YZ103.5 Big Bore

Motorcycles Yamaha Kit

Please call to order 608-842-0680

Regular Price: $900.00

Special Price: $549


Quick Overview

fits 2002-2014 YZ85

Product Description

Actual Displacement = 103.48cc

Engine Modifications Included:

Cylinder: Bore, Port and Plate.

Head: Re-chamber to work with the Big Bore piston. 100 octane suggested for most conditions.

Notes: Crankcase mods required to clear piston.

Notes: This kit requires you to send us your cylinder and head for modification.


The YZ103.5 is an kick butt  supermini bore-only kit.  It is the fastest thing you can buy without stroking it.

The YZ85 needs more bottom and mid and this kit does it no problem.  However just because you need more bottom does not mean you want less top.  The way we modify this engine you get the best of both worlds.  More grunt out of the hole, tons of mid, and a screaming top with good over-rev.

Our big bore piston is not the 52.5 that everybody and their brother is running.  Our 52.5 piston has been designed to be as light as the stock part and just as durable.   It also allows us to make the exhaust port work much better.

The only downside is that the 52.5 bore does not fit in the stock YZ cases with out giving the piston some more room at bottom dead center (BDC).  However that is only a down side if you don’t want the spend the quality time with your little speed demon teaching them the finer points of performance engine building 😉

With excellent power gains across the board, awesome durability, and piston change intervals longer than any super mini you will ever own, you can’t go wrong with the Max Power-RPMs YZ103.5.

PS,  If you are short on the quality time part look at the YZ98.  It is not quite as bad-ass as the 103.5 but it will save you some time with the grinder.

PSS,  It can also be later stroked to 112cc with head mods.


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