted by R66 View Post
Thanks Gentlemen,

Going shopping today for materials. I have tried a cheap wheel cleaner with no success. Tried test spots of white vinegar, bleach, and cream of tarter. Little success. I have learned that muriatic acid will clean, but also pit aluminum. Looking to try coil clean (potassium hydroxide) and Eagle 1 wheel cleaner, Aluminum Navel Jelly, and Alumina prep. All are acid based and should be used outside, but in IL right now it is below freezing. Cast Blast paint may be the fastest answer, but I hate to paint intakes due to the heat passages always burn the paint.
Glass bead blasting would appear to be desirable if I had a blast cabinet, might have to get one.

Ron
If you decide that you want to try bead blasting, you could probably buy a 5-gallon container of the Ballotini beads that I use and have someone with a blast cabinet clean the intake for you (or better yet, have them let you use their cabinet). The key is to use the right media.

An alternative would be to send me your intake and I will bead blast it using my cabinet. My cabinet is already loaded with the correct media. I'd be happy to do this for you at no charge, but the round trip shipping would exceed the cost of buying the media yourself and finding a nearby shop that will let you use their cabinet.

One cautionary note about bead blasting is that the stamped steel heat shield on the bottom of the intake should be taken off first because glass beads can get trapped between the shied and the intake. Removing the shield for cleaning is a good idea anyway, because a lot of carbon buildup usually occurs in that area. I've seen some pretty gross looking deposits under the shield.
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Old 12-07-2018, 02:54 PM
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As mentioned, glass media blasting will make it look new. Go to any machine shop and ask if they have a bead blaster. Bring your own new glass media, and have them blast it, or ask if you can do it. I’ve blasted my intake every time it’s off the car. Use low pressure and fine media.
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Old 12-07-2018, 09:03 PM
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Lots of folks have had good luck cleaning whitewalls using Totally Awesome so I tried it on my aluminum intake, then followed up with naval jelly (phosphoric acid) and they cleaned it really well, just couldn’t remove stains. I think blasting is the only way. Anybody tried walnut shells?
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Old 12-07-2018, 10:06 PM
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Mr. R66,
Do to the parts dept. at your local ROAD TRACTOR dealership. (like Peterbuilt, Frieghtliner, International,etc.) Ask the parts guys what does the dealership cleanup dept use on the aluminum wheels.
I've seen some cleaner that will turn dull to bright look.
Just mt .02 worth

Max
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Old 12-08-2018, 12:21 AM
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Guess my memory is failing, my son is a foreman at an International dealer. Sometimes it takes a boot in my butt to bring my mind back on line.
I'll give him a call and see what he can come up with. I looked around after my morning saw bones appointment but didn't really find anything. The Eagle 1 cleaner is now safe for coated wheels and paint and non-acidic, at least what I found.
Thanks Max, that $.02 would get you a beer if we were closer.

Ron

Last edited by R66; 12-08-2018 at 12:22 AM. Reason: sp
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Old 12-10-2018, 07:31 PM
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The glass beads that I have used very successfully on aluminum intakes are made by Ballotini and the bead size is classified as "170-325 Seive" as shown on the photo below of the label. I buy it in 5-gallon buckets from www.grainger.com, an industrial supplier with warehouses located in many cities nationwide. The Grainger/Ballotini part number is 6ZC13, currently listed at $62.25. You can buy this from the Grainger web site, but check the shipping cost first.

As shown in the second photo of some of this media in the palm of my hand, the "170-325 Seive" glass beads are very small. The lumps you see in the photo are just some clumps held together by moisture.

Keep in mind that glass beads come in a variety of sizes, and this size is one of smallest sizes available. So, if someone says they can glass bead your intake, find out what size beads they are using. While all glass beads are generally more gentle than sand, this very fine size of glass bead is the only size I would recommend for an aluminum intake manifold.




.
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Old 12-11-2018, 12:09 AM
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Thanks Joe and everyone,

I checked with my son and they don't clean trailers and also, he sold the blast cabinet. My luck.
I did find a friend with industrial strength acid cleaner for aluminum trailers and wheels. I cut it 4 to 1 (recommended is 70 to 1) and sprayed it on and keep it wet for over 90 minutes. Minimal improvement. My Luck. May try it full strength.
Headed to find Aluminum Navel Jelly. Also oven cleaner and toilet bowl cleaner. Might as well make an experiment out of it as I have 5 aluminum intakes and 3 sets of valve covers I would like to clean. Problem is I have 5 saw bones appointments a week and my wife has one this week. Sucks to get old.
Have to resist the erg to paint them.
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Old 12-11-2018, 12:25 AM
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Originally Posted by R66 View Post
Thanks Joe and everyone,

I checked with my son and they don't clean trailers and also, he sold the blast cabinet. My luck.
I did find a friend with industrial strength acid cleaner for aluminum trailers and wheels. I cut it 4 to 1 (recommended is 70 to 1) and sprayed it on and keep it wet for over 90 minutes. Minimal improvement. My Luck. May try it full strength.
Headed to find Aluminum Navel Jelly. Also oven cleaner and toilet bowl cleaner. Might as well make an experiment out of it as I have 5 aluminum intakes and 3 sets of valve covers I would like to clean. Problem is I have 5 saw bones appointments a week and my wife has one this week. Sucks to get old.
Have to resist the erg to paint them.
If you have five intakes to clean, a single 5-gallon bucket of the correct glass beads would handle all of them just fine. I've never tried glass beads on valve covers, but I know that it works great on intake manifolds.

I don't know what "saw bones" are, but they sound painful. If you think you can stand at a blast cabinet for about 15 minutes per intake, then all you need is one bucket of glass beads and someone who will let you use their blast cabinet. Just about all restoration shops have a blast cabinet, and it's likely that many members of your local Corvette club have them too.
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