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rustcollector
United Kingdom
410 Posts |
 Posted - 02/09/2014 : 14:52:14
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Wanted Parts to uprate my PA to PB specs.
PB c/ratio gearbox
PB speedo
PB tacho (without the mph conversion )
PB dash
also
8 day clock
Supercharger ( prefer under bonnet but anything considered )
Alfin brake drums
thanks. |
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Robin Macmillan
United Kingdom
415 Posts |
Posted - 02/09/2014 : 15:56:47
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I stand to be corrected but believe the MPH scale on the tachometer is to be found on both the PA and PB tachometer.
PB 0527 |
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john joynes
United Kingdom
18 Posts |
Posted - 02/09/2014 : 17:36:11
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| I understood the PB had a separate tachometer (rpm) and speedometer with odometer (mph),whereas the PA has a combined tachometer and speedometer with a separate ododometer. |
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Peter Green
United Kingdom
1682 Posts |
Posted - 02/09/2014 : 17:39:01
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John,
Your understanding is correct.
Peter |
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Robin Macmillan
United Kingdom
415 Posts |
Posted - 02/09/2014 : 19:24:59
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Thus I take it that the PB tachometer has NO mph markings ? ....... Has anyone a picture of same
PB 0527 |
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john joynes
United Kingdom
18 Posts |
Posted - 02/09/2014 : 20:51:46
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| Page 266 in 'Blower' is one example or Malcolm Greens ' MG Sports Cars', there may be others! |
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Robin Macmillan
United Kingdom
415 Posts |
Posted - 02/09/2014 : 20:58:26
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As ever I stand corrected. The reason for my doubt is that my PB which I bought circa 1965 and was released from a garage where it had been stored for at least 15 years with a defunct diff has a tachy with MPH markings.
So it goes
Robin
PB 0527 |
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john joynes
United Kingdom
18 Posts |
Posted - 02/09/2014 : 21:11:10
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Robin
My belief is that is part of the cars history, enjoy it.
John |
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ags
United Kingdom
275 Posts |
Posted - 02/09/2014 : 23:41:22
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Hi Michael,
If you wish to do a complete update of your PA you have omitted one of the most important parts (at least in my opinion). That is the steering box, which on the PB has the lowest ratio (ie most responsive steering) of all the road cars. The part number of the standard PA Bishop Cam box is MG635 whilst the PB is MG635/1. The difference is in the cam which gives a ratio of 7:1 and the number of turns of the wheel lock to lock of 1 1/4. The standard PA cam gives 9:1 and 1 1/2 turns. The difference is noticeable to the driver.
These items are rare as not many people have noticed the difference in specifications. To the best of my knowledge the only way to get one of these cams is to get a good used box, to open it and check the cam. They are therefore expensive and indeed I have only got the one on my car. The other implication of all this is that you need to start your "specialisation" process with a Bishop Cam chassis.
More technical ramblings from
Andrew Smith MMM571
PB Abergavenny (who used, back in the Fifties to live in Woodmansterne close to your part of the world) |
Edited by - ags on 02/09/2014 23:44:02 |
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rustcollector
United Kingdom
410 Posts |
Posted - 03/09/2014 : 08:00:35
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Thanks Agas,
What do you mean by a "bishop cam chassis" is this a latter chassis than the PA used. Am I right in thinking mine uses a Marles Weller.
I'm new to this MG scene and reading as much as I can. Although it's not as easy as previous project research, where there were lots of books. I suppose I should be thankful that I don't have a one off vehicle, where research has to be done by the odd photo and archaeology type deduction and reverse engineering.
I'm not after converting my PA to make a PB to defraud people. I just happen to like the PB dash and the PB gearbox seems like a good addition. After the information you kindly added, it seems the steering box is a very worthwhile addition as well.
Also interested to know of any period racing modifications that used to be done, back in the day, works or privater. I've discovered the mod to stop spring wind up, by the cable and brackets between axle and chassis.
Keep up the "ramblings", I'm keen to learn as much as I can. |
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john joynes
United Kingdom
18 Posts |
Posted - 03/09/2014 : 08:15:45
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| The bracket on the steering box cross tube is different on the PB to suit the bishop cam box. |
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rustcollector
United Kingdom
410 Posts |
Posted - 03/09/2014 : 09:13:16
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| AAHH thanks for that, nothings simple. |
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Bruce Sutherland
United Kingdom
1569 Posts |
Posted - 03/09/2014 : 10:42:08
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(1) Robin,
There's a photo of a PB Tachometer on our website 'Pictures', 'Technical Pictures', 'Type - PB', 'Category - Instruments', 'Sub-category - Tachometer'.
(2) Nick F,
There's an error in the Technical Pictures as the PB speedometer has 'migrated' to the 'Type PA'. Can you rectify? Or shall I?
Bruce. (PB0564) |
Edited by - Bruce Sutherland on 03/09/2014 11:13:30 |
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Nick Feakes
USA
3378 Posts |
Posted - 03/09/2014 : 13:06:58
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Bruce
Finger trouble most likely. I have corrected it.
Michael
Have a look at http://www.triple-mregister.org/select_type.asp You can select which type you are interested in. This is an on-going project so not complete.
Nick
Webmaster |
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ags
United Kingdom
275 Posts |
Posted - 03/09/2014 : 21:31:25
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Hi Michael and John,
John is correct that the the critical difference between the "Marles" and the "Bishop Cam" types of chassis is the bracket on the steering supporting cross tube. If you search the Technical Information forum you will find further details of this difference, and advice on what to do about it if you choose, or are forced, to change.
The change from Marles Weller to Bishop Cam steering gear occurred before the change from PA to PB, so that whether your car should have Marles steering depends on its chassis number. Up to chassis number PA1286 cars left the Works with Marles steering. (That is just over half of all the PAs built.) From PA1287 to the last PA, PA2250, they had Bishop Cam with the details which I mentioned earlier. All PBs PB0251 to PB0776 were built with the "PB" Bishop Cam, including the Works converted PAs, but the PA and PB cam ratios were different as I pointed out earlier. For completeness the Marles Weller box had a ratio of 10 7/8:1 giving 1 3/4 turns lock to lock, so that there is a continuous change from early PA to late PA to PB. (Though of course this refinement may have had little to do with the choice, the overriding factors probably being ease of supply and cost as always.)
Comparison of the external appearance of your box with the pictures in Blower, Marles Weller in Fig. 1 on page 411 and Bishop Cam in Fig. 2 on page 414, may help you to confirm that your parts do correspond to your chassis number. (The latter drawing is rotated by about 90 degrees from the normal top view of the box in the chassis.)
You may find a number of rather rude comments about the Bishop box and its propensity to wear but I believe that if maintained conscientiously it is no worse than the Marles. The thickness of the top of the box is not necessarily quite sufficient for the loads and ratio used by the PB, but it does have the advantage of not relying for its accuracy upon four small hemispheres.
The choice as always is yours, but I would not swap mine for an alternative.
More technical ramblings from
Andrew Smith MMM571
PB Abergavenny |
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rustcollector
United Kingdom
410 Posts |
Posted - 05/09/2014 : 11:25:25
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Ags,
Where do you get your information, is it a long time of chatting and discovery or are there books I should get.
Obviously I am getting a lot of help from this forum and members. There is yourself, Horst and Carl, I'm particularly grateful to, thanks.
Thinking about it I have a parts list, this probably states the chassis no and type of steering box.
I'm trying to get blowers book at the moment, but seem to fetch high prices £65 to £85 on ebay. I have a bid on a cheaper copy at the moment.
I might be able to get some useful books at beaulie on saturday.
Thanks again. |
Edited by - rustcollector on 05/09/2014 11:26:12 |
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