Tranny Bearing Question

[alexbrown64]

Hi,
I have purchased all the bearings for my YZ125K from Partzilla.  Main bearings, tranny bearings, clutch arm etc.. anyway, the only one that is slightly different is one of the large tranny bearings.  It has the same bearing number and has the same dimensions..  except the last letter on the bearing must denote the type of seal it has.. the one supplied has a black rubber seal on both sides.  The Yamaha one in the bike has a metal seal on one side and no seal on the other.  The new bearing is packaged by Yamaha and the one in the bike has been superseded by the supplied one.  Both are 6303's.  My question is, does this come up often and do people just use them.  If used, do i just take one side of the bearing seal off to allow lubrication?  Pic below....

Cheers,
Alex

[PEZBerq]

Yes you can pry out the seal on one side. I don't know why a metal seal was used originally. Need a Yamaha person on here to advise if having a metal seal is critical but I would be surprised if it was.

[kdx Geoff]

l recently replaced some wheel bearings that had metal seals for new bearings that had rubbers seals on both sides and asked the bearing bloke about the difference, he said the metal seals had less friction/resistance than the rubber seals.

[David Lahey]

the bearings with metal "seals" are called shielded bearings. Sorry I don't know why Yamaha used a shield there but it is a common thing on many Yamaha motors to originally have a shield on the clutch side only of that bearing.
It's probably important to have the seal or shield on the clutch side rather than the gearbox side of the bearing because of the way that bearing gets its oil supply. It is pretty well hidden from oil by the clutch basket on the outside so would get a better oil supply from the gearbox side.

An interesting aside is that on some modern trials bike two stroke singles that have poor ventilation/cooling/lubrication of the main bearings, they found that the main bearings enjoy a longer service life by fitting (rubber) sealed bearings instead of open bearings

[GMC]

An interesting aside is that on some modern trials bike two stroke singles that have poor ventilation/cooling/lubrication of the main bearings, they found that the main bearings enjoy a longer service life by fitting (rubber) sealed bearings instead of open bearings

Interesting,
I have always removed the seals from the oil side to let the oil flow through.
In wheel bearings I have always removed the seal on the inner side and packed with extra grease.

[pancho]

 Interesting story about sealed bearings. Not shielded bearings.
 
As an older person who is always starting off diatribes with "I remember when", here is the rest of it-
 While working at a Holden dealership forever replacing rear gearbox bearings in F.Cs EK, EJs and early EHs, GM came out with a new fix, (Double row bearing kits were only a partial success). anyhow the new fix was a single row bearing sealed on both sides. The mechanics in unison said, "What Bull**** is this? it'l never work". But it did. Problem solved! The bearings have sufficient high melting point grease to last the considerable life of the bearing.
 
 Dont remove the seals.
cheers pancho.

[matcho mick]

i agree,done plenty of motors where i left the rubber seals in,generally only gearbox applications,c/s output mains,behind the clutch,(as above) yamaha did it,so did ducati,i'm talking "our" early stuff,don't work on moderns so nfi on what goes on in them suckers!!,think it's mainly to keep gearbox contaminates out,as Pancho states theres enough intial lube in them to last !!,also good insurance against leaks to a lesser extent,my ossa's all run c/s sealed bearings,my SL350 roadrace camshaft roller bearing conversion runs them,works for me , :-

[alexbrown64]

Thanks for the input fella's.  I will go with just whacking it in as is. 
Cheers,
Alex

[matcho mick]

um,by whacking you meant heat cases,freeze bearing whacking in  ,

[alexbrown64]

Big sledge hammer!!

Matcho, your correct, heat cases etc.. another thing i tried yesterday on my RM80N build that i saw on Youtube and worked a treat was this:
When fitting your crank in, get a socket that fits tight in the bearing.  Then heat the socket right up with an extension bar on the end.  I used the gas cooker in the kitchen.  Then put the socket in the bearing.  The heat transfers to the bearing and opens it up a whisker.  I tried the crank before heating the bearing and it wasnt going to go in without a fight.  After heating with the hot socket... it fell in!

Cheers,
Alex

[shelpi]

um,by whacking you meant heat cases,freeze bearing whacking in  ,

Nah he meant wack it in with a sledge hammer, you hold it and nod your head and Ill hit it LOL

[matcho mick]

hmmm suppose that way would work,it's always a bastard getting the crank outa the freezer  ,

[Tim754]

Metal shielding is just older manufacturing  technology. Rubber/plastics seals are efficient and most importantly to bearing manufacture ,    Cheaper per item to make....

[Lozza]

Most snowmobiles run "dry" bottom ends well the direct injected ones do anyway, they have sealed bearings on the crank that last 3-5yrs with year round use. I normaly pull the seals in the gearbox