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TTP 904s Sports Big Bore Kit
TTP 904s Sports Big Bore Kit

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 have no broken fins and no scratches on the bore or mating surfaces.
Shipping details will be on your emailed order receipt.

  • 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.

Available for the air cooled Bonneville, Thruxton, Scrambler, America
and Speedmaster from 2001-2016.

Click HERE to read the TTP X-Files
about performance bolt-on mods
for the Bonneville & Thruxton.

Dyno graph with 904s Big Bore Kit
904s Dyno graph.
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List Price: £890.00
Price: £890.00 (£1,068.00 Inc. VAT)
€995.47 EUR (+VAT)    $1,170.59 USD    $1,608.16 AUD

The later barrels have machined and polished edges which
after processing need to have the powder coat removed
and the fin edges polished back to a shine.

Like for like core exchange only.

Early Barrels  Late Barrels
Early Barrels                    Late Barrels
This gasket kit includes all of the OEM gaskets
required when installing the big bore kit.
(except head gasket which comes with 904s kit)

904s Gasket Set
904s Gasket Set

With a 904s Big Bore Kit installed,
the standard clutch springs are
pushed to their limit, so we offer
the Barnet Green clutch springs
along with a Triumph clutch case
gasket as an upgrade.

Barnet Green Clutch Springs
Barnet Green Clutch Springs

The Safe Start is a good preventative measure for
a standard engine, with the 904s Big Bore Kit
installed giving an increased compression ratio,
the Safe Start will give protection from the only
engine structural weakness of the air cooled
Triumph twins.

NB: If you're upgrading to the green clutch springs,
why not install the Safe Start while the clutch cover
is off, for complete peace of mind.

TTP Safe Start
TTP Safe Start

Installation of the 904s Big Bore Kit at our
workshop in Bournemouth, Dorset, England.


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