PRG366EH07 snapped surface burner orifice holder

[RAB_LAC]

Hi there, I'm a brand new member and haven't poked around the forums much yet, so I apologize in advance if my etiquette is poor and I welcome all suggestions for improvement.

I caused myself a pretty straightforward problem today. For background: We had warranty service on our Thermador range years ago, and I watched the technician unscrew the venturi tubes from the brass burner bases to remove the drip tray to replace the main control board.

What happened today: The wife has been wanting to give the drip trays a good cleaning for a long time, so while I was dealing with another issue, I decided to remove the drip trays for a good soaking. I got one of the venturi tubes unscrewed with considerable effort, but on the second one, I ended up breaking the orifice (or jet) holder that it screws into. It looks like I'll need to get a different drip tray off in order to secure the broken holder and get the venturi tube off to replace it, but all the venturi tubes feel pretty seized and I'm worried about breaking more of them.

It looks like all the replacement parts I need are pretty easily available, so I think I just need advice for removing the venturi tubes safely. They just backed out without any problem for the service tech I watched, so I'm guessing the years of heat cycling have caused some corrosion buildup on the threads. Anyone have suggestions other than soaking them in penetrating oil for days?

[johntech]

You could try soaking them with pb blaster for a while but when the screws expand they will normally break during removal.  I would not take the unit apart unless necessary and plan on replacing parts when they do break. 

[vee8power]

He's committed to taking it apart now; there's a broken orifice holder and possibly a broken gas line under there.

If they feel seized together, drill the venturi tubes out as LI-NY suggests in the following post. That way, you'll still be replacing all the venturis and holders, but you'll save the tubes.

 

[certified tech group 51]

try this...dremel tool with a 1/2 cutter..........................................Cut from the inside out......Cut both tops off of the "Jet Holder"....Just below the nut........remove the drip tray...remove the damaged  jet holders.....New nuts P/N 188978..Order the  correct orifice holder by location, new jet holder has a new orifice of the correct size.......

[RAB_LAC]

Okay, I appreciate the advice, everyone. Thanks much for the diagram, too, CTG51. I was wondering about anti-seize. I'll consider this my painful lesson learned.

[RAB_LAC]

Well, I got the broken jet holder off with a dremel tool, and sure enough I ended up breaking the gas supply tubes to three burners yesterday. Only two of the tubes are showing as available through Sears and RepairClinic, and it seems like a good repair shop would probably be able to make replacements. Has anyone had gas supply tubes made to order? Is there anything I should beware of if I investigate this option?

[Aapltech]

On some of our units that used to Ventura tube style this is very very common for sure a tube is a brass tube screwed into another metal. The two overtime weld them selves together. If welded the only way to service/access the ignitors is to use the step bit and drill out the top of the Venturi tube. And doing that you can save the burner base and you must replace the jet holder with a new jet holder and orifice. When you going back together with the new Venturi I always Add a good  dab of anti-seize compound and that alleviates the problem in the future

[RAB_LAC]

Here's a quick update on the still-in-progress fix. The Venturi tube and replacement jet holder are in transit and I found replacement aluminum tubing (5/16" diameter took some digging). I tried following the suggestion of a couple old hands to use a brass compression fitting in place of the bead put on the factory tubes, but I didn't achieve a seal before I backed off for fear of snapping the jet holders by applying too much torque on the compression nut while tightening it down (see picture):

Original tube bead, compression fitting, and broken jet holder

I found some Delrin compression inserts, but decided to see how hot the fittings and tubes could get before I went that route. After about ten minutes, the fitting was too hot to touch, so I decided not to risk melting the polymer (which is only good to 350F). It turns out that GM used this type of tubing seal on fuel lines, and I found a number of auto repair forum posts discussing the use of a double flare (or bubble flare) in place of the bead in that application. Unfortunately none of the local shops I've visited so far have been willing or able to put the flare on the tubes for me, and I have yet to find a local who even recognizes the bead!

The current plan is to contact Graham Tool next week and see if I can get my hands on the proper tool to recreate the factory bead:

Graham Tool small tube beading tool

Even with the cost of the tool, I'm still looking at saving about $100 versus buying all the tubes premade (if they were all even available).

I'm rather disappointed I've had so little luck finding a repair shop with even a decent flaring tool, much less a tube beader. I've talked to about a dozen places and followed every follow-up recommendation I've gotten. The tube diameter and bead do seem to be somewhat exotic, but I would have expected to find a local Samurai who can do anything by now.

[lvasquez11]

Google  11-293 robertshaw pilot tubing.

[RAB_LAC]

That part number gets quarter-inch tubing. That and 3/8-inch are much more common than 5/16-inch. Googling 5/16 aluminum tubing will return plenty of sources, though. The tougher thing to find is the means to put a bead on the properly sized and bent tube.

The advice I got was to use a brass ferrule with a compression nut and leave the tubing straight. The ferrule must seal two surfaces in order to completely seal: it must shrink its inner diameter to seal against the aluminum tube, and it must also compress its beveled edge against the flange face of the jet holder. That flange face is not machined and polished like it is on a brass fitting, and I'm pretty sure that's where it was leaking when I tried it. The aluminum tubing is clearly much softer than the brass ferrule. The bead also eliminates the need to form a second seal.

The other option would be to try either a double flare or bubble flare. The difference between those and a bead in this application appears to be that the short length of straight tubing after the bead helps maintain alignment of the sealing surface, so even as the length of tubing expands and contracts, the flange face will experience less torque. I can only speculate how necessary this property is; since there is little difference in price between a good-quality flaring tool and the beading tool I found, and I don't expect to need either tool regularly in the future, I figure I might as well go with the factory method.