Heater Control Box Meltdown

[frankc]

I removed my heater control boxes to have them powder coated along with some other parts, and upon dis-assembly noticed that the butterfly valve in one of them has melted (see photo) - the other one was fine. Obviously the materials used was different between the two (I replaced the boxes many years ago), with the black material being inferior.

PET shows that the valve part can be ordered separately (and it appears to still be available), but all that is really needed is to drill out the rivets and replace the melted sandwiched material with something a little more heat resistant. Any suggestions?

[Cooper911SC]

Wow that's interesting! Wonder if the original material has asbestos in it?

Can't think of any heat resistant material, but here's a bump for help.

Cooper

[ILXLR8]

My question would be not how to repair the heater valve, but rather, what is making the exhaust so hot on one side? Exhaust valves on one side of the engine not closing, or valve guide issue?

[GH85Carrera]

The heaters on air cooled Porsches can blow some very hot air. On my 914 I used to drive in the winter on a clear day with the roof off and the heaters cranking. After 30 or 40 minutes the plastic air diverters by my feet would get soft. They never completely melted but they were deformed.

A few months ago I was in my 911 driving in 0-F weather at 75 MPH. That is the first time ever for me that I had both heater levers all the way open for more than a few minutes. After about 90 minutes of driving the heater vents were pretty warm.

[ILXLR8]

I never saw this type of meltdown in any of my 914's or 76-88 911's in the past. Most had SS exchangers that were in good shape. All driven daily in Chicago winters over a 15 year period.

I have smelled my shoes many times, but never other flapper box meltdown.

[frankc]

I am running SSIs on a 2.7 w/Webers & 8.5:1 CR (RS P&Cs), so I don't think that I would be generating that much heat, and I would expect less heat than some of the higher output motors.

Given the obvious different material used (even the galvanizing on the plates is different), I suspect different suppliers were used, with one using material not suitable for the application.

If the part were $10 or $20, I wouldn't waste my time and just order a new one - but at $50, I begin to search for alternative solutions that would yield as good or better results and cost only a few dollars.

If I find that I'm investing too much time or money trying to save $50, then I'll just buy the part. If it was NLA, then that's a different story. Actually, I don't know for certain that the part is still available - I'm just going on the fact that Pelican has a price listed instead of NLA, which is not always an accurate indication as I have found.

[frankc]

Originally Posted by ILXLR8

My question would be not how to repair the heater valve, but rather, what is making the exhaust so hot on one side? Exhaust valves on one side of the engine not closing, or valve guide issue?

The heads were reworked about 20K miles ago (new valves, guides, etc.), so I would not expect any issues there.

[r-mm]

I recently tore mine down and they looked like the non melted one. Gasket material was white. If you go to mcmaster carr you can search plastics by operational temp. Those that go up to high 200 maybe 300 f are very expensive even for letter sized sheets. If the oem part is at all affordable, get it.

Really wonder if someone hacked the black one or if it was an inferior oem supplier...

[r-mm]

Just noticd the price of the oem part. You can def. get some very high temp plastics from mcmaster under fifty bucks.

[Jeff Burger]

Hello Frank,

There are plenty of those original ones that rusted to death you should be able to buy one cheap and use the unmelted control plate from it.

[frankc]

I may have found a suitable material - Teflon sheet. Working temps up to 500F. The products I've seen look very much like the white gasket material in my photo. Here's an example:

2 Pcs x Teflon PTFE 150mm x 200mm x 1mm Thick Polytetrafluoroethylene Sheet | eBay

[Tom_in_NH]

Frank,

Give the hi-temp silicone sheet material a look at McMaster-Carr:

McMaster-Carr

Tom

[frankc]

Tom,
Thanks for the silicone sheet suggestion. Temperature range to +400F, so a little less than the Teflon. Is 400F cutting it close for this application?

McMaster-Carr


I also noticed that McMaster sells the Teflon sheets for a few dollars more:

McMaster-Carr

I plan to just go ahead and order the Teflon sheet after I get home and measure the thickness of the original white gasket. I'll post back here how things turn out.

[frankc]

Update: I measured the thickness of the white gasket material - it is 1mm. So I ordered a 6" x 6" sheet of the .039" white Teflon from McMaster - $8.11 plus shipping.

[frankc]

Another update: I received the Teflon sheet from McMaster and performed the repair using 3mm aluminum rivets. I'm pleased with the results.

Part number for Teflon sheeting:


Melted butterfly valve material:


New material cut to shape:


Repaired (left) Vs. original (right):

[Cooper911SC]

Thanks for the update frankc!
Nice to know there is a reasonable DIY fix.

Cooper

[Ferrino]

Frank, I am currently restoring my flapper boxes and want to have those valves re-plated. Can I please ask what style of rivet you used to re-fasten the plastic to the metal? I am only familiar with the pop-rivets that leave a large "blob" of deformed metal on the backside. These look almost flush, like the factory ones. Thanks.

[frankc]

Ferrino,

Sorry for the delay in responding. I used a standard 3mm (1/8") aluminum pop-rivet, and then after installation, I tapped down the side shown in the picture so that it was a little flatter than normal. Hopefully that answers your question.

[Ferrino]

Excellent - thanks!