Engine bearings XT600-2KF

[carlhenrik_80]

Hello folks!
So far I have read several threads on this site about wich bearings I am supposed to / can use when I am rebuilding my engine, and I find them really useful.
I have owned my bike, an XT600-2KF, -89 since 2002 and about a year ago i decided to rebuild it with original spare parts from my local Yamaha dealer. And I still remember the cost... A couple of months ago I bought one more bike, same sort, different color, and this time I wanted to keep the price of the rebuilding parts down by buying all bearings in a separately bearing store. Not japanese bearings so to speak.
Im writing this thread as ment to be an object of discussion, what bearings XT600 owners can or should use in their engines. And offcourse The so called C3 play question: to have or not?

Here comes something to start with:

Crankshaft:
Must be C3 bearings, I believe that no Crankshaft is absolutely 100% straight, even if it is brand new you bend it a few 1/100mm anyway when youre doing high rpm:s, if you dont use C3 you worn out the crank-journals on the axle that lies inside the bearing.
Another reason, offcourse, is the heat!
6306-C3
6307-C3, Yamaha pdf says: 6307SH2-9TC4, C4-play=expensive!!= I dont think so...

Balanceshaft:
Question: Why does Yamaha use Koyo on the right side and NSK on the left side of the balanceshaft? They also have different Yamaha art. numbers, but i really cant find the difference between them. Cant even measure the difference in the play with a special 1/100 mm clock...
I have been told and have seen for myself that the left side of the balanceshaft can be worn..? C3 bearings or not?! Does this axle bend itself under high rpm:s? I have anyway hard to think so. Standard play for me.
6305
6305

Transmission, In: clutch axle
6305N-C3 pdf-file from Yamaha says: 6305NRX1C3 so i think C3.
Other reason why it needs to be C3 is that it is possible that the axle bends itself a few 1/100mm or so when you drop the clutch standing still in first gear, thats when the highest amount of torque goes in to the gearbox.
6004-RSR, Oil Sealed bearing, works best with small play?!! Otherwise the sealing will be wornout very fast. I think?!

Transmission Out: sprocket axle, driving chain
6305-RSR, the original bearing from Yamaha have rather small play, i choose standard. Also because of the oil Sealing in the bearing.
6004-C3, Yamaha has changed the original part to a C3, thats 100% sure.

Gear Drum:
16005-C3 Stamped on the original bearing. I changed it "just in case"..

I can also tell I found out one of the significant differences in the number of balls in 6305 bearings. You know there can be 7 or 8 balls?!
Found out that a 6305 bearing with 7 balls can take 2000Newton = 200kg more in Dynamic Pressure( When it is rotating fast, with lubrication) But why does Yamaha still use 6305-bearings with 8 balls? Exept on one place in the engine: the one behind the sprocket/driving chain, it has 7 balls??!
My first thought was: It could have happened someting in the bearing industry in the last 20 years, but then I bought brand new (Yamaha original spare parts) japanese ones with 8 balls....

If there is someone who thinks they know something useful, maybe that can change what I wrote above, then I certainly would like to hear it!!
Get the words out!! Speak up!!

Best regards from "the swede"

Carl Henrik

[Panzer]

could you give us a bit more info please ?

[BlackDogZulu]

Hehe

[carlhenrik_80]

Would you really like some more info about bearings?

If this looks too much to everyone, maybe I can give you a shorter version, that seems to have worked out fine for a few others:

Crankshaft bearings must have C3 play. Also the Gear drum.
To minimize the wear of the 4th and 5th gear sprockets in the gearbox you can put in the rest of the bearings with standard play!
Thats All!

You just have to change the service interval, mostly the oil changes, whats in the oil, and it just got more important to check the oil level...

And some people also say there is no point to have a C3 bearing if you have a regular bearing in the other end of the axle, vice versa.
That seems logical to me.

After all the research i have done in this subject maybe the most simple solution is the best... Also the cheapest.

Any other thoughts about the XT600 Engine bearings??!

/ Carl Henrik

[G600]

Carl Henrik.

Thanks for this thread. Most interesting.

I read someplace that crankshaft bearings are “special” bearings that you should not buy from the local bearing house?? (This was not for an XT, but a 2-stroke MX bike, but I guess the same should apply) Have you heard this? Do you know if there is any difference in “genuine” bearings from the dealership and “ordinary” C3 bearings from the local bearing house?

[pusser65]

Hi Carl Henrik,

Please excuse our British sense of humour.

Cheers.

[G600]

Carl Henrik, I sent you a PM, please be kind enough to take a look.

[G600]

Hmmm. I was not joking. I never have found out if “genuine” crankshaft bearings are indeed somehow different from “regular” bearings, or just three times more expensive.

[carlhenrik_80]

Hello folks!

Straightening things out: The bearing-standard-number that is stamped on a genuine Yamaha bearings outer ring doesent always say if the bearing are having the C3 play or not. Mostly cases it dont say. You have to measure it up yourself.
But I suppose this could be different from Yamahappy to another brand, when the bearings are not japanese, FAG or SKF maybe.

I have been lucky to have been helped by the local Yamaha dealers own mechanics who have told me specially that a crankshaft bearing always needs to have C3 play, because the crankshaft is never doing high rpm:s being 100% straight. even if it is brand new. Too much weight and force going on in there. AND ofcourse the heat, that will take away the play and just precise give enough space for lubrication.

The conclusion would be: You should have C3 play on a 2-strokers crankshaft because the oil is only 2% mix with the gasoline, this makes the C3 play ( by the mechanics called "heatplay") even more necessary.

And yes, it should be enough with a "standard" bearing from the local bearing store.

Someone who know something I don´t??

Regards Carl Henrik

[carlhenrik_80]

In my opinion Standard bearings from a local bearing store could be made of even better material than japanese ones mounted as "Yamaha Original".
You know the japs arent leading that development anymore.

Depending on what bearing-brand you choose, you should look up the specific facts about the brand your local bearing-store sells, for example 6306 that are often used as crankshaft bearings, in this case you could check for the C value, Dynamic bearing capacity, and compare it to the same 6306 in the other original mounted brands list. If there is a difference, there you have it.

I have learned in my former studies at The Royal Technical University in Stockholm how to test the hardness in a piece of metal, but in this case I leave that assignment to someone else, when I dont have access to the right equipment anymore... But I know Swedish bearings are good

I hope this sounds what you asked for?!! Or even better I hope!

Come on now, give me some info I dont allready know!!

/ Carl Henrik

[Panzer]

When I used to buy things like swing arm bearings for Jap Motorcross bikes they tended to be a funny Japanese size and you couldn't get them from a normal bearing supplier.

Yeah I was only joking Carl Henrik

[aukeboss]

Well, we are travelling on two Tenere´s - one has the original Yamaha crankshaft bearings in, the other had aftermarket bearings (german I think from Kedo). On this last one we had to change the bearings in Colombia - believe me, they felt like sandpaper when turned by hand. I estimate the lifetime of the original Yamaha bearings now in at about 70.000 kms - and still going strong. For the aftermarket ones, I reached 50.000 kms and was just in time changing them before anything worse happened.
I will go for the Yamaha originals in the future!

BTW, the new bearings were marked with the 4 number code, no inidication of C3 or C4 and the letters ´SH´apparently indicating that they are specifically made for Yammie.

Auke

[carlhenrik_80]

This is the kind of comments im looking for!

Witch bearings in the engine took the most damage?
All of the engines bearings worn or just the crankshaft bearings?
Do you remember whats the brand of the bearings you bought?
The ones you bought, where they regular or stamped C3 ?
And what was the condition of the gears in the gearbox? Mostly interested in the 4th and 5th gear sprockets.

I can imagine this happens when the wrong kind of bearings are used, and thats why im trying to find out what is the big deal with the "genuine" ones.
I mean, it seems a bit secret whats with the Yamaha genuine ones.
One more bullet (8 instead of 7) for ex. in the 6305 bearings cant be the answer...

In my case my last bike has done about 65.000km, and the oil I poured out told me I should give it a real survey. And if I still own the bike when it has gone about 50.000km or more, Im probably going to disassemble it again anyway... And then I can afford to switch the bearings again

Now this is getting interesting.

Regards Carl Henrik

[carlhenrik_80]

Oh, sorry i didnt see you wrote "were marked with the 4 number code, no inidication of C3 or C4 and the letters".
Probably were those ones not C3 IF they were something else than japanese... Could be a reason of the wear you describe.

/ Carl Henrik

[Jens Eskildsen]

I bet, oil, service intervals,defensive/ofensive driving and so on has a lot to say to. Meaning its wothless to change bearings, if you run it like ypu stole while the bike being cold, low on oil, and with tight valves and so on.

Even theese things in low scale, could be the difference between 50k km and 100k km, no doubt about it.

My 03 has done 72k km, ive ridden the last 22k of 'em with frequent oilchanges.

The sucker has attended 2 enduros, and stuff like that, and still use no oil and sounds really healthy (fingers crossed)

My buddys startet knocking before 20k km. Guess some are just unlucky

When that beeing said, please contunie the debate and keep us posted. Uh, and it ya wanna, please explain the c3-thing stuff, gues it has something to do with tolerances? Im wondering, if you know the stock ones work, arent it worth paying for it you know for sure it'll work?