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Clubroom => Tech Talk => Topic started by: Snowy 76 on July 05, 2014, 05:01:50 pm

Title: cr480 blowing base gaskets
Post by: Snowy 76 on July 05, 2014, 05:01:50 pm

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???

Title: Re: cr480 blowing base gaskets
Post by: Mick D on July 05, 2014, 05:56:30 pm

Quote from: Snowy 76 on July 05, 2014, 05:01:50 pm

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

Title: Re: cr480 blowing base gaskets
Post by: Mick D on July 05, 2014, 06:02:50 pm

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.

Title: Re: cr480 blowing base gaskets
Post by: ARN on July 05, 2014, 07:47:56 pm

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

Title: Re: cr480 blowing base gaskets
Post by: sa63 on July 05, 2014, 07:48:42 pm

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..

Title: Re: cr480 blowing base gaskets
Post by: marshallmech on July 05, 2014, 07:54:13 pm

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

Title: Re: cr480 blowing base gaskets
Post by: oldyzman on July 05, 2014, 08:09:03 pm

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

Title: Re: cr480 blowing base gaskets
Post by: Paul552 on July 05, 2014, 08:32:36 pm

Quote from: oldyzman on July 05, 2014, 08:09:03 pm

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

Title: Re: cr480 blowing base gaskets
Post by: oldyzman on July 06, 2014, 07:25:29 pm

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

Title: Re: cr480 blowing base gaskets
Post by: Lozza on July 06, 2014, 09:42:54 pm

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.

Quote from: oldyzman on July 05, 2014, 08:09:03 pm

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.