650R cyl wall inspection question??

I am freshening my XR's top end. I got a Hot Cams camshaft/Kibblewhite springs and an Edelbrock carb. The bike was burning oil so I want to replace the rings. Should I change the piston?

In this picture, that visible line across the lower end of the cylinder wall. Is it normaly there? When I run my finger across it, it feels like a depression.

Thanks

cylinder.jpg

Isn't that where the rings stop when the piston is at BDC?

Looks like you might have some cylinder bore wear. Can you feel a ridge at the top of the cylinder? If you have a set of micrometers, measure the bore at the top (under the ridge), middle and bottom and again 90 deg. from your first measurement to find out how much wear there is and if the bore is tapered. If you don't have the mics, take the cylinder to a machine shop and have it checked out. Check your shop manual for specs. If you do not have a manual, you can download it at this site: http://www.borynack.com/Bruce/XR650R/xr650r.htm Good luck. :applause:

I would take it to a professional to examine, cant tell much from a photograph ... but, I suspect you don't have a worn cylinder, what with good 'cross-hatch' in the bore, (unless you ran a hone thru it) ..

I'm only concerned about that dark ring. Anyone ever seen that?

you would need a dial bore gauge to deturmine the diff. in cyl wear. I'd say go with the next size up piston and have fun!

that dark ring is probably a carbon deposit ... normal

that dark ring is probably a carbon deposit ... normal

Agreed. I did a top end on mine last summer, and I knew it was bad because at the top of the cyl, there were gouges where there was piston slap going on... bad... If the top of your cyl looks/feels okay, then you should be okay.

If you want to do it anyways while its apart, theres a company in Minnesota called Millenium Technologies, and they will replate your cyl for $200; thats what it costed me. Good luck.

that dark ring is probably a carbon deposit ... normal

Yeah, I think you're right. I just checked it and it's at the top. It's where the pistons stops and changes direction. And because the cyl still has cross hatch marks, it is prabably not worn out. I will check it with a bore gauge.

Thanks guys.

Just in case, can I not bore out the cylinder? Or is it that nikacil crap that can't be bored out?

you can bore out a plated cylinder, but you would want to re-plate it ... usually, a plated cylinder will be much harder than the rings, so the rings wear without damaging the cylinder ... if you can still see crosshatch, you should be able to get away with a set of rings ..

Ok thanks.

Yeah, I think you're right. I just checked it and it's at the top. It's where the pistons stops and changes direction. And because the cyl still has cross hatch marks, it is prabably not worn out. I will check it with a bore gauge.

Thanks guys.

Just in case, can I not bore out the cylinder? Or is it that nikacil crap that can't be bored out?

First, if you have a gouge at the top, thats probably piston slap; thats what I had. Its like a nice ring right around just below the top of the cyl. If its bad, you'll have to get it replated. When I took mine apart, the rest of the cyl still had the nice cross-hatching, except for that ring around the top. When it comes to cylinders, if you can feel something in there, you need to get it re-done.

Secondly, when I was doing my rebuild, I thought you could bore-out the nikasil lining; I found out you CAN'T. I went to several different machine shops around here, and everyone said they couldn't bore it, and that I have to send it off. Reasoning being is that the nikasil plating is so hard, that to get it off, they actually have to put it in an acid bath to corrode the lining off. And after they get the liner off, THEN you can bore it. You could check around your local machine shops, but you'll most likely run into the same problem I did. Good luck.

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