Sealing Valves

[stevehuckss396]

I am currently working on the Bob Shores V4. I am having problems getting the valves sealed. I have tried lapping and that failed. Then i tried re-cutting the seats and then lapping and that failed. Then i tried to recut the valve, then lapp and that also failed. I'm not sure what to try next.

How did you get your valves to seal?

 

[cobra428]

Steve,
You need to make a "reverse countersink" kind of thing. Think of a counter bore with a long pilot. This way you can get perfect concentricity from the guide to the seat. Then lap. Had the same problems with my hit and miss. I bought a set of plans from Upshur, the opposed twin, and there was the "valve seating tool" oh:
Tony

 

[gmac]

.....and I've read of some people seating valves the old way (the days of Ford Model A's etc) - do your best at machining, set them in place, put a brass drift against the valve head, and giving them a good wack with the hammer. Bear in mind you're talking to a noob here :big:

Garry

 

[gbritnell]

Steve, here's several of the ways that I do it. For very small valves with small stems I do all the machining in one setup. I first center drill for my hole making sure that when I get to depth I let the center drill dwell for a few seconds to clean up any runout it might have. Next I under size drill the hole then ream for the guide size. I then undersize drill for the port and finally I use a proper sized endmill or make up my own special diameter cutter from drill rod to clean up the drilled hole. This will leave you with a square edged hole. I don't use a cutter for the seat rather I take a very fine mounted stone (round shape) and put it into a small chuck and by hand just rotate it on the edge of the seat to break the sharp edge. I then mix up a slurry of oil and grit that I have rubbed off of some very fine emery paper and put a dab on the seating face of the valve. With the valve in place and held on the shank by a pin vise I rotate it back and forth lifting and rotating so that I don't sit in one spot. I only do this for just a few seconds then check the valve seat surface on the valve with a maginifying glass and look to see if I have a nice matt gray looking circle on the seat. This should be sufficient.
For larger valves I do all of the above with this exception. After cutting the port I then cut the seat with a purpose made cutter. I turn a piece of drill rod down to the diameter of the valve guide and long enough to go completely through the guide. I make this as close to size as possible (-.0003) On this piece of stock I then swing my compound over to 45 degrees and cut a chamfer. After doing this I put the piece of stock in my mill and cut at least 3 flutes, more if the valve head is bigger. When finished I harden this cutter and stone all the edges nice and sharp. I don't worry about tempering it as I only use it by hand so I have never broken one. I then put it into a chuck, oil the valve stem shaft, insert it into the valve guide hole and twist by hand until I get a nice small seat. The width will depend on the size of the valve but it doesn't need to be very wide. Finish up as above and you should be good to go. The biggest problem I have found is keeping the seat concentric with the guide hole. It seems like once it's been cut the least little bit off center any successive cutting will only follow what's already there. That's why I don't even cut very small seats.
gbritnell

 

[stevehuckss396]

Thanks for the reply's!

G, I did cut the valves and seats in one setup. I also made a seat cutting bit only it was a 4 flute. The valves are 1/4 inch I even put blue die on the seat and twisted a valve on it and saw nice bronze ring.

I'll keep trying! I can always press out the cages and make new ones.

 

[mu38&Bg#]

I've seen model airplane engines with excessive clearance between the valve stem and guide. I couldn't get them to seal well at all.

 

[stevehuckss396]

I am convinced the leak is between the cage and the head. The plan is making new cages and valves. It is way to hot to get started on it tonight.

 

[steamer]

Keep at it Steve!

Can you put a groove on the OD of the cages for a spot of loctite?....might be enough to guarantee a seal of cage/head............just a thought

Dave

 

[RonGinger]

I dont think you really want a seat on such small valves. As George suggested just the slightest break of the edge is all that needed.

Think about the scale- a full size valve might be 1" or more diameter and have a seat line of only .025-.030. Scale that down by 1/4 or 1/6 for a model engine and the seat line ought to be no more than a few thous.

 

[Cedge]

The Victorian engine head was milled from cast iron and the guides and 45° seats were to be cut directly into the head, as opposed to pressing in brass seats and guides. I made a small 45° point on a piece of drill rod which I hardened and used to ream a 1/16 x 45° seat. This was then hand lapped using Permatex valve lapping compound, which has a nice self degrading grit. The more you lap, the finer it gets until it is worn away. I then lapped the valves using a super fine metal polish.

The results were great and the valves sealed tight as Dick's hat band. With the tiny 5/16 inch valves, I used a small drill chuck to hold the valve stems and turn them in the seats. The whole operation took about an hour of slow careful work.

Steve

 

[stevehuckss396]

Keep at it Steve!

Can you put a groove on the OD of the cages for a spot of loctite?....might be enough to guarantee a seal of cage/head............just a thought

Dave

I'll get er!!

I plan to get the cages and valves ready. Then i'm going to redrill and re-ream another .010 and press the guide. Then move to the next one. That way i can make a tool to get a straight push on the cage.