The Stovebolt Site Forums The Shop Area Engine Shop the Rochester "B" still has the drip

Little did they know!
Just about the time I think I might have the ‘B’ reliable enough so I can drive it, something new pops up. While doing all the work on my original ‘B’ one of the problems that surfaced was the 1/8” npt inlet thread. From decades of people installing brass fittings in and out of the thread and retightening it a little more each time, the thread has gotten deeper and deeper to the point now, that I’ve inharited it, a new fitting is just about bottomed out. I would have liked to take it one more turn but I would have run out of thread on the new fitting that I was using. So, I tried sealing the threads with Permatex #2B non-hardening sealer.
http://rides.webshots.com/photo/2418709310098611668MRDBui
http://rides.webshots.com/photo/2900381040098611668fmjEQz

One hundred miles down the road I noticed a little dampness around the threads and a few more and it turned to a drip and now when I shut her down, I can see it bubbling out and running down till the line is empty, apparently it’s washed the thread sealer out. Now I’ve got a Fire just waiting to happen!
So, any one got any ideas for sealing it up? Other than that she runs great.
Denny Graham
Sandwich, IL

Use a small copper crush washer betwen the fitting and fuel bowl,available at your local hardware store.I don't like any sealer on a carb.

Denny - on a numbers-matching show vehicle, I would advocate machining a new fitting with slightly oversize threads.

While the product advertising may indicate otherwise, after almost 50 years of working on carbs, I can recommend NO sealer; AND RECOMMEND NOT using any sealer around fuel.

Jon.

69', we talkin' npt here not straight threads.

I wouldn't argue with ya on that one Jon, I didn't like using the little dab of Permatex as a thread sealer but was kind of out of ideas and I didn't have another full turn left. My thinking was kind of stuck in one direction, that being, making the female threads smaller, never even thought of making the male thread bigger.
It could be a little bit of a hassle because I need to keep the elbow in there to fit the fuel filter in and I also want clearance at the horn. I suppose I could machine a new oversize 1/8 x 1/8 female x male adaptor that would only push it out from the carb another 1/2" or so.
An over size f/m elbow would be the ideal fix but that's an impossibility because I have been trying for a year to figure out how to produce the inverted flare. After having to spring for a couple hundred dollars worth of new fitting while doing the brake job, I wanted to make my own fittings, since I’ve got a Bridgeport and lathes and know how to use them no-less. I couldn't find any pre-made tooling to machine the flare, with.
Any way you look at it I'll have to add an extra fitting at that point. I need to think about this one a little more now that I have some "food for thought".
Thanks for the redirection, I guess that's why you’re the "carbking".
Denny Graham
Sandwich, IL

here ya go web page

Can't disagree with the king, who helped me many times with my carbs in the past.
However, I always enjoy and learn the most from safe experimentation and found this fuel resistant 2 part epoxy sealer that has worked for me for many years:

I have used Loctite Weld compound from the parts store with excellent results on both my Carter W-1s sealing the worn input threads. See my 235 link.
It's my daily driver and the seals hold up nicely at 200* and hours of freeway driving.
On this 235 I also use compression fittings, rather than flared, which would be arguably better, as in safer.

Also used the same Loctite Weld many years ago to patch a small hole on a gas tank - it didn't leak until I replaced it 6 years later after daily use.
Another great use is to seal the bottom plugs on the offy intakes.

Maybe not the most elegant nor professional solutions, but it all works for me safely without any leaks.

Denny - the thread for the various size inverted flare should be a tubing thread, and a tap should be available (at least they were when we ground our tooling for flares years ago). If not locally, try J & L Industrial Supply.

Start with an end mill the proper size for the thread, and grind out the center of the cutting end to cut the flare.

Now grind out the center of the appropriate taps (you will need a plug tap and a bottom tap) so they do not disturb the flare.

We had to fabricate these tools in order to do "number maching" factory multiple carb restorations. Many of the fittings on the factory multiple carb set-ups are absolutely unique.

Sometimes one simply has to look "outside the box" to repair something.

Anything that has been made by man CAN be made again by man. The important criteria often is the cost.

Jon.

Taint had time to digest the last two replies, look at them later. In the mean time I got her goin real nice and purty.

Thanks again for the idea Jon, I took it to the shop today and turned up an adaptor, put new brass fittings and a fresh 90° short fuel line from the filter. Leak, gone! At least it wasn’t leaking after a five-mile run. One of the things that has really concerned me is splitting the air horn where the inlet boss is located. A taper can exert a lot of pressure and I was afraid that it may have had a very small hairline split that I couldn’t see but that opened up when the fitting was tightened. I’m sure I’m not the first one that has run into this sort of problem. If any one cares to see I posted a couple of pictures.
This was the problem every time I would shut her down:
http://rides.webshots.com/photo/2366801090098611668EbYpHb
I’m machining the new oversize 1/8”npt adaptor here:
http://rides.webshots.com/photo/2180753650098611668ncXdXe
This shows the weak boss on the air horn and a close up of the new adaptor:
http://rides.webshots.com/photo/2819454540098611668BmAmCM
Installing the oversized adaptor and new fuel line and fitting here:
http://rides.webshots.com/photo/2773827560098611668RBMCRp

So hopefully this ‘B’ has a few more miles in her.

Denny Graham
Sandwich, IL

Denny - the use of Teflon (either tape or paste) has cracked TONS of airhorns. Glad yours is OK.

Jon.

Yep, teflon tape can fool ya into thinking a tapered fitting isn't tight and that last turn can split the female thread. All of the Rochester 'B' inlets were poorly designed, even though they beefed up the cross section of the air horn a bunch they didn't increase the wall thickness on the inlet boss. I'll bet there are a lot of them out there that have problems in this area.
Thanks for the discription of the tooling for the flairs. I bought a tap a while back for the 1/4" brake lines, the nuts are a 7/16-24 NS. A "national special" botton tap makes it a pretty pricy tap so I was a little reluctant to start grinding on it. Where I used to work the machine shop forman told me to bring it in and he could relieve it in the center with their EDM. I was going to grind a single flute tool from drill rod for the flair but never could find the standards to get the correct dimensions.
Well, one extra fitting and I'm back in business with a nice clean fix.
Thanks again.
Denny Graham
Sandwich, IL

Denny,Looks like a job well done.Even with NPT,I would have put a copper crush washer on it since it was almost bottomed out to the airhorn.

Looking through some web pictures, I ran across this picture, hope the owner doesn’t mind my using his picture as another example of the Rochester “B” plague.
I brought my feelings about this up to Jon a couple of weeks ago, that I felt that this enlarging of the 1/8” npt inlet was probably fairly common. Here you can see the forensic evidence of another over sized thread and the fitting having been screwed in all the way and still leaking.
http://rides.webshots.com/photo/2982051020098611668iRtRxw
This problem could be cured with Jon’s idea of an over size male thread on the fitting.
Denny Graham
Sandwich, IL

Denny Graham,

Is the fuel filter pictured in the very first post on backwards, or does fuel flow from the Rochester to the tank?

Stuart

By reversing the flow, there is no way for dirt to get into the carb.
Boy Stu, and you have the nerve to call me a nit picker!
Yep, you got it right, your about the only guy that would have noticed that. Got so caught up with the “B”s problems I must not have been paying attention when I plumbed it in. She’s been running for almost 300 miles now like that and it doesn’t seem to make any deference. However, I will be swapping ends real soon, thanks for pointing that out.
Denny Graham
Sandwich, IL