2023 is the last year I will produce PORTED big bore kits with my own two hands.
I will continue to sell and market my custom pistons and gaskets and manufactured cylinders.
Starting January 1, 2023 you need to call or text for an appointment because I have limited space
in my workshop. No more sending engines without paperwork or a clear ability to pay for the work.
Text or call Eric Gorr for a time estimate and appointment (630) 825-5645



VINTAGE PORTING $150 (for dirt bikes 1994 and older)

Eric raced motocross since 4-strokes were popular the first time (1970) with his Ducati 250 Scrambler. Working as a mechanic and tuner since 1971, Eric has accumulated porting specs from all sorts of sources like factory racing directives, practical experience, and the use of modeling software. You might say he’s a bit of a vintage freak and sympathetic to vintage meisters like yourselves.


Eric is particularly skilled at Maicos and Yamahas, and works on all brands of Japanese and European motocross bikes. If you are a vintage freak and have historical specifications that you would like machined to a cylinder, Eric will cater to your needs. He has also ported cylinders to exact historical factory specifications from Harley Davidson Racing directives from Dick O’Brien to Team Green to Yamaha Wrench Report and even Swedish-language blue-prints from Husqvarna. If you have an antique cylinder with a cast-iron sleeve and you want to preserve the bore size, we can have the cylinder bore nickel-composite plated for an additional $225.


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Cylinder head and cylinder bases can be turned and machined to produce a powerband that is better for beginners and trail-riders. The technical reasoning is that this modification serves to retard the port timing and increase the squish velocity produced in the cylinder head. If you just want more low end and don’t want to spend a fortune, this is the best mod that will give you the biggest bang for your buck! $75: 50-112cc $100: 125-550cc



This service includes all machining modifications per situation and application. Services include gasket surfacing, turning, clearance-machining for big bores and or strokers, flat-top piston conversions as well as hemi and conical dome shaping, lowering compression for low octane pump gas with ethanol, raising compression for high altitude, TIG-welding, o-ring groove cutting, plug-hole turning and threading.



Powervalves are built into the cylinder around the exhaust port. They’re supposed to make the exhaust port bigger when you twist the throttle open. Powervalves are complicated mechanisms prone to failure. We offer a service to clean, inspect, and adjust the powervalves. This service comes standard with all porting and big bore packages.



Crankcases can be improved with porting and a set of new ceramic bearings and Teflon seals. Crankcases can be ported for smooth transitions to the transfer ports, clearance mods for big bores and stroker cranks, re-surfacing or even welding or epoxy repairs. Send a set of bare cases or with your cylinder.


CYLINDER PLATING (aluminum cylinders) $250

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Most modern dirt bikes use hard coatings applied directly to the aluminum cylinder bore. Nickel-composite plating is the hardest low friction coating available. We can plate a cylinder back to original size or to a big bore size for no extra charge. This service is covered by a 1-Year warranty and includes cylinder head resurfacing, stud removal and thread repair, and powervalve service and assembly on applicable models.


CYLINDER PLATING (iron cylinders) $225

This service is especially great for vintage cylinders with cast iron sleeved bores and CR500s. It is designed to preserve the bore at a particular size. Nickel-composite coating that is very hard and longwearing and comes with a 1-year warranty.


BORING and HONING for iron-lined cylinders $65

This service includes cleaning, boring, diamond-honing, port chamfering, exhaust bridge relieving and polishing. We offer Wiseco, Pro-X, JE, Athena, Magnum, and Vertex piston kits as well as generic gaskets and bearings.


Bead-Blasting Bare Finish $35

We can bead-blast any stripped down engine parts to a bare finish. We also offer custom powder coating services in factory colors.


Head Mods and Button Decompressors

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We offer head mods to lower the compression so big bikes run on pump gas and rev out better for only $35. We also offer more complex services like TIG welding and re-shaping and even button decompressor installation for air-cooled bikes for $85.




This is a photo of Eric and the bike he most regrets selling, a 1974 YZ250A. This picture was shot during the “Forward Mounted Shock Revolution” of 1974, shows Eric’s long travel YZ that he built in high school shop class during senior year. Eric blew his prom budget on racing the 250A class in District 16/17 with his fellow racers and present day motocross icons like Scott Wallenberg (RacerX), Mark Barnett (Team Suzuki), Jeff Surwall (No Fear), Rick Doughty (Vintage Iron) and Ron Lindsey (Midwest Action Cycle)


This group shot is the team that built the modern supercoss bike. Back in 1981 Eric and company started with a RM125 and changed the whole concept of a dirt bike. By making the bike skinny with a long seat and a low center of gravity and streamlined shape that enabled a rider to move around, the “INVADER 125” featured many innovations that exist on modern mx bikes.

The Invader was copied by Honda in 1984 in the CR250 factory bikes and eventually trickled down to production bikes throughout the 1980s. The test bike fearured many innovations and 2 US Patents were awarded that were referenced by HRC with regards to cross-charged manifolds for automobiles and a new thinking in the “polar moment” on motorcycle handling patents. 

(Pictured from left to right; Richard Rohrich Jr., Eric Gorr, Troy Anderson, and Chuck Gordon)


Eric’s favorite Vintage pic, Danny “Magoo” Chandler with his little buddy Endo wearing a Flow-Porting t-shirt in the summer of 1981. Eric sponsored Magoo in his last year as a privateer racing the nationals on an RM125 before Team Honda sighned him to ride the Trans Am series in the autumn. Magoo was the driving motivational force behind the Invader project, emphasizing the need for a mx bike with a low CG.