Just to add to this I know that some of the guys here use the later TR6
bellhousing with the additional ribs vertically and horizontally, but in
addition (especially when using a dog gear set which exerts vertical pressure
which stretches the casing) they use straps to clamp the gearbox together over
the remote housing. I've avoided this by careful selection of casings and a
few bits of steel bracketry at critical points and stiffer engine and gearbox
mounts, all of which do a little but often as I can't use a dog set due to
regs.
A lot of other things have been tried, such as TIG welding, epoxy bonding etc
but the strap arrangement seems to be the better option at the moment. As Kas
says a little flex in the downstream mounting is essential.
Fundamentally the main gearbox casings are not strong laterally or vertically
so anything you can do to stop them stretching will give benefit. The late CC
TR6 casings seem to be the best, maybe also the Dolomite Sprint then followed
by the LD and KD series stag. The old alloy is now quite brittle so once a
fault develops it quickly turns into a major oil loss which means rapid
gearbox failure due to heat.
Also beware tapping the casing in a weak spot for an oil cooler take off.
Enough said.
Regards
Tony
Sent from my iPhone
> On 22 Oct 2014, at 05:42, Kas Kastner <kaskastner@gmail.com> wrote:
>
> The gearbox is probably unusable and welding will just make the chance of
> more expense very probable. I believe it is a matter of harmonics
> vibration. I found this to be true in the Early TR-4 cases where they
> cracked a the bellousing tot he gearbox . We had a terrible time with
> this. I did find one way to help the situation. I made two steel hangers
> out of 1/8" cold roll steel trap 1.5" wide and attached them on each side
> of the gearbox at the bell housing then up to each side of where the
> battery box is. I then mounted these straps hangers to small rubber mounts
> to help with the shock and to take soem of the weight.. This saved me many
> races until the factory finally understood my problem nd then added the big
> ribs down each side. I also added 1/2" thick aluminum ribs on the side of
> the gearbox. One case worked fine but another made it impossible to line
> up the shafts due to the case changing shape under heat. The hangers will
> work though.
>
> *Never be beaten by equipment.*
>
> On Tue, Oct 21, 2014 at 2:50 PM, Van Mulders Marcel <
> van.mulders.marcel@telenet.be> wrote:
>
>> In 2 years, I had 4 broken gearbox casing : maybe one of these can be
>> repaired : it has a crack where the bottom of the gear casing and the rear
>> wall are mating. Considering the weight of the engine and gearbox, the
>> stresses at that point must be very high : the 4 cylinder TR's have 2
>> mountings at the front of the engine and 1 mounting at the gearbox
>> extension. A gearbox with overdrive has this rear mounting at the very end
>> of this extension : the shearing force between casing and extension must
be
>> very high, one should think that the rear wall of the casing should be
>> pulled out all the time in racing. Has someone tried welding a gearbox
>> casing?
>> Marcel
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