How to repair the cylinder head of a Cummins KTA50 engine

How to repair the cylinder head of a Cummins KTA50 engine, Cylinder Head Surface Machining

If the cylinder head surface is scratched, corroded, or uneven at the gasket sealing area, it can be repaired using milling or grinding methods.

Steps

1. Use the ST-1323 valve seat remover to remove all valve seats and intake air guide plates.
2. After surface machining, measure the cylinder head height with a micrometer or depth gauge.
3. Recess the valve seat holes; the recess depth should match the machining depth of the cylinder head surface.
4. Polish the cylinder head surface using a hand grinder. Do not use a disc-type grinder.
5. Thoroughly clean the polished surface.
6. Install suitable injector seals to compensate for material removed during cylinder head machining.

Replacing Valve Guides

1. Mark the valve guides to be replaced, then press them out from the valve head side of the cylinder head. Install new guides using the ST-1265 valve guide installation tool.
2. If no special installation tool is available, press the guides into the cylinder head manually, ensuring correct alignment.

Replacing Crosshead Guides

1. Use the ST-667 or ST-1134 locating pin puller to remove marked crosshead guides.
2. Install new guides using the ST-1264 crosshead guide press sleeve. If unavailable, press manually and ensure proper assembly height.

Replacing Valve Seats

1. Use the ST-1323 valve seat remover to remove marked valve seats and intake air guide plates, if not already removed.
2. Recess the seat holes to the next larger size to accommodate available valve seats (refer to the parts microfiche).
3. Using the 3375946 valve guide mandrel and ST-257 valve seat tool, hold and drive the valve seat cutter to machine the seat hole.
4. Machine the seat to 0.15–0.25 mm deeper than the seat thickness to allow press-fit installation. Stop feeding once the required depth is reached, keeping the cutter rotating to ensure a flat sealing surface.
5. Install the valve seat and intake air guide plate using the ST-1288 press tool with ST-1122 punch. If unavailable, a 6.35 mm diameter round punch may be used.
6. Note: Excessive pressing around the seat may crack the cylinder head.

Grinding Valve Seats

1. Use the ST-685 valve seat grinding tool with an appropriate mandrel from the 3375946 set.
2. Grind the valve seat to ensure proper valve insertion depth into the cylinder head. Select the correct grinding stone for rough and fine grinding. Rough stones should be pre-shaped to 30°. Check seat width; it should be 1.52–2.54 mm. If too wide, use a specially shaped stone to narrow the contact surface without extending to the chamfer.
3. Check total roundness with a valve seat micrometer; it must not exceed the specified tolerance.

Grinding Valves

1. Check the valve grinding machine adjustment with a new valve and micrometer:
   1. Place the valve stem in the grinding machine chuck. Ends not clamped may not be concentric with the stem guide section.
   2. Position the micrometer probe on the valve face.
   3. Mark the high point on the valve face.
   4. Release the chuck, rotate the valve 180°, and reclamp.
   5. Repeat steps (b) and (c). If high points match, the valve is straight; otherwise, the chuck alignment may be off. Total roundness tolerance ≤0.03 mm.
2. Wet grind the valve at a 30° angle relative to horizontal. Check edge thickness; valves thinner than 2.67 mm must be discarded.
3. Mark the valve face with pencil, install the valve in the guide, and rotate 10° against the newly ground seat. If the pencil mark is removed in the center, the seat contact is good. Verify with a vacuum tester for sealing.

Valve Springs

Soft valve springs can cause valve float, excessive valve and seat wear, timing disruption, and possible piston-valve contact.

1. Test the valve spring using the 3375182 spring tester, applying the required load based on compressed spring length. Discard springs below the "scrap limit" specified for the length.
2. If total valve and seat grinding exceeds 0.76 mm, install shims under the valve springs, with a maximum of two shims per spring.