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I have a 2007 CRF 250r that I am trying to replace the base gasket on. I replaced it with a after market one (that was paper material) and seemed to fit fine but I suspected that it was causing water to get in my oil. So I replace the paper gasket with a OEM metal one. I tried to slip that one on but it is so tight that it scrapes off little metal pieces off the outside of the cylinder itself. The cylinder is bored out to a 270 but it is the OEM cylinder that came from the factory. Has anyone else had this problem and remember what you did to fix this? I have picture if needed.

Swift-Rider please post a picture because I need to see what the issue is.

If you mean it is scraping metal of the outside of the cylinder sleeve then I would think the cylinder has been sleeved rather than nickasil like factory.
Or is it scraping alloy off the cylinder?

It may need a different base gasket if this is the case.
Compare the new gasket to the paper on that came off.

Post the picture so we can best advise you.
We like pictures.

Swift-Rider please post a picture because I need to see what the issue is.

If you mean it is scraping metal of the outside of the cylinder sleeve then I would think the cylinder has been sleeved rather than nickasil like factory.
Or is it scraping alloy off the cylinder?

It may need a different base gasket if this is the case.
Compare the new gasket to the paper on that came off.

Post the picture so we can best advise you.
We like pictures.

Here is a link to some pictures: https://imgur.com/a/hQvJ0kJ

You can tell how tight it is trying to put on the gasket, it actually starts to warp because its so tight. It also like, overlaps the cylinder itself. I cant compare it to the other gasket because that one ripped into pieces trying to take it off. Tell me if these pictures help or if I need to take some pictures of specific things. Also where it is scraping off the metal is where the two kind of things that come out father than everything else does. I know it might not make sense but it is hard to explain.

Can you post a a side view so gasket edge on.
Is this a OEM cylinder machined for larger bore or is it an aftermarket cylinder from a big bore company?
Do you have an original cylinder to compare the diameter too?

I am going to guess and say there is specific gasket for this bigbore cylinder.
I assume the head gasket has a bigger hole so how does that align on the cylinder as well as the head. You don't what the head gasket overhanging the head or cylinder or it will burn away.

Here is a link to the pictures: https://imgur.com/a/snv4cjH

I hope that's what you meant by side view, if not let me know ill give it another shot lol.

The head gasket does hang off a little bit. I think it is OEM cylinder that was bored out because in the last picture you can see it say 249 CM3. I have no idea because we bought this bike off somebody when it was bored to a 270. I do remember though that the paper gasket looked like it was crawling up the side of the cylinder probably because it didn't fit right and since it was only paper, when we put it on it just bent it and we didn't know about it.

Well if it is a factory cylinder and gasket I am surprised it is that tight.
I have had tight ones on occasion but only slightly catching.
Maybe being a metal one the are tight.

I am sure Jim or Neil will chime in soon with their experience.

Are you saying the head gasket bore hole is smaller than the bore of the cylinder?

Athena sell big bore top end gasket kits so I guess you know why now.
Have a look on the site in the parts for your ride. I bet they are in there.

Yes, the cylinder head gasket bore is smaller than the cylinder bore. It is crazy insane how tight it is. The first time we tried me and my dad absolutely mangled the metal gasket and it looks like from this one where gonna need to replace it again. That’s why we decided it was best to take a break and post a thread on here because y’all have been so helpful before.

As I said above Athena does big bore gasket kits which I am sure Ken sells on the site.

Might be worth a question to him based on your bore size. Not sure if they make one size fits all or a few different sizes.

As I said above Athena does big bore gasket kits which I am sure Ken sells on the site.

Might be worth a question to him based on your bore size. Not sure if they make one size fits all or a few different sizes.

How could I get in contact with him if I had to take that route?

https://www.crfsonly.com/forum/memberli ... rofile&u=3

Go here and you can PM private message him.

Let him know what piston and size and issues you have with standard gaskets.
Ask him which top-end kit will fit your needs.

Will do I appreciate the help.