Putting it all back together
 

I’ve finally (after an expensive battle with the magneto) got the case open and am looking at what I need to replace before I start putting it all back together again.

My reason for opening it is that the bike had just half a litre of oil in it when I got it and I had no idea how long it had been ridden like that. So I’ve spent the last year riding it and wondering if every knock and rattle was a sign of impending disaster. I decided the only way to be sure was to open it up over the winter, renew where necessary and put it all back together for some carefree riding next year.

The oil on the inside of the case is rust-coloured and filled with loads of tiny black particles. They are too fine to feel with my fingers but I can see them. Most of the ‘rust’ seems to be coming from the main bearing which I guess is shot. I’m thinking about replacing all the bearings anyway just to be sure.

Attachment 20482

I also have some doubts about the crankshaft. There is some blueing around the pin joining the crank halves so I’m guessing there has been overheating at some time. There is no noticeable up and down play in the rod, but sideways it moves up to 1.4mm (the manual says 0,8mm should be the max).

Attachment 20483

- Given these signs should I get it rebuilt with a new big end bearing, rod and pin?
- Kedo seems to be a good, but pricey, choice but I’ve been quoted a much better figure for a Mitaka set. Does anyone have any views, good or bad, on this brand?

Thanks as always for the help.

the blueing at the crank is normal, my guess is they use in the factory some kind of induction heating when pressing together the crank. a true burned big end would feel very sloppy...
if the side to side clearance is ok and you dont feel pure up and down play, you are fine.
wash the bearing with some paraifn to eliminate the oil so you get a true feeling for the play

Given the visually rusty main bearing, I would personally replace ALL bearings (and seals) without hesitation, including the big end - it may be "ok" but taking it apart - again - when you could have done it all in one go and be DONE is not worth the stress of wondering imho.

Do it once, right. :thumbup1:

C4 bearings
 

Hi there,

if I remember correctly some of the bearings are C4 bearings, and on my journey around the world I replaced all bearings at 100.000km and at 200.000km with genuine Yamaha bearings. Pls make sure if you dont use genuine bearings that you use the right ones.

crankshaft. I would give the crankshaft to a workshop that is specialised in overhauling them, a long time ago Kedo offered this service but I dont know if they still do it.

all the best.

mika :scooter:

Agreed, it takes expertise to do the crank. I've done lots, and seen what can go wrong even when you need what you're doing and have all the right tools, like a 10 or 20 ton press and an alignment setup. It needs to be RIGHT.
Replacement bearings SKF or FAG are excellent quality bearings, take yours into a local supplier and have them pick out the right replacements. Don't buy weird brands and don't try to pick them yourself, every detail stamped on the bearing matters. Guys that know what they're doing can match you you up easily.

Side ways movement on a crank is totally normal. As is the blueing. It's from the process where the rod is pressed on.

I'm assuming you have a detailed workshop manual for the bike. They often give the specifications for how much movement is acceptable. When sideways movement is too great, the rod will float and create up and down movement (Rod-Knock). So 'usually', if there is no rod-knock, the sideways movement is acceptable. But measure it all the same.

If there is no up and down movement in the Connecting rod then I would use it. But measure the small end internal first.

Rusted bearings need inspecting. It could just be surface rust from sitting dry. Sometimes it will wipe off with paraffin or brake cleaner. But If the bearing balls are not clean and shiny underneath then replace them. And be prepared for a big bill. They're often odd sized and not available as pattern parts. Sneaky buggers.

Main bearings will generally last the life of a life if they're kept lubricated and not contaminated.

Before you re-assemble this motor make sure the inside of the cases are IMMACULATELY clean, all oil passages are cleaned out with compressed air and mating surfaces are dressed.

You don't mention the condition of the barrel liner, piston and top end etc.

These are the first things to suffer when you have too little oil in a motor.

Thank you for all the advice. As always I’m blown away by how the people on this forum are so willing to share their experience and knowledge.

The main bearings on my 3TB have identical markings – Koyo 6307 SH – which I have read stands for special heat and means the bearing will last ten times longer. The right hand one is listed on MSP for 83 euros. I did a quick internet search and found a C3 Koyo 6307 (which I’ve read will do the job just as well) for under 14 euros. The SKF C3 6307 was under 12 euros. Am I missing something?

I'm no bearing engineer. But bearings can differ massively in quality and application.

SKF etc, do make good bearings. They also put their names to cheaply made pattern parts made in sweat shops. A brand does not tell the full story.

It's all about the codes.... Sorry I can't tell you more. Simplybearings website has some info and guides if I remember correctly.


Many people buy genuine for this very reason. To remove the confusion. But with a little more research you should be able to save at least 50% on OEM prices.

However, if they're special cut bearings (Honda are a bugger for this) then you will have no choice but OEM.

Ted makes good points, especially "it's all about the codes" - and that's why I said take the originals to a bearing supplier to make sure you have the right ones.

Substituting an SH for a non-SH would make me nervous. They specified an expensive special bearing for a reason. You can be sure they tested with a cheaper standard type bearing first, and subbed it for a much more expensive one because they had issues.

If in doubt buy OEM.

Beware of fakes too they are out there nowadays :

Anti-counterfeiting

Counterfeit SKF bearings seized in West Yorkshire raid

The C4 and C3 designation is the bearing tolerance for internal sizes . A c4 bearing is actually a little looser than a C3 , Yamaha used it possibly due to the heat expansion of the parts . As the motor heats up things expand and the bearing should get tighter , maybe too tight so they went with a looser bearing . This has been discussed here before and many have used the more common C3 without troubles.



.

I've researched everything I could find on here about bearings and learned a lot about C3 and C4, but I'm still not clear on which one, if either, is the equivalent of an SH.

This would be a good left side bearing , https://bpracingatv.com/product/rapt...crank-bearing/

still looking for the right .


.

Well I finally got enough money together to do the rebuild properly and am now waiting for a delivery of bearings, gaskets, oil seals and other bits from Kedo along with a con rod kit from ProX. I hope I've got all the bases covered but have got two questions I hope someone can help with.

- My manual says I should replace the oil strainer that sits inside the crankcase (part no. 5Y1W13430000) but the MSP site says this part is no longer available and all my internet searches come up with it being obsolete. Is it ok to just put the old one back as it is or can it be opened and cleaned without totally destroying it?

- Can anyone recommend a good crankcase sealant for putting the two halves back together? The dealership here in Portugal looked mystified when I asked for the Yamaha bond No. 1215 that is recommended in the manual.

Thanks as always for the help.

i'm pretty sold on loctite 518 for crankcases closing

it's anaerobic, so will harden only when the two halves are pressed, will never gum up into balls that can fall off, neat...

a bit pricey though

to clean external surplus use nitrocelulose thinner