Hairline Crack In Cylinder - 55 KHK

[Mayday53]

After cleaning and honing the intake valve seat on the rear cylinder, we found a small crack on the edge of the valve seat. The other seat after honing smooth, became too "low" and we risk sucking a exhaust valve.

Anyone had any success or recommendations for machining the valve seats down and pressing in a new seat? That was suggested by one builder and I do not know if it is a good practice or not on a KHK model.

[EKHKHK56]

Yes the use of stellite valve seats is common practice to repair worn out seats, or dropped seats as they are called. When the seat can not be refinished because it is beat down into the cylinder, cracked or won't clean up without machining it down too low, the new seat is the way to repair that. Need a machine shop experienced in this process of course. General automotive head shop should be able to handle. Dropped seats significantly lower flow and performance. Another method to fix is oversized valves, so you can make a new seat where there is plenty of material. I make oversized K intake valves with a KR 30° angle instead of 45°, which also is a benefit for having more material to work with on the seat area with the shallow angle. They have large K stems and 2 mm larger on the face. Exhaust seats wear much more with today's fuels and should be hard seated. The intake seats do ok from my experience. To hardseat exhaust and intake you have to cut into one of the new inserts to install the other. Erik

[Mayday53]

Yes the use of stellite valve seats is common practice to repair worn out seats, or dropped seats as they are called. When the seat can not be refinished because it is beat down into the cylinder, cracked or won't clean up without machining it down too low, the new seat is the way to repair that. Need a machine shop experienced in this process of course. General automotive head shop should be able to handle. Dropped seats significantly lower flow and performance. Another method to fix is oversized valves, so you can make a new seat where there is plenty of material. I make oversized K intake valves with a KR 30° angle instead of 45°, which also is a benefit for having more material to work with on the seat area with the shallow angle. They have large K stems and 2 mm larger on the face. Exhaust seats wear much more with today's fuels and should be hard seated. The intake seats do ok from my experience. To hardseat exhaust and intake you have to cut into one of the new inserts to install the other. Erik

Erik, can you explain "Dropped seats significantly lower flow and performance."? If seated in tight, how does the cylinder lose flow (assuming you mean compression)? Also, do you have an original (or remanufacturer) part number for the oversized K intakes you have used for this?

ALSO, is it possible for an experienced welder to put a good bead on the seat, then cut it down for the current valve size? Or...is that too vulnerable to particulates breaking off and obviously ruining the seal and the other components?

Mayday

[EKHKHK56]

Hello MayDay. The dropped seat lowers the valve head into the port blocking flow, particularly in a design such as the Ricardo which uses a lot of side flow before entering port. The valves should stick up above the deck when closed with proper seat. Head to valve clearance needs to be addressed also before assembly. The intake valve I use is a Sealed Power #V-1076. You have to trim stem length and machine keeper groove. It uses the flatter 30° angle face like KR. Stock Ks are 45°. I noticed some stock K replacement valves are semi-fit at the keeper, requiring final machining to fit keepers.

[EKHKHK56]

Application for that intake valve is 1956 Chevrolet Six Cylinder.

[Mayday53]

OK, I talked to a machine shop today. Here is what I understand the process to be. First, he bores out the valve port to the O.D. and depth of the seat to be inserted. Then, he machine presses the new iron seat into the valve port. Finally, he hones the seat top edge to the angle and depth required by the valve. So, if he does all that and it is the same depth, Port I.D., and seat edge angle as the original, how does it lose compression? Essentially, isn't the port the exact same size as before?

Mayday

[EKHKHK56]

Once repaired with new seat or larger diameter seat for larger valve, the seat is no longer dropped, normal flow is restored. Just do not try and grind a new seat on one that is dropped below specs.

[Mayday53]

Roger that...thanks.

[Mayday53]

So, the machine shop has the cylinder and is boring out both the intake and exhaust ports, pressing in a nickel based seat, and then honing the top edges. He is leaving the seat top edge work until I can find him an answer to his question; is there a spec on how high the seat should sit/ Is it level with the die cast cylinder housing, slightly below, etc. Is there a spec for that, and if so where can I find it?

Mayday

[EKHKHK56]

Ok. The only info I have is from the H-D Competition Racer Manual. It shows a cross section of the seats, but no actual numbers. After studying the diagram the seats are below the deck. The seats, like guides, etc, are tilted to the bore and deck. The Exhaust seat is around .020" lower than the deck at the highest point. The Intake seat is about .100" lower than the deck at the highest point. Highest point being the closest distance to the deck from the tilted seat. When I say seats I mean the actual machined seat angle where the valve face touches the seat. Not the top of the seat insert. So they do sit down below the deck the amounts stated. Erik