The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: groily on 18.03. 2008 11:22
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Part of my excuse for not fitting a new sump plate with magnetic drain plug was I was waiting till the next oil change, but a bigger part of it I was a fearful of what I'd find in the thread department. So the last but one oil change went without the new bits going on, but today I thought I'd just get on with it. Although the 4 studs all seemed tight when the plate was off last time and the time before, having three whitworth and one BSF nut on what should have been, I imagine, studs threaded whitworth into the crankcases and cycle or bsf for the nuts, was what had caused me to pause. As those who have fitted the upgraded sump plate kit will recall, the dimensions are such that the original studs are too short and have to be replaced. The SRM kit comes with allen screws (which I don't like in these applications one little bit) but they are at least long enough to do the job, and if one had the engine on the bench one could sort out anything nasty . . . Anyway, typically enough, one horrible thread was revealed . . . So a longer stud and Loctite threadlocker and washer and nut and lock-nut went in after all, after a plug tap to clean it all up as best I could from underneath. It's OK, but not ideal and is one more job for when the motor has to come apart - but I bet there are many among us who have found the same thing. I was seriously thinking about ways of modifying the mod to be able to use the old fasteners without disturbing them, but there is no way without milling half the thickness off the new plate at each corner, which ain't a great idea. Ah well, nobody drowned I suppose! Groily
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longer studs are available
all the best - bill
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Groily,
I suppose you know this, but just in case, the original crankcase holes for the studs were 1/4-20 BSW and the studs took 1/4-26 CEI (or BSC) nuts. I know this contradicts what you said regarding BSF, but, over here, British only lists the 02-0051 as a CEI nut and British Fasteners says "Most, but by no means all, fasteners on post-War BSA's (through the late '60's, when it got more complicated) were CEI." So, maybe thats correct. Anyway, the thing I don't understand (really, one of a plethora of things I don't understand) is why you object to allen screws. Furthermore, you could get hex-head cap screw as well. With studs, you're always fussing with them staying in when you're taking off the nuts.
My sump plate is held by three 6mm bolts and one 1/4-20 BSW. The 6mm helicoils I did myself, the latter has been in since the '70s. I suppose I will be be barbequed for the mix and match of Whitworth and metric, but, alas!
Richard
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1/4" BSF is 26tpi the same as cycle thread.
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I will confess to being the one more likely to be confused and swayed by "what I read in the papers," but as I read it at britishfasteners.com, the BSF has a 55 degree thread angle while the CEI is 60 degrees. I guess I want to know if I'm wrong, so I can admonish myself later.
Richard
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That is probably correct about the angles but in practice a BSF nut fits perfectly well on a cycle thread stud.
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Yep, no need for admonishment or self-flagellation anywhere - bsf (and all Whitworth form threads) are 55 and cycle is 60; metric and UNC/UNF are 60 and BA is 47.5. In practice, 1/4 bsf and cycle fasteners can be mixed (the only size it works for), as can several ww and UNC sizes - but only, IMHO, in emergencies and/or where there is no possible risk of catastrophe if the thing comes undone. My studs weren't studs really - bits of ww threaded rod in 3 cases, and one which may or may not have been the right object. I'd have expected cycle nuts, which tallies with the comment here, and it could well be the fine-thread nut was just that. Didn't look at it that closely and even if I had, almost impossible to tell. Was going to make new set of longer studs in ww and cycle, but ended up using three of the screws supplied and just making up one longer stud for the worn hole cos I was lazy and it was cold in the shed. Next time, I'll make the other 3 and do it right, and helicoil - now we all know from previous discussion here how good they are - said worn hole. Main thing is - still on the road, nothing can fall off except me, no oil leak, couple of hundred miles to do this week same as every week. And at least I now have the magnetic plug and the means to empty the crankcase without having to disturb the plate again 'til I'm ready. Very gratified to see no discernible metal particles anywhere with this unknown bottom end that's run sweetly for 5000 since I bought the thing in the summer. . . and the dirty oil looked quite clean. As it should, I suppose, since I change it every few weeks. Hope fate isn't lurking round the corner with a brick. Groily.
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Most of the 1/4" nuts on my A7 have been replaced with BSF stainless ones and I've not noticed any greater tendency for them to come undone. I do have trouble with the 2 10mm bolts holding the saddle on and I must get round to replacing them with the correct 3/8" cycle thread ones.
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Sorry, a bit ambiguous what I said there.
I wouldn't personally knowingly mix even 1/4 BSF and Cycle inside an engine, although I'm guilty of doing it in other places - but it's hard to tell the bits apart anyway, unless you have brand new nuts labelled in packets. I suppose one could run a BSF tap or die over a doubtful part to reduce the angle of a known Cycle part and get a better match?
With the coarser thread forms of WW and UNC, of which the pitch is the same in many diameters, the contact area with a mix of the two will be seriously reduced - loads of daylight in the larger sizes - and I personally don't think it is a very good plan. As well as having AF spanner sizing on any UNC hexes. Groily