Top end rebuild - pics!

[wjp]

Hi,

this is the first time I've ever tried to rebuild my top engine. I brought the bike about 3 months ago, and I decided last night to strip the bike down and try and rebuild the top engine. I have a top end kit that came with the bike. Its a Yamaha WR 125 1998 (french special - its really a YZ made road legal).

I started doing it because the bike was running rich and I rejetted the carb but I'm now also doing the top end.

I have some questions, and I'd appeciate it if any of you more experience people could give me some advice?

Firstly when I took off the cover for the exhaust values it was complety filled up with spooge. Is this normal? do I need to clean this out (I've cleaned it with a cloth so far). Any specific maintaince I need to do here?

As you can see from the photo's below it looks like the piston has been rubbing slightly against the side. Is this going to be a major problem if just clean up, and replace rings/piston/etc?

Any comments on the state of the piston etc are welcome as its the first time I've done this and can't really tell what kind of state they are in.

Please note that the pics of the piston are before I cleaned it. The photo's where taken as soon as I took off the head. I'm going to change the piston/etc this weekend, so any advice is welcome. (I've got Erics book BTW..)

thanks,
Wayne

 

[mackay]

That looks like a major scuff on the piston...the pics of the cylinder don't have enough light but I'm guessing its not much better.....take the cylinder to the shop and have it checked out...a pass or two with a hone might clean it up. Dont just throw it back together without getting it checked...man that is a bad scuff.
The spooge thing sounds like the machine was neglected before you got it, there should be a spooge drain on the power valve cover that the previous owner should have opened to let it drain out.
Has that engine ever seized??? That is a nasty looking piston!!! Get that cylinder checked by a pro, oh and that piston would make a nice paperweight and thats all its good for now... :eek:

 

[wjp]

It seized once, when I first got it. I was going nearly flat out in 5th gear, and it seized! Then just as I was about to stop after skidding about a mile(!) it jumped started itself again.
The cylinder looks Ok for me, except for the marks - I can't feel anything with my fingers (if you know what I mean). Obviously the piston had it.

PS I've adjust the pic so you should be able to see it more clearly:

 

[mackay]

My 97 WR250 has a series of graduated pistons sized A thru D and as the cylinder wears you increase piston size...look into this you might need a slightly larger piston...I notice some verticle lines on the cylinder wall but you say that its smooth to your fingernail?? Just for your piece of mind you should get a pro to check it out and they can measure the bore and reccomend the correct size piston for you (the A-D piston thing)
Good Luck

 

[Joepro9]

id definatly bore that cyl.

 

[smb_racing]

I'm assuming it's a plated cylinder (it looks like it, and given the age it probably is) but see the variation in the color on the cylinder in the one area? That is probably aluminum that was deposited on the cylinder wall when it seized. This is not a good thing, take the cylinder to a shop and have them remove that, they can probably do it with acid. However if that's not aluminum from the piston then it's a worn spot through the plating and you'll have to have it repaired, don't know about in the UK but Eric Gorr does an excellent job here in the states.
Do not install a new piston without fixing that area first! Aluminum on a cylinder wall is much more abraisive than the nikasil and will score the new piston first shot out of the box.

 

[Durt Cycler]

Wow that looks like a pretty serious scoring in that plating. You can tell easily that there isn't a sleeve in the cylinder so your best bet would be to have that cylinder look at perfessionally and either re-plate it or bore it out and have a sleeve installed.

 

[yzeater]

I agree with everybody else here. Take it to a professional, and have them plate it or bore it. And fix your jetting so that it doesn't seize again

 

[dell30rb]

wow, looks like a very nice 4 point seizure.

 

[wjp]

Yes , its definitly a 4 point seizure - I had the piston off this weekend.
Thanks all for your help and advice. I'll take it to the shop and see what they say about the cyclinder.
thanks,
Wayne