Author Topic: B40 Star air filter - what's the best option now  (Read 2030 times)

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AWJDThumper

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Re: B40 Star air filter - what's the best option now
« Reply #15 on: 17 February, 2018, 09:08:43 »
The earlier B40's used the same carb size as the C15 and were able to use the same filter arrangement and connecting rubber hose. However, in 1962, they changed to a larger carb and at that point had to change how it connected to the filter - connection by rubber hose was no longer possible. Instead, they used a metal adaptor screwed on to the end of the carb which projected through the rear panel to the separate filter. My B40 is from 1965 and uses this arrangement. If the filter was still attached to the rear panel as per C15, it's difficult to see how the adaptor could be fitted. The parts book from 1965 is simply wrong and shows the much earlier rear panel and filter arrangement pertaining to 1960/1961.

I can't remember where my filter came from when I restored my B40. However, if you are careful, you can detach the filter from a C15/ early B40 rear panel and use that as a separate filter to plug into a suitable adaptor for you carb.


AWJDThumper

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Re: B40 Star air filter - what's the best option now
« Reply #16 on: 17 February, 2018, 12:06:08 »
I was wrong about the change in carb size for the B40 - I was looking at incorrect data. They all used a larger carb than the C15. I was convinced that was the reason for the switch from the earlier C15-like use of rubber hose and attached filter to the later metal adaptor and separate filter.

One way of checking whether a B40 originally had an attached filter (which may have become attached) might be to measure the size of the hole in the back panel. If the filter was originally attached, the hole would have been 1 1/5" in diameter. If it was designed for the metal adaptor it would have had a diameter of at least 1 7/8".

Phil C

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Re: B40 Star air filter - what's the best option now
« Reply #17 on: 17 February, 2018, 16:52:31 »
My 1965 B40 filter appears to be attached to the carb by a rubber hose which pokes through a hole into the side panel. The filter housing appears to be rammed in hard against the frame, which makes me wonder if the hose is a bit too long. I guess I'll find out soon when I try to get the filter out to clean it.   Phil (novice)

hoogerbooger

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Re: B40 Star air filter - what's the best option now
« Reply #18 on: 19 February, 2018, 16:46:32 »
I have an air filter now (pic attached) .... but looks like it's not as originally fitted. I have a 1965 B40F and the aperture through to the tool box is indeed 1 7/8 inches. So looks like it never had an attached air filter originally & it was the separate type .

So need to consider if I can use what I have & how. The outlet from the air filter is 1 1/2 inches (38mm) The protruding part of the outlet tube extends only about 5mm from the tool box plate.  Not much to clamp against. The concentric carb inlet is 43mm threaded.  So how did the rubber connector work ? It must have gone over the carb inlet but did it did it go over or within the air filter outlet ? Was it jammed in or over or were clips used to hold in place ( none shown on parts diagrams)

If  the same arrangement was used on earlier B40's and C15's I'm presuming I have something that can be used and allow enough air flow .....If I work out how it should be fitted ?


(may be easier to detach  and use as a separate if I can borrow a dremel)

Phil C

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Re: B40 Star air filter - what's the best option now
« Reply #19 on: 19 February, 2018, 18:53:29 »
Mine (1965 B40F) appears to be a hose (1 and 7/8 o/d) fixed to both the concentric carb and filter by jubilee clips. The filter I think is separate from the side panel but sits inside it. I'll soon be trying to get the filter off (next few weeks), which might be an issue as it seems to be rammed in pretty hard against the frame inside the side panel, making me wonder if the hose is too long.  But then I know pretty much nothing.    Phil (novice.)

AdrianS

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Re: B40 Star air filter - what's the best option now
« Reply #20 on: 19 February, 2018, 18:54:06 »
Thats the same as my 1961 B40. I've got the monobloc carb.
I am missing the rubber seal that looks present on  you filter.
I still wonder how effective the filter is though as the pipe from the carb to the filter housing I don't feel is a very good fit.
Also a lot of British bikes had no air filters fitted. Often a chrome ring or trumpet with a wire gauze inside was fitted to the carb.
The problem with running no filter is that the bike probably will be running lean.

AWJDThumper

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Re: B40 Star air filter - what's the best option now
« Reply #21 on: 20 February, 2018, 11:06:14 »
hoogerbooger. The ideal solution would be to acquire a suitable metal adaptor tube which pushes through the hole from the back of the rear panel and then screws on to the end of the carb. The filter would then be a push fit into the end of the adaptor. When I got my B40, I had to machine up a suitable adaptor for the filter.

The proper filter has a 10 mm flange on it relative to the 5 mm flange on the attached type of filter - however, the latter is still sufficient for the metal adaptor. As an alternative, I would be tempted to use a suitable length of rubber or plastic tube which can be held on to the end of the carb with a Jubilee clip and then glue or expoxy the filter into the other end. Of course, you would need to remove the filter from the rear panel you have which is held on by 3 thin welds if similar to mine. I would use a cutting disk on a Dremel to cut through the welds.


hoogerbooger

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Re: B40 Star air filter - what's the best option now
« Reply #22 on: 20 February, 2018, 22:00:17 »
Blimey 3 blobs of braze can be tenacious. One hour with a small file and junior hack saw later  & I have the attached .....now with 10mm of outlet to attach to. ( no dremel available unfortunately)

AWJDThumper: Thank you for both suggestions which look sound. I will investigate both.

I presume it would also be sensible to see if I can fabricate an equivalent to the gauze cover ?  Looks like it was 50% metal 50% perforation. I'm guessing if I do that so that the air filter is as close as possible to the original set-up....... then I can probably use the the 'original main jet size of 140



AWJDThumper

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Re: B40 Star air filter - what's the best option now
« Reply #23 on: 20 February, 2018, 22:47:55 »
I'll post a picture of the perforated end cap. I thought I had a spare but it turned out the one that was missing from my B40 filter!

AWJDThumper

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Re: B40 Star air filter - what's the best option now
« Reply #24 on: 21 February, 2018, 05:13:06 »
On reflection, I think the perforated, concave end cover is completely unnecessary and is just an piece of over engineering by BSA. You need to ask yourself what the filter is designed to keep out of the engine with the main concern being abrasive dust. In that regard, the perforated plate plays absolutely no role in keeping out the dust (that's the job of the inner filter) and, at most, will filter out larger particles which the inner filter will do anyway. So unless you are restoring the B40 to factory spec (like I did), I would not worry about the perforated plate.

AdrianS

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Re: B40 Star air filter - what's the best option now
« Reply #25 on: 21 February, 2018, 11:28:13 »
The filter hasn't been put in back to front has it? It looks like the perforated gauze may be resting against the filter housing plate!

hoogerbooger

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Re: B40 Star air filter - what's the best option now
« Reply #26 on: 21 February, 2018, 16:45:48 »
no I just have the actual air filter wire gauze and not the perforated metal concave gauze cover ( photo attached from some American site of whatI don't have  & that's a copy) But  sounds like that can catch up later.

I've just checked on the standard air hose part 40-7835. Apparently it measures approx 44mm OD and 35mm ID. Whereas the concentric inlet is 43mm and air filter outlet is 39mm. Anyone know if this hose is likely to be flexible enough to go over 43mm. ( heat it up in boiling water first ?) 

( for info I measured wrong before,  in that the aperture in the tool box for the hose to go through is actually 2" (50mm))

( My 1965 B40F is not fully original spec with some B25 and other parts, but I'm trying to keep it looking in the right ball park - photo attached for other B40F owners interest)

AWJDThumper

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Re: B40 Star air filter - what's the best option now
« Reply #27 on: 21 February, 2018, 17:24:02 »
The first picture shows the standard C15 inlet hose fitted over the outlet from my B40 filter - the hose stretches easily. The second picture shows my filter with the corrugated plate now fitted.

MelC

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Re: B40 Star air filter - what's the best option now
« Reply #28 on: 01 March, 2018, 14:25:38 »
This is my setup as I could never source the correct air filter for a 1961 B40.
I will continue  the quest at autojumbles but don't hold out much hope.

MelC

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Re: B40 Star air filter - what's the best option now
« Reply #29 on: 01 March, 2018, 14:56:23 »
Unfortunately the photo is too large, but the setup comprises of the standard rubber tube to the filter inlet.
then a conical air filter on the inside stub. As its hidden by the tool box cover it will do until the genuine article can be found.