Engine Building

​​​​The engine building process is an extremely critical part of building a bike: 

Stocked facility and fast build times

We control the full build process, not only with how the machining process is done but also with how quick we can have an engine completed. We have an average build time of 14 to 21 days! This will depend on the current work load (engines in Front of yours), but we keep all OEM and aftermarket in stock at our facility, CP-Carrillo Rods and Pistons,Kawasaki,Suzuki and Yamaha OEM Parts  to meet the demand of most customers.


Spears Racing will completely inspect all of the working components of the engine:

The top end will be torn down and careful measurement of the piston to head (squish) must be taken to avoid collision of the moving parts and the cylinder heads will be completely inspected. Increasing the compression ratio of an engine by machining the gasket surface of the cylinder head is where most of an engine’s power increase comes from. Compression ratios can also be increased by machining the engine cylinder deck or changing the thickness of the head gasket or a combination of the aforementioned,Spears Racing has designed several different pistons for all of the lightweight engines that often are a great fit.


Other modifications on the bottom end can include bead blasting piston crowns, checking piston to cylinder wall clearances and changing/setting if necessary, oil pump and oil pressure relief valve modification for changing pressure output and transmission modifications.The cylinders will be installed and the proper deck height will be obtained to give the best reliable power and torque. Next are the cylinder head(s) - a process that only Spears does. The heads are bolted to the cylinders and are CC'd to find out the current compression ratio. After this is completed, the heads are ready for there finial assembly to the cylinders. The transmission will be clearanced in the cases and new transmission carrier bearings will be installed if needed (upgrade to Ceramic). The crankshaft will be magnafluxed to ensure that it has no cracks at the time of installation and this too will be clearanced in the cases for the correct clearances. The connecting rods will also be clearanced at this time. If an upgrade is wanted, we suggest the Carrillo connecting rods. The cases will be prepped with new main crankshaft bearings as well. After final inspection, the Spears crank case defuser (depending on the engine type) and the cases will be closed up.While the cylinder head is disassembled and being machined, it is recommended to have a valve job performed to give the valve seat better flow and sealing characteristics.

A complete review of the work, Pictures and all of the documents are part of this and will be given to the owner.

​Spears Racing offers several types of head work to match your needs. First there is a STANDARD valve job, which machines the valves and seat area of the head exactly to the manufacturers required specifications.Second there is the competitive valve job (Referred to a SUPERSPORT Style) the valve faces and stems are machined, and the intake valves are given a special double cut. The exhaust seats are given a three angle cut. The intake seats receive a blended four angle cut or full radius cut depending on the application. Finally all valves are hand lapped and checked for correct sealing. All of the seat work is done on our state-of-the-art valve machine.Once the cylinder head has been machined and thoroughly cleaned, it is time for reassembly. Careful assembly of the cylinder head involves checking valve spring height and pressures as well as setting the valve lash for proper clearance.

Degreeing camshafts :

​Camshaft timing is so critical on a sport twin (see our cam timing article), there cannot be any deviation between the front and the back cylinder opening and closing numbers (you're only going to be as strong as the weakest cylinder).​After the final cam timing numbers are obtained, the cams will be pulled for the final time and the sprocket carriers will be welded to the camshaft bodies (to ensure no movement of the holder) and reinstalled. The engine will be closed up and be ready to ship. 

​The Lower end is disassembled after the cylinder head has been removed from the engine. While the factories do a fine job on assembly, they leave a few small details to be taken care of.Oil clearances can be carefully set at a higher clearance and checked with Plastic gauge, oil pumps can be modified and things like ceramic transmission bearings and Cyroing and Micro-Polishing can be done to “free up”  inertial and frictional power losses.

For those not wishing to radically modify the ports, port irregularities and casting lumps (called flashings) are removed. The critical area of valve-seat-to-port is blended and the junction of the carburetor-adapter to-manifold is also matched and blended,the complete port and combustion chamber reshaping, the area is shaped and contoured to maximum flow and  while maintaining flow velocity for power increases throughout the RPM range.​