is this a cracked block wall?

[yvescheung]

Hi guys I am from Hong Kong and looking for some advices.

my bike is 95 cb400 project big one. Few weeks back the bike was overheated and I realized the coolant level was low. I top it up and level was low again after few days, and oil mixed with coolant. So I thought it is a blown head gasket.

I took the head off and one of the cylinders was having some coolant. The head is fine and head gasket seems to be alright then I found something likes a crack on the wall of that cylinder, attached pictures.

Any ideas?




Thank you!
Yves

[yvescheung]

please see pictures in bigger size through the links here

http://postimg.org/image/xpk0wag2n/
http://postimg.org/image/nioow62ah/

[dobbslc]

You might find that the mark is from water rusting the liner, like a tide mark. Was the bike left standing for a long time with this problem? Also at the level that mark is at it looks like it's below the coolant jacket anyway.
Try some fine emery cloth on it to see if it comes off, don't get the grit down the side of the piston though!

[yvescheung]

thanks dobbslc for the reply

the bike was sitting there for few days after I removed the head... i will try to wipe it off and see...the coolant flows through around the cylinders so if it is a crack, might be possible that coolant goes in?

I also take pictures of the head gasket... would you please see if I was wrong that it is alright? I can see there are "clean" areas around that cylinder when it should be rust/dirt around other cylinders. good chance that the coolant goes in through the gasket?

Thanks again...

pics here:
http://postimg.org/image/49ceqzk3n/
http://postimg.org/image/jzp4ku02v/

[Superjack44]

There is a very fine film of a rubber like substance on the head gasket when it is fitted new, when you removed the cylinder head you disturbed that seal and why it looks the way it does.
I cant judge from your pictures if it is a crack or not , what I would do is make sure all the bores are as clean as possible and with the pistons of the effected clyinders at the bottom of the bore fill the cylinder jacket with neat antifreeze (Flourescent pink which is silica free) watch to see if it emerges through what you think is the crack if there is a crack it will come through ,if nothing shows let it stand overnight if nothing shows after say 24hrs I would think it should be ok.
You could also try pushing a thin feeler gauge against it to see if it comes against an edge.