polini porting part 2


yesterday i finally got the dremel collets i needed to hook up my dremel flex shaft. i was holding off porting my polini exhaust until then so i could get all the angles i wanted inside the exhaust port, making it a lot easier. a pros only porting tip i picked up from peter is to make sure you’re always comfortable the way you hold both the dremel and cylinder. it helps give you a steady hand to avoid having the bit skip around and reduces fatigue (i spent 2.5 hours porting this). having good lighting is also something not to overlook. i have a tendency to get excited and jump right into things, but taking your time and getting set up properly is key to get the porting results you want. *note that i’m pretty anal about this stuff. it might be overkill to some people, but i like to know i’m doing everything i can to ensure good results.
port town
as an extra precaution i put masking tape on the cylinder walls incase the bit skipped (a tip from markryan). no errant bit moves happened, but it took 2 minutes and doesn’t hurt.
masking tape safety net

then i measured out what i wanted with my micrometer and marked the cylinder with a sharpie. if you want to get really intense/accurate, graham from the cranks has a sweet blog post on creating portmaps and laying them out in the cylinder.

time to grind! slow and steady is the way to go. i started at the cylinder wall and then worked my way down to the bottom of the exhaust port.
2.5 hours later
the widening and raising extends all the way to the flange
opened up all the way through

after some re-chamfering and exhaust port polishing, this little duder is ready to race.
race ready


5 Responses to “polini porting part 2”

  1. Gabe’s new nickname: “Anal guy”

  2. nice work. slow and steady (hand) wins the race

  3. 3 Maize

    how are the results with this porting? top speed with gearing. hows the pull. what pipe, carb. . .

    also how did the reed block mod work out for you?

    • 4 gabeb

      i never got a top speed run on it after porting, i should probably do that at some point. before porting with 18×40 gearing, a 15 bing and MLM Rev-Run it hit 58. i’m going to open the cylinder up a little more and do a few other things for the races.

  1. 1 GUIDE: Pro tips to building a Puch Polini « MAGNUM DASH!

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