2008 EC250 Top End

[Louis069]

EDIT: Just measured it and it's a 300 not a 250 which it was sold to me as, so the stuff about the clearance is irrelevant now
Hi guys, this is my first top end rebuild ever so I could do with some advice. I have removed the cylinder on my bike and to do a new piston and have noticed that the top conrod bearing has gone beacuse the piston doesnt move smoothly on the rod it jumps from position to position like it is notched, I assume this isnt normal. I also cannot remove the piston pin, I have removed both circlips and heated the piston too but it wont budge. I haven't tried tapping it with a hammer because I dont want to damage the bottom bearing, would this be ok?

I ordered a wiseco piston for a 1997 - 2018 ec250 which is 66.40mm (the only size the wiseco come in), would this provide the correct clearance for a 12 year old cylinder? I currently have no way to measure the cylinder bore.

I know that I am at least the third owner and the bottom end has been rebuilt at some point because it has a wossner rod fitted not sure if the cylinder has been replated at any point though which would affect clearance i assume.

If you have any other tips for me they would be appreciated

Thanks for all your help in advanced

[Gasser Nate]

Very unusual to have a seized little end bearing. Do not hammer it out, buy a piston pin puller and press it out. Was it ran with no oil? I would be having a good hard look at everything...

[Louis069]

Originally Posted by Gasser Nate

Very unusual to have a seized little end bearing. Do not hammer it out, buy a piston pin puller and press it out. Was it ran with no oil? I would be having a good hard look at everything...

It has always been ran with oil under my ownership the bottom end bearing seems ok and no scoring of the cylinder or piston so not sure what the deal is

[Louis069]

So it turns out its a 300cc . Was sold to me as a 250 so thats a nice suprise
Just measured the bore with some telescoping gauges I was lent from school and found it to be about 72mm not 66mm.
I got the piston pin out using some sockets and a threaded rod however the small end bearing is very loose in its housing. It slides in and out very easily and there is slight play up and down inside the rod. Does anyone know what the spec for the bore of the small end of the rod is supposed to be, I'm hoping it's just the bearing worn but not sure.
EDIT: just measured the small end bore and its 22.00-22.01mm
Thanks

[hannesd]

with the piston pin in the small end , you shoud not feel any play.
if the hole is oval, you should get the con rod replaced :/
hope you can send the 250 piston back and swap it for a 300 piston?

[Louis069]

Originally Posted by hannesd

with the piston pin in the small end , you shoud not feel any play.
if the hole is oval, you should get the con rod replaced :/
hope you can send the 250 piston back and swap it for a 300 piston?

I didnt feel any play from the piston when it was intalled on the conrod, but as noted in my first post the piston did not move smoothly at all, and was very jumpy on the rod so it was hard to tell.

The hole doesnt seem visually oval but I will measure it up to make sure in the morning thanks. Hopefully its just the bearing worn out

[Doc Brown]

As Hannes said, there should be no play with piston pin in the small end. It happens that the small end bearings sit very loose.

best test is put bearing in small end, then slide piston pin in so that it only protrudes about 5mm (0.20 inches) on one side. Then take the long side between your fingers and try to move it up/down and fdw/aft while holding the con rod with your other hand. Then do the same with the longer part of the pin on the other side. If you feel no play all is good. If you feel play....all is clear

Good luck!

[Louis069]

Ended up reaplacing the small end bearing which fixed the roughness much smoother now. Then ordered a 71.94mm wossner piston and she started up 4th or 5th kick so all worked out.
Thanks for your help again