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MG MGB GT V8 Factory Originals Technical - Roadster shell stiffness
|Roger Williams book recommends that you don't use a rubber bumper shell, but use a chrome bumper one (brand new as well!!) and do loads of cutting and fabricating the shell needs, because its stiffer than the rubber bumper shell.|
Frankly I think he's WRONG as I've found quite a few mistakes in the book. (It gives you a good basic idea but don't trust the detail)
If the older style shell is stiffer it's got to be possible to strengthen a later shell.
I'm doing a '79 roadster with an EFI V8 and I have no intention of buying a new shell, unless I twist it in half when I floor it!! (and it's going to be fun trying).
Does anyone have any details or advice?
|I too have found Roger's book to have MANY minor errors. Having seen the guts of both CB and RB shells many times, it's not at all evident to me that one would be any stiffer or less stiff than the other. I do agree with Roger's basic premise that a GT shell is much stronger and stiffer than a roadster shell. That's just basic physics -- a GT has a truss structure, whereas a roadster is basically a beam. But a roadster shell in prime condition is, as we all know, certainly stiff enough to get the job done. Welding in a set of tophats, as per RV8 spec, should be helpful in a roadster and should help the shell deal with even the mightiest V8s.|
Can you give me some detail of the top hats.
Dimensions and where they are fitted. I am not familliar with the RV8 shell mods.
I've just finished the tunnel mods and gearbox cross member so the motor and rover box now fits. I'm probably going to do one of the sills so while the torch is hot I may as well add som more strength!
Thanks for your comments
|When my father had his V8 Roadster built we had the "luxury" of cutting all the special "bits" out of the original BGT V8 'shell (which he had soundly wrecked !) and grafting them onto a CB Heritage 'shell. Had to sort some mountings as we fitted a 5-speed 'box, but I'm not sure what the "tophats" are. As for strengthening, we had all the un-necessary holes, access plates, slots etc in the body welded up and "strong" points welded in for the roll-over hoop to mount on. The holes for the chrome swage-line trim on the body were also welded and ground flush for a smooth exteria look. |
My understanding is that the roadster 'shell is quite stiff torsionally, so I wouldn't worry too much which one you use. The're not bad with scuttle-shake for example. As for extra strength I'm not sure where you would put it, maybe ask a BCV8 racer what they do.
|I don't have the relevant books to hand to check but I don't recall there being any major difference between chrome and rubber bumper shells in the area of the sills/floors/chassisrails. Maybe panel thicknesses where reduced to try and save some weight - personally I thick thats unlikely.|
I have been told on a number of occasions that heritage shells are not as good as a properly rebuilt original shell. The justification each time being that the quality and quantity of the spotwelds holding the bits together does not match an original shell.
|There were some quality issues with the Heritage 'shell we used, mainly poor panel fit and shutlines. This was partly due to time in build, remember each original MG shell was "hand finished" or fettled to use a good old english term, and partly because the old panel pressings had 30 years of wear in them, the re-manufactured pressings were crisp and new. Therefore individual panels which comprise the 'shell were not necessarily all the correct shape........ Spot welds were fine on our example.|
The ‘tophats’ extend from the crossmember under the gearbox to below the leaf spring mount. The front of the ‘tophat’ is at the same level as the crossmember while the rear taper down to a point some 2 inches below the (chrome bumper) spring mount to from a new mount. That means of course that the spring is lower at the front but it is the way the RV8 and the Heritage V8 roadster shell is made. The ‘tophat’ is bolted through and welded to the original spring mount and welded along its length. In my opinion it would be better to have the leaf spring bolted through the original mount and use the lower hole in the ‘tophat’ for anti-tramp bars.
My car is still up on axle stands, I’ll crawl underneath and take some measurements tonight and post later.
The panel gaps and general build quality of the 60’s and 70’s are reproduced very accurately by Heritage - so are bordering on appalling, poor at best. However, there is no doubt there are more than enough spot welds and rust proofing is excellent.
Top hats - this will not be easy to explain. From the crossmember back towards the spring hanger an upside down, top hat section, 18 ½ inches long, 2 3/8 wide, 1 ¼ high, the brim ¾ wide. Welded to each side of the top hat, 9 ¾ back from the crossmember to the spring hanger, a wedge shaped piece 14 inches long, 1 ½ high at the front and 4 ¼ at the back. The rear top of this wedge has an ‘ear’ extending up and bolted to the existing spring hanger. 1 ¾ down from the original spring hanger is the new spring position. 2 ½ down from that another hole for an anti tramp bar. These pieces are about 1/16 thick.
Still with me?
Now it gets tricky. Inside the rear of the tophat wedge pieces is a brace for the spring hanger, two vertical channel sections back to back. The one facing the front is 1 ½ wide, the one facing the rear is 2 3/8 wide with holes for the original and new spring mount and the anti tramp bar. Neither of these channel sections are parallel in profile, the front one is 1 ½ from front to back at the top tapering to nothing at the bottom. The rear channel section is 1 ¾ from front to back at the bottom and extends up to and is bolted to the original spring mount. These channels are not even vertical, leaning forward at the top about ¾ inch. They are about 1/8 or less thick.
Where the chrome bumper spring would normally be attached is a tube with a plate welded to it extending up and welded to the body. I would prefer the spring to use this upper position but without cutting the welds and removing the tube it can’t.
I hope that helps but it is not easy to describe.
|My Heritage shell seemed well welded, although some of the gaps were pretty horrific, luckily the worst was the gap between the front wing and scuttle, hidden by the screen|
I welded top hat section from crossmember to spring hanger, and also wedge shaped sections from chassis rail to cill (there's a pic on one of the V8 websites)
It certainly looks impressive, the car feels very rigid
compared with my previous shell.
This thread was discussed between 09/04/2002 and 11/04/2002
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