Rear Hub Bearing oil leak

[Storkfoot]

I have a very slight oil leak between the outside of a rear bearing and the casing. The casing is an old Italian GP150 which, as an empty casing, I had owned for years before building a Casa 185 engine into it a couple of years ago. I have tried silicon sealant between the casing and the bearing but oil still weeps slightly through after a couple of hundred miles.

Is a bearing with a recess for an O ring likely to remedy this, with an O ring fitted of course?

https://www.lambrettaspares.com/mbp0712a.html

The link above is for an oversize bearing which, I presume, is not what I need as my bearing is still an interference fit in the casing.

[dickie]

If yours is leaking, but still a tight fit then the hole in the casing must have an imperfection. Maybe slightly oval or some damage.

Going oversize would get rid of that, depending on how deep the damage is of course.

[Storkfoot]

If yours is leaking, but still a tight fit then the hole in the casing must have an imperfection. Maybe slightly oval or some damage.

Going oversize would get rid of that, depending on how deep the damage is of course.

I suspect that is the case. The last time I had the bearing out, I did think that there were one or two witness marks on the casing where it meets with the bearing.

I have the proper tool to pull the bearing into a hot casing so, perhaps, the first oversize with an O ring and a smear of silicon sealant would be worth a go

I am just a bit concerned that an oversize bearing may be swapping one problem for another.

[dickie]

I'd be concerned about pulling an oversize bearing into standard sized hole. As a minimum, I'd rub the inside face with wet and dry to try to remove those witness marks first.

I'd be worried about stress cracking. Those marks might turn into cracks if they're sharp and there's a lot of stress from the oversize bearing

[LambrettaMarky]

Paul - You could try a mild loctite on there perhaps?

I wouldn't use silicone personally other than in a bathroom..

Loctite can be overcome with heat & you know to be careful with the casting already. Depending on the material section and bearing options you may just need to go up 0.5mm deep, so +1.0mm on outside Diameter of the bearing which may clean up the material?

If the path is all the way through the case, then can you get at it from the other side with a TIG? Apologies if that's a daft question..

I was opening up this case the other day on my Bantam trials bike build for a larger diameter kick start shaft plus put in the O Ring recess as they tend to seep over time, so should be easy enough to open up the bearing..

Larger Kicker Case Boring by KTM Marky, on Flickr

Kicker O Ring by KTM Marky, on Flickr

[Storkfoot]

I'd be concerned about pulling an oversize bearing into standard sized hole. As a minimum, I'd rub the inside face with wet and dry to try to remove those witness marks first.

I'd be worried about stress cracking. Those marks might turn into cracks if they're sharp and there's a lot of stress from the oversize bearing

Thanks. I’m no engineer but I too was thinking that it could be an easy way to crack a casing.

[Storkfoot]

Paul - You could try a mild loctite on there perhaps?

I wouldn't use silicone personally other than in a bathroom..

Loctite can be overcome with heat & you know to be careful with the casting already. Depending on the material section and bearing options you may just need to go up 0.5mm deep, so +1.0mm on outside Diameter of the bearing which may clean up the material?

If the path is all the way through the case, then can you get at it from the other side with a TIG? Apologies if that's a daft question..

Mark, you are speaking to a man who only invested in a small pillar drill, for the first time, last year. Welding is way above my comfort zone.

I do like your loctite suggestion on the existing bearing though. I had initially discounted Loctite as I was concerned about not being able to get the bearing out again, if needed. But, my interpretation of the specs for Loctite 603 and 660 is that they would start braking down above about 150 degrees. On that basis, I’ll give Loctite ago go when I finally get round pulling the engine apart again.

Thanks for the suggestions

[LambrettaMarky]

Paul - You could try a mild loctite on there perhaps?

I wouldn't use silicone personally other than in a bathroom..

Loctite can be overcome with heat & you know to be careful with the casting already. Depending on the material section and bearing options you may just need to go up 0.5mm deep, so +1.0mm on outside Diameter of the bearing which may clean up the material?

If the path is all the way through the case, then can you get at it from the other side with a TIG? Apologies if that's a daft question..

Mark, you are speaking to a man who only invested in a small pillar drill, for the first time, last year. Welding is way above my comfort zone.

I do like your loctite suggestion on the existing bearing though. I had initially discounted Loctite as I was concerned about not being able to get the bearing out again, if needed. But, my interpretation of the specs for Loctite 603 and 660 is that they would start braking down above about 150 degrees. On that basis, I’ll give Loctite ago go when I finally get round pulling the engine apart again.

Thanks for the suggestions

There are as you've seen Paul a whole load of options with the Loctite products. Folk will use the word Loctite and use Stud Lock on a thread for example only to find they can;t then remove it!!

Loctite have good on line product guides, so be sure to get the correct compound for your application.

Happy to bore your case out too if you like..

[Storkfoot]

This looks to fit the bill, I think

https://datasheets.tdx.henkel.com/LOCTITE-660-en_GL.pdf

[LambrettaMarky]

"LOCTITE®
660™ is designed for the bonding of cylindrical
fitting parts, particularly where bond gaps can approach 0.50
mm (0.02 in.)The product cures when confined in the absence
of air between close fitting metal surfaces and prevents
loosening and leakage from shock and vibrationThis product
possesses excellent gap cure characteristicsTypical
applications include restoring correct fits on worn shafts, spun
bearings, and damaged keyways"


It's as if they knew Lambretta owners would need the stuff Paul!!

Sounds ideal.