Should I weld mycracked gearbox?
Discussion
Guys,
I'm restoring a 67 Triumph GT6 and during the resto, I noticed that I have a crack in the gearbox casing just above the output bearing.
It's right at the top of the output bearing, and right at the back of the box, so should't be "immersed" in any oil, and certainly no pressure. I think temperature will be pretty low too, so I don't THINK it will leak, but if I'm going to get it welded then now would be the time (before I put my body tub back on etc).
I don't have too much cash to splash for the next couple of months either, so don't want to get it welded if I don't need to.
By the way, oil flows through that bearing anyway to fill the overdrive, so most probably 90% of any leak will go into the OD, or hit the OD gasket.
Any advice would be much appreciated.
thanks
Guy
I'm restoring a 67 Triumph GT6 and during the resto, I noticed that I have a crack in the gearbox casing just above the output bearing.
It's right at the top of the output bearing, and right at the back of the box, so should't be "immersed" in any oil, and certainly no pressure. I think temperature will be pretty low too, so I don't THINK it will leak, but if I'm going to get it welded then now would be the time (before I put my body tub back on etc).
I don't have too much cash to splash for the next couple of months either, so don't want to get it welded if I don't need to.
By the way, oil flows through that bearing anyway to fill the overdrive, so most probably 90% of any leak will go into the OD, or hit the OD gasket.
Any advice would be much appreciated.
thanks
Guy
Edited by bluphoto on Monday 28th June 09:34
Edited by bluphoto on Monday 28th June 09:48
Don't like the look of that. If you get it welded you'll need to have the bearing hole resurfaced so the bearing will fit back in it so more expense. Would it not be easier and cheaper to pick up a replacmeent gearbox casing from a breakers and start again?
Danger if you leave it is what's going to happen with the crack? Will it propagate and snap off a section and how hard would it then be to change the box at a later stage? For my moiney I'd look to get a s/hand casting and replace it. Try calling Steve at A1 Gearboxes in St Neots, he MIGHT be able to help 01480 213571
Danger if you leave it is what's going to happen with the crack? Will it propagate and snap off a section and how hard would it then be to change the box at a later stage? For my moiney I'd look to get a s/hand casting and replace it. Try calling Steve at A1 Gearboxes in St Neots, he MIGHT be able to help 01480 213571
'Plastic Metal' would do a good job of repairing that as long as you chemically clean it first. I'd be inclined to grind a small V into the crack to allow more material to penetrate. I've repaired much larger holes in gearboxes (well a gearbox, singular) that way and they are still going fine ten years on. Mate of mine did the same on an alloy sump and that's been oil tight ever since too.
It looks like cast iron so it'll need to be heated first (bung it in the oven when the mrs is away!) As mentioned grind out a groove for good penetration, the bearing surace should be reworked if your welding that part up but I'd be inclined to weld up to it carefully leaving the bearing surface alone.
camelotr said:
I think the best would be to replace this gearbox. Though it is possible to veld, it allways brings in some scale of hazard. Plus striping the whole box, velding, refacing, maybe line-boring, rebuilding must be a nice sum - maybe more than a 2nd hand unit.
i think your boring experience is clouding your judgement 
The gearbox is custom (okay built out of old bits of other gearboxes):
It's a Dolomite 1850 casing with the innards out of another Triumph which I forget. Had to use the Dolomite casing to be able to take the J-Type overdrive apparently, which is stronger than the D-Type overdrive of the standard GT6, as I'm now looking at approx 170BHP.
So finding a direct replacement gearbox to slot in wouldn't be an option. I like the sound (or the price) of the JBWeld - that said, do I even need to bother with that? It's well above the oil line.
It's a Dolomite 1850 casing with the innards out of another Triumph which I forget. Had to use the Dolomite casing to be able to take the J-Type overdrive apparently, which is stronger than the D-Type overdrive of the standard GT6, as I'm now looking at approx 170BHP.
So finding a direct replacement gearbox to slot in wouldn't be an option. I like the sound (or the price) of the JBWeld - that said, do I even need to bother with that? It's well above the oil line.
Edited by bluphoto on Tuesday 29th June 09:36
BliarOut said:
camelotr said:
I think the best would be to replace this gearbox. Though it is possible to veld, it allways brings in some scale of hazard. Plus striping the whole box, velding, refacing, maybe line-boring, rebuilding must be a nice sum - maybe more than a 2nd hand unit.
i think your boring experience is clouding your judgement 
It may be true.
But some moons ago I have helped a friend mine in his build of a sporty mini. We hae found a crack in the dif case (not that bad lookin). After inspecion, we decided to leave it as is. After about 2000kms the box exploded after a change from 3 to 2. The result was a ruined gearbor (nice dog-box
) and a partly riuned Salisbury LSD...Steve_D said:
Castings don't just crack so there must be some amount of stress taking place around the bearing.
No I'm pretty sure I cracked it by hammering the bearing in squint. I straightened it up okay so I think there's no stress left.The OD on the back holds the face together, and there's a top plate with a bolt either side of the crack too, which should brace it from the face and top edges.
There's a rounded machined slot in the bearing hole at 12-o-clock, which is where it cracked from. I think a weld could come down into this without interfering with the bearing.
I think the box could be welded from INSIDE as I wouldn't have to dress up the weld afterwards. I'd like to stay away from the top edge too rather that recreating a gasket face.
I was just hoping not to have to strip it down again.
Edited by bluphoto on Monday 28th June 22:20
Hammering a bearing into cast iron casing is always going to end in tears.
JB weld may suffice as a bodge, but make sure you clean the area up properley. As others noted - use a die grinder to put a V into the crack - which will also clean the area up.
Welding needs to be done carefully as its cast iron and it may distort.
JB weld may suffice as a bodge, but make sure you clean the area up properley. As others noted - use a die grinder to put a V into the crack - which will also clean the area up.
Welding needs to be done carefully as its cast iron and it may distort.
As I told earlier, I would replace the casting - especialy for a 150+ bhp engine.
BUT if You accept the hazard, You may try to attach a thick piece of steel (some kind of strap) and brigde the two halves using high tensile bolts. In this case You may also need to drill a coupl of extra threads in the casting.
BUT if You accept the hazard, You may try to attach a thick piece of steel (some kind of strap) and brigde the two halves using high tensile bolts. In this case You may also need to drill a coupl of extra threads in the casting.
Okay, it was really niggling at me after talking to you guys, so I managed to get hold of another Vitesse 3-rail casing and rebuilt the gearbox into that.
It's amazing how loose the bearing was in that cracked casing - it practically fell out - I actually pushed it out with my finger.
Peace of mind is a wonderful thing!
Thanks for your help,
Guy
It's amazing how loose the bearing was in that cracked casing - it practically fell out - I actually pushed it out with my finger.
Peace of mind is a wonderful thing!
Thanks for your help,
Guy
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