750 dynamo service - bearings?

[arancia]

I took the dynamo to bits to look at bearings and brushes. This one had a big dent in the front of the case from impact before my ownership and getting the end covers off was a long operation as the bearings did not want to slide off the armature and the brush end bearing was well stuck in the cap. Don't know if those are related, it did rotate fairly freely before disassembly.

I'm guessing it had not been apart before - brushes are well worn so looks to have done many miles.

On the 750, the dynamo is in direct line of fire of all the road dirt and moisture from the front wheel, the end caps are snug but certainly not sealed and there are felt filled holes in the bottom I imagine intended to let water seep out. Evidence inside of dirt and water entry.

Question then is whether it would be better to replace original bearings (SKF 6202 without shields) with 2RS bearings to keep the grease clean. Outer surface of the >50 year old grease was black, probably mostly brush dust, but under that layer still brown though congealed. Bearings turn freely but with grease stiction. Will be washing them out and regreasing but given the low cost of bearings, even 2RS, thinking I should just put in new sealed bearings.

Any reason not to use sealed bearings? Anybody done this and any experience either way?

 

[Andy]

I would prefer to use sealed bearings.

 

[1200ts]

I put sealed bearing in my 750 dynamo 32 years ago and they are still OK.

 

[chrisk]

My ex enduro racing mate always adds extra grease to new sealed bearings with a syringe of grease. Reckons he doesn’t trust bearing factory grease.

Given his previous racing environment's, I guess he knows what he’s talking about.

 

[1200ts]

My ex enduro racing mate always adds extra grease to new sealed bearings with a syringe of grease. Reckons he doesn’t trust bearing factory grease.

Given his previous racing environment's, I guess he knows what he’s talking about.

Yes adding grease to slow turning bearings such as a wheel bearing is OK. It is thought that on bike used off road the extra grease will keep dirt and water from getting past the seal. Even on a fast street bike it is probably OK as even at 100MPH the wheel is only turning about 1200 rpm.

High speed bearings, a bad idea as the extra grease will make the bearing run hot. As the dynamo could see 8000 rpm, I think more grease may not be a good idea for this application.