Undersized bolts?

[RobW]

I'm having a problem finding the right bolts for my Nipper.
The ones in question relate to control horn/bell-crank pivots etc.
The originals were, I believe 2BA, i.e. with diameter 0.185 inch. Some look to have been replaced with AN3 (0.187 inch). However, on closer inspection many are in fact 0.180 (in similar sized holes), meaning standard bolts won't fit.
It's possible that the bolts have been ground to a smaller diameter, but I'm reluctant to do this. Would it be better simply to ream out the holes to 2BA?
Alternatively, is there a source of 'undersized bolts' that I can use? Is such a thing as a 0.180 inch bolt available??
Thanks

PS Does anybody know where I can find a new 2BA reamer without paying LAS prices...?

[RobW]

Its been suggested to me that early nippers might have had metric hardware (i.e. 4.5mm bolts, which are about 0.178 inch). Is this correct??? Might explain what's going on. In which case is it OK to ream out to 2BA or 3/16 AN ???

[G-BLMW]

Hi Rob

Looks like my info might have lead you up the preverbial garden path . Perhaps the fixings were changed to B.A. when Slingsby started to build Nippers, I have no knowledge of Fairey Avions built Nippers.Try Raymond Cuypers in Belgium, he is founder member of the Belgian Nipper Club and is very knowledgeable on Nippers, I'm sure he will be able to help. He can be contacted at RAR (Raymonds Aircraft Restorations) email raymond.cuypers@rar.be
Let me know how you get on.

Stuart

[JimCrawford]

Hi Rob,

While early Nippers may have been metric I think that 4.5mm is very unlikely as it is not a preferred size. Also, on small, simple light aircraft, undersize or precision fit hardware is most unlikely, just too expensive or difficult to source.
I guess this thread follows on from your previous one about aileron play. The old mechanism is prone to lost motion with all those bolted joints, I believe that there are some Nippers about with rod ends fitted to the aileron push/pull rod. This is certainly the way I will go if I ever detect unacceptable slop in the mechanism.

My first suggestion is to re-measure the bolts and holes. 0.180 is so unlikely as to warrant a check, you are quoting some sizes to 1 thou and others as ‘similar’. That isn’t going to produce an explanation. I bet you have worn 2BA hardware, in which case a 2BA reamer isn’t going to help. I couldn’t find one on the LAS site, but they do special sizes for ~ £70 which is about the going rate. They are, however, straight flute which isn’t optimum for hand use. Somewhere in my records I have the address of a firm which does bespoke sizes with a spiral flute. I’ve had to do this to take worn glider fittings up to the next oversize.

What does the fit feel like with a new 2BA A25 bolt? If it is acceptable, then new bolts - end of story. If it is still too loose, but only just, you could try reaming out for a 10-32 AN3 bolt. Although 2BA and 10-32 are often erroneously called 3/16” , the 2BA is 4.70mm and the 10-32 is 4.83mm [ 3/16” is 4.76mm ]. I’ve never quite understood why, the ‘3’ in AN3 is supposed to denote the diameter of the bolt in 16ths, but the 10-32 thread is based on a wire scale and is ~0.07mm bigger. This was brought up on the LAA forum a while ago when somebody was wondering why inserting a AN3 bolt into a 3/16 reamed hole was a/ very hard and b/ took all the plating off the bolt. If the American size works – job sorted. An advantage here is that the AN bolts are much cheaper than the obsolete A25 series and readily available in a vast range of sizes. They are also ready available with drilled threads which saves a bunch of pain if you need to use castle nuts and split pins. I automatically replace the A25 series with AN alternatives for this reason.

Next step, if the wear is really bad, is to go up to 5.0mm and use metric hardware. This can be difficult to source, the glider community uses commercial spec bolts – very reasonable from RS and similar. The thread length can be rather long, I use the stainless bolts so that they can be cut down, and you will have to drill the split pin hole.

Still no good? The wear must be horrendous and the next standard bolt will be 6.00mm, almost worth going to AN4, 6.35mm, for the availability. But is there enough edge distance left.?

Good luck

Jim

[Neil Spooner]

......if the wear at the blade end of the rod is the problem they could be welded/brazed and redrilled to any size you like.

Neil

[RobW]

Thanks Chaps, I'm beginning to learn a lot on this forum!
Actually the wear that I noted was to the bolt shank. The 'eye' of the rod was fine and would allow a new 2 BA bolt through, but not AN3. The problem I had was the small tube welded into the bell crank, as a 2BA bolt simply wouldnt fit (too tight). I think the internal diameter is about 5 thou smaller than that needed to accept AN3.
I think what I'll do before permit time is simply to run a 3/16 reamer through the crank and the eye, which will allow a nice fit for an AN3-12 bolt. It will also let me upgrade using a standard rod end if need be. The standard design subjects the bolt to bending loads at full aileron deflection and could be improved with rod ends at each end of the push rod. Sounds like a better bet than attempting to source metric hardware etc...!
Regards, Rob

[RobW]

Just spotted Jim's comment about AN3 being tight in a 3/16 hole. Well I've got 2BA bolts as well as AN3 so I'll see what fits best... !

[G-BLMW]

Rob
Stupid question, have you tried a 2BA nut on the old bolt?? Is the 2BA bolt a good fit in the rod end?? I still feel that as Jim has suggested that these are worn 2BA bolts. Incidentaley the plans quote A59 not A25 bolts. According to my Zeus tables the clearance for 2BA is 4.8mm. Is the bellcrank hole 0.005" down? or are there burrs on the edge of the hole? Get yourself some letter drills. 14 =4.62mm, 13 is 4.7mm, 12 is 4.8mm. If the 4.7 goes thru the hole then use the 4.8mm to clean the hole out. (0.1mm =0.0039") you could do this by hand if your careful. Double drilling is nearly as good as reaming.

Good Luck

Stuart

[jantar]

Hi I had same situation when I tried to replace these bolts with new. There was only slight polishing on the originals and definitely no wear so I reused them. It has occured to me later that these could be "high tolerance"grade bolts. I have no slop in the aileron circuit. Jantar

[JimCrawford]

I stand corrected here. As Stuart has said the plans call for an A59 series close tolerance bolt rather than the A25 standard tolerance I had assumed. Unless the drawings call for a reamed hole it seems inconsistent to call up a precision bolt for a drilled hole assembly. But maybe I'm trying to second guess the design decisions made quite some time ago now, particularly when the British hardware was certainly much easier to get and, of course, Slingsby were manufacturing a public transport C of A aircraft not a permit type. It would be worth trying an A59 to see if it reduces the lost motion to an acceptable level. This would be the swiftest solution. Otherwise the rod end mod would be my favoured route, I've used rod ends on my Taylor Monoplane aileron push rods and there is no lost motion.. An alternative worth considering if the rod end method maybe won't work, perhaps not enough space, would be Neil's suggestion of rebuilding the wear with weld. A variation that I have used on glider control hinges, is to ream out to a size that allows insertion of thin bearing liners. This has the advantage that, if and when they wear again, the liner can be pushed out and a new one inserted. The disadvantage is that there must be enough material to ream out to the oversize.

Good hunting!

Jim

[RobW]

Yes - I had an AN3 bolt in the Port bellcrank ('X' on the head), and an A25 (circle around the head) in starboard. That's rather academic as both had been 'ground' down to a smaller diameter to make them fit (it wasn't wear - the surface scuff marks were longitudinal and the reduced diameter extended beyond the bellcrank tube).
I tried new A59 bolts (0.185 inch) - still too big! So I'm off to purchase some reamers/letter drills to restore the situation to a standard spec. But I'm still curious why it's like that. The diameter isn't smaller at the ends of the tube, i.e. it isn't noticeably distorted or burred. And after all, the previous installer seemingly saw fit to reduce the bolt shank, which puzzles me greatly.
If it was a car or a bike I'd have no hesitation in reaming it out, but as it's an aeroplane - best to ask these questions before removing lumps of metal from it!
I'll post some piccies later....

[JimCrawford]

Rob, I think we are in the business here of making things work in an acceptable manner, rather than trying to guess what somebody did many years ago! It certainly makes my head ache trying to imagine how your mechanism got assembled like that. I've been amused by the variety of bolts I've found used to fasten to the 4BA nut plates, including one self tapper !! !!

Good Luck

Jim