Changing the spark plugs on a Triumph Stag

Why, and how often

Eight plugs, and reading them is a useful health check. Check and clean at each service and renew as needed. On a Stag that only sees a few hundred miles a year, changing plugs annually with the oil is honest practice.

Steps

1. 01. Work on a COOL engine

   Hot alloy heads strip easily.

2. 02. Pull each lead one at a time

   Pull each plug lead by the connector (not the wire), one cylinder at a time so leads return in the correct firing order (refer to the manual for the V8 firing order). The rear plugs can be awkward — take your time.

3. 03. Clean the plug wells and remove the plugs

   Brush or blow debris from each plug well so nothing drops in. Undo each plug with a proper plug socket.

4. 04. Read the old plugs

   Light tan/grey = healthy; black/sooty = rich or weak spark; oily = oil past guides/rings; white/blistered = too hot or weak.

5. 05. Gap the new plugs

   Gap the new plugs to 0.025" with a feeler gauge, bending only the side electrode.

6. 06. Anti-seize, hand-start, nip gently

   Smear a little anti-seize on the threads, start each plug BY HAND, then nip up gently. Refit the lead.

7. 07. Start and confirm even running

   Start up and check it runs evenly on all eight.