From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Amount of 'nip' or interference fit for AC.9 bearings.
| Identifier | ExFiles\Box 114\3\ scan0019 | |
| Date | 8th February 1939 | |
| GWH.{George W. Hancock - Head Chateauroux} (K). BY.12/G.8.2.39. RE: NIP ON AC.9 BEARINGS. In view of the fact that AC.9 has a brinell range of between 65 and 75 whereas AC.7 has a mean figure only of about 48, I think it is somewhat risky to overdo on the AC.9 to give excessive nip effects in fitting new big ends, as there seems to me to be a possibility of the metal returning somewhat elastically after the reaming operation and thereby reducing running clearance. I do not consider that B.125-JY. is affected by this, but I would certainly like to limit the amount of nip on a bearing to a maximum of .003 on each side. This would be, assuming that the bearing slipped in easily, if the bearing was oversize I should certainly not exceed .002 on each face. To make quite clear what I have in mind, I would add that the first proposal means that if one side of a bearing is made flush with the cap, the other side will stand .006 proud, this being true for each half of the bearing. In the second case with one side flush the bearing would stand .004 proud, again this is true of each half of the bearing. Whilst it still may be true that you could put the extra nip on, I am certain that there is no advantage in going beyond a definitely specified amount, and that amount I would fix at the figures quoted above. I am certain that this allowance will ensure the whole of the bearing being pressed adequately up against its retaining surface, and would ensure very close metallic contacts, in fact just as good as if one doubles the figures quoted, but by using the lesser amount it removes any question about work hardening taking place and a certain amount of recovery occurring when the bearing is in service. BY.{R.W. Bailey - Chief Engineer} By | ||