Mistral - to grind or not to grind?

[ScubaLawyer]

I'm overhauling a Mistral and it turns out the volcano orifice is pretty severely nicked. The HP seat looks brand new so I'm sure it's the orifice causing the leak (The guy who sold it to me off the back of the truck told me it worked fine. )

I used steel wool, pencil eraser, etc... but no joy. Is it worth trying to grind / resurface the volcano orifice with a dremel or will it widen the orifice too much so the HP seat will not seal properly?

Your collective sage advice is welcome.

[URL=https://imgbox.com/7bczn7ru]

[swimjim]

Doesn't look good... This will be an interesting thread. I hope it turns out well Mark. This is the place where it has a chance!

[Vancetp]

I think a little tool with a guide that fits down in the orifice could cut a flat on that volcano and make it seal. Would have to make one...

[captain]

A wood dowel the size of the bore with a piece of 400 grit wet or dry sandpaper glued on it. Use a light oil and work the dowel back and forth between your palms. Lift it every few cycles and check progress often. You don't want to remove any more the necessary.

Similar to lapping engine valves.

https://www.youtube.com/watch?v=pVp04atZoc0

[ScubaLawyer]

A wood dowel the size of the bore with a piece of 400 grit wet or dry sandpaper glued on it. Use a light oil and work the dowel back and forth between your palms. Lift it every few cycles and check progress often. You don't want to remove any more the necessary.

Similar to lapping engine valves.

https://www.youtube.com/watch?v=pVp04atZoc0

Thanks Tom,

Herman suggested the same thing to me and I did that. I got it down to just a slight barely perceptible leak and then tried taking off just a little more. Big mistake. It leaks worse now than ever. Argh?

[h2operations]

Can you see if it is out of round so to speak after sanding? Since the tolerance is pretty slim you may have to use a guide around the dowel to keep the sanding in a tight circular pattern. Please post a post sanding photo.

[ScubaLawyer]

UPDATE: After further sanding, polishing and certain incantations involving goat-leggings and scotch I achieved a great seal of the HP seat and volcano orifice. Thanks for everyone's suggestions.

[Vancetp]

Toothpaste makes a great , very fine lapping compound. I've used it for years to open up bores, etc.