Transmission Bearing Shield

Classic short-frame models

Transmission Bearing Shield

Postby jOe » Fri Oct 16, 2020 10:27 pm

I scored a transmission the other day. I inspected it and everything seems to check good -,looks like a take off from a running machine. The only thing that looks odd is the large main shaft ball bearing in the trapdoor isn’t shielded on the outboard side. Seems fine - just not shielded. The assembly looks to have been together and run for a long time. Is this good to go, or should I put a shielded one in?
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Re: Transmission Bearing Shield

Postby Ferrous_Head » Sat Oct 17, 2020 12:26 am

Gearbox and primary share their oil anyway. As long as that bearing isn't loose, don't bother with it.
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Re: Transmission Bearing Shield

Postby dr dick » Sat Oct 24, 2020 9:46 pm

flip the bearing. so the shielded side is facing away from trans.
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Re: Transmission Bearing Shield

Postby Ferrous_Head » Sat Oct 24, 2020 11:01 pm

Sorry, I'm giving the cheap "lazy" answer.

It can be a PITA to get the circlip out, remove the bearing and then remove the clutch gear and then to re-install it all.

If I was going to do that I would replace the bearing as a matter of course. They are about $25 worth, so no big deal.

Is this a shielded bearing or a "sealed" bearing ? The shielded version has a small bap which can still allow some contaminants in.

Doc, I'm presuming your thinking there will be more particles flying around on the primary side than inside the gearbox ?

I have seen quite a few trapdoors with a single sided shielded bearing there and presumed they cam that way from the factory. But I don't know if that's true or not.

Joe, There will be some clearance in the bearing housing that can effect your mainshaft end play. Are you aware of all of that ?
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Re: Transmission Bearing Shield

Postby jOe » Sat Oct 24, 2020 11:33 pm

Yes- very aware of clearance/ end play. I’m reluctant to flip it. The gearbox looks like it’s been together for a long time, came out of a running machine and checks out good in all respects. It’s obvious that it worked as advertised. Just looks odd.
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Re: Transmission Bearing Shield

Postby Ferrous_Head » Sun Oct 25, 2020 12:37 am

I sometimes worry about doing more damage than I repair when I do things.

Sometimes I find the bearing housing is worn and the bearing slips out with no effort at all. Other times pressing things apart I think, "Wow ! that one was tight !"

But the Doc knows his stuff and he would have a good reason for doing this. I'm guessing there might be more debris floatng around on the primary side. But then I've seen a fair bit of metal coming out of worn gearboxes too.

Generally, shielded bearings are designed to face the outside of gearboxes, But when you have oil on both side, does it matter ?
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Re: Transmission Bearing Shield

Postby jOe » Sun Oct 25, 2020 11:59 am

Good point. I’ve dug debris out of a number of gear box drain plugs but haven’t seen much in the primary. My biggest question was the starter ratchet spring, but it fits well and doesn’t interfere. Lubrication wise, it’s likely a toss up.
I can’t see any great difference. Apparently it was run that way and didn’t cause any issues.
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Re: Transmission Bearing Shield

Postby Ferrous_Head » Sun Oct 25, 2020 4:20 pm

Doc ?


Possibly the biggest problem simply is that people don't change their oil often enough. There will always be some debris in there. And as the engine and primary gearbox share oil at times, anything can go anywhere.
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