motor services

Pro Circuit In-House Motor Modifications

Building a reliable engine that is still capable of creating usable horsepower can be difficult for other tuners. Luckily for our customers, we have more than three decades of experience building and tuning performance engines that help riders stay on the track and win races. Many hours have been spent at the track and in our dyno rooms looking for ways to add reliability and winning performance into every customer's engine that shows up in our shop. We take pride in building some of the fastest and most dependable racing engines in the world for two-stroke and four-stroke dirt bikes.

Next to the full-sized engines, mini bike engines also find their way to our service benches looking for improvements. We've been a long-time supporter of the mini riders; many of which have gone on to become some of the biggest names in the sport such as Ricky Carmichael, Ryan Villopoto and Adam Cianciarulo. Mini bike modifications are in high-demand for amateur events, especially our supermini engines. Any Honda, Husqvarna, Kawasaki, KTM, Suzuki or Yamaha mini engine will benefit from one of our engine modifications.

Get Started

Before you send in your engine, download our service form for your bike, print it, fill it out and send it along with your motor. A sales representative will call you once it is received to go over the work you want done. Please allow 5-7 business days for your motor modifications (turn-around times may vary). Once your work is completed, your sales representative will call you and go over the billing and shipping if it has not already been discussed. Our motor modifications department hours are from 9:00am - 5:00pm Pacific Standard Time.

Note: Prices, depending on bike/model may change or be different. For an accurate quote, please call Pro Circuit at (951) 738-8050 or email us at

Engine Services, Modifications and Service Numbers (SRV)

Two-Stroke SRV
Head and Cylinder Modification 001
Cylinder Modification 007
Head Modification 008
Carburetor Boring (KX85/100, CRF150R, KTM 85/Supermini) 024
REM Isotropic Finishing (Transmission) 036
Carburetor Service 0100
Remove and Replace Head and Cylinder 0110
Bore and Hone Steel Cylinder 0120
Remove and Replace Engine in Frame 0130
Split Engine Cases 0140
Crankshaft Rebuild 0150
Re-Pack Silencer 0170
Bleed Brakes (Front and Rear) 0190
High Pressure Wash/Clean Bike 0200
Replace Tire on Bike 0210
Replace Tire off Bike 0220
Powder Coat Frame (Minis) 0260
Remove and Replace Power Valves 0330
Remove and Replace Studs 0350
Replate Cylinder 100
Bore and Replate Cylinder 103
Kawasaki Supermini Engine KX109
Short Carburetor Modification (KX85/100 '02-14) KX85-CARB
Suzuki Supermini Engine RM112
Yamaha Supermini Engine YZ112
Four-Stroke SRV
Carburetor Service 0101
Remove and Replace Engine in Frame 0130
Crankshaft Rebuild 0150
Re-Pack Silencer 0170
Bleed Brakes (Front and Rear) 0190
High Pressure Wash/Clean Bike 0200
Replace Tire on Bike 0210
Replace Tire off Bike 0220
Head Modification 027
Split Engine Cases 0300
Remove and Replace Head and Cylinder 0310
Re-Cut Valve Seats 0320
Pressure Check Head 0325
Copper Valve Seat Installation (Per Seat) 035
Remove and Replace Studs 0350
REM Isotropic Finishing (Transmission) 036
Guide/Rocker Installation CRF250

Note: All prices are subject to change. Not all modifications apply to all makes and models. Please call for specific details. Additional parts may be required for certain services and/or modifications. Hazmat fees not included.

How to Ship Your Package to Us

1. Packaging: Pro Circuit recommends you visit your local UPS or FedEx store for shipping recommendations or contact our service department at (951) 738-8050.

2. Mark Your Engine: Please fill out our printable service form and include it with your engine.

3. Protect Your Engine: Pro Circuit recommends insuring your engine for at least $5,000. If you are shipping us a 4-stroke head or 2-stroke cylinder, we recommend ensuring it for the appropriate value of the parts.

Questions? Contact our shipping department for any questions you may have, or to learn how you can get the best rates on shipping! (951) 738-8050

We accept/use:


prop 65