Frame rigidness warning for al enfield riders, please read

[arnaud]

I'm not totally sure if my concern is justified, but please read my findings.

I was cleaning the enfield frame ( a little) when i got puzzled, and then scared..
From the back, the enfield frame makes a triangle. The upper side is going to the big frametube above the gearbox. The lower side goes beneath the gearbox,the latter supporting on it(but not the way around since it is an open fit)

Original, this frame end was bolted to the engine to get support (by the 2 supports I had to grind partly down to make the engine fit) .But now the gearbox + half the weight of the engine is leaning on it! (yes, also hanging at the upper side of the gearbox, but that doesn't look very sturdy)
I'm afraid that the frame rigidness is damaged by this! what do you think?

Thanks to the dirt on the frame i could see the difference. When the bike is on the centre-stand, the plate
on the down side of the gearbox(yes, where the footpeg-shaft is going through) is about 2,3mm (i measured it afterwards) higher then it is on the side stand!!
And this is not supporting 2 people going on the road..
starting to panic..

[Anorak_ian]

The frame is a 1940's design and it is absolutely awful.

I think it was the mid 1960's when Royal Enfield were approached by The Madras Motor company who wanted to build bullets, but Royal Enfield only gave permission to build the 1940's patent frame design which they hadn't made for some years.

I have an Indian frame that I'm going to cut up, as I bent it taking off a bolt. The things made of tissue paper, really soft metal.

I bought a late 1960's twin frame for my next project, you can really see and feel the difference, the late Brit frames were a lot stronger.

If I were you I'd brace it as much as you can, getting a Brit frame with a v5 is next to impossible.

[Diesel Dave]

I'm going to disagree about the earlier model and Indian Frames being less rigid.

The latter English frames are made of much heavier tube to make up for the lack of triangulation at the back and the twins needed a stiffening plate behind the gearbox - don't omit this from your build.

At th rear mounting position the two arms finish in welded bosses where the engine plates start from - there is a substantial stud with heafty spacers between them - the next link in the chain is the gearbox which is located by the double triangle plates at the top and the pinch stud through the engine plates - effectively making a solid structure - the later frames omit the top mountings and I believe have to have a much heavier frame to compensate. There is only a small locating stud beween the rear engine plates and the engine - all of the strain must be taken by the 4 gearbox to engine studs.

A mate has a 1960's 350 Bullet with the 17" wheels, in theory this should be much stiffer but I can deflect his engine further than mine by pushing sideways with a boot on the bottom of the engine.

My Indian frame did take impact from a Fiesta at 70 mph from the rear and was still rideable with just 10mm deflection - it's a tough frame.

Regards
Dave

[arnaud]

What i try to explain is;
the lower back of the frame goed underneatch the gearbox but is not fixated to it in any way. The shaft for the footpegs only stretches underneath it.
The engine is connected to the subframe which in his turn is only held by the 4 supports of the gearbox. Leaving the 2 lower tubes free in space. (you can see them move up and down when you take the bike from the centre stand!)the 2 plates underneath the gearbox end with a pair of ears with holes which are originally attaced to the engine to keep it rigid.
At my conversion this is not mounted in any way.

[Sphere]

Did you hear about this crazy new feat called "digital photography" yet?

[arnaud]

In the meanwhile, i welded 2 triangle shaped steel plates bordering the lower tranny plates and the subframe. maybe the frame has some cracks form the heavy duty, especially from the heavy-loaded summer holidays.. but since you cannot see them like this, i will do like the austrich and carry on...
I think the welded mounts of the swingarm took most care of it.