BENTLEY DRIVERS CLUB FORUM

I have a 4.9 litre S1 engine and propose to have it rebuilt with a view to having it installed in my Mk VI. Is there anyone who can recommend someone who could rebuild it? I'd be particularly grateful for information from someone who has direct experience of having a similar engine rebuilt (and if you think someone ought to be avoided, please feel free to PM me!). All suggestions gratefully received.

Regards,

James

Even with an early 4.9 litre engine and a 13:40 axle, the car is still going to have the acceleration of a brick.

My reason for needing to replace the engine has nothing to do with acceleration.

Christopher Carnley wrote:Even with an early 4.9 litre engine and a 13:40 axle, the car is still going to have the acceleration of a brick.

Oh Christopher, don't be so negative!

John,

My experience shows that it is a fact, and several others included.
The post war 6 cylinder cars with the 4 1/2" stroke, very restricting exhaust systems and no vacuum advance, do not "rev" as well as one may believe or expect. The S1 saloon with the high compression head and 12:41 axle has to be floored to get any sort of performance.
The previous 1955 -1957 engine was really little better than the big bore MK VI.

As I've already mentioned, Chris, I don't claim that NPO999 is a tyre-ripping dragster; but according to the conservative* rolling-road figure in 2011, the S1 with big-valve head, but without the high-compression head-gasket, and the 2" SUs, was pulling 230 ft/lb in an almost-straight band between 1500 & 2500 rpm. The latter is +/- 70mph in top, and so getting to that point is reasonably sprightly if you use the gears. 80mph in 3rd is routinely-seen for overtaking (in fact the engine's pulling 80 in 3rd at about the revs of the original-axled MkVIs in top at 70mph). And, obviously, what's the point of staying in any of the gears beyond about 3,500rpm? Far better to change up and get back into the torque band, although 110mph (indicated) is no problem (+/- 4,000rpm), but for obvious reasons I rarely play with that end of the scale (due to the wind-noise, of course..).

Now depending on what sort of brick you had in mind for the competition between it and a 4.9-engined MkVI, I'd suggest that's a little more performant not just than a 4.25, but than a 4.5** - repeating the proviso that I realise the above is not exactly dragster-level oomph, but it's still not bad! (And of course it's nothing compared to modern values - even my 6-yr-old Subaru's far better on all counts...but it's not a MkVI.)

Peter

(*Done at an outfit in Gillingham, Dorset, which makes a point of not giving classic Jaguar owners ideas above their station by inflating the figures, as some such places do. This same test gave NPO999 100bhp at the wheels, and a calculated 'flywheel' figure of 145bhp...the power-loss between the two was probably entirely due to the clunky old gearbox, of course!!

**Prior to giving it its 4.9, I drove NPO999 extensively with a re-built 4.5, and the same '3-to-1' back-axle ratio, without any frustration at all - overtaking flying bricks on many occasions, in fact.)

We are in the USA, so not much use to the person who started this thread. Here is an article I did for the USA club on V8 engine overhaul that may have some relevance to your job

http://robisonservice.blogspot.com/2016 ... royce.html

All old engines have problems due to deterioration, especially when taken out as seized, and stored badly for 40 years.

I saw your piece some time ago regarding the rebuilding of the Jack Phillips designed R-R V8, using re-machined GM or Ford 4.1" pistons, and very interesting, following in the war time Roll-Royce Merlin parts reclamation schemes tradition.

Did you ever meet the late Frank Cooke, the former English teacher, and optics expert who worked with the famous Edwin Land, or the tragic Bob Shaffner?

Have you now retired from business,to be offering your services?

Frank Cooke was about 20 miles from me, so yes. He and Bob Jefferson were experts on the prewar cars where we have traditionally done postwar cars.

I am not retired but I don't do the main work of running the shop anymore. I travel and speak at workshops about half-time now. I'll be doing several sessions at the RROC national meet in French Lick IN this year for example.