I drilled out a 12mm bung and tapped it for 18mm - Suzuki GSX-R Motorcycle Forums Gixxer.com

 
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post #1 of 8 (permalink) Old 12-19-2018, 09:30 AM Thread Starter
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I drilled out a 12mm bung and tapped it for 18mm

On my 2011 GSX-R750, I successfully drilled out the stock 12mm O2 sensor bung--while still mounted on the bike (didn't even loosen header)--and tapped it for 18mm x1.5 thread pitch. First, I removed the stock sensor and put a 5/8" dowel 6 inches long into the hole to simulate the drill bit and see exactly where "straight" is. I could then use a corner of the crankcase as a landmark. (Note: If I had loosened the header, this marker wouldn't mean anything.) I then drilled it with a 16.5mm bit with a 1/2" chuck. I had to get a drill with a 1/2" chuck (most drills are 3/8") and a 90 degree elbow to drill around corners. Power Commanders require you leave the stock O2 sensor in place and drill a new bung hole and Bazzaz requires that it no longer be connected, so drilling the stock bung only works if you're going with Bazzaz.

Last edited by Superbike Racer; 12-19-2018 at 09:34 AM.
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post #2 of 8 (permalink) Old 12-19-2018, 07:05 PM Thread Starter
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Re: I drilled out a 12mm bung and tapped it for 18mm

Here's a pic with the dowel and the finished 18mm.
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post #3 of 8 (permalink) Old 12-21-2018, 09:41 AM Thread Starter
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Re: I drilled out a 12mm bung and tapped it for 18mm

Here's the drill I used. If I used a straight/conventional drill, the chuck would hit the engine case. Another alternative would be to get a drill bit longer than 6 inches (16.5mm x 6" was hard enough to find in the first place) or find a bit extender (don't know if they exist).
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post #4 of 8 (permalink) Old 12-23-2018, 12:50 AM
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Why did you do this?
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post #5 of 8 (permalink) Old 12-23-2018, 01:11 AM
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Re: I drilled out a 12mm bung and tapped it for 18mm

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Originally Posted by 2017Dave View Post
Why did you do this?
Probably to run an autotuner without going to a full exhaust. Which is really weird, because that's going to pick up very little power. Even if you gut the cat.
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post #6 of 8 (permalink) Old 12-24-2018, 03:26 PM Thread Starter
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Re: I drilled out a 12mm bung and tapped it for 18mm

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Probably to run an autotuner without going to a full exhaust. Which is really weird, because that's going to pick up very little power. Even if you gut the cat.
Yes, that's why. With the SET valve in the way, there's no place for a second bung, and that's why I had to go with Bazzaz rather than Power Commander (requires you keep stock O2 sensor).

Not much power increase? Really? I thought that mapping correctly (whether via auto-tuner or dyno map) gives you more power even on a stock bike. So changing the exhaust can (Yoshi Alpha), disabling the SET valve (now stuck open), adding a K&N air filter, and adding the fuel controller and auto-tuner would give up to 10 additional HP. No? All of these mods increase air flow, which will lean out my mixture, so I need a fuel controller. I figure an auto-tuner costs about the same as a dyno run and is also a long-term solution whereas a dyno run is a one-shot deal.

Also, I've heard that the CAT doesn't inhibit air flow much; that the advantage is in weight reduction. Then, because the CAT is located so low, it's not as important as the same weight higher up. It also occurred to me that a quick way to lose a few pounds would be to swap out the battery for a lithium ion battery. They make them the same large size to fit the bike, but they're very light--and this weight is high up where it matters more. I would do that myself except I just bought a frikking new lead battery.

Last edited by Superbike Racer; 12-24-2018 at 04:59 PM.
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post #7 of 8 (permalink) Old 12-25-2018, 03:44 AM
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If you are going to keep the stock header please gut the cat and the valves and remove the cables and servo. You will need to plug all the holes or weld something so there are no holes in the exhaust. Id like to see what that does. I thought about trying to do it but decided to just go full exhaust.
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post #8 of 8 (permalink) Old 12-25-2018, 09:42 PM Thread Starter
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Re: I drilled out a 12mm bung and tapped it for 18mm

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If you are going to keep the stock header please gut the cat and the valves and remove the cables and servo. You will need to plug all the holes or weld something so there are no holes in the exhaust. Id like to see what that does. I thought about trying to do it but decided to just go full exhaust.
Well, you don't "gut" the CAT, you have to cut it off and use an after-market mid-pipe (no reputable manufacturers make one). Don't want to do that. As for the SET valve, it's already stuck open with no error code. I see no need to take out the servo, cables, valve, etc. I did this by gently pulling the brown wire with a black stripe (and I think green dots) out of the ECU and taped it off. I did not cut this wire.
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