TheSamba.com :: View topic - Fixing the heating: removing/repairing heat exchangers

Thu Oct 06, 2016 1:46 am

I'm on a mission to repair the original heating on my bus ('79 Westy, 2.0l GE engine with FI). After spending some time on it last weekend, I noticed a few things:

1) This is how a working heat exchange system (not mine) should look like:
https://www.thesamba.com/vw/gallery/pix/1529310.jpg

2) My heat exchangers' covers have huge rust holes. Notice also on this pic from the right hand side exchanger: the hole did away with the thread that allows connecting the cold air heater pipe (more on this below) coming from the engine compartment to the heater. The circular port on the exchanger, other than surface rust, seems ok, though. But I believe the exchanger's fin inside looks rusted too (not too sure, as I could only see it from the picture I took via the opening for the heater pipe in the engine compartment from above!). I'm wondering if they're made of aluminium or another metal and what I'm seeing is just dirt instead of rust.

3) As the bottom of the heater pipe (#021256332A) has been disintegrated by rust, it's a less than tight fit to the exchanger. Here's again a pic taken from the end, right hand side of the bus of the right heat exchanger showing the connection. Notice the other thread that should secure the head exchanger intact, but the bit of metal that should be bolted to (seen at the middle of the picture, in front of the heater pipe) has lost its lower end to rust too.

4) The heater pipe has lost part of its bottom, including the appended strip that would house the bolt that secures the pipe to the heat exchanger

I've got no pictures of the left heat exchanger and pipe, but at least the pipe looks a bit better than the right one. In any case, both heat exchanger and pipe need replacing or fixing.

One issue that I see is that at least here in Europe none of the parts dealers have the heater pipe available. Heat exchangers are available as repro, but what I've heard (not experienced it myself) is that either the quality leaves a bit to be desired or that they do not produce as much heat as the originals.

Given the cost of a heat pipe, I'm not sure it makes sense to send it for repair, as probably the fix would be more expensive than getting a proper part. In any case, I don't have access to a welding kit and the part is not available, so I might have to settle for a quick and dirty fix until I can find a replacement. But given the cost of repro heat exchangers vs. quality, it might be worth trying to get them fixed, I guess.

At this point I thought I'd consult the experts for guidance :)

• Can the heat exchangers be removed from the underside of the bus without removing the motor?
• What would you recommend as a quick and dirty way to fix the untight connection between pipe and heat exchanger, until I manage to get a proper fix?
• If I were to reuse my original heat exchangers and try to remove the rust from the inside fin, has anyone attempted to take the covers apart and put them back in? Looking at a German forum, this one guy did, but he never explained if he managed to put it all back together :)
• Would someone know the part # of that bit of metal that secures the heat exchanger to the chassis, from picture #3?

UPDATE: I stumbled upon this nice writeup, which seems to hint that it's possible to remove the heat exchangers without removing the engine.

Thanks!

Thu Oct 06, 2016 3:25 am

Where you live and how you use your bus are going to have an effect on what repairs you want to do. I would recommend searching the classiffieds for a decent set of heat exchangers. I picked up a very nice set of '79 heat exchangers for $10 US at a swap meet once so it pays to spend some time searching.

furgo wrote:
• Can the heat exchangers be removed from the underside of the bus without removing the motor?

Yes but it can be a bear to do if the fasteners are badly corroded.

Quote: • What would you recommend as a quick and dirty way to fix the untight connection between pipe and heat exchanger, until I manage to get a proper fix?

The easy fix is just to block off all the holes and live without the heater booster fan, it only has an effect at idle and does almost nothing while you are cruising.

Quote: • If I were to reuse my original heat exchangers and try to remove the rust from the inside fin, has anyone attempted to take the covers apart and put them back in? Looking at a German forum, this one guy did, but he never explained if he managed to put it all back together :)

The corrosion on the aluminum fins is a non issue, but any oil inside the exchangers is going to burn off and stink like crazy for a while.

Quote: • Would someone know the part # of that bit of metal that secures the heat exchanger to the chassis, from picture #3?

If you eliminate the entire heater booster fan system then fixing all of its pieces will not be necessary. If you need additional heat in the winter over what the stock system was capable of there are ways to accomplish that that are way more effective than fixing the booster fan system.

Thu Oct 06, 2016 7:57 am

I agree that the booster fan is really not necessary to achieve good heat. But you will need to block off the holes that are left behind. For example, the round hole on the top rear of the right HE (your first photo) can be capped with the bottom of an aluminum beverage can, held in place with a bit of high-temperature RTV. Now, that's cheap! Also seal up the holes through the tin. A cheap way to do that is to use aluminum HVAC tape -- the stuff that is a thick aluminum foil with a sticky backing. That can hole up for a season or two.

Thu Oct 06, 2016 9:37 am

I found a guy who was able to fix/braze minor damage to my heat exchanger shells, particularly where they start to disintegrate close to the hot exhaust pipes. But yours look pretty far gone and I'd search around for better candidates to restore.

After the repair, I had them powder coated with a high temperature powder coat. Not "ceramic"... they guy who did mine said that he had very bad results with ceramic. It's just regular powder coat formulated for high temperature. I believe it is silicone based. Seems to be holding up very well 8,000 miles later.

Wed Jul 04, 2018 4:20 am

Whew, look at this, a year and a half has passed, and I'm slowly coming back to one of the first projects I wanted to tackle when I got the bus. Other more important bits such as fuel line replacement and ignition system refresh took priority, so nevermind that.

In any case... I finally* got some decent heat exchangers and I'm going to get to this one job soon. My plan is to:

1. Pry open the two shell halves of each heat exchanger
2. Get the tubes and the shells sandblasted
3. Fix some rusted bits on the shells that need repair. It will be my first incursion into brazing, which I had wanted to try for a while
4. Get the inside side of the shells and tubes painted
5. Reassembly shells with the insulation mats
6. Get the outside side of the shells painted

To this, I have some questions to those who've restored their heat exchangers in the past:

• Do the steps make sense? Anything I've forgotten?
• Are the insulation mats actually made of asbestos? The reason I'm asking is to know how to best handle them. In some of the other threads discussing asbestos parts (e.g. heater tube rings), there was someone who had the material tested and confirmed it. The only references I've found on the composition of the mats in this case are from a Type 3 thread, where they claimed them to be "a ceramic and fiberglass composition"
• In any case, what did you replace the worn mats with?
• Did you reuse the inner metal plates?
• How did you seal the part where the shells meet the exhaust pipes from the cylinder head? I saw some folks tack welding the circumference completely, but it seems VW originally only bothered point welding them at one location if at all.
• Which high-temp paint did you use?

Pictures of the "new" heat exchangers to follow. I'm cleaning them up a bit before taking them to get them sandblasted. They are in "ok" shape, certainly better than my original ones.

Some HE restoration threads I've found particularly useful:

• Heat exchanger repair: https://www.thesamba.com/vw/forum/viewtopic.php?t=520989
• My heat exchanger restoration project: https://www.thesamba.com/vw//forum/viewtopic.php?t=474812

(*) It's difficult to find Type 2 HEs with one-year-only square ports where I live. It's generally from reimported US busses, and when they do come up for sale, they're in not much better shape than my old ones, at an astronomical price. I also considered the new Dansk ones, but I was put off by the tales of ill fitting, and I enjoy restoring original parts anyway.

Wed Jul 04, 2018 8:13 am

There is asbestos(?) insulation inside the boxes that gets oil-soaked, and gives off toxic fumes.
Burning it or soaking it in more chemical is only going to make it worse.

Pop them apart and clean them inside like they show you how in the Bentley.
Plus, they are easier to repair that way..

http://shoptalkforums.com/viewtopic.php?f=1&t=145853&start=75

Wed Jul 04, 2018 8:53 am

Quote: Are the insulation mats actually made of asbestos?

some have asbestos and some have a fiberglass mat. Assume it is asbestos and be careful.

Sun Jul 15, 2018 6:04 am

Thanks for the previous replies. I'll go ahead with the restoration in the way I planned then.

Some progress:

Not too much time this week, but I managed to separate the outer shells for a start:

Not on the picture are the thin aluminum plates and the (asbestos?) fiber mats stuck to them, as I removed them for disposal. I'll replace the mats with a modern equivalent, and I'll redo the aluminum plates from blank stock.

The original plates could still be reusable, but I decided against it for two reasons: a) if the mat is indeed asbestos, I don't really want to mess around with it by removing it, and b) there were cuts on the plates already, caused by the ribs on the heat exchanger body.

I've seen some threads where folks have left out the plates in their restoration, but I think they also play a role as the first line of defense to protect the under-/overlying mat and ultimately the outer tin shells from friction caused by vibration. Having already gone to a non-trivial amount of effort to open them up, I think making new plates should not be too much work and should pay off in terms of durability.

The shells were not too bad when comparing them to the ones on my bus. Rust had completely eaten the metal at the usual places, but they are still in pretty good shape for 1984 heat exchangers.

The challenging part in splitting the shells was the fact that in many places they were stuck due to rust underneath the crimped fold at the outer edges. Other than cleaning up the old oil, I submerged them in a bath of citric acid to do an initial rust removal iteration. That worked well and actually dissolved most of the rust, which allowed me to simply push the fold outwards with an old chisel, without having it to bend with pliers in some places. That was quite useful, as the angle to undo the crimping around most of the perimeter of the shells is quite awkward.

Other than that, for reference, there were a few weld spots to remove before separating the shells:

• Underneath the arches where the shells meet the cylinder head exhaust pipes. Most of them were either gone or no longer welded to the pipes
• At the joint between the two exhaust pipes to the muffler. One of them was gone to rust, and the other one I could actually break by repeatedly bending the two shells with care
• One single spot on top of the crimping, on the engine side of the shells. I used a Dremel with the metal cutting wheel to remove it. It ended up much cleaner and with less material removed than a drill
• On each side where the shells join to form the rounc port that connects to the heater control boxes' pipes. That was a tricky one to do without removing too much material. I used a combination of tin cutter pliers and the Dremel with the metal cutting wheel.

Next step, sandblasting to remove the last bits of rust. The shells will still need some fixing via brazing afterwards.

I'm also considering galvanizing the shells before the high-temp paint coat, but I'll look into that when I get there.

More pictures on my gallery.

Sun Jul 15, 2018 7:02 am

Found in
Tech Tips

https://www.thesamba.com/vw/forum/viewtopic.php?p=7586322#7586322
https://www.thesamba.com/vw/forum/viewtopic.php?t=474812
https://www.thesamba.com/vw/forum/viewtopic.php?p=8126792#8126792
https://www.thesamba.com/vw/forum/viewtopic.php?p=7460628#7460628

Sun Jul 15, 2018 1:05 pm

Were you able to purchase the repair pieces I sent you the link to? They looked to be extremely well made. You may want to do some reading on galvanized metal and heat. I am sure Ray will chime in with the temperatures needed to produce the toxic gas that is emitted from the zinc in the galvanized piece. Those heater shells get hot enough that I would not even think about it. The air you are breathing from the heat comes directly from them. I had my shells ceramic coated inside and out with the aluminum chermachrome. Then the went through the tumbler to get the insides the “polished chrome” appearance for maximum heat reflection. I left the mesh and the aluminum flashing out altogether. I then re-crimped the the shells back onto the pipes and had the entire exterior recoated with a gray ceramic coating after they initial coating was re-etched. I left the mesh and foil out for a couple reasons. They will be simple to clean out in the event of an oil leak, and the ceramic coating will do a much better job of radiating heat not to mention keeping the temperature of the metal box itself cooler. My boxes and exhaust are the stock 78 set up. The entire set up was ceramic coated inside and out with the exception of the aluminum heat sinks in the boxes and the inside of the muffler.

Sun Jul 15, 2018 2:21 pm

Hoody wrote: Were you able to purchase the repair pieces I sent you the link to? They looked to be extremely well made.

I've been doing one thing at a time and haven't had much time recently, so I've not contacted the guy yet (and thanks again for the details!).

Hoody wrote: You may want to do some reading on galvanized metal and heat. I am sure Ray will chime in with the temperatures needed to produce the toxic gas that is emitted from the zinc in the galvanized piece. Those heater shells get hot enough that I would not even think about it. The air you are breathing from the heat comes directly from them.

I thought this might be the case, but not being an expert, I didn't know for certain. Doing some reading now, it seems that with zinc coating:

• Peeling of the external layer occurs at 200°C (390 F) [1]
• Zinc oxide fumes are released into the air at temperatures above 500°C (932 F) [2]. These are poisonous and known to cause metal fume fever.

Looking at the heat exchanger temperatures measured by ratwell (88 °C/190F) [3], they would seem to be well below the threshold for any of those effects.

Again, I'll stress that I'm not an expert and these figures might serve as an orientation, but can't be guaranteed to be correct. In any case, now that I know, I'd be weary of galvanizing the shells. If I were to consider it, I'd ask the galvanizer first.

Hoody wrote: I had my shells ceramic coated inside and out with the aluminum chermachrome. Then the went through the tumbler to get the insides the “polished chrome” appearance for maximum heat reflection. I left the mesh and the aluminum flashing out altogether. I then re-crimped the the shells back onto the pipes and had the entire exterior recoated with a gray ceramic coating after they initial coating was re-etched. I left the mesh and foil out for a couple reasons. They will be simple to clean out in the event of an oil leak, and the ceramic coating will do a much better job of radiating heat not to mention keeping the temperature of the metal box itself cooler. My boxes and exhaust are the stock 78 set up. The entire set up was ceramic coated inside and out with the exception of the aluminum heat sinks in the boxes and the inside of the muffler.

Excellent, thanks for the detailed description of your setup!

[1] https://galvanizeit.org/education-and-resources/re...mperatures
[2] http://onlinelibrary.wiley.com/doi/10.1002/3527600418.mb131413raue0018/pdf
[3] http://www.ratwell.com/technical/Temps.html

Mon Jul 16, 2018 5:19 am

Repaired my heat exchangers recently as well (on a 1978 bus). Some lessons I learned worth sharing:

- A MIG welder will do a much better job repairing the shells than brazing, particularly where the sheet metal meets the exhaust pipe.

-Replace the asbestos matts with fiberglass heat shielding (which usually comes with a foil facing and adhesive backed) This stuff is about the same thickness as the asbestos.

-Use pieces of disposable Aluminum Pizza or Turkey baking trays to wrap around your fiberglass heat shield. This aluminum is thick but also very malleable to conform to the contours of your heat exchanger shells.

-VHT High heat paint (in rattle cans) works very well on your heat exchangers (both the tins and the exhaust pipe). 500deg F for the Tins and 1300degF for the pipes. You will need to use your BBQ grille to cure this paint according to the instructions on the can. If you don't follow the curing procedure exactly and in the prescribed time, the paint will just rub off

-Closely check your exhaust pipes for pin holes (around where the tins attach) Mine had holes that needed welding shut, or you get exhaust fumes going into your heating air.

Mon Jul 16, 2018 10:27 am

This is excellent, thanks for the pictures and the detailed tips!

Indeed, I'm aware that welding would be better than brazing. Unfortunately I don't have access to welding equipment and after seeing the good job other folks had had with on other HE restoration threads, I had wanted an excuse/project to give brazing a go.

Mon Jul 16, 2018 12:26 pm

You will use a MIG welder for so many things, it will pay for itself in one use. A Lincoln Handy MIG that plugs into any 110V AC electrical outlet cost about $200 brand new off Amazon; add an Argon / CO2 blend gas cylinder from your local industrial gases shop for another $100. A $25 auto darkening welding helmet, $10 gloves, and a $19 Chicago Electric grinder from Harbor Freight, and you can make anything metal look like brand new. Read the manual and practice on a few pieces of scrap sheet metal and you'll be welding like a pro in 2-3 hrs; that's no joke. These things are so easy, I don't know how any bus owner can go without one :D

Mon Jul 16, 2018 12:49 pm

Cant find the pictures I took of my fiberglass insulation, but my heat exchanger tins were in excellent shape, except for the areas circled below. I just made templates out of cardboard for the repair areas and traced that onto new sheet metal, which you can cut with tin snips and bend with a hand seamer and pliers. You use the MIG welder on lowest heat setting to make a series of spot welds (each about the size of a BB) until you have the new metal completely joined, then just grind down the welds, and you have a nearly invisible repair.

The very best thing about replacing the asbestos is that your heat will no longer smell like a VW; in fact, you'll be absolutely amazed that heat will smell just like any water cooled car.

Mon Jul 16, 2018 1:46 pm

69BahamaYellow wrote: You will use a MIG welder for so many things, it will pay for itself in one use. A Lincoln Handy MIG that plugs into any 110V AC electrical outlet cost about $200 brand new off Amazon; add an Argon / CO2 blend gas cylinder from your local industrial gases shop for another $100. A $25 auto darkening welding helmet, $10 gloves, and a $19 Chicago Electric grinder from Harbor Freight, and you can make anything metal look like brand new. Read the manual and practice on a few pieces of scrap sheet metal and you'll be welding like a pro in 2-3 hrs; that's no joke. These things are so easy, I don't know how any bus owner can go without one :D

Oh, believe me, I'd love to get started on welding! Not as much for big jobs, which so far I've left to the pros (and would continue to do so), but rather for small projects like this one.

In my personal case it's not about the cost, it's mostly about not having the workshop space to work with high heat, and... currently time :).

Btw, really good job with your fixed heat exchangers.

Mon Jul 16, 2018 2:05 pm

They make laser cut new flanges identical to the originals. Based on that last picture you posted of where the flanges are bolted together you may want to consider buying new ones and mig welding them on your restored boxes. Maybe it’s just shadowing but it looks as though there is virtually nothing left of the flange. Almost looks like multiple gaskets were sandwiched together with rtv.

Tue Jul 17, 2018 6:01 am

Hoody wrote: They make laser cut new flanges identical to the originals. Based on that last picture you posted of where the flanges are bolted together you may want to consider buying new ones and mig welding them on your restored boxes. Maybe it’s just shadowing but it looks as though there is virtually nothing left of the flange. Almost looks like multiple gaskets were sandwiched together with rtv.

Yep, those flanges are rusted to pieces, but they don't leak and they've been like that for years, so I decided to not touch them. What looks like multiple gaskets and RTV is actually just the original 40 yr old, very swollen and rusty laminated gasket. One day, I may need to cut those off and weld on replacements. Do you have a source for those laser cut flanges you referenced? I could make some, but pre-made would be much easier :D

Tue Jul 17, 2018 7:35 am

Yes, the exact best ones that I have seen are from German Supply. Email
Scott and ask him if he has them in stock. PayPal him and you will be good to go. I have never had any issues with doing business with Scott. Many times stuff gets tied up in customs. Hope this helps.

Tue Jul 17, 2018 7:45 am

If you are good a welding you can just build both sides of the flanges back up and then grind the surface that mates to the gasket back flat. Using SS wire will prevent the flange from thinning in the future.