Symptoms
- Oil consumption didn't drop after replacing the valve seals.
- Compression drops, the valve overheats.
What's included
- As it wears, the valve develops lateral movement: contact with the seat deteriorates, compression falls, oil passes the stem seal into the combustion chamber, and the valve overheats and may burn. Worn guides often explain why replacing stem seals has not reduced oil consumption. We measure the clearance in every guide and replace worn ones, then ream them to suit the valve size. Seat machining and valve lapping are mandatory afterwards because a new guide changes the axis. We finish by checking cylinder-head sealing.
Additional checks
- Measuring clearance in each valve guide
- Reaming new guides to the valve size
- Checking cylinder-head sealing after assembly
Why it matters
Worn guides are a common reason why replacing the seals doesn't lower oil consumption. A new guide shifts the valve's axis, so seat work and lapping are a mandatory step afterward.
More details
The valve guide sets the precise travel of the valve. When it wears out, the valve starts to wobble: it no longer seats properly, compression drops, oil passes into the combustion chamber past the seal, and the valve itself overheats and can burn. Worn guides are a common reason oil consumption doesn't drop after seals have been replaced. We measure the clearance in every guide and replace the worn ones, reaming them to the valve size afterward. A mandatory step after replacement is refacing the seats and lapping the valves, because a new guide shifts the axis. We finish the job by checking the head for a proper seal.
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