A.C. Bell Housing

[B.P.Bird]

When you look at the bell housing, which joins the A.C. straight six to its gearbox, you will see a cover plate mounted on two studs. It looks like this:



What is this access panel for ? I could speculate that it was a hangover from the days when clutch fingers were adjustable. However, with the advent of the light weight gearbox  A.C. produced a different, thinner and lighter bell housing. Moreover the new bell housing still incorporated this access panel, not only that but the panel was redesigned with the mounting studs N/S rather than E/W (it had to be that way as the new bell housing was a continuous curve from side to side.) Why did they go to such trouble ? I make the assumption that somewhere there is a panel cover which looks like the ones in the photo' except that the mounting holes are top and bottom rather than side to side - has anyone got such a cover or were the old covers used so that the Company motif lay on its side ?
You could dismiss all this as a harmless eccentricity, but to go to all this trouble, to retain an access, seems to point to some useful function ?

[Klassik Metall]

Well Barrie I think you deserve some kind of prize for the most esoteric AC question ever asked. :o

Therefore it also clearly deserves a comprehensive reply. The only reason I can think of for the access panel is to view the condition of the thrust bearing & possibly clutch. It doesn't make it any easier to swap them though when they need replacing.

I have an original lightweight gearbox (No. AC 21), it is only fitted with a somewhat crudely made aluminum cover sheared from a piece of 1/8" thick sheet & is identical to the cover on the only other lightweight box that I've seen. It does have the studs in the north south configuration as you state but the cover is on a raised plinth, as per the Moss bell housing so there was easily space to position the studs as per the earlier version.

I look forward to any further ramblings on this important area of AC design. :)

[B.P.Bird]

Luke,
That is very helpful: Now that you mention it I too remember a roughly guillotined plate on the bell housing of a lightweight gearbox installation. I supposed it must have been a non original part, but if you have seen two that makes it very likely to have been the Thames Ditton solution. Of course it begs the question of what the inspection port was for and why, as you correctly observe, the plates were fitted with spacers to allow a gap - ventilation? You are also correct in noting that the later bell housing could have used the earlier East/West stud mounting without a problem: Again why did they go to the trouble of changing the studs to North/South ?
Another slightly less esoteric question arises from all this - when the lightweight gearbox was installed in an Ace or Aceca how was the damper cradle fastened to the bell housing ? On the Moss 'box bell housing mounting pads are designed in and the cradle bolts to these. On the lightweight bell housing these pads are deleted. To speculate one could suppose that the A.C. engined G'hound was the planned recipient of the light weight installation and in that chassis the engine damper acts on the cylinder head from the two battery boxes and thus no damper is required to be mounted on the bell housing. However the light weight 'box was used on Ace and Aceca so how was damping arranged ?

[Robin A Woolmer]

I anticipate that the cover gives visual access to inspect the clutch release carbon thrust bearing, these do wear & need replacement of the carbon ring which is clamped into the housing!
I believe this is likely similar to Morgan cars which also used the Moss Box!

Robin 

[B.P.Bird]

Robin,
In considering the Moss 'box the points you make are completely valid. However the light weight gearbox did not use a carbon release bearing and inspecting the more modern sealed release bearing seems pointless. I would be convinced that the inspection port and cover were simply a carried over 'habit' from previous practice were it not for the redesign of the cover mounting studs and, as Luke reminds us, the consequent use of a sheet metal cover instead of the neat casting previously used.
It all seems such an effort for no discernible reason - engineering at Thames Ditton was generally straightforward and avoided expensive and needless complications. Comparing the Tojeiro Ace chassis and running gear with the three Turner Cobra chassis and running gear illustrates that philosophy.
If you have access to the later version of the 'Ace and Aceca General Instructions' turn to pages 27 and 30 where there are drawings of the Moss and Lightweight gearboxes and bell housings. The drawings shew how different the lightweight bell housings and inspection ports were.
I do feel that there might have been a reason, just wonder what it was......

[TTM]

If we were talking about a more modern car I would have thought this could have been a way to measure clutch wear through the position of the resting fork between two points easy to spot, but I guess the fork is not even oriented accordingly...

[Klassik Metall]

Barrie,
The Ace & Aceca light weight gearbox installation does not have any bell housing or other torque dampening rubber mounts. The only mountings are the two front engine mounts & the large Triumph TR3 gearbox mounting. I'd also add that as the name implies the light weight gearbox is considerably lighter than the Moss box, with the main case being a magnesium alloy casting. Apart from the bell housing mountings on the Moss box the rear of the box is only supported by quite a small mounting with only a central 3/8" stud holding it to the chassis. Maybe AC thought that the larger TR3 mounting offered adequate torque damping?

Further to this, I'm presently working on a Zephyr engined Aceca fitted from new with a Moss overdrive box. This car was converted by AC from chassis AEX 780 to become RSX 5501, part of this conversion work was to rather crudely cut off the front bell housing mountings. As new mountings could have easily been fitted at the time AC obviously did not see them as necessary, even when fitting a 170HP spec Zephyr engine

[B.P.Bird]

Interesting information, thank you.
Thomas,
As an inspection port for clutch wear by assessing release bearing position I cannot see it would give you any information beyond what would be apparent by inspecting the clutch release arm position outwith the bell housing. Here of course the problem is datum - no one ever knows where the arm was when the friction plate was new, we do know that it will move as the plate wears, but we would have to measure from the unknown starting point.
Luke,
That is most helpful: In discussing the damping situation with David Sanderson he remembers having to retrospectively fit the damping cross member to an A.C. installation because of the degree of unwanted movement on the engine. Perhaps, in the combination of parts he used, the smaller, earlier, gear box mount was employed: I shall tax his memory on the point. It is certainly true that the rear A.C. gear box mount, on the end of the tailshaft housing, has much wider spaced mounting holes than on the Moss 'box.
I have been intending to weigh the Lightweight 'box and the Moss 'box for a while. I'll get around to it although I rather suspect that the Moss installation is something approaching twice the weight of the A.C. 'box.
The installation in RSX 5501 - Moss 'box plus Laycock overdrive, must have weighed as much as the Ford six ?
As I said previously when this installation was made in the G'hound and I suspect that the Lightweight 'box with remote change was intended for the four seater, it was considered necessary to include a torque damper albeit at the rear of the cylinder head, by means of the same rubber snubbers found on the Ace and Aceca Bristol, rather than the cross beam on the bell housing previously used.
I wonder if you have reached the point with '5501 where the engine can be run in the chassis and if so whether or not it shews signs of rocking about at any resonant RPM ?

[Klassik Metall]

RSX 5501 is only with me for chassis & body work & is currently stripped to a bare shell. I did have a passenger ride in the car some years ago but I don't recall there being any issues with engine stability or resonance. Yes, the Moss box fitted with an A type overdrive is a heavy bulky unit, not quite as heavy as the Zephyr motor though.

Something else to bear in mind regarding the zephyr engine mountings, is that they are substantially larger than the AC mounts & are fitted some distance above the crank centre line. They are also fitted in a "V" formation & I think these two factors provide adequate torque reaction damping.

Also, when looking at the installation of the light weight box, there is easily enough space to fit a similar fabricated mounting as per the Moss box bolted through the bottom of the bell housing. This strap type mounting could be fitted with the same rubber cotton reel type mounts & would directly align with the Moss box chassis brackets.

One further point with regard to the LW box. I seem to remember a photo in ACtion some time ago showing one of these boxes fitted a prototype AC flat twin or flat four engine. Maybe this proposed new range of engines was the original reason behind the development of the new gearbox type. It must have cost a considerable sum for such a small manufacturer to develop this new engine & box, before subsequently deciding the engine was not viable but at least they could still make use of the new gearbox design?

[B.P.Bird]

Luke,
I did wonder about the engine mounts on the 2.6 Ford engine and given your description, they do sound much more resistant to movement. So far as the origins of the Lightweight gearbox go it might well be associated with the flat engine development, although, as published in ACtion many years ago, there was a five speed transaxle designed, but never built, to go with the 2.4 litre flat six. In addition the flat six test mule G'hound, FEF 2583, was fitted with the 5 speed ZF gearbox.
I did get around to a rather shaky weighing exercise, using our bathroom scales, this morning with the predictable result as follows:

Moss 'box and bell housing with damper cradle - 122 lbs
Lightweight 'box and bell housing                    -   85 lbs

Discussing this again with David Sanderson the combination he was installing was the Lightweight 'box with the A.C. straight six, but the specific gearbox mounts are less certain. I had a look at the mount I have, which goes with the Lightweight box and it seems to be much stiffer than the Moss 'box mount as well as having two , not one, chassis mounting holes.
I feel the reasons for the original and then continuing presence, of the inspection cover may never be explained. Certainly in the days when the Weller Six was being developed the automobile clutch could be a weak link and an inspection/adjustment access could be explained - washing off oil and/or the introduction of Fullers Earth, balancing clutch release fingers, spotting release bearing problems and so on. Nevertheless to continue the inspection cover through a major redesign when modern clutches were reliable seems odd.