Big Bore Conversions

Call us for expert advice and a quotation for your engine machining requirements.

An easy route to increased capacity and performance for your motorcycle engine is to fit a “Big Bore” kit.  There are a huge number of kits available from a wide variety of manufacturers but all will require a degree of engineering or machining work in order to achieve the finished result.  Once you have decided on which kit will best meet your needs H T Howard & Co can assist in making sure everything is engineered to work as the designer intended.

For modest increases in capacity a simple overbore of the existing cylinders might be all that is required.  Techniques for this are the same as for conventional re-bores however more material is removed to increase the finished bore diameter and therefore final engine capacity.  To minimise distortion in the barrel during these operations, the excess material is removed in a series of smaller cuts with a roughing cutter until within 0.5mm of the final size.  A finishing cutter will be set (allowing for the honing tolerance) and will be used to finish each of the bores to size following the roughing operations.

For more extreme conversions however, the fitting of larger cylinder liners will be necessary. To facilitate this, enlargement of the liner housing in the barrel itself will be required sometimes accompanied by an increase in the diameter of the crankcase mouth to accept the new, oversize liners.

Additional machining operations including decking the cylinder head and/or barrel faces for increased compression and machining cylinder heads to accept oversize valves might also be required as part of a conversion.

Many high performance piston kits are supplied with piston rings that may need “gapping“.

At H T Howard we have the expertise and experience to ensure you get the best solution for your requirements.

Call us for expert advice and a quotation for your engine machining requirements.