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Fitting a MCT 75 box to a std or spyder stressed skin frame

PostPosted: Mon May 30, 2011 10:20 am
by worzel

Some progress and a fair bit of improvisation- plus the odd question for others who have done this before me!

I'll put up a definitive article when it's finished for those who might be considering something similar- might help them avoid my mistakes at least.

To recap- I'm fitting a MCT 75 box to a std early Spyder Stressed Skin frame so these comments will definitely apply to the std Lotus frame also. Since the MCT box does not have an integral bellhousing this will be bolted direct to an allot Rocket to BDA bellhousing which in turn bolts direct to the elan block. I've gone this route to avoid the need for sandwich plates etc. Since this bellhousing is a carbon copy of the std cast iron one fitted to the 4 speed box (apart from the end that mates to the box obviously) I can retain the std flywheel, starter, external clutch cylinder and pressure plate (but I have to use a suitable friction plate because the input shaft of the box is 23 splines).
Up to now pretty straightforward but-the MCT box uses two diagonal smallish dowels to centralise it against the bellhousing and because it is designed to accept a co-axial clutch release system (which I don't wish to use) around the input shaft is a large recessed area. I've made use of this by having a plate machined to fit pretty tightly into this and to projest proud of the front face of the gearcase. The projecting part fits into the bellhousing to securely and accurately locate it against the box. The original smaller dowels can be eliminated using this method. See next post-

Re: Fitting a MCT 75 box to a std or spyder stressed skin fr

PostPosted: Mon May 30, 2011 10:37 am
by worzel
This plate is drilled and tapped and two adjacent holes are drilled and tapped in the adjacent face of the bellhousing and the plate retained in position with two small plates and wirelocked bolts. Next problem was the input shaft- the box came without a sleeve for the clutch release bearing so I got hold of the std MT75 sleeve and had it turned down to accept the std release bearing. Fortunately the nose of the MCT box is the same diameter as the std spigot bearing (at least it is on the engine in question) so no alterations required.

Two other biggish problems to solve before even thinking of fitting the box- firstly the std Spyder gearlinkage kit won't work in the frame I'm using so I've redesigned it (a bit). The problem is that apart from the lever being too far back the lever actually jams against the chassis in 2nd and 4th and the bracket that fixes to the input shaft is obstructed by the top part of the inward facing reinforcing on the chassis centre box section. To get around this I've retained the use of the linkage part that affixes to the selector rod- this is a metal case with a rubber insert (for refinement presumably) that is held on the selector rod by a case-hardened pin and special clip. In the Spyder version the gearlever bolts thru the hole in this bracket. In my case I've had a double "L" shaped bracket made that bolts to the afore-mentioned selector rod attachment, this is lower than the Spyder version and extends forward to approx 1 inch behind the std 4 speed lever position. The end of this extension is internally threaded to accept the gearlever which is retained in place by a grubscrew. See next post

Re: Fitting a MCT 75 box to a std or spyder stressed skin fr

PostPosted: Mon May 30, 2011 10:52 am
by worzel
The lever could easily be repositioned to bring it to exactly the 4 speed location if wished but is perfectly ok as is. The other problem- in the process of being solved concerns the size of the gearbox output flange- it's somewhat large so won't pass thru the centre spine. As far as I'm aware the only feasible option is to to have two of the opposing sides very accurately machined down to narrow the flange and to leave 4 holes only instead of the original 6. I intend to have this done by GKN when they make the new prop and have the flange and prop balanced as a complete unit. Fortunately on the stressed skin chassis there is an access hole right by the gearbox output flange which enables the prop to be bolted up without the need for carving out extra holes in the frame. The (only) other problems I foresee are attaching the speedo cable but Spyder offer an attachment that circlips to the box and enable a right angle drive to be used so this should not be a big issue, the second is a garage job unfortunately. Because the MCT box (and also presumably the MT75) is pretty deep I reckon the exhaust won't clear the underside of the casing. I'm referring to that part of the system just behind the "Y" piece so a small custom section will probably be required to route around the side of the box to rejoin the centre pipe. Doesn't sound much all of this but is probably just a matter of patience. Anyway, I'll post the pictures of the alterations/sizes etc when it's up and running- and this time I'm keeping all of the dimensions of the altered parts for future reference (unlike the last time I did something similar). On a related note I've got a second brand new MCT box available- ?475 plus carriage for anyone interested.