Topic: Replace All Bearings When Rebuilding?

[Ellz10]

I've read a couple posts, but nothing definitive or concrete on the topic. Is it really necessary to replace ALL bearings on a fresh rebuild? I mean I've already forked out over $5k in motor work, so a few extra bucks to replace them brand new wouldn't be too bad, but if I can SAVE those few bucks and put them towards something else, then I'm definitely okay with that.

[69cb750]

Only if bearings are worn ...
When babbitt wears away bearing gets very shiney.

[Don R]

  How about the trans bearings? I've only split a couple cases and they were low mile motors so I haven't yet.

[newday777]

I've read a couple posts, but nothing definitive or concrete on the topic. Is it really necessary to replace ALL bearings on a fresh rebuild? I mean I've already forked out over $5k in motor work, so a few extra bucks to replace them brand new wouldn't be too bad, but if I can SAVE those few bucks and put them towards something else, then I'm definitely okay with that.

You statement really didn't differentiate what you mean in $5k motor work. Does that include the rod and main bearings already in the motor work? And are you asking of the remaining ball bearings?

[Ellz10]

Only if bearings are worn ...
When babbitt wears away bearing gets very shiney.

Where exactly would it begin to get shiny at?

  How about the trans bearings? I've only split a couple cases and they were low mile motors so I haven't yet.

Motor had 22k on it when I disassembled it. Trans bearing looks alright, but I'd rather be safe than sorry.

I've read a couple posts, but nothing definitive or concrete on the topic. Is it really necessary to replace ALL bearings on a fresh rebuild? I mean I've already forked out over $5k in motor work, so a few extra bucks to replace them brand new wouldn't be too bad, but if I can SAVE those few bucks and put them towards something else, then I'm definitely okay with that.

You statement really didn't differentiate what you mean in $5k motor work. Does that include the rod and main bearings already in the motor work? And are you asking of the remaining ball bearings?

Among other things, I had the crank lightened and balanced and replaced the old connecting rods with Carillo ones and I know he replaced the bearings there. All the others within the motor have not been.

[jonda500]

A Honda dealer once told me that the main bearings are good for a hundred thousand kilometres when I tried to order new ones for my 400-4, so I re-used the originals.
John

[pjlogue]

I would be inclined to replace all ball bearings if I had a bike with unknown history.  The reason being is it is fairly cheap to do it when the engine case is already out of the bike and case halves are split.  I would get the best quality bearings I could find.  For journal bearings, I would examine them and plastigage them before ordering new.  If they are within speck, reuse them.

For roller and ball bearings, be aware that many are now produced in China.  The quality isn't that good.  Use the best quality you can find.

-P.

[flybackwards]

In my book the peace of mind is worth the dollars - given that the youngest sohc cb750 is now getting to be 45 years old - time and corrosion are more common than than mechanical wear. Of course replacing a high quality original bearing with minor wear is probably not a good idea if the replacement is a low quality generic item. I did replace every bearing and bushing in the entire bike on my K7 rebuild and the result is a very quiet smooth riding machine.

[Ellz10]

A Honda dealer once told me that the main bearings are good for a hundred thousand kilometres when I tried to order new ones for my 400-4, so I re-used the originals.
John

I think I might keep the .ain't bearings, but replace all the rest. Thank you.

I would be inclined to replace all ball bearings if I had a bike with unknown history.  The reason being is it is fairly cheap to do it when the engine case is already out of the bike and case halves are split.  I would get the best quality bearings I could find.  For journal bearings, I would examine them and plastigage them before ordering new.  If they are within speck, reuse them.

For roller and ball bearings, be aware that many are now produced in China.  The quality isn't that good.  Use the best quality you can find.

-P.

In my book the peace of mind is worth the dollars - given that the youngest sohc cb750 is now getting to be 45 years old - time and corrosion are more common than than mechanical wear. Of course replacing a high quality original bearing with minor wear is probably not a good idea if the replacement is a low quality generic item. I did replace every bearing and bushing in the entire bike on my K7 rebuild and the result is a very quiet smooth riding machine.

If I can find a credible place to buy new high quality bearings, then I'd be inclined to go that route just so, as you mentioned, I have that peace of mind. Any ideas where I can find some? I'll try to do some research on my own of course too.

[bryanj]

You wont get all of them aftermarket especially those with grooves

[PeWe]

One bearing in lower case for main shaft is easy to replace. It look like not seated. Warm it and it will fall out. Yamiya sell stock bearings. I could not resist to order a complete set or 2  except for the needle bearings (which are std needle beerings found on eBay) when order other things. Still not used them.

But I doubt a low miler need all ball bearings replaced.
If you found them rusty another thing.

Replace the cush rubbers inside the primary hub is more important. Its needle bearings must be OK as well as the bigger bearing sitting on same unit after only 22k miles.

I had a bearing that sat very loose in the clutch pressure plate.
It just fell out when I handled the plate when doing the clutch. I guess too small play made the clutch mechanism to constantly spinn the bearing instead of when using the clutch. I replaced the plate with a billet one and new ball bearing.