Banjo 3 Flange Fittings

[Ulrike Dweck]

Note: Sprayer dealer in town, has mostly bare shelves = he is waiting till closer to Spring to order fittings = thus, I will probably ordering over the internet, so I can get stuff done.

Just got back from a hardware store that handles a few Banjo fittings, some 200 and some 220 series = nice to see the difference and the flange size difference, plus they will have a few seals available, if there is a leaker, during the season, if I was to misplace any spares, that I will order.

Hi everyone! I'm currently going through the turbo kit that I received for my NB Miata. The turbo itself is a chinese turbo, so of course the oil fittings that came with it are as well. The oil feed that goes on the turbo is a flange fitting. From my very quick research I just did, it seems that there are a lot of people who say the flange fittings leak severely and can cause oil starvation, and they recommend using a regular fitting instead (is that what they're called? New to this).

Now I know its a cheap turbo but I really don't want the turbo blowing on the dyno while its at the tuner. So I just wanted to come here for some insight; is it better that I buy a true fitting for the turbo, or will I be fine using the flange fitting? I'm not sure what other factors go into deciding which to use, so I can provide additional information if needed.

Thanks! I guess I could try grooving for the O-ring...I just know I will mess it up if I try and it will leak anyway. Are oil restrictors usually all the same size, or are there different sizes? I have no idea what size the restrictor hole is for this flange fitting, since I didn't get any kind of specs on that. I do know that the turbo is a replica of a Garrett T3.

Gotcha, thank you! Do you thread the fitting in with some high temp thread sealant on it? I'm not sure how hot that part of the turbo system gets, but I was thinking that it would be a good idea to use that on the fitting for the oil feed.

Thanks! I don't know how different the FM supplied turbos are to a chinese T3 (besides the obvious quality differences), but I contacted the kit manufacturer (hes a one man shop, might be able to guess who it is) and he said he hasn't ever had a problem or heard of one with the flange. I could just get a fitting and be done with it, just not sure what the restrictor size is.

Got it, thank you! I didn't know what kind of pressures there are at different points, so thats good to know. Yeah, I figure the restrictor was included in the flange for a reason, so might as well run with it. Hopefully it all goes well.

So after thinking if over for awhile, I may just buy a fitting rather than the flange. Going to buy a .035 and compare it to the opening on the flange. When looking at restrictors though, I saw two different types:

Besides the price, is there a difference in the performance of the two, or does it not really matter which end the restrictor is on? My flange type has the larger opening on the AN side and then the small restrictor opening on the flat flange surface.

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ARCHIVED TOPIC: Fitting new RK 10 11/16" flange to '68 RB-250?

Please note this is an archived topic, so it is locked and unable to be replied to. You may, however, start a new topic and refer to this topic with a link:

The RK parts fit together like a glove. The rim has two ledges on its circumference each lathe cut at 90* to the side of the rim. The RK flange has matching machine cuts allowing the flange to fit over both of them in a very precision way. All is good here, i.e. perfect fit.

Both Gibson rims, and every prewar Gibson I've had, have a ledge cut at 90* to the rim side and then a flared out section just above the ledge. For a flange to fit the Gibson rims I've had, including these two, the top inside surface of the flange must flare out to match this flared out increased diameter of the rim just above the 90* ledge.

Since I can't seem to get my hands on a Gibson brand (one with a Gibson logo on it) flange I bought a Prucha flange (10 13/16th"), which fits over the bottom of my '29 rim snuggly and then hand cut the flare in the top surface of it so it pulls up about 1/4" more allowing the 90* ledge of the rim to contact the 90* matching ledge of the flange. That set-up now fits quite well. If I hadn't slightly opened up the top of the flange with a flare out so the flange would pull up to the proper position on the rim, the 90* ledges would have remained about 1/4" apart in an un-seated condition.

'68 RB-250: This rim also has the tapered/flared surface above the 90* ledge. I just received a 10 11/16th" RK flange for it (the correct size) and now must decide whether to alter the flange with a flare at the top allowing it to pull up properly and allowing the 90* ledges to engage or, on my DIY router table, cut the Gibson rim so it looks like my RK rim and so the flange and rim mate up.

None of my rims (none of which are Gibson) flare out in the way you describe. I've certainly seen cross-section drawings showing that the band between flange tone ring skirt starts out at less than 11 inches .o.d. inside the bead area of the flange, ending up at 11 inches where it butts up against and aligns with the tone ring skirt.

In fact, since the top of the flange is typically a hair under 11 inches inner diameter, I think people turned rims so that the top part of the flange goes ever-so-slightly under the uppermost ledge at the same time as the lower/inner step of the flange -- the part with the 10-11/16, 10-13/16, 10-3/4 or other inside diamter -- engages the lower ledge. Sort of the same type of accuracy that results in the tone ring hitting both the top inner edge of the rim and top outer band of the rim at the same time.

I think the "flair" the OP is referring to is the machining of the "bead" of wood below the tonering/flange cut. There have been rims that have this bead cut so that it bevels from narrower at the bottom, to wider at the top. As the flange is pulled up by tightening, it is forced against this wideneing.

This was a rim machining that Gibson actually used, I think during the mid to late 80s and I've seen it used on other rims. The cross sectional pic that Ken posted shows this outward bevel/ "flair". The flange will have the groove machined at an angle to fit this upward bevel, verses a "straight" ledge as shown in the second cross section. The first cross section shows how the bead is tapered outwards at about 20 degrees or so. The drawing below that show a "straight" 90 degrees machining for the flange to rest upon.

No apologies needed but I appreciate that others chimed in to prove that I am not totally crazy about this flared out rim, and corresponding flange shape on OPF Gibsons. Since no other banjo makers I know of do this I expect it's a hold over from Gibson tube and plate where in the tighter you torqued the head down the tighter the tube squeezed in against the rim.

Hand cutting the top of a non Gibson flange (RK, Prucha, etc.) to fit a Gibson rim does not make for a very precision fit where the flare is but it does allow a full seating of the flange on the 90* ledge which, without altering the flange, would not occurr. So, I will have to live with the less than precision fit on my , '29 as I don't want to alter that rim. The '68 rim I may cut on my router table to properly fit the RK flange...undecided for now.

I've never seen a one-piece-flange banjo with the wood band extending so far outside the tone ring. I don't know if that aspect of the drawing is accurate. I would think it makes more sense to modify your rim to fit a modern flange, since it seems no flanges are made with an inner wall angled to the degree that you need.

I think both cross sections that I posted (from Bill Palmer's site) are inaccurate in regards to the geometry of a typical one-piece flange. It's my understanding -- mainly from reading the specs of flanges for sale and measuring the very few that I've owned -- that the inner diameter at the top of the flange bead is at or just hair under 11 inches. This would impy that even if the band were tapered in the area inside the flange, it would have to straighten up to vertical so it could align with the tone ring.

This is all academic and just a mental exercise for me. I'm into non-Gibson 1-piece flanges or Gibson spec flange tubes for potential future projects. Two years ago, I replaced the Gibson-style RK flange on my most recent project with a flange from a 1970s Kasuga banjo. The inner diameter was only 10-5/8, so I had the lower step milled away, leaving a flush walled interior with an i.d. of about 10-3/4. So the way the flange fits now is the top of the bead simply slams up against the bottom of the band (the 90-degree cut that 1xsculler refers to). The rim was originally turned for a 10-13/16 flange. The modified flange went on with a push, but it did go on. Deering 1-piece flanges fit this way. Makes so much sense.

Stepped flanges can be modified to fit this way by adding a metal bar on top of the step. Transforms the inner wall to a flush surface. Hangout member Razorback did that to changeout the Deering flange on his Sierra to a Gibson-style flange.

It's a bit ironic that the Prucha flange sold by Stew-Mac doesn't actually taper inside to match up with a rim turned as shown in their own drawing. I'm guessing the inside wall of the bead area of the flange doesn't actually need to taper like that. Seems to me the only thin that matters is that the topmost edge of the flange (the highest point of its inner diameter) gets stopped by the wood band at the same time as the lower step of the flange gets stopped by the ledge that it's supposed to butt against.

That's why I think scraping or sanding the rim a bit is a better way to adjust the fit than filing or milling out the inside of the flange to give it a taper. I suppose a skilled person could put the rim on a lather.

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