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.



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).



- 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.

__________________
Grant Johnson
Seek, and ye shall find.
------------------------
Inspiring, Informing and Connecting travellers since 1997!
www.HorizonsUnlimited.com

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

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.

__________________
Grant Johnson
Seek, and ye shall find.
------------------------
Inspiring, Informing and Connecting travellers since 1997!
www.HorizonsUnlimited.com

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.

__________________
Did some trips.
Rode some bikes.
Fix them for a living.
Can't say anymore.

If your old piston gudgeon clip is 100% un-damaged then it's safe to use again.

Every manual will tell you to replace it though.
Because they have to take into account that it was damaged on removal.

To be safe, I would recommend that you replace it.

But you don't have to if you can 100% guarantee that you didn't deform, crack or twist it on its way out.

They're made from spring steel. It's strong and fairly forgiving but once you take it past it's stress point , it's junk.

I always replace them in customers bikes because it's not worth the risk as Grant says. And a customer would expect them to be replaced.

Out of the countless engines I've rebuilt for myself and friends, I have never replaced them and ive had zero failures. But I am very careful when I remove them and use the correct tools. Not twisting them out with screw drivers etc.


Re your gasket question. With modern liquid RTV sealants, it is indeed possible to use them instead of the paper or steel gaskets they come with.
The exception here is multi layer compression gaskets such as your head gasket.

Also, some cases or covers require the genuine gasket as it is part of the tolerance and dimension when the motor was designed. Such as cam cover when the cam carrier is built into the cover.

On engine side covers or faceplates, you're usually okay though. But that does depend on the bike !!

I still prefer to use the physical gaskets. They're just cleaner and easier to use. And if you need to wiggle something you know it's not been wiped off in the process.


Last note.

When building an engine it always pays to take your time and not take shortcuts if you have any doubts. They always bite you in your arse.

I spent twenty years learning that the hardway.

__________________
Did some trips.
Rode some bikes.
Fix them for a living.
Can't say anymore.

Agree with Ted, I wouldnt worry to much about is.


As for gaskets, the really important one are whre they provide clearence, like Ted mentions about the cam on certain bikes.

Sidecover gaskets can be nescessery aswell, it is on my E-start xt600. Startermotor binds up a bit with no gasket, and on the right side you have the oil return valve which can also act up.

Order the gasket and change circlip, its not like you are doing this same job next week..Its something about that feeling when your done that its all in place and new!

Thanks for all the information. I realised I was letting impatience override common sense so have ordered the circlips so I can do the job properly. The minimum order was five so I've got a few spares in case I bend any more during installation.

Minimum order 5 ?? Huh ?? Never heard of that. Use Fowler's if you're in the UK. All fiches online.

Sent from my Moto G (5) using Tapatalk

__________________
Did some trips.
Rode some bikes.
Fix them for a living.
Can't say anymore.

Pull it out and install a new one. Apply Oiled cling film over the shaft and slide the new seal on straight.

__________________
Did some trips.
Rode some bikes.
Fix them for a living.
Can't say anymore.

Thanks ~Ted. Am I right in thinking that I wrap the cling film around the thread to stop it damaging the seal as I slide it on?

Indeed. Lots of oil too. Keeping the seal straight is very important. You need a deep socket or something that will fit over the shaft to drive the new seal in. You can't wiggle them on as that is what damages the seal lips.

__________________
Did some trips.
Rode some bikes.
Fix them for a living.
Can't say anymore.