XT600 Engine rebuild questions (crank, bearings, valveseals etc)
 

Hi all,

New here with a XT600Z 3AJ from 89.

I'm currently in the progress of rebuilding the engine and have some general questions:

1) I've seen an excellent topic here from 8 years ago regarding bearings ( this one ) and was wondering if there is any update on this?
Is C3 sufficient for a lot of KMs or is it recommended to use C4?
I'm thinking about replacing all bearings with SKF/FAG ones. I can get C4 SKF for 25euros.

2) If I want to get the main bearing off of the crank, I will need to put it back in the same spot with a gap in between the crank and the bearing. Is this a fixed gap or do I just measure it and put it back approximately? It seems kinda vague to me.

3) I'm also replacing the valve seals. Are aftermarket ones any good? OEM ones will be €50 total...

4) I can also order everything aftermarket from Kedo.de (bearings, valveseals), but there's no info on these items. Are these any good?

Thanks! bier

3: Regarding valve seals, theyre inkluded in the gasgetkit from Kedo, and work fine. Be carefull when you install them.

Really?

In this one?

KEDO - Product Details

edit:

"ventilshaftdichting" on the catalog, I guess that's it :). You just saved me 12 euros
I wish they would put more info on the products though, the kedo bearings don't have any info.
edit: just got word from kedo: the bearing they sell is a C3 bearing... makes me think, I guess C3 is fine too?

You can see the valveseals in the middle of the gasgetkit =)

I haven bought enginebearings for mine yet, but I would trust Kedo to provide the right parts.

Well apparently they are C3 bearings. I can get those for very cheap.
I wonder why yamaha is using C4. I think these still have play when under operating temperature, while C3 do not. (or not as much).

I can't really find any decisive info. It's too bad the yamaha ones are so expensive.

There is some instances where the wrong spec bearing will cause vibrations under certain rpms and may be more likely to have the balls skid in the races rather than roll smoothly (also a cause of vibration) . I do wonder why it would be the Yamaha had the special spec , but C4 is a (looser) tolerance than C3, IIRC ,Honda aircooled motors have the same spec.

Hm.. what about the bearings from the transmission that have oil seal and/or snap ring groove? It would be much easier and cheaper to order 4x 6305 and 2x 6004 regular. Not sure what the snap ring groove is even used for? (and the oil seal for that matter, since it's a blind bearing anyway?)

Buy original, its not like you change these bearing every 2 year? Make it like brand new when you first do the job!

Fair point but if I want to replace all 8 OEM it'll be 150-300 euros for sure. That's too much for just the bearings, the project will become too expensive.

I can't remember offhand which bearings go where and such but there is one spot the the seal in the bearing directs oil through the shaft and out the cross holes rather than straight though and around the bearing . could be thinking of another motor , I don't remember .I do remember Honda has a cam bearing similar that requires the oil seal so all the oil has to go into the cam to oil the rockers , if it was just a standard bearing, parts would get starved of oil.

Doubleyoupee, to help decide if C3 bearings are OK to use in place of the C4 larger clearance bearings, you could ask XT/TT600 guru David Lambeth.
Welcome - David Lambeth 00 44 (0)1205 871945

Bob

Thing is depending how tight the bearing is pressed on the crank , it'll tighten up the inner clearances , then add the high heat which also tightens the clearance is possible to be a bit too tight , probably why the C4 was spec'd in the first place , I guarantee if the less expensive/common bearing was known to be fine , they would have used them from the factory rather than some special high dollar versions . Modern bearings are probably better quality than back in the '80's, so may be fine then .

I would say nothing is better quality these days than the 80s, original parts last 20-30 years no problem. But new parts different brands known for quality earlier dont last more than some years, rubber specially. Car parts specially, and all other things from China are made for changing often, i would say you get what you pay for it. It seem expensive at the time, but its worth every penny if it last. And i have to pay twice the price you see!

I understand, but in my opinion there's a difference between "things from china" and SKF or FAG bearings from Europe, wouldn't you say?
To be honest I wouldn't know but I can imagine that bearings from the 21st century from a well known company like SKF are actually good if not better.
Not to mention I can order bearings from NTN as well - which is what Yamaha uses from factory (along with Koyo).

Correct me if I'm wrong...

Anyway I sent a message to David Lambeth. Not sure if he'll reply, but we'll see :)

Yes i was talking in general now, SKF/FAG have quality and used from many frabricators. So if you find match with same spec use it.