| Author | Message | ||
     Alexander R Lynch Yet to post message Username: lex Post Number: 1 Registered: 5-2003 |
I am about to dismantle the differential and centre casing of my 1950 MK V1, B111 JN. At present the pinion is fitted with a multiple bearing and I was wondering if any members had any experience with either replacing with a modern inline bearing or converting to tapered bearings, I have on hand the service hand book which details the procedure. The reason for this exercise is to install a 14/41 CWP. Any advice would be welcomely recieved. Regards Lex Lynch. | ||
| Richard Treacy Grand Master Username: richard_treacy Post Number: 341 Registered: 4-2003 |
I have done this change on my R-Type. That was about 80,000 miles ago. Instead of fitting a new triple row bearing, which costs as much as a new kitchen, I fitted three discrete bearings in a pack. The configuration is unchanged. The outer two bearings are ball thrust races, and the inner is a straight roller race. The dimensions are standard. I used SKF bearings, something like N37 series springs to mind, but there is any number of brands. Your bearing shop will find you a match to sample ex-stock, and setup is the same as described in the book. You will need a few shims to set the load between the housing cover and the bearings the same way as with the original type. The alternative is to fit a pair of tapered roller bearings as on later R-Types. Again, your bearing shop can sort that out, and you should follow the book. I didn't go for that as a spacer would be needed between the two outer shells, whereas the triple arrangement requires no modifications at all, and is a 1:1 swap. I suggest you contact Norman Geeson in the UK. He specialises in this field especially on these cars, and has some very useful tips. I learned the hard way that a new or re-set pinion bearing set should only be fitted along with a new or relapped crown and pinion pair. Resetting high mileage gears, regardless of condition, without lapping them leads to gear stress, and in my case gear failure shortly afterwards. What is a 14:41 c&p ? I only know of 11:41 (standard), 12:41 (export, like mine), 13:40 (Continental) and 8:34 (Silver Wraith). Is 14:41 a special ? | ||
| Alexander R Lynch New User Username: lex Post Number: 2 Registered: 5-2003 |
Richard - thankyou for your reply, the 14/41 CWP is a remake from the Bentley Drver Club UK. They have been made up specially for the club under their spares scheme. At this stage I am unsure whether the pinion design is for tapered bearings or not. My car has the inline set but there would be no problem in making up a new sleve with the inner flange incorporated. I will contact the club tonight and clarify the situation and also speak with Norman as you suggested. Regards Lex | ||
| Ashley James Unregistered guest Posted From: 62.255.0.5 |
I recommend getting in touch with Norman Geeson, he is cc6@lineone.net and specialises in the overhaul of the rear axles. He has all the spares including bearings and the oil seal adaptor plate in stock and can advise on what to replace to avoid the need to strip again. I've fitted two of his high ratio conversions to my cars. (Message approved by david_gore) | ||
| Norman Geeson Unregistered guest Posted From: 80.225.213.226 |
Alex You will indeed meet a few problem trying to fit a BDC 2.98:1 ratio gear set. Neither this conversion or the one from triple type bearing to tapers is quite straight forward. All the probems can be overcome, but are not generally known. Firstly the JN series axle is as you know fitted with a 3.73:1 ratio, but the main axle case is different and needs modifying for taper bearings to a RG 6196 casing, and also needs a new bearing housing. These points I can advise upon later. Firstly have you considered the implications of fitting a 2.92:1 ratio to a normal MKVI saloon. I am presuming that the car is standard and not a special. The ratio you are preparing to fit is some 21.5% higher than the existing one. For a given road speed the brake servo is revolving that much slower.Total braking effort will therefore be reduced for a given input effort.Depending on what modification have been carried out since the car was new will also depend upon the individual braking effort front to rear and needs seriously considering.The braking system is best altered to suit this axle ratio. An opinion only, but considering I have fitted untold numbers of these ratios and driven a very high number of cars so fitted, including my own, I would be careful fitting one to a standard 4.25 ltr MKVI. Once again depending just which gearbox is fitted to your car will depend upon the ratio spread. Another point is that the third gear final ratio will be slightly higher than your existing top gear. Will the operating terrain and type of use permit such up gearing? Hopefully your clutch does not shudder at the moment and you will be happy starting off in first gear each and every time! Personally I am not against using this ratio, with considerations, but it is more suited to the very late R type with the higher compression cylinder head and Continental combustion chambers. A 4.5 ltr MKVI can handle it, and no doubt there are some users of 4.25 ltrs who have fitted the ratio, but most of the latter I find want to swap them back again for the 3.42:1 late R type ratio.The 2.92:1 ratio has a very distinct advantage in an R type automatic, which is the best suited of all the cars for the ratio.In the automatic it has the advantage of reducing the ratio spread between second and third gears when all the clutches and brake bands change over.The change can then be made from good to superlative if the gearbox is set up right.It is also suitable for all MKVI specials, as they are lighter than the standard car. It is not really possible to convert the pinion housing from a triple bearing set up to tapers, nor to fit any sleeve that you may have considered. For one thing the 14 tooth pinion you have in your possession will most probably have an imperial shaft size and the existing MKVI triple bearing is metric. I said "probably" as I have not yet seen a BDC metric one.Yes, you may measure it, and maybe come to the conclusion that both are the same, because the sizes are close, but they will be different. Also not normally realised, even by bearing agents, is that the fitting tolerance on imperial and metric bearings are exactly oppposite to each other.In addition the inside of the MKVI pinion bearing housing is metric and will not accept R type tapers. Incidentally the pinion nose bearing is also metric, as are the rear wheel bearings. In short, if you intend to fit the 2.92:1 ratio you need a complete late R type taper bearing housing including the oil thrower, and a basket full of spacers.These are almost impossible to obtain in Europe, (don't now about Oz) but if you are stuck I have newly made housings including the oil thrower. In practice users attempting their own overhauls usually come unstuck, they do not have the necessary spacers for preloading, and I finish up building and setting their pinion. If you contact me by e-mail I will send you a drawing/ photo of how to convert the main axle case. It is actually very easy, a true five minute job, but harder to describe in words. One of the biggest problem you will face is setting the GD or gauging point of the pinion to the axle centre line unless you are prepared to manufacture some setting tools.The new pinion you have will be inscribed with the MD or manufacturing setting at 4.525 inch. Although it is necessary to calculate the GD measurement (this will be about 2.931 inch on a BDC unit). This measurement will depend upon who made and ground the pinion, if you provide me with the other numbers on the pinion it would at least tell (me) who made it. As the GD dimension on the new pinion will be so much different from the old pinion a totally different pinion housing to main case spacer will be needed. In case of an emergency arising, do not on any account polish or mechanically clean the EXISTING pinion or you are liable to destroy the GD setting etching from the nose area. In addition do not let the existing nine hole spacer washer leave your sight.The reason is that with these two "knowns" it is easier to replicate the centre line of your case on a setting jig.You may not quite understand the reasoning for the above comment on "knowns",( if you did, you might be building axles all day long) but do not worry just follow the suggestions. At this point it may be helpful and save you money to point out that about every six months I fill the equivalent of a large American domestic fridge with broken gear sets. No exaggeration,but a large proportion come from dealers and specialists who believe that their staff are skilled enough to set the gears up with engineering blue.The average miss setting is out by 0.015 inch and they never know until the gear set goes bang. The moral is, be prepared to make the tooling if you attempt the job, if not leave it alone. If you contact me direct by e-mail I will attempt to talk you through that exercise to produce simple tooling after we establish the GD dimension of your new pinion. A few other points the side backlash setting serrated nut is LEFT hand thread, as is the pinion bearing retaining nut.In the case of the 2.92:1 gear set you have it will be necesary to shorten the 12 crown wheel set screws by approx 0.180 inch. Do NOT try to tighten these set screws without shortening them! As an aside to your original question it is possible to covert the original type triple bearing axle to metric tapers. That is when it is desired to retain the original triple bearing sized pinion, on say a 3.73 or 3.42 gear set.In this instance a special metric bearing housing is needed and only one particular metric taper bearing will suffice.The bearing is not normally listed even in the thickest brochures, but are available. In the case of the other bearings on your axle, including any imperial pinion tapers you may use, it is vital that all these bearings are suffix "X". This is because the bearing radii is special.The twin track pinion nose bearing is particularly special and was produced especially for all the post war axles up to Phantom VI, forget your bearing agent on this one, he will not have one! For the record R-R produced three ratios for this axle original, but using SIX types of pinions. Each ratio being produced in taper and in triple bearing sizes.The 8/34 ratio that Richard mentioned was never fitted to this axle, but is the source of belief in hand setting gear sets. Some can do it, but very few, and R-R never hand set gears sets after circa 1925. As you might realise it is impossible to completely describe overhauling and particularly converting one of these axles on this site. Hopefully I have at least given you a few pointers. Best Regards Norman Norman Geeson (Message approved by david_gore) |
