cr480 blowing base gaskets

[Snowy 76]

Any Advice Second time its happened, first time it sucked the gasket in , now it`s blown gasket out ?? both times on the LHS.... Have been fitting gaskets Dry, maybe just need some sealant/gasket goo???

[Mick D]

Any Advice Second time its happened, first time it sucked the gasket in , now it`s blown gasket out ?? both times on the LHS.... Have been fitted gaskets Dry, maybe just need some sealant/gasket go???

Obviously the studs into the crankcase aren't moving? Are they?

Take it to a Center Lathe and do "fly cut" of the sealing area on the bottom surface of the cylinder.
There is not an easier job in the world for a lathe and its operator.
Loctite Master Gasket 518

[Mick D]

A Fly Cut, is to remove the most minimal amount possible until the surface just cleans up, which indicates that it is true again.

The normal finding is that the thin area to the sides of the transfers will clean up last, proving the distortion is now gone.

[ARN]

hi
on my Yamaha 465 I was missing a dowel which I didn't spot till I removed barrel cause it blew gasket out ,do Hondas have dowels ?
cheers arno

[sa63]

you should check the torque on the cylinder studs if the threads are tired and the stud is detensioning....if so helicoil and start again...

An ex GP racer from way back told me on their race motors they would helicoil (using Wurth inserts) all threads that were of any consequence as a matter of routine, not after failure..

[marshallmech]

Wurth insertes are great but you need a fair area to use them they have a large diameter bur are fantastic of you can fit them

[oldyzman]

I do also wonder if the flycut is done with a reasonably coarse feed that the machining lines would also bite into the gasket and help hold it. Maybe an idea to check the squish setting and amend that at the same time...
Brett

[Paul552]

I do also wonder if the flycut is done with a reasonably coarse feed that the machining lines would also bite into the gasket and help hold it. Maybe an idea to check the squish setting and amend that at the same time...
Brett

Scroll (facing) is used allot in large pipe flanges for sealing purposes.
I reckon you are on to the right track

[oldyzman]

aah scroll facing is the terminology eh... I see

[Lozza]

Check case surfaces with a straight edge with a light behind it and/or a feeler gauge, the base of the cylinder would be first on the list to machine.

I do also wonder if the flycut is done with a reasonably coarse feed that the machining lines would also bite into the gasket and help hold it. Maybe an idea to check the squish setting and amend that at the same time...
Brett

Proper GP engines have o rings or flat surfaces for sealing.Crankcase will never see higher than 5psi on a good day.