30

Port and Polish

By
booneylander
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Intake runners are cleaned of casting flash but cast surface left intact to promote turbulence. Ports are matched from head to throttle body boots.

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Exhaust ports are heavily machined to smooth the path as much as possible, diameter is left close to stock to keep gas velocity high. Mirror finish is desirable to prevent buildup of particulates.

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Combustion chambers are machined as little as possible, but enough to remove any sharp edges that could be heat risers and promote preignition. Valves and seats are given 5-angle radius. Head is milled to true. This motor is already at near the limit for piston-to-valve clearance, so intake valves are slightly recessed in the seats to allow for milling.

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Stock bottom end per 600 class rules, combustion chambers, pistons cleaned and inspected. Piston-to-deck height is measured. New head gasket installed.

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Head is installed and torqued. Stock cams are used, APE adjustable cam sprockets are installed to adjust to the mint cam timing numbers. Cams are installed, sprockets, chain, tensioner, cam clearances are checked and valve shims adjusted to account for machining. Cam timing is set. Piston to valve clearance is checked and cams re-adjusted if needed to maintain limit of PTV clearance.

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There are other factors too than just the power. The bike will run cooler, maintain power better over it's life, but you also will see less valve stem / seal life because of the reduced guide area. Also when starting with a used bike like I did, it's good to do even just to make sure that everything is optimized, make sure there are no defects/damage etc. With a stock motor, sometimes you can have more or less power out of the box depending how good the castings were, how well it was put together, etc. So if you had a brand new motor that was a bit lazy you could see a big gain doing this work, if you have a motor that's already strong out of the crate, you might see less gain. - booneylander November 12th 2014
All of the work, compression bump, port/polish, degreed cams, will net like 4-5hp over a base of like 100hp. That's for this Honda, some bike models will give you a lot more with similar work, some slightly less. They are all pretty good from the factory nowadays. - booneylander November 12th 2014
Nice work, whats the estimate increase in power for the porting? It is usually marginal on stock car motors, but for a small modified bike motor, it must be a decent percentage. - ripcurl November 10th 2014

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