More OHC6 Rebuild Questions
Short answer: Answers to the common OHC-6 rebuild questions — with one recurring theme: INFORMATION. Keep the service manuals on hand.
- Valve height: measure from the machined surface the cam-cover gasket sits on to the valve tip, with the springs installed after the valve job — and give this spec to your machinist (find another if he won’t listen).
- Oil restrictor: in the head between cylinders 2 and 3 — a ~2″ tube with an hourglass crimp (~1/8″ ID) and an .080″ hole drilled in the crimp. Both sizes are critical to oil flow and pressure to the cam and lash adjusters; it’s fragile and easily damaged during cleaning.
- Valve angle (30 vs 45): refers to the valve face/seat. Only the second-design 1969 head uses 45°; all earlier heads are 30°. (A 3- or 5-angle valve job improves flow.)
- Cam followers: replacements have a rough surface that must be machined smooth (e.g., by hand on a fine sharpening stone, ~30–45 min each with cutting oil).
- Lifters: use new ones (a slightly different design without the top-hole pin — don’t mix old and new).
- Pistons/overbore: 230 pistons are available; 250 pistons are hard to find. Stay at .030″ if possible (up to .060″ has been done). Rings and bearings are industry-standard six-cylinder sizes.
- Driveshaft/crossmember: the same across 1967–69 (only the THM400 used a different crossmember).
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Content last modified: June 13, 2026 at 10:06 am
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