Big Bore Kits

TSP two stroke big bore


We offer Big Bore kits for most late model two stroke dirtbikes. These kits are a great way to bump up power and torque and often dont cost much more than a normal top end rebuild, especially if your stock plated cylinder is worn or damaged.

These big bore kits have proper porting and proper head designs to suit local fuels and conditions and as a result they offer MUCH better performance than most of the usual aftermarket big bore cylinder kits.

Send us your complete top end (old base gasket, cylinder, old head gasket, old piston, head) and we will bore, port and replate your cylinder, machine your powervalve to suit the new bore size, design and machine the head to give correct squish clearance and compression ratio and we’ll also supply a piston kit and top end gasket set.

When you receive the big bore kit it will be ready to install onto your bottom end and ride! Some kits may require carb and powervalve tuning to get the most of the new setup. Some kits require case mods. Please allow 2-4 weeks for return of your parts.

Final tuning will be the responsibility of the installer unless dyno tuning is requested.


Big bore kit From
Below 134cc (up to 52mm bore) $1399
134, 139 and 144cc (up to 58mm bore) $1500
265cc (68.5mm bore) $1600
295cc (72mm bore) $1650



Check out the following list to see what big bore kits we offer for your model…

Model Year Displacement Special Notes
CR80/85 1986-07 92cc
CR80 1986-07 100cc
CR85 2005-07 92/100cc Must install oversized radiator
CR125 1972-88 134cc
CR125 1989-04 134cc
CR125 1989-99 144cc
CR125 2005-07 134cc
CR125 2005-07 139 or 144cc
CR250 1978-80 265cc
CR250 1986-07 265cc
Model Year Displacement Special Notes
KX60 1983-2003 66cc
KX65 2000-14 72cc
KX80/85 1988-2014 92cc
KX80/85 1988-2014 100cc
KX80/85/100 1988-2014 107cc
KX125 1985-1993 134cc
KX125 1994-2014 144cc
KDX200 1986-88 212cc
KDX200 1995-2006 225cc
KX250 1987-2007 265cc
KX250 1993-2007 295cc
KX500 1985-2001 525cc
Model Year Displacement Special Notes
RM65 2003-05 72cc
RM85 2002-14 92cc Crankcase clearance mods needed
RM85 2002-14 100cc Crankcase clearance mods needed
RM125 1976-88 134cc
RM125 1989-2009 144cc Crankcase clearance mods needed
RM250 1989-2008 265cc
RM250 2003-08 295cc
Model Year Displacement Notes
PW50 1990-14 60cc
YZ80/85 1993-2014 105cc Crankcase clearance mods needed
YZ125 1976-89 134cc
YZ125 1990-93 129cc
YZ125 1994-2014 134cc
YZ125 1994-2014 144cc Crankcase clearance mods needed
YZ250 1979-89 265cc
YZ250 1990-2014 265cc
YZ250 1999-2014 295cc
YZ/IT465 1980-81 478cc
YZ490/WR500 1983-93 510cc
Model Year Displacement Special Notes
CR/WR125 1998-2011 144cc
CR250 1998-2009 265cc
CR250 1998-2014 295cc
Gas Gas
Model Year Displacement Special Notes
125 all models 2000-2014 144cc
250 all models 2000-14 265cc
Model Year Displacement Special Notes
50SX LC 2001-08 58cc
50SX 2009-14 58cc
65SX/XC 1999-08 72cc
65SX/XC 2009-14 72cc
105SX 2004-14 112cc
125SX/EXC 2001 134cc
125SX/EXC 2001 144cc
125SX/EXC 2002-14 144cc
150SX 2007-14 155cc
200EXC/MXC/XC-W 1998-12 212cc
250SX/EXC 1996-05 295cc
300EXC/MXC 1991-14 310cc
Model Year Displacement Special Notes
125 1998-2007 144cc
250 1998-2013 265cc