Cracked gearbox shell fix idea

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Fast Eddie

Fast Eddie

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Gents,
I've researched loads of threads re the infamous crack between layshaft and main shaft bearings. I'm no transmission designer, but one has to wonder what the thinking was around designing such a wafer thin piece of alloy between the bearings!?

Anyway, what about fixes?

Does the thicker shell help this? It will clearly strengthen the general surrounding area, reducing flex etc. does that stop the cracking?

And what about this as an idea: imagine machining two steel bearing sleeves out of one piece, so it looked like a figure of 8, then machining a figure of 8 hole in the case and pressing the sleeve in. There would now be no wafer thin alloy at all, and the figure of 8 sleeve will distribute the loads to a much larger area of the case.

I've probably overlooked some reason why this is impossible / impracticable. What say you chaps?
 
The figure eight even if made from unobtainium would still retain the thickness of old between the bearing bores based on the shaft centres/centers.
Perhaps a slightly smaller OD output bearing would gain material in the figure 8 insert or a needle roller at the layshaft instead.
Or depending on running clearance from the case to gear back faces a figure 8 strong back that had bores of the outer race ID's and secured with countersunk head capscrews.

Cracked gearbox shell fix idea
 
How would you align the bearings with those in the other end of the box ? And if the material for the 8 is titanium, it would be difficult to get it on dimension. If it is steel you would still have a sealing/expansion problem where it is pressed in. You might do better to machine a complete new end to the box out if high strength thin steel and find a way to fit it to the faced off shell under tension with through bolts.
 
Fast Eddie said:
Gents,
I've researched loads of threads re the infamous crack between layshaft and main shaft bearings. I'm no transmission designer, but one has to wonder what the thinking was around designing such a wafer thin piece of alloy between the bearings!?

Anyway, what about fixes?

Does the thicker shell help this? It will clearly strengthen the general surrounding area, reducing flex etc. does that stop the cracking?

And what about this as an idea: imagine machining two steel bearing sleeves out of one piece, so it looked like a figure of 8, then machining a figure of 8 hole in the case and pressing the sleeve in. There would now be no wafer thin alloy at all, and the figure of 8 sleeve will distribute the loads to a much larger area of the case.

I've probably overlooked some reason why this is impossible / impracticable. What say you chaps?
Click to expand...
Imagine a $10,000 bearing.
 
I've seen a couple Norton gearbox shells with this "cracking between bearings" problem. One of them just destroyed all the gears and the shell broke into two pieces. :evil: If it was only cracked, perhaps weld in the entire layshaft hole ... and then machine it for a needle bearing instead ??? (like a Triumph 650 gearbox) Seems like alot of work though, and way above my skill level. I have instead just obtained a good used shell and put a roller bearing in it. Just my 2 cents ...
 
I see quaife sells a strengthened shell, price is 255 £ , quite reasonable, tho it does say "prices starting at". They also do a complete magnesium cased box. p.O.A, so presumably the £255 is for an aluminium shell.

Glen
 
worntorn said:
I see quaife sells a strengthened shell, price is 255 £ , quite reasonable, tho it does say "prices starting at". They also do a complete magnesium cased box. p.O.A, so presumably the £255 is for an aluminium shell.

Glen
Click to expand...

Well spotted Glen, they do indeed. And you're right, £255 is for the alloy shell, which is only £9.00 more than a new, standard, AN shell.

Actually, alloy is stronger, size for size, than magnesium (but weaker weight for weight) so the alloy shell will be stronger than the magnesium shell, albeit heavier, and a lot cheaper!

People interested in originality would prefer the AN shell I'm sure, but I'll be calling Quaife on Monday morning.

Thanks!
 
What's the worst case scenario of running a cracked gearbox? Loss of lubrication and eventual seizure or catastrophic failure followed by death? I have a hard time accepting that a crack across this tiny isthmus of alloy changing the structural integrity of the gearbox very much. If we are talking about loss of lube, why not work on sealing the crack and use the case?

More than one bearing race has been drilled and pinned to keep it from rotating in a case. Why not assemble the case with bearings, drill the crack, and pin it. A properly machined fit with some JB Weld or other sealant of choice seems like a fairly easy fix.

Russ
 
I wonder if anyone has tried casting a gearbox shell and then machining the layshaft bearing hole to accept a Torrington type needle bearing. A needle bearing would have a much smaller outside diameter than the original ball bearing that is now used. BSA and Triumph have been using needle bearings for their layshafts which seem to work just fine. Of course when you change one thing, you end up changing a hundred things. It would probably require a different layshaft, hardened thrush washers, etc. to get the job done. But it would sure give a lot of material in the gearbox between the sleeve gear bearing and the layshaft bearing.

It is way beyond my engineering skills but if a gearbox became available with that type of setup I would be tempted to buy it.
 
ludwig said:
Long ago I have seen gearboxes where the layshaft bearing was replaced by a bronze bushing , like in the kickstart shaft .
Not for road use , but on a Wasp outfit .
Machine the back of the bearing recess out and weld in a fat alloy plug ( machined for the bush ) from the outside .
There is enough clearance with the chain to let it stick out everal mm .
the same principle like the needle bearing of Peterjoe .
What have you got to loose ? ..
Click to expand...

Hi Ludwig,
Funnily enough, I have had similar thoughts. I've had needle rollers on unit Triumphs replaced by specially made bushes with an oversize OD before to make good a problem casing and it worked well.
I think it is a good idea. It wouldn't be straight forward though as there'd be lots of opportunity for dimensions to slip during the process. I think making a fixture would be the answer to this.
It's all a bit out of scope / ability for me right now. It's probably a good idea for one of the pro outfits who could make a good turn around or exchange service of this nature.
For my own build this time, I'm going to explore the Quaife shell option.
 
OK - here is another idea: how about casting a gearbox shell out of aluminum alloy complete with stiffening ribs and then having a separate bearing end machined from chrome moly steel which is then bolted to the side of the gearbox shell.

As far as the existing gearbox shells are concerned, whether it be an Andover Norton or Quaife part I would check the edges of the bearing bores to ensure that there are no sharp or rough edges. If there is I would sand and polish them to help reduce any stress risers between those bearing bores.
 
The DS shell wall is like 1/16" thick. If the whole DS of shell made of steel to hold bearings then could bolt it up to the shell and replace as needed rather longer than alloy shells last. I like the idea of a pin in the cleavage and maybe one more in meaty area of each bore to hold stable. TTI has gone to needles instead of sleeve bushes.
 
worntorn said:
I see quaife sells a strengthened shell, price is 255 £ , quite reasonable, tho it does say "prices starting at". They also do a complete magnesium cased box. p.O.A, so presumably the £255 is for an aluminium shell.

Glen
Click to expand...

Anyone have a pic on how they strengthened it?
 
swooshdave said:
worntorn said:
I see quaife sells a strengthened shell, price is 255 £ , quite reasonable, tho it does say "prices starting at". They also do a complete magnesium cased box. p.O.A, so presumably the £255 is for an aluminium shell.

Glen
Click to expand...

Anyone have a pic on how they strengthened it?
Click to expand...

Their site doesn't show specifics, other than a generally beefed up case: http://quaife.co.uk/shop/products/a1h100a

I hope to gain more info from them, hopefully tomorrow.
 
I have Quafe shell and besides the big ribs its DS is definitely thicker by about 1/4"+ in the whole area so had to grind out cradle and some off shell to fit it in Peel that held the AMC just fine. A last ain't so much the weak shell as the thin shafts bowing that give up first then damages bores and can blow out the shell.
 
I got a strengthened case and the uprated ball-layshaft-bearing from Mick Hemmings, Commando gearboxes and I have an odd-history! (7 trans rebuilds in 9 years!)

Vince
 
Unclviny said:
I got a strengthened case and the uprated ball-layshaft-bearing from Mick Hemmings, Commando gearboxes and I have an odd-history! (7 trans rebuilds in 9 years!)

Vince
Click to expand...

Is that a Quaife case, an Andover Norton case, or something else Vince?

Did it fit the cradle well? And have you 'tested it' yet... You seem like an ideal gearbox tester with that record! Why the history, what are you running?
 
I run a heavy-hand and no brain! (in my defense I was young) I eventually learned that all the rebuilds in the world do not help if you have twisted the case out of square. The trans is in Colorado getting a rebuild right now (into the new box) but I believe it to be a Quaife.

Vince
 
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