Which loctite?

I have found that both the layshaft and mainshaft bearings in gearbox are loose again. A couple of years ago I used 609 but may not have applied it correctly, anyway it obviously didn't work. So debating whether to use the same (a new bottle) or to use 603 (assuming it is available in Australia). On the one hand I don't want them to get loose again but on the other hand I don't want something that is impossible to dismantle if required. Anyone with experience of using loctite for this application who can advise me?

I tried to fix a spinning main bearing twice with loctite, both times it failed within a 1000 miles, loctite does not seem to work with steel bearing in an aluminium alloy housing, maybe its the heat cycles breaking the bond as the alloy expands faster than steel. That said it should work for longer in a separate gearbox where the temperatures are less. So as I see it you have 2 choices, use a stronger loctite as if it fails again disassembly will not be an issue and if it works it only becomes an issue if the bearings fail so fit new ones, or have the OD of new bearings plated to give the required interference fit. Making an oversize housing in steel is ruled out by how close the 2 bearings run together.

I don't believe there is a loctite product which will meet your needs.
The reason is that an adhesive or gap filler like loctite cannot accommodate an aluminium housing expanding away from a steel insert (bearing)
As the gap becomes larger at operating temperature the loctite (or similar) simply becomes flakes to contaminate your oil.
There is no substitute for good fit (transition or shrink) in this situation in my opinion.
Cheers
Rob

It may be an option to have the outer ring of the bearing copper plated to obtain the correct fit.
Found this information on another forum , never tried this method myself.

Peter R said:

It may be an option to have the outer ring of the bearing copper plated to obtain the correct fit.
Found this information on another forum , never tried this method myself.

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That used to be a reasonably common technique to tighten the fit of loose main bearings in aluminum and magnesium crankcases. I've done it to get a tighter fit of main bearing inner races on the crankshaft. Copper plating is a simple procedure, and kits are available at reasonable cost. The only concern is making sure to mask the bearing to prevent plating on the rolling elements and races. If there is room in the cases to fit a bronze sleeve and bore it to the correct size, I think that would be a better solution, but I think kommando is correct that there is not enough material to do that in the gearbox shell.

On the other hand, I've used Loctite RC 620 for loose mainshaft bearings in a Commando gearboxes a couple of times with good success. It is commonly used by manufacturers to hold bushings in aluminum automatic transmission cases, so seems appropriate for a Norton gearbox. But, like kommando, I have also used it a couple of times for Commando main bearings in crankcases, and on later disassembly found it had failed, allowing the bearings to spin in the case.

Ken

I am currently working on zinc plating outer bearing races for a Triumph for the same reason. Achieved .0009-.0014" additional diameter in 25 minutes with two D cell batteries. Did have leakage into the bearing race and balls on first try with duct tape with old bearing. Have "plater's tape" on order from E-Bay. Hard to measure precisely with micrometer. Interesting to measure expansion of case hole and bearing at 220F. Case opening grows .0045". Bearing race grows .0030 to .0035". So, if no interference fit, easy to see how bearing race would spin in case.
Doug

Pinning the outer race will stop rotation in the case.
It's a bit of work tho.

Glen

Pin them both in place with set screws. Machinist work. No glues. Or obviously find a tighter $hell. My MK111 has a roller type mainshaft bearing where the machinist fitted an aluminum sleeve in the case to accommodate the bearing. Again $.

Douglass Harroun said:

I am currently working on zinc plating outer bearing races for a Triumph for the same reason. Achieved .0009-.0014" additional diameter in 25 minutes with two D cell batteries. Did have leakage into the bearing race and balls on first try with duct tape with old bearing. Have "plater's tape" on order from E-Bay. Hard to measure precisely with micrometer. Interesting to measure expansion of case hole and bearing at 220F. Case opening grows .0045". Bearing race grows .0030 to .0035". So, if no interference fit, easy to see how bearing race would spin in case.
Doug

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When I did the copper plating on the inside of the main bearing race, I dipped it in a soft wax (half paraffin and half bees wax), and then carefully trimmed the was off in the area to be plated. I also twisted a copper wire around the race for the electrical connection, before dipping it in wax. Worked pretty well. You might be able to do something similar with a ball or roller bearing by first taping the bearing area, and then dipping it in wax.

Ken