| Author | Message | ||
     Ron Lewis Yet to post message Username: great48 Post Number: 1 Registered: 1-2009 |
Have recently purchased a 1947 Bentley Mark VI (B146BH) and wish I had bought one years earlier – what a great car! There are, however, some pressing mechanical problems requiring attention, the first of which is the front wheel bearings; these are the original ball bearing type. My query is whether it is possible to replace the ball bearing assemblies with the tapered roller variety (i.e. to fit tapered roller bearings to the existing hubs and stub axles). The reason for wanting to do this is that (in my limited experience, at least) tapered roller bearings tolerate a bit of accidental kerb bashing better than the ball bearing type do. Of course, I’m not saying that the ball bearings collapse on impact, but their life is considerably shortened, even after a relatively minor bump with a gutter. I believe this is because the added pressure experienced during an impact is a massive load on the relatively small contact area, where the ball contacts the bearing cup and/or cone. This I’ve been told, makes a small impression in the hardening (of the cup and/or cone) which then becomes a “high wear rate” area, eventually necessitating earlier-than-normal bearing replacement. Each tapered roller has more contact area compared to a ball, and there are usually more rollers per bearing assembly than in a ball bearing, meaning the tapered roller unit provides a better distribution of bearing load. If it is possible to substitute tapered rollers in lieu of the ball type, does anyone have some current part numbers for same? Failing that, are the ball bearings still available as a genuine part? No-one seems to have a cross reference, or size data, for Fischer (#6308 [Genuine P/N RG7081] & MS11 [RG7077]) or Hoffman (#340 [RG4446] & MS11 [RG4445]) or for any other bearings of the ‘40s era for that matter. I notice in the parts manuals that later Mark VI models have tapered roller bearings, but the cross-sectional drawings of the hubs/stubs look slightly different and there are no dimensions noted to compare the sizes of the different types. Also, if fitting tapered rollers to the existing hubs/stubs is possible, will the existing grease retainer (fitted to the inside of the hub) still fit okay and not foul the inner bearing cone or cup of the new bearing assembly? I would greatly appreciate the comments, or input, of the forum members regarding the above, as I would rather make any improvement changes now, at the time when the bearings need to be replaced, and not have to repeat the job later. Thanks for a great site, Ron Lewis | ||
| Paul Yorke Prolific User Username: paul_yorke Post Number: 278 Registered: 6-2006 |
I'm sure that you will get a few more responses to this, but There are plenty of these cars going around with 200k miles plus on the wheel bearings. I suppose it depends on how many miles a year you intend to do and how many curbs you find along the way!  The other question is, I guess, will today's bearings be as strong as the original ones? | ||
| Laurie Fox Frequent User Username: laurie_fox Post Number: 54 Registered: 6-2004 |
My B420EY MK VI has the early type front hub with ball bearings. These bearings intentionally have more side play than normal so as to accommodate side thrust better (see Section T, Subsection 1 in the workshop manual) and are fairly easy to inspect. The car was bought in 1959 with 97000 miles on the odometer and I had no workshop manual until much later. On the offside hub I replaced the small bearing in 1961 at 114986 miles because I though it had to much side play, not realising that it was probably OK. I passed the large bearing OK and refitted it. These bearings are still in the offside hub and the mileage is now over 412000. On the nearside hub I fitted new bearings (large and small) in 1962 at 139217 miles because I thought that there was too much side play. In 1969 (by which time I had a workshop manual) at 210822 miles the bearings were examined again with the large bearing being passed as OK and the small bearing was scrapped and replaced by the small bearing previously removed in 1961. In 1989 at 335854 miles both bearings were replaced in an attempt to locate a squeaking noise which was eventually traced to the rear nearside hub bearing. I found nothing wrong with either of the offside front hub bearings and I still have them as serviceable spares. The correct adjustment for the hub bearings is no play but no preload by selecting the correct thickness for the hardened adjusting washer and having the retaining nut fully tightened up and pinned. I have a variety of adjusting washers of different thickness but, or course, none of these really suit when it comes to correcting the play which I do from time to time. But one of my several thick adjusting washers will enable me to get zero play with the retaining nut correctly aligned for the split pin, although not fully tightened. So I put the split pin in and leave it at that. The workshop manual talks about using a Hub Extractor Tool to remove a front hub, complete with brake drum. Both of mine come off with a hand pull and I remove the brake drum first which saves any brake drum debris getting to the large bearing. I like this hand pull because it means that both bearings are free to move along the stub axle so there is no risk of the large bearing not seating properly against the distance piece at the thick end of the stub axle. It also means that the inner race of the small bearing will move out again if you accidentally overtighten and then back off. If it is not free to move then there will probably be some preload on the bearings even when you think you have got it correct. So my feeling is that the old type bearings in the front hubs are not a significant weak point but that there are some fitting points to be watched. Do others agree? The adjustment has been done professionally on some occasions and I have then needed to check and remove any preload which is sometimes there. Regards Laurie | ||
| Colin Silver Experienced User Username: colsilver Post Number: 32 Registered: 8-2008 |
Ron Lewis says: I've nothing to add to your question Ron. But that line takes me back to the wheel bearing workings of the original Malvern Star Dragster push bike I tried to win in the 60's by buying a Tarax soft drink bottle each morning before school. Yes, I have all my own teeth 40 years later. (For Global friends, Tarax was a soft drink company in Melbourne, Australia) | ||
| Ron Lewis New User Username: great48 Post Number: 2 Registered: 1-2009 |
Thank you everybody for the replies, especially to Laurie for the reassurance on bearing quality, as illustrated by the work done, and bearings reused, on the front hubs of his Mark VI. A very comprehensive and helpful reply, thanks Laurie. Based on the opinions and information provided thus far, it seems my experiences on the ball bearings (albeit rear axle) in the locally produced cars I worked on in the past, will not apply to the front ball bearings of the Mark VI. I'll now remove the hub and ascertain which bearing is the noisy one requiring replacement. Are these bearings still available as a genuine Bentley part? If so, would someone have the part numbers of both? If not available as genuine or NOS, can anyone provide part numbers from a current day bearing manufacturer? I have made enquiries at a couple of bearing suppliers prior to lodging this initial query, but the only response was a blank look when I mentioned the 1947 production year. Thanks again. Ron Lewis | ||
| Laurie Fox Frequent User Username: laurie_fox Post Number: 55 Registered: 6-2004 |
Ron There is another point that is worth mentioning. If the front hubs will come off without the use of a hub puller (as with B420EY) then this means that the inner races are not held very tightly on the stub axles. In this case any side thrust which arises from cornering etc will only be taken on one of the bearings and not shared between them and the wear due to the sidethrust will only affect one side of each bearing. If you find that a bearing is OK radially and has only taken thrust in one direction only then it will be OK to use if you assemble it the other way round from the way it was installed previously so that the thrust is taken on the unworn part of the race. So if you take the bearings out to have a good look at them note which way the faces were pointing and thus the direction in which they were taking thrust. I have no experience of front wheel bearings other than the ones which Rolls list in the Spares Manual. But I have measured up my spare bearings with the following results. Large bearing 6308 ID 40mm. OD 90mm. width 23mm. Small bearing ms11 ID 1.1250 in. OD 2.8125 in. width 0.8125 in. The 6308 bearing is available from http://www.simplybearings.co.uk and they can also supply the small bearing with an mj number. I would expect them to be quite suitable. Both are deep groove unshielded bearings but not made by Fischer who apparently do not make bearings any more. Given the dimensions your local stockist might well be able to supply. Regards Laurie | ||
| Ron Lewis New User Username: great48 Post Number: 3 Registered: 1-2009 |
Thanks, again, Laurie. Will certainly look at repositioning them if their condition is not too bad and greatly appreciate the measurements and parts source information, so I can make some preliminary enquiries on availability. Much obliged, Ron |
