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904s Sports Big Bore Kit

*** This kit is not currently in local stock, please allow 5-7 working days ***

There are very few modifications you can perform on an engine that will improve power and torque right through the rev range, but TTP's 904s big bore kit is one of those modifications. Increasing cubic capacity and compression ratio give improved performance from idle to the rev limit, with no downside.

Designed by TTP, the 904s kit includes race quality pistons, a custom 904 MLS steel head gasket together with OEM cylinders which are bored, Nikasil plated and then powder coated externally to give a virtually new set of barrels.

Core must be in good condition. Shipping details will be emailed on receipt of order
Note:additional shipping charges apply sending your cylinder core in for rework circa $135
Note:add $250 for the full OEM top end rebuild gasket set, this is optional, also options are the safe start idler boss reinforcement and green Barnett clutch springs to enable the clutch to handle the extra power.

12:1 compression ratio.
Larger valve pockets for +2mm valves.
Tight quench to improve tubulence & combustion burn.
Anti-friction coating on the piston skirts.
Pistons hand balanced to within 0.1gms of each other.
Nikasil plated barrels give tighter cylinder/piston clearance.
Hand gapped piston rings.
Custom 904 MLS steel head gasket.
Optional OEM gasket kit.

Coming soon 2mm larger valve kit.

Last image is a Dyno Graph comparison for Bonneville / Thruxton with the 904s Big Bore Kit

Available for the air cooled Bonneville, Thruxton, Scrambler, America
and Speedmaster from 2001-2016. Please click here to ask a question
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Shipping options

  • Tracked Not Rural$32.00
  • Rural$35.90
  • Seller allows pick-ups
  • Seller location: Darfield, Canterbury, NZ

Payment options

  • Other options
    Cash, NZ bank deposit