Amongst other 130mph-plus laps, the DAO Racing Kawasaki star moved to the top of the leaderboard with a lap of 131.767mph.
Harrison was followed by Davey Todd (Milenco by Padgett’s Motorcycles) who set a lap of 131.655mph from a standing start before stopping on the Mountain on his second lap. Peter Hickman was again quickest in the Superstock class, the Gas Monkey Garage by FHO Racing man lapping at 130.695mph.
Michael Dunlop (MD Racing) and Jamie Coward (KTS Racing by Steadplan) topped the Supersport and Supertwin timesheets respectively with speeds of 125.938mph and 119.775mph.
Newcomer Glenn Irwin’s TT debut continued to get better with a superb lap of 124.797mph.
Unfortunately, a non-racing medical urgency brought the session to a temporary halt shortly after 7pm with an ambulance needing to get onto the course to attend to the patient. The session resumed just before 7.30pm for the Supersport and Supertwin classes.
After a further delay of almost 30 minutes because of an incident in the latter classes, the Sidecars were able to get out onto the Mountain Course for the first time since Sunday afternoon but, with both time and light disappearing, it was only for one lap.
As expected, Ben and Tom Birchall on the Haith Honda set the pace through all the sectors but Pete Founds/Jevan Walmsley (FHO Racing) stayed in touch.
Unfortunately, both Dave Molyneux/Darryl Gibson (DMR) and John Holden/Jason Pitt (Barnes Racing) stopped at Cronk-y-Voddy and Sulby respectively.
The Birchalls completed their solitary lap at 115.663mph, not surprisingly the quickest of the week so far.
Founds/Walmsley slotted into second 13.7s adrift at 114.326mph but ahead of Ryan and Callum Crowe (112.545mph), Lewis Blackstock/Patrick Rosney (111.164mph) and Tim Reeves/Kevin Rousseau (110.768mph).
Newcomers Harry Payne/Mark Wilkes and Lee Crawford/Scott Hardie were next up at 109.733mph and 109.709mph respectively.
More in this week’s TT News edition three, free inside Thursday’s Manx Independent.
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