Gibbits YZ490A

[Gibbit]

And so it begins!!



It's already started! As you can see the rear guard is sticking up a bit so I stripped the rear end to straighten the frame. I found the pop rivets in the exhaust where flogged out so I took it to a mate to weld the holes in the alloy so I could redrill them. All good for now but it will get a new exhaust when the full resto starts.



Gave it a bit of a clean up.





My plan at this stage is to get it in A1 mechanical condition and enjoy it for a while. I'll start the full resto in 6 months or so.
I've been over it pretty well and can't really fault it.
Suspension. Good apart from needing a rear shock bump rubber.
Wheels. Will polish up well and bearings are good.
Steering bearings good.
Crank bearings. Good.
I think it might be down on compression so it may get a new topend before long. I'll do a compression test soon.

It came with a full set of OEM plastics too!

I plan to race QVMX and maybe also do Finke on it for a bit of a challenge. 

[Gibbit]

Got the bump rubber today from Dave at suspension matters. So it's, strip the rear end again to get the shock out. Not as easy to work on as the newer bikes!
I need a spring compressor to get the spring out.

[evo550]

You should be able to loosen the preload nuts until the spring falls out, no spring compressor required.
How you going to fit the bump stop?

[Gibbit]

I've wound the preload nut right off and there is still tension on the spring.

I'm hoping that once I have the spring off, I can undo the bottom mount off the shaft somehow.

[evo550]

If there is any tension on the spring, it should only be light, a bit of pressure with a big screwdriver/tyre lever should allow the collar to drop out ( number 9 on your shock diagram)
Have you rebuilt a shock before?

[sa63]

I have wondered how viable it is slice (or other glue)the bumper, slip it on and super glue it rather than get the eye of the shock off or complete dismantle.have always dismantled though...

[evo550]

Tried and failed Sean.
Glue splits when shock bump is compressed when shock bottoms.
Zip ties slice through...

[Gibbit]

If there is any tension on the spring, it should only be light, a bit of pressure with a big screwdriver/tyre lever should allow the collar to drop out ( number 9 on your shock diagram)
Have you rebuilt a shock before?

You don't need to disassemble the shock. I just used a spring compressor to get the spring off, then unscrewed the bottom end off the shaft and slid the new bump stop on. Only took about two beers. It took a lot longer to clean and grease all the linkage bearing though.

I pulled the carby apart to have a look and found the needle was lowered one clip from standard and had a 490MJ (470mj standard). I lifted the needle and put a 480mj in. There is no point trying to tune it too much as I think it might be due for a new top end. It will get one soon wether it needs it or not anyway.

I took it out for a good ride around the Goondiwindi MX track today. It ran really well and I was quite surprised how well it handled.

[alexbrown64]

Thats a beast.  I had a 490J and loved the torque.  Always a bitch to start though.. flooding.  Have fun with it!!

[Gibbit]

Well I went away over the xmas break so decided to take the wheels apart and clean them up. I got them polished, hubs painted and back together.  Polishing to all by hand was a stupid and time consuming idea but the results are quite good.

[Graeme M]

All looking pretty good. It's surprising what good results you can get polishing by hand, I've done quite a few rims and all the plastics on my IT175 with what I consider a fine outcome. Painful tho...

[80-85 husky]

you should have at least reoiled and gassed the shock having gone to all the trouble of pulling it out .

[Gibbit]

you should have at least reoiled and gassed the shock having gone to all the trouble of pulling it out .

It was only done recently.  At some stage I will send it and the forks away to be serviced and have a few nice bits put in.

[Gibbit]

I've ripped the head off the big girl to see what the piston and bore look like.

Not as pretty as I was hoping.

The bore is 1.00mm 4th oversize which is the limit, but that doesn't matter because the sleeve is cracked in three places so its off the Serco for a new sleeve.

The piston has grabbed the side of the bore a bit and the bottom piston ring is seized in the piston. Sh$t was about to go bad in a big way.

There is also what looks like cracks in the head but I'm not sure if its that or just imperfections in the casting.

On the upside, the crank has no play and I'm going to end up with a fresh engine.















Also can anyone tell me what brand piston this is? Wiseco??

[sa63]

Nice timing on the top end! I recently had the same experience with a cracked piston on a 480CR.. its definitely a golden rule to tear down the top end on any new (old) purchase, no matter what you've been told by the previous owner!