subframe rupture! need advice

[arnaud]

Dear everyone,
half a year ago i realized i negelcted the enfield frame design and welded the lower gearbox plates, which originally are bolted to the engine(so it cannot be pulled down, for rigidness, or else all the downforce will be transferred to the connecting plates at the swingarm axle)
to the lower subframe. After our holiday trhough the Swiss and Austrian alps i noticed these welds were broken!

it is a subframe of the 'altmann; type, only at the front end i welded a hook from the front plate to the ground plate to give the front end the support it normal has from the engine, so the front tube will not bend forward and the frame wont get too much tension when weight is added.
(since my engine is out of the middel, i could not use the starter motor connections for it)

Anyway, now the 5mm plate bolted to the gearbox has a rupture!
just under the 2 lower bolts keeping thje subframe to the gearbox.
So, i guess that was the only bit were vibration was possible, since above the lower bolts the 4-poit mount is stiff.
I need another way or design, Some say make it more solid, other say make it light so it can move and bend(and how about metalfatique?)

I've seen the pricepartys subframe which seems only to be connected to tthe lower frame tube and plates which original need the support of the engine, which is now not bolted to the gearbox so no support and rigidness?
or do i not know something..
Anyway, helpfull comments are welcome!

[arnaud]

the picture is 90 degree twisted, just have another computer and cannot solve this.., so the broken part is gearbox-side..

[Sphere]

Rotated.

[andrewaust]

My design is similar, although a little different that it also uses the two rear supports that stops forward and aft movements.

Best to look here http://www.dieselbike.net/AndrewsRoyalE ... nfield.htm





Till now no cracking



A

[arnaud]

Hi, how thick is the tranny plate you use? and how many km/miles does it last untill now?

anyway, the lower gearboxplates have 2 ears which are original bolted to the engine, i think for making this triangle (to the iron weld whre the swingarm axle is mounted in) stiff, so that not all the downforce goes to this (forementioned) framepart.
The priceparts subframe seems to be entirely supporting on this part though..no engien weight on the gearbox.
But the original construction also has the engine weight on the gearbox! the latter only suspended on the 2 upper 3-angle plates! (doesn't look so sturdy to me)
the lower ones support nothing upwards, only stabilizing the construction..

You have to seem this weld on separately? i cannot see on your website how you do this with the lower gearbox plates themselves?

Anyway, i was thinking about redesigning these lower gearbox plates, making them go all the way to the lower(moving) part of the gearbox subframe plate(tranny plate).
I am worried about a couple of things though..
Doing this transfers the vibration to the -not so big & sturdy) bolts which connect the 2 lower gearbox plates. won't these collapse or the 2mm wide plates eat up in the bolts?
Second, now the engine has eaten up this tranny plate, when i make it stiff, the vibration won't be absorbed as much and is there danger of gearbox-ruptures?
(some say make the subframe smooth & flexible so it can absorb the movement, but what about metal fatique? (besides, original the engine is a stiff part, supporting the frame construction)

Okay, any comments and teachings about this subject welcome!

Since i have to make it all difefrent, i am thinking about placing the engine in the middle, this means getting a longer gearbox shaft(difficult to switch? how stuck are the sprockets..)
and inner gearbox..

[arnaud]

Dear people,
I just got a very interesting picture of a subframe which looks a lot lighter and maybe capable of absorbing the vibration.
althuoh i would make sme reinforcements at the side my stuff broke..
Comments, reflections please!

[andrewaust]

Hey Arnaud


From memory the base was 2.8mm RHS channel, plate was 6mm, pipe 4mm, front cradle lugs 6mm in thickness. Also used the original side lugs and braced the rear. The bike has done over 11,000.00 klms. I also supported the head with a good robust mount. Just inspected the subframe when the engine died and was OK.

The last post of the cradle! Looks to flimsy to me, I can see it cracking at the bends.






A

[arnaud]

Yes, i can imagine ruptures there over time.
absorbing is good but metal gets tired..i think?

[Pat Pending]

Re : Robustness of engine mounting subframe.
Thought the attached .jpg may be of intrest, it shows my own design of gearbox/ emgine mounting.
The the substantial vertical plate forms the backbone to which the lower gearbox mounting plates and rear engine mountings are welded. The gearbox effectivly sits in its own little subframe which is bolted rigidly to the Enfields main frame via the normal through bolts.
The main engine cradle (tubular with cross mounts for the engine fixings) is attached at the front on the std Enfield lower frame stud, and bolts at the rear (via substantial bolts) to the backbone plate as can be seen. This has the advantage of being able to be swung out of the way during engine decking. The plates used are substantial and the bolts high tensile. So far no issues have been noted in use.

The other advantage this solution gives is the neater and more compact frame package allowing the exhaust to be run in frunt of the engine over to the RHS.

Regards Pat Pending

[arnaud]

Hi, it looks like a priceparts subframe..
the lower gearbox plates which are originally bolted to the engine are welded to the subframe, also the tubular ends of the lower rearframe, i see. Now all the downforce(or at least half of it) has to be carried by the (now open) triange.
The weld between the rear frame tubes, (where the swingarm axle is mounted in) must endure all this torque its producing. or am i missing something here?
Since original the engine is hanging on the gearbox, i can imagine it is not meant to cope with this tsrengt, and i can imagine bending out of these tubular ends.
The same, but force coming fron the other side is when the engine is hanging on the gearbox but the lower plates(which are now wleded to the subframe) are hanging free.
I had this situation and could see difference in position when the bike was on its center stand or side stand(then imagine sitting ont it with 2 people!)

[arnaud]

My design is similar, although a little different that it also uses the two rear supports that stops forward and aft movements.

Best to look here http://www.dieselbike.net/AndrewsRoyalE ... nfield.htm





Till now no cracking



A

your design is better for the rear part, but i can imagine that alle the force wich broke mu tranny plate, can get its revenge just between the point under the 2 lower geaarbox bolts, and the upper part of the reinforcments at the back side..
it could 'nick' in a way.. if you understand what i mean. It is not secure untill above the lower gearbox bolts, so to be sure/rigid, the reinforcements should get a little hihger the the lower gearbox mounting bolts holding the tranny plate, right?

[andrewaust]

Yes! Them little side mounted threaded lugs at the rear takes the rocking motion out of the cradle and transfers it to the frame mounts, that is why I didn't grind the frame lugs off, to put more strength into it I've braced the rear overlapping the braced lugs.

I watched what the engine done whilst loose on mounts (actually used rolled up newspaper/tube sitting the engine on that and my floor creeper), revving it up etc to see what kind of movement I'd get.

From the K's I've done it seems the cradle design has worked out well, to bad other parts isn't up to par! Gearbox main shaft just broke = GGGRRRRR!



A

[arnaud]

Did you have the longer taurus type shaft?
And did it have an extra support in the inner primary or not?

i think it is not ideal because these shafts are too long so you have to use an adaptor plate between engine and gearbox.
Since the strain on the inner-primary-bearing is transferred to this part, which is already weaker..
If you want the engine in the middle you should have the possibility to get a shaft at extact needed length (lenght taurus shaft - width adaptor plate)

[andrewaust]

Yes longer Taurus shaft from India - no support, but shaft broke where threads are at start of clutch splines, nut was tightened to only 18 ft-lb and chain was on the loose side, so either it had a fault from the start or vibration ? was the culprit. Cannot think of anything else, definitely a fatigue crack that's been going for a while.

Hopefully it should be on the road at the end of the week, hopefully it will not need any more attention for a while after this.

So I'm on the dirt bikes for the week




A

[Sphere]

I would be interested in seeing some pics of where it failed. For an inner primary and a taurus shaft I have been quoted 70GBP and 26 shipping through ebay-royalspares. Dunno what the shaft costs by itself.

[Sphere]

Well, his website lists the "Extended Gearbox main shaft" and the "Inner Primary drive case" for 100GBP (total) + tax + shipping. Unfortunately the pic doesn't work, I don't have access to your mailbox (fortunately for you )

[andrewaust]

Oh bugger mate Yeah my fault, didn't read the post properly the first time = bugger . Actually 70 GBP isn't a bad price for the both.

I'll try and move the pic to another location, short for time "as you can tell "



A

[arnaud]

here's a pic of the redesigned subframe..
maybe it can inspire someone