A guide has a tough job to do...often at extreme temps.

Buryllium is the ultimate valve seat/guide material. Bit very hard to machine...but once setup...lifespan is measured by how many valves it's seen.

Darin Morgan has some good detailed info on guides.

The reality is that guide clearance depends on a few factors...just like piston to wall clearances.

Start with a 0.0015" Int and 0.002-0.0025" exh and go tighter or larger dependiing on your intended use.

Going tighter...you need to make sure the quide is round and straight.

I like good umbrella seals on exh guides. Lets some oil get in there...but limits it. You don't have the vacuum issue of the Int guide.

Tartilla,

Do you mean pure beryllium, or beryllium copper? I’ve never machined pure beryllium, but I’ve heard it’s not that difficult, with a few caveats, along with a few significant health hazards. I wouldn’t think it would make a good bushing. BeCu, I have machined. It is tough, but machines easy enough. Again, you can’t hardly tap or ream it. A common variety is called MoldMax, and, yes, it is incredibly durable and wear resistant.

Thanks. Brad.

Roger, beryllium copper alloy.

ToughMet 3 is another exotic alloy used for seats. You have to sharpen the multi-angle cutter for every valve seat.

Tartilla,

That's a new one on me. Had to look it up. Sounds like some brutal stuff. Hope to never get an RFQ for it. :rolleyes: Although, it sounds easier than AMPCO25. I'd be interested to see the cutting tool used for the valve seat. I'm envisioning something very similar to a piloted hydraulic port tool.

Curiously, our model boat props are cast in BeCu. These are surface props, typically with far less than half the diameter in the water, usually 2 blade, that continuously run in excess of 25K RPM. I've cut on them quite a bit, and hand worked them for balance and sharpening. It's pretty tough sh!t.

Thanks. Brad.

I wonder how the new single point valve seat machines do on that material.

Need to find the correct rpm to reduce chatter, and have everything tight. Even with chatter on the seat face, a quick fine seat stone cleanup by hand will get you to under a 0.001" runout, and cleanup the chatter.

Sharpen after every seat.

My live pilot cutter system, (pilot turns in the guide) uses carbid pilots and you're looking for 0.0005" pilot to guide tolerance...and use a thick oil to lube/center.

Some powdered seats are tough to cut as well...but some are softer...work hardening on 'break in", so the valve face forces the full mating contact.

Setting up valve and seat angles needs some planning. There's tolerance. Old school was to use a 1° interference fit. We can be a bit tighter now, hedging on the primary contact on the outer portion of the valve face. The other way...would put combustion into the seat contact area. Not so good.

Sutphen,


Wow. This is really cool. You program it like you would a turned profile on a CNC lathe, with an X and a Z axis, and it interprets that into axis travel for a boring head, only with a pilot in the valve guide. That’s just badass. This is one of those reasons why we have the term “machining porn”.

Thabks. Brad.

I work w/ a serdi 100,I cut seats in every head imaginable and every type of material.I always wanted the single point machine.they had profiles that could go into the port a good bit.

My bad...I thought you were speaking to the multi-angle seat cutters...vs the cnc-style seat cutters.

Shaping the port deeper than standard cutters would be good for cnc machined chambers and ports...ans well as as-cast. Saves a lot of extra work/time on blending the valve job. I would expect the seat finish to be similar to what you would achieve on a lathe. High speed focused cutting would elimonated most chatter, even on the harder to cut materials.